keithl1967

Looking at an 86 that needs a motor. Currently has a 350 TPI in it. I would like to keep the original "look" of the car, but possibly build a 400 block that I have--using dart heads, etc.

How badly will the original TPI limit what the motor is capable of? Bigger injectors, etc? In short, what's the best a TPI can do?

aliceempire

iTrader: (14)

A factory tpi isn't a great manifold for larger ci. 350s kinda got peak hp rpm limited to 4500. Bigger displacement only makes it worse. Not undoable but not great if you want to go faster.
Richard Holdener did a test looooong ago and recently made a nice vid for us. It's a 383 but the concept it the same. Decide what you want to do.

keithl1967

good info in that video. any idea what AFR heads he was running on that 383 test mule? 200cc? 215? 185?

motor I am considering putting together is a 406, 10:1 compression, Dart Iron eagle 215cc, comp cam XR 282HR.

aliceempire

iTrader: (14)

He didn't remember or know so we have no idea what the heads were.

With that much motor, a factory tpi is worthless imo. A HSR, FIRST, or a good ol' dual plane are all better. It all depends on your build/goals. Either way, I wouldn't waste time with a factory manifold.

Komet

It's not a great idea, stock TPI is ideal for stock and not a lot more. Look into the FIRST intake if you want a very stock appearance that can flow substantially more air, or something with shorter runners like a Holley Stealth Ram for better breathing at higher rpm.

sofakingdom

iTrader: (1)

TPI stands for Tuned Port Injection.

THIMK about the concept of "tuned" for a moment. That term implies that, at some certain frequency or frequencies, something happens that's different from what happens at other frequencies.

Let that idea sink in.

Now: the speed of sound in air at STP (standard temperature and pressure: about 760mm or 30" of pressure, aka 1 atmosphere, and 0°C or 32°F, aka freezing of pure water) is right around 1100 feet per second.

That means, if you have a tube (something like, let's say, a musical instrument), that the "note" it produces, which is controlled by the frequency at which the length of the tubing it's made out of has a resonance, is related to its length. Pretty basic stuff really.

In any engine, the air rushing down the intake tract, will slam into the back of the intake valve, just as it closes, producing a pulse of significant POSITIVE pressure. All intakes on all engines do this of course, but in a general way, it's not often used as a direct method of augmenting cylinder fill (power output), in anything resembling a "street stock" sort of application.

TPI however took advantage of this fact of physics. It is designed such that the pulse of positive pressure from ONE cylinder travels BACK UP the intake tube (which is about 22" long), into the plenum, and then down into ALL THE OTHER intake tubes. Let's keep the numbers nice and round: let's say that the sum of the 22" up the one tube, plus the 22" down the other tube, plus the length rattling around in the plenum, is 48", on average. That's 4'. TPI uses this reflected pulse to AUGMENT the fill of the NEXT firling cylinder, but only at some RPM at which the pulse arrives at the next cylinder after it has travelled about 4'.

Butt, the pressure in the intake tract is somewhat less than atmospheric, otherwise the air wouldn't be motivated to go down it. The speed of sound is somewhat less when the pressure is lower. Once again. to keep the numbers REAL SIMPLE, let's simplify the speed of sound inside a running engine's intake manifold, to 1000' per second.

What this means then, is that at some engine RPM at which the POSITIVE PRESSURE pulse generated by the sudden closing of the intake valve while air is rushing down the tube and SLAMS into the back of that valve, and then that pulse bounces back from that valve and finds its way to some OTHER intake valve that happens to be OPEN at the moment, would result in GREATER cylinder fill (torque, aka output) than would happen at ANY OTHER engine RPM. By selecting that length - 4' - we have TUNED the engine's intake tract to REINFORCE cylinder fill at some particular RPM, or more accurately in some range centered on that RPM, that corresponds to the time it takes for sound to travel 4'.

RPM is a count of events per minute; "frequency" is usually considered in terms of events per second; so all we have to do to convert from one to the other, is to apply a conversion factor of 60. Trivial to say the least.

Make sense so far?

All that remains then, is to find this RPM. So: the time it takes for sound to travel 4', is 1000 ÷ 4. How convenient: that's exactly 4 milliseconds, or, 1/256 of a second. What RPM is that?

Well, a V8 engine fires 4 of its cylinders per revolution. That means that the RPM at which the cylinders are firing exactly 4 milliseconds apart is the RPM at which it make one full revolution in 16 milliseconds. What RPM is that? 1 second ÷ .016 = 62.5; again, let's simplify it so the numbers come out even (which happens to take out some of the error of the last simplification), and call it an even 60. 60 revolutions per second is ... 3600 revolutions per minute. 3600 RPM. Let THAT number sink in.

TPI is carefully, rigorously, mathematically designed, according to well and widely proven and demonstrated principles of physics, to produce its optimum torque at 3600 RPM.

Now: did you notice ANYTHING about a real-world engine that was CONSPICUOUSLY ABSENT from all of these calculations? I certainly hope so.

The thing that is COMPLETELY missing is CUBIC INCHES.

What does this tell you? Basically, that NO MATTER WHAT SIZE the engine you put TPI on is, its peak torque is going to occur at 3600 RPM. Doesn't matter how large the tubes are; doesn't matter what cam you put in it; doesn't matter what the head flow is; doesn't matter what the throttle body diameter is; 3600 RPM. It's DOMINATED by the properties of those tubes on the intake. The best you can do is to make sure that the engine is as restriction-free as you can get it, at 3600 RPM; and that the cam you select produces the largest possible pulse of "reversion" pressure at ... 3600 RPM. Which is why TPI is SO PICKY about cam selection. Just jamming a bigger cam under it will often make it produce LESS power, if said cam doesn't agree with TPI's ... 3600 RPM ... constraint.

OK, so once again, lets go back to numbers. (after all, everything in life is numbers, whether you humans are willing to admit it or not) Power, whether measured in HP, kW, or whatever, is the time rate of the production (or expenditure, depending on which way you're looking at it from) of energy. X number of units of energy per Y units of time, in all cases. So how do we get from torque (work, or energy), to power?

1 HP = 33,000 lbs of weight lifted 1 foot in 1 minute. Pretty simple really.

Back in the 1700s, when steam engines were replacing horses, the single biggest use of such a thing was pumping water out of coal mines. (coal being the fuel that powered the early Industrial Revolution worldwide, but particularly in England and Germany) Everybody that built engines, was charging people that used them, according to how many horses their engine could replace. Well, how do you put a number on that? They would look at a horse walking around a turnstile sort of thing that was connected to a pump shaft, and taking into account how long the horse would live depending on how hard you worked it, they would figure out how much water the horse could lift in some unit of time, without working it to death. Believe it or not, people all over the industrializing world all seemed to come up with pretty similar numbers. Turns out, d00d named James Watt (ever heard of a unit of power called the watt?) in England, determined that one horse, under conditions that the horse could sustain more or less indefinitely (over a normal horse lifetime anyway), could lift 33,000 lbs of water 1 foot out of a coal mine, every minute; and could do this more or less all day, every day, day in and day out, from attaining full growth to visiting the knacker. That's one horsepower then: 33,000 lbs, 1 foot, 1 minute. In Germany, whoever made the same calculation there, came up with a number that was closer to 31,000 lbs. (maybe Germans didn't work their horses as hard? maybe theirs weren't as big or as powerful? maybe they didn't feed them as much or as well? iunno) Keep in mind this was all going on before the metric system was invented in France during the French Revolution, as some kind of pure scientific measurement method devoid of any religious or historical taint. (read about the French Revolution: you'll be simultaneously inspired and horrified, it was a time when things got tried that couldn't possibly ever be tried again under any other circumstances, even besides the guillotine)

Torque is a twisting force. 1 ft-lb is the amount of twisting that occurs when one pound of force is applied (or expended) on a rotating object 1 foot in radius (2 feet diameter) that applies 1 pound of force at its circumference. Think, a tire being spun, pushing a car. A point on a rotating thing with a 1 foot radius moves 2 pi feet in one revolution.

So do we get from torque, to horsepower?

Well, if horsepower is the time rate of doing work, and something that has 1 ft-lb of torque does 2 pi of work every time it rotates, then all it takes is another conversion factor. 33,000 ÷ (2 pi), or 5252.11, is this new Magic Number. Often referred to on dyno pulls as 5250 RPM, where the torque and HP curves intersect, if plotted on the same axis. Horsepower (at any given RPM) = the torque at that RPM, times the RPM, divided by 5252.11. Simple: it's all numbers.

A typical real-world engine like ours, capable of running on fuel we can actually buy at the street corner, under conditions we actually can run the engine under, can produce about 1¼ ft-lbs of torque per cubic inch, at whatever RPM it produces its peak torque at. You can move that RPM up or down by selection of cam, intake, exhaust, etc.; but in the end, it's still 1¼ ft-lbs of torque per CI. Therefore a 305 can produce roughly 380 ft-lbs max, a 350 about 440 ft-lbs, and a 400 about 500 ft-lbs. Butt, don't forget, you're working with TPI: by definition torque peaks at 3600 RPM. So if you have a 305, your HP will be around 265. All you have to do to find the horsepower you're going to make (assuming you've optimized everything... it's all downhill from the number this calculation gives you, in the RW) is plug your CID into that simple equation.

400 CID × 1.25 = 500 ft-lbs. If that occurs at 3600 RPM, then your HP will be 500 × 3600 ÷ 5252.11; or, around 340 HP. For a 350, you're going to get real close to 300 HP.

BUTT: that whole "reinforcement" thing comes with a penalty. And that is, at any HIGHER RPM than 3600, the pulse provides less and less reinforcement, which means the help it gives you is less and less (the torque falls off REAL FAST as RPM increases); and, worst of all, at SOME RPM, the pulse actually begins to INTERFERE with cylinder fill. It REDUCES engine output BELOW what it would be WITHOUT the tuned effect at all. And THAT RPM is real close to 1.5 times the peak RPM; or, 4500. What you get is the classic "Mt Everest" TPI torque curve: MASSIVE peak at 3600, craters above 4000, is ALL DONE by 4500.

Real simple. It's all numbers.

thainglo

iTrader: (1)

A terrific, detailed explanation. Great read!

Evilokc

i think the highest HP the factory put in a TPI engine was 350HP. they are much better at making torque than HP. im building a 383 and got myself a FIRST TPI unit.

sofakingdom

iTrader: (1)

The highest HP "rating" I know of from the factory was 260; in certain years of Vette L98. 240 or 245 tops in Camaro, slightly less in the Firebirds because of their different air filter tract before the TB. Never cracked 300 or even came very close, let alone 350.

Now of course, we all know that "factory" "ratings" aren't the same as hard measured physical reality, in several different ways, both that tend to reduce the "number" and tend to increase it; and we all know people whose cars produced more, or less, at a guess, than whatever the factory's "number" was; but still...

goldandblue

Wow! I am impressed.

Abubaca

iTrader: (3)

I built a nice, 383 TPI, cam, heads, heavily modded TPI, geared appropriately, and it was just WAY too much effort and money for the performance. In my opinion, and you know what they say about opinions, but....if you want the stock look, and are ok knowing your car isn't gonna beat up on modern muscle, I'd say headers/exhaust, rear gears, and a manual transmission or torque converter. Leave the engine alone. The torque of the stock L98, with gears and a fun transmission makes a great, fun to drive car.

1989karr

TPI might limit your potential but dammmnn does it look good!!!

keithl1967

ok, so assuming I stick with a 350, and do a full rebuild (go 355), shoot for around 10:1 compression...

what cam would you best recommend with the TPI? Doesn’t have to be a power monster, but a cam that would match well to the TPI, but produce optimum power without intake mods?

aliceempire

iTrader: (14)

I've built that and used a Comp 8-501-8 cam. 212 218 duration. Thru a 5 speed and 9 bolt axle netted 250hp and 350trq at the wheels.

keithl1967

That is one of the cams I was looking at...did you need to get a new chip for it?

aliceempire

iTrader: (14)

I'm running speed density so yes. MAF cars can possibly get away without it. My car idled at 650 700 at that time.

Thirdgen89GTA

iTrader: (5)

Honestly, a Superram is probably the best all around intake for a street car, followed by the First Intake.

However, if you want to see a TPI under the hood? First Intake.

If you want to rev the moon, then HSR, or Miniram. But to really make use of either of those intakes you absolutely need good heads, and to either spin it to the moon, or move to bigger cubes.

dmccain

iTrader: (2)

Id rather have the looks of a nice TPI engine. To hang with new cars you really have to build an animal of an engine and that requires all other sorts of things on these cars.. rear end, subframe connectors, etc etc. 240-300hp in these lightweight cars is fun enough in my opinion.

BadSS

Cut and pasted from an earlier post about that video.

Here's a link to the written article from 2005. In the video he says Air Flow Research heads were used. However, the printed version indicates Trick Flow heads were used and the corresponding pictures validate it (pretty sure they were TFS 195s).
http://xtremecarzone.com.au/STORAGE/...akeOptions.pdf

Back when the article came out I painstakingly used a triangular ruler to chart the HP numbers to be able do a better comparison.

RPM -- TPI -- TPiS - ASM -- ASR -- HSP -- HSR - MR
2600 - 200 -- 207 -- 198 -- 188 -- 190 -- 190 -- 186
2800 - 222 -- 235 -- 221 -- 205 -- 206 -- 206 -- 202
3000 - 260 -- 271 -- 262 -- 240 -- 230 -- 237 -- 215
3200 - 290 -- 308 -- 290 -- 278 -- 258 -- 270 -- 258
3400 - 316 -- 332 -- 319 -- 314 -- 286 -- 297 -- 282
3600 - 338 -- 355 -- 340 -- 337 -- 307 -- 320 -- 308
3800 - 360 -- 381 -- 360 -- 359 -- 332 -- 340 -- 328
4000 - 379 -- 410 -- 383 -- 382 -- 357 -- 363 -- 348
4200 - 390 -- 420 -- 408 -- 405 -- 377 -- 387 -- 370
4400 - 400 -- 438 -- 422 -- 421 -- 398 -- 411 -- 388
4600 - 406 -- 441 -- 440 -- 430 -- 418 -- 431 -- 409
4800 - 410 -- 448 -- 450 -- 443 -- 440 -- 449 -- 425
5000 - 409 -- 453 -- 457 -- 453 -- 456 -- 460 -- 449
5200 - 410 -- 447 -- 463 -- 470 -- 465 -- 475 -- 468
5400 - 407 -- 445 -- 460 -- 474 -- 475 -- 485 -- 475
5600 - 409 -- 448 -- 452 -- 480 -- 488 -- 497 -- 485
5800 - 407 -- 450 -- 450 -- 474 -- 493 -- 499 -- 500
6000 - 406 -- 450 -- 449 -- 453 -- 490 -- 501 -- 501
6200 - 404 -- 448 -- 448 -- 452 -- 486 -- 495 -- 504

TPI - Stock TPI, unported plenum, 47mm t/b
TPIS – Stock Extrude Honed base, TPiS LTR, ported plenum, 52mm
ASM - BigMouth base, AZ S&M Semi-Siamessed Tubes, ported plenum, 52mm
ASR – BigMouth base, Accel SuperRam Upper, Accel 1000cfm
HSP - Holley Single Plane MPFI, 1000cfm 4bbl T/B
HSR - Holley StealthRam, 58mm
MR - TPiS MiniRam, 52mm

Regardless of the discrepancy of the heads used, the main point of the test (article and video) is how the power curves react to different intakes. My biggest complaint when the article came out was the lack of information on the engine (explained why in the video) and the use of different sized throttle bodies - so keep that in mind when comparing the curves.

BadSS

As others have said, the stock TPI will strangle a 400 with 215 heads and the cam you’re thinking about running. If you want to keep a factory type look, then the FIRST is your best option. Here are a few reasons why you can benefit going with the larger FIRST.

DISCLAIMER – These are general statements and as with most general statements there can be and usually are exceptions. Never the less, I thought they might be helpful in this thread.

The maximum POTENTIAL HP and RPM capability of any given engine relies solely in the heads. Everything else (displacement, compression, cam, intake, headers, etc.) pretty much determines how much of that potential you can make and at what RPM it will occur.

RPM potential (specific to an intake manifold) is determined by the intake runner length AND the diameter or cross-sectional area (CSA). If the intake’s cross-sectional area is smaller than that of the heads, the intake will restrict the maximum potential HP and RPM. In a long runner combination the length has more an impact on peak HP capability and at what RPM it occurs while the diameter (CSA) has more an impact on peak TQ capability and at what RPM it occurs.

For instance, if length stays the same and you increase diameter, peak HP can increase, but the peak HP, regardless of whatever the difference may, will remain very close to the same peak RPM. When all else remains the same, by increasing the diameter, peak TQ may or may not increase, but peak torque WILL be made at a higher RPM (this is very obvious on heads with a larger MCSA). In a racing situation this is very beneficial because there is more average power delivered in 2nd and 3rd gear. TPI cars are notorious for dropping off considerably in 2nd and 3rd gears because the peak torque in many of these combinations is close to and sometimes below the shift recovery RPM. So, the majority of the tuned effect in most cookie-cutter TPI combinations is only utilized in 1st gear - this is especially so when using small/undersized diameter runners on large/larger engines.

While a tuned intake can make excellent peak TQ numbers, the torque curve is bell shaped and for a typical/stock TPI intake, this tuned effect only takes place over a narrow RPM band - then it drops off very quickly. As pointed out by Sofa earlier, since HP is determined mathematically from TQ, this means HP drops off rather quickly as well. If you move peak TQ up the RPM band, you’ll have more average power in 2nd and 3rd gear typically resulting in a faster car. TPI cars are infamous for having tractions problems, so moving the TQ curve up the RPM band can also be very beneficial during the launch.

I know this first hand when I swapped a fully ported (not welded) TPI with hogged and siamesed SLP runners (not welded) to a box stock FIRST on a mild (rather typical) 355 combination. The effective runner length was shorter on the TPI/SLP combo than the FIRST, but the base and runner diameter/CSA of the FIRST was larger. The increased runner diameter/CSA and resulting flow of the FIRST made a huge difference and resulted in almost a half-second reduction in ETs. The larger intake rolled off a little TQ at the stall speed and moved it up the RPM band helping the launch (60ft times) and making better use of the tuned curve in 2nd and 3rd gear. Shift point for the SLP/TPI combo was 5500/5300 and 5800/5500 for the FIRST, but it ran the same ET’s shifting as high as 6000/5800.

While intake flow numbers in and by themselves have little to do with RPM capability, typically the higher flowing intakes are larger in cross-sectional area and subsequently have the POTENTIAL to pull to a higher RPM – again, this is especially so when the head’s MCSA is larger than the intake’s.