SBC TPI 383 ways to reduce torque

[nilak]

Hello,
I'm upgrading my 1991 Corvette to a 383SBC but the torque output is much higher than stock, especially with the stock manifold-long runners, 480Nm vs 650Nm. That would put stress on the transmission, diff and C beam, so I'm searching for ways to reduce max torque to about 500Nm. Power can still remain the same for the upper range.4500-5600. I will use stock manifold and large intake tubes AZS because I need the stock appearance so I need to do it by ECM tuning. One I know is by reducing the spark advance but this I understand would use the same amount of fuel and producing less torque/power. I thought of trying remapping the EGR to run at high throttle and mid rpm so that the amount of oxygen is reduced. Is this a bad idea?
Thank you.

[Fast355]

Hello,
I'm upgrading my 1991 Corvette to a 383SBC but the torque output is much higher than stock, especially with the stock manifold-long runners, 480Nm vs 650Nm. That would put stress on the transmission, diff and C beam, so I'm searching for ways to reduce max torque to about 500Nm. Power can still remain the same for the upper range.4500-5600. I will use stock manifold and large intake tubes AZS because I need the stock appearance so I need to do it by ECM tuning. One I know is by reducing the spark advance but this I understand would use the same amount of fuel and producing less torque/power. I thought of trying remapping the EGR to run at high throttle and mid rpm so that the amount of oxygen is reduced. Is this a bad idea?
Thank you.

EGR is a bad idea all the way around it will cause massive amounts of carbon buildup in the plenum, runners, etc as well as heat the plenum. Best to just cut torque by retarding timing like the OEMs do. Likely you only need to pull around where the TPI runners resonate the highest. Be careful though too much retard will create high exhaust gas temperatures. Another way to cut torque is to prevent power enrichment and run in stoich. Alot of GM and Dodge trucks run in that manner. They will stay in closed loop with less timing at 14.7:1 even at WOT.

[nilak]

Thank you fast355
How safe is to block the acceleration enrichment since less fuel means less cooling effect through evaporation of the fuel?

[sanderson231]

If torque is a concern why a stroker motor? A 350 can make 425 HP

[steveo]

let me ask the question in a way that makes more sense

"how do i reduce the volumetric efficiency of an engine within a certain powerband"

assuming the bore/stroke is already selected the following things affect volumetric efficiency in specific ranges (without affecting it across the board like a restrictor plate)

- camshaft profile (huge effect)
- ignition timing (medium effect)
- scavenging from exhaust configuration (small effect)
- intake runner length (small effect)

so yeah by that logic you probably want a different cam to achieve this goal that i don't agree with


How safe is to block the acceleration enrichment since less fuel means less cooling effect through evaporation of the fuel?

the cooling effect is small and needs to be proportioned against ignition timing to avoid knock. it's really hard to blow up an n/a engine even under heavy load unless you go really lean.

[nilak]

Thank you, The cam profile with a carburettor setup has 468lbft @4000rpm, and 400lbft@5500 420hp495”/.502” Lift, 220°/224° Duration @ .050”, 112 LSA, a different option they tested is 450hp[/B]: .510”/.521” Lift, 231°/236° Duration @ .050”, 111 LSA with 488lbft @4000. So the first cam seems good. I don’t know if it’s worth looking for a different cam with flatter curve, if that’s even possible. The TPI will probably make it worse. I can use large runners, these will raise the torque by like 40lbft everywhere according to a test I’ve seen. Probably they won’t be able to produce as much power as the carburettor configuration which has a smoother flow. I’ve seen test with as much as 80lbft reduction when using 11 degrees of total advance but for that I plan to install and EGT. I already have 1 extra slot for AFR and 2 more at the front of the preconverters (these are 100CPSI metallic).

[el Jefe]

Hello,
I'm upgrading my 1991 Corvette to a 383SBC but the torque output is much higher than stock, especially with the stock manifold-long runners, 480Nm vs 650Nm. That would put stress on the transmission, diff and C beam, so I'm searching for ways to reduce max torque to about 500Nm. Power can still remain the same for the upper range.4500-5600. I will use stock manifold and large intake tubes AZS because I need the stock appearance so I need to do it by ECM tuning. One I know is by reducing the spark advance but this I understand would use the same amount of fuel and producing less torque/power. I thought of trying remapping the EGR to run at high throttle and mid rpm so that the amount of oxygen is reduced. Is this a bad idea?
Thank you.

I face a similar problem with my 75' Vette so, I know where you are coming from. One thing I think you are missing is all the torque in the world won't do a thing if the tires aren't gripping. You can use your tires as a "safety valve" so to speak. Select tires that have a higher wear rating or a narrower footprint and they will begin to slip, AKA burnout, once your torque passes a certain level.

Or build a stronger transmission? I believe a C4 has 2 options for the differential, late C3 did. One is stronger than the other.

You've already hunted the bear, might as well enjoy the fruit of your labors...

[nilak]

Yes, tires will limit the differential torque, I think my car has a dana 44, they can handle street legal tires or better. Output rated torque is 3460lbft. A braking coefficient of 1 for a street tire would mean about 2000lbft.
Now in a low gear you will break traction at below 350lbft engine torque (@low rmp) but in a higher gear tires will not help and a high engine torque will have to be managed by the transmission gears. the transmission is said to be able to withstand even 480lbft but I prefer it as low as possible (400 is plentiful, lower than that would mean low power because I canÂ’t go higher than 5600rpm).
the plan wii be: timing retard and egt monitoring.

[sanderson231]

I still don't get it. Is someone giving you a 383? Everybody I know that stroked a 350 to 383 with the 400 crank was looking to increase torque. Just install a 350 and spin it faster.

[nilak]

I still don't get it. Is someone giving you a 383? Everybody I know that stroked a 350 to 383 with the 400 crank was looking to increase torque. Just install a 350 and spin it faster.
My old engine is at the point where it might need some refreshing soon, 135k miles, it still runs well though, but I wanted a bit more power, stock 245hp is not bad considering the high torque also. I donÂ’t think upgrades for this engine are a good idea because it would require a lot of components to be changed and there is a change of something not working as planned so while I still can I wanted to take the opportunity to buy a new engine. I can also try preserve the old one.
IÂ’ve been searching for a while for a new engine and the most interesting was this 383, a 350 wasnÂ’t available there because most people appreciate the 383. Anyway. At 4500-5000 (tel:4500-5000) rpm where I think is a safe limit to run it when I want to go fast the, 383 makes enough power. Would a 350 would make more power there or more likely above 5500 ?there it enters different territory upgrades. definitely not with a TPI manifold that I want to stick with, and less reliability

[sanderson231]

My old engine is at the point where it might need some refreshing soon, 135k miles, it still runs well though, but I wanted a bit more power, stock 245hp is not bad considering the high torque also. I donÂ’t think upgrades for this engine are a good idea because it would require a lot of components to be changed and there is a change of something not working as planned so while I still can I wanted to take the opportunity to buy a new engine. I can also try preserve the old one.
IÂ’ve been searching for a while for a new engine and the most interesting was this 383, a 350 wasnÂ’t available there because most people appreciate the 383. Anyway. At 4500-5000 (tel:4500-5000) rpm where I think is a safe limit to run it when I want to go fast the, 383 makes enough power. Would a 350 would make more power there or more likely above 5500 ?there it enters different territory upgrades. definitely not with a TPI manifold that I want to stick with, and less reliability

A TPI intake is like a restrictor plate on a 383. I'm not sure that peak torque will be a problem. I have DynoSim which has the TPI intake option built in. Tell me more about the engine and I will plug it into DynoSim and sees what it says about torque and HP.

[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.

[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)

[sanderson231]

IÂ’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 itÂ’s rated by the manufacturer dor a lower torque (I think 400lbft). But taking into account itÂ’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.

What I read is that the 92 and earlier ZF6's were German made and rated for 450 ft-lbs. GM licensed the design and in 1993 began making their own. They changed the design of some of the helical gears to lessen gear noise and then rating dropped to 400 ft-lbs.

I also came across a thread where corvette owners were successfully drag racing with the Dana 44 differential and laying down some low 60 ft times. Not sure is you have Dana 36 or the Dana 44 but the 44 sounds strong. I did find info that said the 1993 and later Dana 44's were somewhat stronger.

I think you are being overly paranoid about breaking stuff. Install a good clutch and drive the car. If something breaks upgrade it.

[sanderson231]

C beam upgrade:

https://www.corvetteactioncenter.com/product-reviews/chassis-and-suspension/product-review-zr51-performance-c4-corvette-beam-plates/

[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.
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[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.
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