Fuel Injection Performance
PAGE 1- THE BASICS
These pages will discuss the various modifications to the TPI system. The potential is virtually unlimited, but just like the old saying- "Speed costs money, how fast do you want to go?", a lot will be determined on how much you are willing to spend.
Some modifications can be done cheap, in a few minutes to just a few hours, others require planning and thought to make it work and then the knowledge to be able to sort out the details, sometimes taking days, weeks or even months. This is true especially if you have a custom set up that requires a prom change and you want to get the parameters just right, to squeeze every ounce of power out of your engine.
Modifications and the law:
I included this subject first, for a good reason. First, this is not like the "good 'ole days", where you can just slap a bigger cam, larger carburetor and a single plane high rise manifold to make a fire breathing hot rod, and then try to sort out the problems of timing, A/F ratio, idle etc, to get it to at least run, with no regard to the amount of pollution you were belching in to the air. Although you can still do that with the old induction set up, this website is dedicated to the modern fuel efficient TPI system. Ounce per ounce, cfm to cfm, given the identical motor, a properly set up tpi will run circles around its carbureted counterpart and still idle smoothly, get respectable mileage and still meet emission laws, if it is going to be a street driven car. You are going to build a tpi "hot rod", there are parts to do it, but like the disclaimer says "not for use on pollution controlled vehicles" or "for off-highway use only". You must be aware of the emission laws in your jurisdiction before attempted any modification.
California has one of the strictest emission laws in the country, starting back in 1966 with the advent of the PCV valve and the air injection reaction or "smog pump". The laws have gotten progressively stricter, and many other areas of the United States has followed suite. While the variations occur, I have included California's here as a worst case scenario. There are three different categories for replacement parts:
Step 1: The following parts can be replace as they do not tamper with the required emission system, (1) air cleaner mods (2) intake manifold screens (3) A/C cut out systems (4) oil separators and filters (5) engine cutoff systems (6) throttle lock outs (7) ignition and coil modifications (8) water, steam or vapor injection (9) intercoolers for original turbochargers and (10) Electronic ignition upgrades on older point ignition systems as long as original advance mechanism is retained.
Step 2: The following parts are allowable, (1) carbs marked as oem replacements (2) replacement oem style gas caps (3) approved aftermarket catalytic converters (4) fuel fill pipe restrictor replacements (5) Headers on non-catalyst vehicles (6) Intakes for non-egr, as long as original emission devices are intact. (7) heat riser pipes for approved headers.
Step 3: These items must have approval and have a certification of acceptability. If you thumb through your favorite performance catalog you may see some items that have a CARB (California Air Resources Board) approval id number. This means the item has been approved as long as the original emission devices are left intact and functioning. These include, (1) Carburetors that replace fuel injection (who would want to do that??!!) (2) fuel injection systems that replace carburetors (3) EGR systems mods (4) Superchargers (5) Turbochargers (6) Exhaust system mods to catalyst equipped cars (7) Electronic ignition enhancements to computerized cars and (8) replacement proms (chips).
Be sure to check to make sure that ANY modification you make is approved. Some jurisdiction may require if you put a late model engine in a older vehicle that you meet the emission standards for the newer motor, some may require that you meet the requirements for the model year of the vehicle. If in doubt, always consult your local department of motor vehicles or similar governing body before you begin.
To start to get any real performance out of your TPI engine this is where you'll have to begin- To get the engine to breathe.
I will begin on the assumption that you putting a new engine together, based on my experience, starting from the bottom up.
To start to get any true performance, the block must be a solid foundation to begin. The block must be in sound condition to begin with, no cracks, anywhere. The machine shop that does your work, must be a clean, reputable place with update, modern equipment and with a knowledgeable staff that knows how to operate it. Be prepared to pay a little more for their services, but it is worth it. Ask yourself this- can you afford to do it twice? The block must be thoroughly cleaned so it can be inspected, the oil galley plugs must be removed and the oil passages cleaned out to remove any remains of old oil and debris. This is important as you don't want any old material circulating through your new rebuild. The cylinders must be bored and honed to proper tolerances, the crankshaft main bearing caps lined bored to be perfectly straight. Just remember that less friction equals freed up horsepower. Always have new camshaft bearings installed and brass core (freeze) plugs installed.
4 bolt vs. 2 bolt: Although the 4 bolt is thought to be ultimate must have, actually there is more hype than fact, as which is better for a street engine. While the 4 bolt has the prestige of being a stronger block, this is true if you are building high performance block that will see a lot of loading plus high horsepower use. The 2 bolt is good for 500 hp and actually is suitable for most applications. If you insist on a 4 bolt, be aware they are getting harder to find, even if you use a used or aftermarket block.
ROTATING ELEMENT: Crankshaft, connecting rods and pistons.
The proper preparation of the rotating element will either make or break an engine. The crankshaft at the very least must be true and free of cracks. Never store a crankshaft lying down on its side, or even buy one that has been in this position. Although the crankshaft looks like it is a solid, unmovable hunk of steel, if not properly stored in a upright position, it will bend. Even 1 or 2 thousandths (.001-.002) inch bend will cause problems. Just look at the oil bearing clearances for a SBC and you'll see what I mean. Give a crankshaft the "ring" test. Tap one of the counter weights lightly with a end of a screwdriver. It should have a clear. high pitch ring that last a for a second or so. A cracked one will have a dull sound.
Also look at the journals on the mains and rods. Wipe the oil off and inspect them carefully for any nicks, scratches, or gouges. If you can feel anything when you run your fingernail across them, be prepared to have the crank turned to remove the gouges and true up the journals. You need to have this done before you can order your bearings for the mains and rods. Standard undersize journals are .010, .020 or .030 undersize. Personally I wouldn't want anything below .020. Talk to your machinist about your options.
The connecting rods must also be checked, and a magniflux or crack test is worth the money. Used rods always run the risk of being fatigued. The rods bolts must also be checked, and is highly advisable to replace. The rods will have to be trued after any bolt replacement.
The pistons are a matter of choice, as they do affect compression ratio, along with your choice of cylinder head chamber size. If you are going to a streetable engine, figure around 9 to 1, to be a good choice. If you are using aluminum heads you can increase this figure to 10 to 1, because aluminum heads dissipate heat better and effectively cool the combustion chamber. The choice between cast, hypereutectic and forged will depend on your intended use. Cast pistons are a good choice for a motor that will not be used for drag racing, or have a turbo, supercharger, or nitrous set up that will be used for extreme, severe duty use. Mild turbo or conservative, and I mean conservative nitrous set up and used properly will not hurt the cast pistons. Cast pistons also have a tighter piston to cylinder wall clearance as they don't expand like forged pistons, which means better oil control, less noise, especially on a cold morning, because the piston is not rocking back and forth in the cylinder, thus it translates into less wear and longer engine life. Forged pistons are the choice for a engine that is going to see a lot of high speed, high performance use. Especially if you are using high compression pistons with a blower, or high horsepower nitrous. The forged pistons will require a looser fit in the cylinder, for they expand much more than cast pistons. Hypereutectic pistons are made from a special alloy, that have some characteristics of forged and cast. While not as strong as forged, they also have less expansion compared to forged, which makes it a good compromise for a mild engine with limited turbo, or nitrous use.
Piston rings also come in choices, from stock, moly and chrome. In my opinion moly rings are the only choice for a street performance motor. They have a impregnated coating of moly, which helps along with motor oil to cool and lubricate the cylinder walls. This translates into less friction and longer life. Also with the cylinder walls properly honed before installation, the moly rings break in very quickly, shorten the break in period from 5,000 miles to around 1,000 miles. Stock rings, although cheap. require a longer break in period and don't have the added benefit of moly coating on the top ring. Chrome rings are not recommended on a street engine, although they would last a long time, the break in period is extremely long. These are usually made for drag strip applications for severe duty.
Most piston ring sets have the gaps already set for use in the engine, but the manufacturing tolerances can vary greatly, usually on the wide end of the scale, because, face it, most people will just install them and not even think about the ring end gap spacing. This "safe" setting will keep the ring ends from butting together and destroying the cylinder walls, rings and pistons. But the safe setting also means a little more blow by and less power. The choice I would suggest is buying the "file fit" rings that will allow you to have either you or your engine builder set the ring gaps to the manufacturers recommendations. The tighter setting will mean more compression, less blow by, which means more power to apply at the rear wheels.
Just be sure to tell your builder the type of piston and rings you are using, so he can bore and hone the block to the proper specs to allow proper break in of the rings, and to allow for piston expansion.
BALANCE, BALANCE, BALANCE
To get longer life out of your engine, plus reduce friction and free up extra power, balancing the rotating element is the only way to go. You will have to supply your machine shop with the crankshaft, connecting rods and bearings, pistons and rings, the harmonic balancer, and the flywheel or flexplate. Be sure to ask first if they have the facilities to do so, before you turn over your parts. Many places will "farm" out the work and then pass on the costs to you. Plus the less hands you have moving your parts around the less likely they will end up missing or damaged.
CLEARANCE, CLEARANCE, CLEARANCE
Besides the piston ring end gap clearances, you also have bearing clearance for the main bearing journals and the connecting rods. While most builders are content with getting with the wide variation of clearances and calling it good, if one is building with longevity and performance in mind, it pays to get the clearances exact on all journals. This requires some work, a little more money, and patience. The topic is just to broad to put here, and there are many good books on the subject of engine rebuilding, and I highly recommend them. If you are doing your first rebuild yourself, these books are indispensable.
STROKER MOTORS: THE SBC 383 CID ENGINE
If you are planning to build one of these, you will also need to be meticulous with details. The stroker motor consists of putting a 400 SBC crank into a 350 block, using the .030 bore of the 350 engine (4.030") and the stroke (3.750") of the 400 crank to produce 383 cubic inches. This engine produces a tremendous amount of low end torque and mid range power. Combined this with a properly tuned TPI and you are talking about a powerful street motor that has enough power to spank a big block.
Be aware of the choices depending on either your motor is 1986 and earlier, or later. The earlier blocks have a two piece rear main seal, the 1987 and later blocks will use a one piece seal, The cranks are different in this respect so be sure you know what you are getting.
NOTE: Always buy a high quality crankshaft from companies such as Eagle or Scat. Stay away from Cat, Cat Power, Bulldog or whatever "off brand" is floating around, where you don't know what it is made of or from, such as China. Cheap, yes, but it will not handle your performance small block and may end up costing you even more money when it breaks or when you found the offsets are not aligned properly. A new Eagle or Scat (cast steel) crank is around $250-300, and is money well spent. Forged cranks are around $500+.
Shown above is a Eagle one-piece seal 383 "stroker" crank. They also make cranks for earlier blocks. Note the 400 harmonic balancer, which is mandatory for an externally balanced crank such as this. Next picture is a 400 flexplate (automatic). You can purchased stroker cranks that are internally balanced, which requires the 350 balancer and flexplate or flywheel (manual transmission). If you are using a late model (1987 and later engine) equipped with the one piece rear main seal you must use the flexplate of flywheel with it. Your machine shop will be able to balance it along with the crank and harmonic balancer.
There are two choices of rods. You can use the 400 rods (5.565") length or the 350 rods (5.700"). You can the 400 rods with 350 forged pistons ONLY. The cast 350 piston skirts will not clear the 400 crank counterweights. I don't know if the hypereutectics will clear or not. Ask your builder or tech department at your performance shop about this. If you are on a tight budget, 350 forged pistons are the way to go as long as you remember the 400 rods short stroke and severe turning angle will limit your engine to around 5,500 rpm. If you want more reliability for high performance use, use the 350 connecting rods. Of course, these means ordering custom pistons made for stroker motors.
Above is a 383 cast piston made by Ohio Piston, a subsidiary of the Dynagear Corporation. A 350 block bored .030" over yields 383 cubic inches. This particular catalogue number (1383P) is for use with the 5.700" (350) rods. the deep dish (25cc) allows it to be used with small 58 and 64 cc heads which gives it around 9.5 to 10 to 1 compression ratio. Be sure to ask your suppliers tech rep about ratio, cylinder heads and intended use to get the proper piston for your set up. Always use a top quality name piston .
Shown above is the Hypereutectic Piston made by Sealed Power. This is a good choice piston for a mild street engine.
Another thing to remember that with this combination, you must be sure the rod bolts will clear the block oil pan rail and that the rod bolt heads will clear the camshaft lobes. You will need to do this before you assemble and install your engine.
Also be aware that using a stroker motor on a tpi set up will mean fuel pressure increase, a calibrated prom and possibly larger injectors. The stock tpi unit will allow the engine to breath up to around 5K rpm, and if you plan to go beyond this, you will need to change the tpi manifold.
The camshaft selection will have a major impact on how the engine breathes. This will have a dramatic impact on the overall characteristics of the engine. Depending on what you decide to use, will also mean whether or not you can still retain your stock ecm chip, and other components such as fuel injectors, regulator and even the intake manifold. Be conservative here, because too large of a cam will mean you will have a engine that is temperamental, and drivability will suffer along with performance. Unless you have modified the engine to the point where it is not a streetable combination, stick with a mild combination, and you'll be happy with the results.
Torque is what gets the vehicle moving, while horsepower measures the amount of work the engine can do in a specific time. It is best to select a cam for street use that has a broad torque band, versus one that has peak horsepower high the engines' power band. Horse power may sound appealing, but at the expense of torque, which is what helps get the vehicle launched off the line. Be sure to keep this in mind what the intended use of your vehicle is .
The stock tpi cam is sufficient, unless you have done slight mods to the cylinder head and exhaust system where you want the engine to breathe. Most camshaft manufactures will have recommendations of what you can do and what you may have to do to get the proper combination. Just remember that duration and lobe centerline, and overlap have more of impact on the engine than lift up to a certain point.
Total lift is base circle- lift height x rocker arm ratio. This is just a approximate due to variations in lash adjustment, manufacturing tolerances etc.
Lobe centerline is measured in degrees, has a relations with the amount of overlap, which is the number in degrees where the intake valve is closing at the same time the exhaust valve is opening. while some overlap will be present, to much overlap will mean more of the fuel charge in the cylinder will be diluted by some of the exhaust gas present. Duration is a measure in degrees on how long the valve is held open. While some manufactures list theirs in advertised duration, the more realistic approach is to to measure the lift at .050 (fifty thousandths) lift. The amount of duration has a big impact on the engine. Large duration cams may sound impressive, but at the expense of drivability and idle quality. Stick with conservative durations, especially if you use a automatic transmission, anything over 224 degrees duration at .050 will definitely mean modifications to the tpi system.
|Camshaft||Up to 195@.050 lift||From 195 to 215@ .050 lift||From 216 to 224@ .050 lift||From 225 to 240@ .050 lift||From 241 to 275@ .050 lift|
|Idle Quality||Good, 18" -20" vacuum||Good, 16-18" vacuum||Good, with slight lope, 14-16" vacuum, may require reserve vacuum tank.||Choppy idle, very low vacuum, needs vacuum pump to operate pwr brakes.||Very rough idle, will need vacuum pump to operate pwr. brakes.|
|Power Band||idle to 3K rpm||power band from 1,500 to 4K rpm||midrange power from 2K to 4,800 rpm||top end power from 3,200 to 7,500 rpm||power band from 3,500 to 7,500 rpm|
|Torque Band||low end torque from idle through midrange, 2,500 rpm||Excellent low end to midrange torque from 1,500 to 3,500 rpm||Midrange from to top end torque from 2,500 to 4K rpm.||Top end torque from 3K to 6K rpm||Excellent low to mid range torque from 3,500 to 7K rpm|
|ECM Controlled Engines||No mods required||No mods required||May require computer mods||Needs major mods to ecm||Needs major mods to ecm|
|Cylinder Heads||Stock heads||Stock or slightly modified||Ported and 3 angle valve job||Ported, 3 angle valve job, may need race preps.||Full race prepped.|
|Final Drive Ratio||Stock ratio, 3:50 or less||Stock or slightly modified up to 3:73||Gears from 3:50 to 3:73||Gears from 3:73 to 4:50||Gears from 4:50 or higher|
|Induction||stock||stock||needs mods to fuel pressure or injectors, slightly modified intake||Needs mods to intake, throttle body, injectors and fuel pressure||Major mods needed|
|Valve Spring Pressures||Seat press-90lbs, open press-250lbs||Seat press-100 lbs, open press-260lbs||Seat press-110lbs, open press-280 lbs||Seat press-120lbs, open press-300 lbs||Seat press-125 lbs, open press-325 lbs|
For those using a 1987 and later small block, there are choices ranging from stock to high performance. If inherited qualities of the roller cam lobes make it easier to have high lift with the duration of a milder cam. Thus, it is possible to have lifts up to .500" and still retain near stock idle qualities.
The above chart is just recommendations, be sure to discuss with your builder or camshaft manufacturer, what you want to do with the vehicle. These will include displacement, compression, transmission type, cylinder head spec, vehicle type and weight, final gearing and tire size. Be totally honest, because the wrong choice will mean a vehicle you are unhappy with plus the added expense of having to do it over.
If you are reusing your old cam and lifters (conventional cam and flat foot tappets), be sure before you pull the lifters out of bores, make a holder in which the lifters will be secured in, mark each holder in the order of the way the lifters are installed in the bores. Failure to put the lifters back on its same cam lobe, will mean engine damage, because each lifter wears differently on its lobe, this pattern needs to be maintained, or the cam lobe and lifter foot will chew itself up.
On roller cams, this is not necessary, as the cam lobes are not ground to help the lifter rotate, the roller lifters are held stationary in the bores by the retainers, the only movement is up and down. But it wouldn't hurt to keep them with their respective cam lobes, just for peace of mind.
Another thing worth mentioning for performance applications is degreeing or indexing the cam. While I won't go into details, it involves getting the cam in phase with the piston as to improve the air velocity and therefore improve power output. If you are interested, there are many good books on the subject.
The timing chain and gears should be a high quality set. Yes, quality does mean more expensive, but a cheap set will stretch and that means sloppy timing. Stay away from cheap imports from overseas (China), they are not a bargain at any price. The best are the true double roller sets that are around $50-80. Even though it may be tempting to go with a gear drive, they produce enough noise that the knock sensor may be activated, thus the ecm will retard timing.
There are many variations, but again the choice here will also affect the performance of your engine. The most common are the "smog" heads, from around 1971 on up. There are good ones and there are bad ones, some are just better choices than others.
Just one note before you start, some of you may think that 305 heads and 350 heads will swap over. Yes, they will bolt on, BUT, the combustion chamber size is significantly different. The 305 heads have a smaller combustion chamber (60.5 cc), that if put on a 350 engine with flat top pistons, will mean a compression ratio so high as to be useless on the street. You can use deep dish pistons, but again the compression ratio may be too high. If you think that 350 heads on a 305 will work, just remember that most 350 heads have a combustion chamber size ranges from 64 to 76cc, and putting a set of these on your 305, will mean a huge compression drop and lost performance.
Another thing is valve size. If you are head hunting at the local salvage yard, be aware that the same casting number can have different valve sizes, ranging from 1.710", 1.940" and 2.02" intakes, and 1.50" to 1.60". The smallest valves are found on the two barrel carb engines, while the most common is the 1.94/1.50 heads used on the 4bbl carb engines. The 2.02/1.60 are for high performance use. The pre-1971 heads also use the large 13/16" socket spark plugs, while the later heads use the more common 5/8" socket plugs.
The best cylinder heads to use for your 350/383 cid engines are the casting numbers: 3973(487), 3973(493), 3998(993) and 3998(997). These heads have very few failures do to it's heavy casting. They have good runners with very few obstructions, and adapt the porting very well and are great street performance heads. While you may heard of the famous "double hump" or fuelie heads, these are rare and expensive, and unless you just have a need to sound impressive, these are best to be left on the original stock engines unless this is what you have to convert to TPI. Some cylinder heads, especially the pre 1968 will not have the accessory bracket mounting holes, and unless you have these parts, you may find it difficult to mount your alternator and A/C compressor.
The heads to stay away from: The "185", "336", "624" and "882" castings. These are light weight, weak castings that are prone to crack, while the "882" has bad port configuration that makes it a poor choice for a performance head.
For quick cylinder head identification, use this chart. Note- be aware that other casting numbers also use these id marks, this is just a general guideline for 350 engine heads.
These are great if you plan to run to high compression engine to around 10.5 to 1. There are many great aftermarket suppliers such as Edlebrock that supply a high quality cylinder head, complete and ready o bolt on and in various chamber sizes. Also the 1986 and later Corvette aluminum heads work great, but with their small 58cc chamber you must get the proper pistons to keep the compression ratio low enough to keep you from pinging under load.
The aluminum Corvette cylinder not only offers a weight savings (19 lbs vs. 45 lbs for cast iron), they will allow you with proper pistons to run up to 10 to 1 compression ratio on pump gas (91+ octane). Note is second picture, the factory installed pushrod guide plates.
The best modification to make to the cylinder heads is to have them port matched and pocket ported. There is no reason to completely port the runners all the way through, except on the exhaust side to help speed up the removal of the exhaust gases.
Port matching is only required on the intake side. Unless you are familiar with the procedure, it is best left to someone who does, as you can destroy a good seat of heads if you go to far. The port matching on the exhaust side is not recommended. The mismatch here is purposely done to act as a "dam" to help in the scavenging of the exhaust gases and to help keep the gases from being sucked back through the intake system.
Pocket porting is the smoothing of the valve bowl just behind the valve to remove casting flash that will interfere with the air flow. Port matching and blending the walls on the air entry to about a inch inside is all you need. Smoothing of the short side radius of the intake runner floor has a significant effect in improving air velocity. Add in a 3 angle valve job and you have a set of cylinder heads that will perform nicely.
There are many aftermarket suppliers who sell bare casting heads, and complete sets that are very competitive in price in what it would cost to have a machinist to build a set of heads for you. Some are cast iron, others are aluminum. The horsepower and performance increase they provide is money well spent, if you are not experienced in doing the port work yourself.
If you are having a machinist build you set of heads, he will ask you for the cam lift, this is important, as the proper spring will have to be chosen and this affects whether or not the valve spring pocket will have to be modified to accommodate the larger spring.
Another important consideration is the quality of valves to use. Most suppliers are competitively price, with name brands that are performance recognized. If you are building a mild cruiser, the stock valves will be fine. But if you are after performance use a quality stainless steel valve. These valves are specially treated and are made for performance use in mind, as is money well spent. Another item to mention on valves are the guides. There are cast iron guides, and silicon bronze. There are benefits to both. The cast iron guides are cheaper, and if set up properly, will last for over 100K miles. The silicone bronze are a little more expensive, self lubricating and will also last a long time, typically over 100K miles. But, I was told by my machinist when ever I had my heads rebuilt, and I asked for bronze, that he did not recommend them, of course, I inquired why, he told me that they have over last 10 years, gotten away from bronze, because of the problems associated with the possibility of the engine overheating, and causing the bronze guide to swell and seize on the valve and end up pulling the guide out of place. I took his advise and went with cast iron inserts. Now, this is a matter of personal preference, ask your machinist for his advise.
Rocker arm studs may be a concern, if you are using a high lift cam and need to use stiffer springs. It is recommended that you use screw in rocker arm studs. There are many types, and some may or may not need machine work done, at the very least will require you to tap the insert hole with a thread tap of the required size. This also needs to be done by a professional if the skills are beyond what you possess. Also change your rocker arms, especially if they have many miles on them and the contact point has a gouge enough for you to feel with your finger nail. Do not be cheap here, damaged rocker arms will tear up the tips of your valve in a hurry. If you are replacing them, and have extra to spend why not go for a set of roller tip rockers. They will reduce the friction on the valve stem tip, plus eliminate the side loading when the rocker arm pushes down on the valve stem. This is good for reducing and again freed up horsepower. Plus the ratio will be kept constant, where all the valves will open up the same amount, meaning a better balance of fuel will enter the cylinders equally, and exhaust gases leaving.
The TPI intake manifold is well suited for a stock or mild SBC engine from 265 to 400 cid, as long as you remember the stocker will run out of breath around 5,000 rpm, this is assuming that you have a balanced, ported engine. Other factors come in play if you just have a "stock" motor your dealing with, limiting the rpm range to around 4,600 rpm. Stock here means no special attention give to the motor mentioned here.
If you want better breathing from your tpi equipped engine as far as intakes, aftermarket pieces such as the Edlebrock High-Flo is hard to beat and is a quality piece. It has provisions for the Corvette EGR system (A) and is made to fit both early and late style cylinder heads (B).
To take full advantage of the performance potential you will need the performance runners and larger (52 or 58mm) throttle body.
The stock intake is really a well engineered piece. It is made to optimize the low and mid range torque by taking advantaged of the engines air charge velocity. The only thing to do really is to make sure the intake ports are matched to the intake gasket like the cylinder heads to remove any obstruction. You may also want to have the intake manifold runners extrude honed to remove the casting flash to improve air flow.
Another thing that can be done is to replace the stock "runners" with slight larger or even siamesed runners to improve the flow to the lower intake. The siamesed runners will improve air flow on the top end.
Shown above is set of SLP runners , showing the Siamese runners.
Edelbrock Hi-Flo TPI Intake
This a a great aftermarket system for stock or modified engines, but if you happen to buy a used set up or needing to change the gaskets be aware of the following:
It may seem normal to use the right (passenger) side gasket for the intake to the runner, it seems it will fit. Right?
Take the same gasket and lay it over the passenger side intake runner shows a severe mismatch between the port and gasket, doing this unknowingly would lead to a nasty intake leak! I don't know why it was designed this way, it would have been very easy for Mr. Edelbrock to match the casting to the intake. Are you listening Mr. Edelbrock?
If you bought a used Edelbrock intake set up and need gaskets you will need two sets so you can have the "drivers" side gasket for the right side as well. Otherwise I have no complaints about the Edelbrock Hi-Flo TPI intake system, it is superb in all aspects except for this one pain in the @ detail.
There are aftermarket kits and even square boxed intakes that have throttle bodies with high cfm ratings. These are made for extreme performance applications.
On the subject of throttle bodies, the stock piece is will suited for applications up to 400hp. The stock throttle body (48 mm) is rated for 650 cfm, which is well above the breathing capabilities of a 350 engine running at 5000 rpm is around 425 cfm based on 80% volumetric efficiency. The larger throttle body will only be helpful if the rest of the engine is modified significantly. If you decide to put a larger throttle body on a otherwise stock motor, it may be more responsive, but the initial throttle tip-in on acceleration may suffer, unless the prom chip is recalibrated to allow for a additional shot of fuel during this time.
The air foil that mounts to the front of the throttle body affords a slight increase in hp of 8-10 at 4500 rpm, by straighten the air flow and reducing the turbulence as it enters the throttle body.
The air cleaner box also can be improved, but again the stock unit is well suited for up to 700 cfm. If you have a need to increase air flow to your throttle body, just remember any bottle neck in the system will negate any performance increase. It is best to start with the cylinder heads and work your way back to the air cleaner, otherwise you will be disappointed with the results.
Here is one tip that can help on your stock unit on the plenum itself. Look down the throttle bores on the plenum. See that ridge covering about the lower 1/4th of the opening. With a special grinder wheel and some patience you cam eliminate this to get rid of the ridge that will improve air flow. But be careful so you don't grind into the passage below. See this picture to see where I have smoothed it down on mine. The arrow shows the idle air passage on the 1985-88 plenums that you don't want to ground through.
Look on your plenum and compare it to the picture above to see what I am talking about.
This is a high performance tpi system. It has the high-flo runners and bottom intake made by Edelbrock, a 52mm throttle body with airfoil. It also has a set of 24 lb/hr injectors and a adjustable fuel regulator. The plenum has been ported to remove the restriction. If you are running a high performance 350, 377. 383, 400 or 406 cubic inch, this is the only way to get the full potential from your tpi. The stock manifold and runners will fall flat at around 4500 to 4800 rpm, the hi flow system with modified throttle body will allow 6500 rpm potential.
Once you have improved the induction side of the engine, it won't do any good unless you have made improvements to the exhaust system. While the stock system is good to a point, improvements for performance will mean modifying the exhaust system. Aftermarket header, free flowing mufflers and larger pipes can help open up the exhaust system. But also going too far as far as pipe diameter can mean the scavenging effect can be reduced where the exhaust pulse is reduced to the point where the effective cleaning of exhaust gases is not effective, hurting performance. As far as header pipe diameter, the rule of thumb is to closely match it to the exhaust valve size. A good size of exhaust pipe for a mild tpi motor is 2" to 2 1/4" in diameter. Of course, for a high performance engine pushing 350 + horsepower needs the proper size system.
If you decide to stay with the stock manifolds, you can improve the flow of a dual system by adding a "H" pipe in the system. The pipe is installed across the left and right side exhaust pipes. This helps improve the flow by reducing the build up of eddy currents on the exhaust flow. To determine where this is needed on your dual exhaust system, you'll need to mark each pipe with black lacquer paint,( if you have catalytic converters, paint between them and the mufflers) Then run the engine at 3,000 rpm for several minutes. Look to see where the paint is burnt or gone, and this is where you need to install the pipe.
Mufflers have also come a long way, in the sense of performance, flow and noise control. A good, quality muffler will help improve performance while at the same time, offer a quiet operation. They have come a long way since the "turbo" muffler, which is now considered old technology.
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