SBC TPI 383 ways to reduce torque

[nilak]

330Hp @~4700 is what I saw in the real dyno test with mild cam, and stock tpi. He is using large headers on all test. The 383 cammed, stock TPI manifold made 410hp constant between 4500 and 6000rpm. So between large tube intake runners and headers, the last seems be a better idea considering your DynoSim results.

[Fast355]

I made some runs with DynoSIM. For ambient conditions I assumed 77 'F, 50% humidity and 1000 ft elevation

I first made a baseline run for a 350 with a TPI intake and the following:

stock port head head with 2.02" intake and 1.6" exhaust valves
9.5:1 compression ratio
48mm throttle body bores
Generic performance street cam
-0.552 valve lift intake and exhaust
-274/286 degrees duration @ 0" lift intake/exhaust
-230/236 degrees duration @ 0.050" lift intake/exhaust
-110 LSA
-60 degrees of overlap

This resulted in 262 HP @ 4500 rpm and 375 ft-lbs @ 3000 rpm. Stroking this engine to a 383 with 9.8:1 CR gives 270 HP @ 4000 rpm and 407 ft-lbs @ 3000 rpm

Using your cam specs for the 383, I get 262 HP @ 3500 rpm and 422 ft-lbs @ 2000 rpm. Increasing throttle body bores to 58mm gave 266 HP @ 4000 rpm and 423 ft-lbs @ 2500 rpm. Sorry but this is what DynoSIM predicts for a TPI intake.

If you want to stay with the 1990's look, you could consider picking up a used 1992-1997 LT1 and getting it rebuilt to your specs.

I can tell you my 383 of similar specs with TPI made 410 tq at the tires and 357 hp through a 700r4 and GM 12 bolt. The 700r4 was the weak link. Put a 5,300 lbs G20 van down the 1/4 at 13.8 @ 99 mph with a 3.07 rear gear. A stock L98 is close to 300 hp at the crank without accessories aka SAE gross rating.

Something is way off in your dyno sim. Mine peaked at 5,200 in hp and about 3,500 in torque.

[steveo]

you can absolutely put a built engine behind a tpi intake and make power. it'll always be at its best with a peanut cam and an engine tuned for low end grunt, though. there's a reason GM stopped making intakes like that - they look cool, but they really suck in the real world. this original point of this thread was about reducing low end torque, and low end torque is the only thing the TPI is really good at, although in my experience tuned intake runners are really unpredictable with modified engines.

[Fast355]

you can absolutely put a built engine behind a tpi intake and make power. it'll always be at its best with a peanut cam and an engine tuned for low end grunt, though. there's a reason GM stopped making intakes like that - they look cool, but they really suck in the real world. this original point of this thread was about reducing low end torque, and low end torque is the only thing the TPI is really good at, although in my experience tuned intake runners are really unpredictable with modified engines.

I do not agree at all. No other intake except the belt driven kind will make more mid-range torque. NONE of them!

[steveo]

i've seen then have good mid range VE boost on some engines at not others. i'm willing to bet the cam was the determining factor, since intake closing events are the primary driving force behind a tuned runner like that. the stock LB9/L89 cams really rip in the mid range..

[nilak]

Something is way off in your dyno sim. Mine peaked at 5,200 in hp and about 3,500 in torque.

Did you run it with headers or with a stock iron manifold? But yes, it still seems off. Can you gain 144hp only by installing large headers and removing water pump, alternator, smog pump?
With the tpi, although it’s made for torque, it can still make power, obviously it’s not optimised for my application but it can still do the job I want if I can get it to 350hp.

[sanderson231]

I can tell you my 383 of similar specs with TPI made 410 tq at the tires and 357 hp through a 700r4 and GM 12 bolt. The 700r4 was the weak link. Put a 5,300 lbs G20 van down the 1/4 at 13.8 @ 99 mph with a 3.07 rear gear. A stock L98 is close to 300 hp at the crank without accessories aka SAE gross rating.

Something is way off in your dyno sim. Mine peaked at 5,200 in hp and about 3,500 in torque.

I selected TPI from the drop down for intake type. Select dual plane, high flow intake with no other changes and you get 295 HP @ 5000 rpm and 360 ft-lbs @ 3500 rpm.

I have limited experience with DynoSIM but on the few engines I have modeled it seems close to the GM published SAE net rating. Why even talk about gross - most cars need accessories.

[sanderson231]

I do not agree at all. No other intake except the belt driven kind will make more mid-range torque. NONE of them!

I do not agree at all. No other intake except the belt driven kind will make more mid-range torque. NONE of them!

I watched a couple of the Richard Holdener videos and it is crazy how much peak torque the TPI intake makes. But the problem is that the OP is concerned about too much torque. So that leaves three options; 1) detune the engine to make less torque (and give up HP), 2) drive the car conservatively or 3) use a different intake. I like sports cars that feel like sports cars (Quad 4 in a Pontiac Fiero) so I would select the latter.

There is a lot of reasonable experience in the Fiero World running V-8's and 3800 supercharged engines on a 5 speed, manual transaxle rated for 200 ft-lb. So I think that GM's torque ratings are conservative. I suspect that the 383 the OP has chosen with a TPI intake would be reliable with no other torque management than reasonable use of the right foot.

[Fast355]

Did you run it with headers or with a stock iron manifold? But yes, it still seems off. Can you gain 144hp only by installing large headers and removing water pump, alternator, smog pump?
With the tpi, although it’s made for torque, it can still make power, obviously it’s not optimised for my application but it can still do the job I want if I can get it to 350hp.

LONG Thorley Tri-Y headers (collectors equal with the trans mount crossmember on the 700r4) and factory GM true dual 2.5" exhaust with a X-pipe added. The exhaust was factory from under the driverside middle passenger seat where I added the X pipe to the tailpipes. Then I had my local muffler shop bend up 2.5" pipes to connect the header collectors to the X-pipe.

[Fast355]

I selected TPI from the drop down for intake type. Select dual plane, high flow intake with no other changes and you get 295 HP @ 5000 rpm and 360 ft-lbs @ 3500 rpm.

I have limited experience with DynoSIM but on the few engines I have modeled it seems close to the GM published SAE net rating. Why even talk about gross - most cars need accessories.

Because gross is what an acurrate engine dyno would reflect in testing you see from the magazines and Richard Holdener. Well aware that NET testing with a full intake system, full exhaust with mufflers and what not will cost 30-40 hp. For a comparison purpose it is good to know. Fuel injector sizing will also be off gross hp.

[nilak]

I watched a couple of the Richard Holdener videos and it is crazy how much peak torque the TPI intake makes. But the problem is that the OP is concerned about too much torque. So that leaves three options; 1) detune the engine to make less torque (and give up HP), 2) drive the car conservatively or 3) use a different intake. I like sports cars that feel like sports cars (Quad 4 in a Pontiac Fiero) so I would select the latter.

There is a lot of reasonable experience in the Fiero World running V-8's and 3800 supercharged engines on a 5 speed, manual transaxle rated for 200 ft-lb. So I think that GM's torque ratings are conservative. I suspect that the 383 the OP has chosen with a TPI intake would be reliable with no other torque management than reasonable use of the right foot.

The car is registered as historical, I have no idea what kind of checking they will do for the next inspections so it’s safer to stick with the stock intake.
I can apply appropriate throttle and that will be more efficient and safer for the engine but I don’t know how consistent can I be. The engine can produce high torque even at a small opening of the flap, but It should be that hard

[steveo]

the logic still seems weird to me. you could choose any engine in the world, you went and chose one that you feel is way too powerful, and you want to repair that error electronically to make exactly the powerband you want.

it's possible to get close by making your ignition and AFR totally incorrect (a purposefully bad tune) but considering there is a gigantic lobe filled rod that contains most of the actual parameters controlling your powerband, if you really want to reduce low end torque and increase high end power, and the bore and stroke must remain the same, the correct parameter to modify is the cam

are you sure you can't just spend the extra time and money beefing a few things up to handle the power?

[sanderson231]

I just looked up specs on 1991 ZF6 transmission and it is rated for 450 ft-lbs. Not sure what the clutch and rear end is good for but doubt that the transmission is too weak unless you like to rev to 3000 rpm and drop the clutch.

[nilak]

I’ve watched this presentation youtu.be/E0yZdLkpvR0 some while ago and these guys did some extensive research on this transmission. They say it can handle even 475lbft although it’s rated by the manufacturer dor a lower torque (I think 400lbft). But taking into account it’s now over 30 years old and 130k miles, I thought something like 400lbft would be better for reliability. Anyway 12% over 400lbft does seem a huge step, it could be safe.
Another problem can be the the C beam, but that basically depends on the output torque not input (engine) torque and I think can be a problem if you use drag tires even with std engine, 1&2 gears can generate enough torque up to race tires traction break up.

[LeMarky Dissod]

nilak, IFF I were stuck in your shoes (big if), I'd start by:
a. calibrating the spark map using 87 octane instead of 91 or 93
b. NOT using WOT-PE below, say, 2750RpM
c. under-utilizing WOT-PE from 2875-4000RpM
d. saving for a smaller cam, if not a smaller crank or engine (whichever happens to turn out cheapest)