SBC TPI 383 ways to reduce torque

[nilak]

That would be interesting
it is a restrictor but it also accelerates the flow at low rpm.
compression 9.8:1.
Rocker Arms: 1.5 Ratio, Full-Roller
Cylinder Heads: Aluminum, 180cc Intake Port, 2.02"/1.60" Valves, 65cc Chambers,
cam: 495”/.502” Lift, 220°/224° Duration @ .050”, 112 LSA
then stock exhaust manifold (then straight pipe track, cats for street) and intake manifold (probably will need match porting),
I’ll try TPIS throttle body but probably -minor differences

there is a guy on Yt, @richardholdener1727 and he did all sorts of tests with these engines, like tpi vs carb manifolds, you can get an idea of what kind of torque curves you can expect, even with different timing advance settings. I have the carburetor dyno chart.
the chart has max 468lbft. I’m expecting 500lbft and 380-400Hp. :)

[sanderson231]

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.

[nilak]

thank you, that’s a little disappointing :)
the guy that made those tests manage 330Hp on a mild cam 98 tpi, but with headers, no air filter, electric water pump, no alternator. I wonder why such differences
266 hp is ok but since this engine can do 420 I should search ways to make it faster, like large runners, with stock look but makes it harder to work on it.

[sanderson231]

The advertised specs for a 1991 TPI are 250 Hp and 375 ft-lbs of torque. DynoSIM was close to that so I think that it is a net HP (with accessories). I have also modeled a 2.3L w41 Quad 4 that is advertised for 190 HP and DyniSIM was also fairly close. I reran the L98 with large tube headers and an open exhaust and it made a huge difference - 330 HP @ 4500 rpm and 467 ft-lbs @ 2500 rpm

An LT-1 intake (requires LT-1 heads) from a 1992 vette has more upside for horsepower production with less torque. If you are locked into a max torque number a 350 will make more horsepower than a 383 at the same peak torque. DynoSIM included a model for a streetable 302 SBC (carbed). It made 433 HP @ 6500 rpm and 397 ft-lbs @ 4500 rpm. Note that HP is higher than torque. Fun engine with a standard transmission. I still dream of owning a 67-69 Z-28 Camaro some day.

[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.

[nilak]

thank you

[1project2many]

This generation of Corvette is traction limited. IME that's going to save the rear axle and transmission. You can reduce the engine torque at a given throttle angle using the tuning methods suggested, by reducing spark advance and delaying or eliminating power enrichment. Eliminating or delaying the onset of power enrichment also reduces fuel consumption. Setting knock retard to quickly reduce spark advance at the start of knock while decreasing the rate at which spark advance is returned to normal is a quick way to pull spark advance without spending large amounts of time re-working the main spark table.

Final drive ratio really is a huge player here. Final drive ratio will determine cruise rpm. Numerically higher or lower FDR will move the engine to an RPM that is below or above peak torque production at a given speed. Numerically higher FDR allows faster acceleration which reduces the amount of time high torque must be applied to the drivetrain. Numerically higher FDR reduces the amount of torque applied to the transmission to result in acceleration. Numerically higher FDR combined with tires selected for acceptable but not excellent traction trains the driver not to apply too much throttle. Mechanically, larger diameter throttle cam and / or altered throttle pedal pivot point will change the ratio of pedal movement to throttle angle change. Changing the relationship so more pedal movement is required per degree of throttle change will allow better control of torque. Many drivers truly appreciate a high torque engine operated by a consistent and easy to control throttle. Many drivetrains live a long and happy life if the car is configured so the driver has more ability to control how much torque is produced.

[steveo]

pedal vs throttle angle is an interesting point to debate. what actually happens when you modify the pedal to throttle plate linkage is there is a very advanced closed loop controller on the other side of the pedal - the driver. the driver takes the input of the desired speed and produces a pedal output and has a neurological response rate that adapts and remembers. i have logged throttle inputs and outputs while modifying drive by wire throttle maps and found the driver naturally compensates to achieve the desired output totally in spite of the linkage over time. in other words, no matter what throttle angle is produced by the pedal, the driver will learn and compensate, and you can't really de-tune an engine with ratios or plate sizes or drive by wire mapping outside of a linear response, for the same reason you can't change the AFR of a closed loop narrowband engine - the controller will just throw your changes out and you are just making things harder for the controller.

[nilak]

I've did a several tests on my new 383. The engine has a 1205 head ports size, ported lower base and ported runners from Edelbrock, ported stock upper plenum, but stock exhaust manifold with racing preconverters and straight trough downpipe and straight through muffler (detachable plugs for noise reduction in town).
I watched some comparisons between different intakes and engines, collected the data and I've made some estimations. The estimated gross power (no accessories and racing headers) would be 434HP@4500rpm which is higher than the builder dyno test on carburettor that is 424@5000rpm. The max net Hp sould be 380HP@4500Rpm; and 657Nm@3800rpm, taking into account the muffler restriction - 5% reduction in power. However, the guys that tested the car, maniflod vs headers probably had a better suited manifold, probably better then mine and in an engine that made 357Hp with good headers. After that, I've decided to make an estimation based on VE and injector BPW as well. I've set a formula in TunerPro that shows instant POWER based on BPW and it shows me 270Hp@3750rpm. Based on VE, by comparing stock charts and stock tune, I got 293@4700rpm and 490Nm@3500rpm. However, when I did some laps on a race track, I pushed it up to 3200 where it would go lean, but still, the telemetry showed it was slightly faster than the stock l98 that was reved to 5000. The spark advance was set to 32* and cut by knock sensor (possibly too sensitive or due to lean mixture 13.2:1) to 29*. So I would say, I should expect around 320 peak HP on the dyno after I finalise the tuning, and at this time. I don't see reasons to need torque reduction spark advance curve. The torque curve is only around 20% higher than stock, and when I drive it, it feels faster, I would say 20% seems close to what it feels like. It pulls hard and spins the wheels much easier but the l98 is not bad either.
VE.jpg
comp.jpg

[nilak]

I've did a several tests on my new 383. The engine has a 1205 head ports size, ported lower base and ported runners from Edelbrock, ported stock upper plenum, but stock exhaust manifold with racing preconverters and straight trough downpipe and straight through muffler (detachable plugs for noise reduction in town).
I watched some comparisons between different intakes and engines, collected the data and I've made some estimations. The estimated gross power (no accessories and racing headers) would be 434HP@4500rpm which is higher than the builder dyno test on carburettor that is 424@5000rpm. The max net Hp sould be 380HP@4500Rpm; and 657Nm@3800rpm, taking into account the muffler restriction - 5% reduction in power. However, the guys that tested the car, maniflod vs headers probably had a better suited manifold, probably better then mine and in an engine that made 357Hp with good headers. After that, I've decided to make an estimation based on VE and injector BPW as well. I've set a formula in TunerPro that shows instant POWER based on BPW and it shows me 270Hp@3750rpm. Based on VE, by comparing stock charts and stock tune, I got 293@4700rpm and 490Nm@3500rpm. However, when I did some laps on a race track, I pushed it up to 3200 where it would go lean, but still, the telemetry showed it was slightly faster than the stock l98 that was reved to 5000. The spark advance was set to 32* and cut by knock sensor (possibly too sensitive or due to lean mixture 13.2:1) to 29*. So I would say, I should expect around 320 peak HP on the dyno after I finalise the tuning, and at this time. I don't see reasons to need torque reduction spark advance curve. The torque curve is only around 20% higher than stock, and when I drive it, it feels faster, I would say 20% seems close to what it feels like. It pulls hard and spins the wheels much easier but the l98 is not bad either.
VE.jpg
comp.jpg

[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..

[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.