Viper motor gurus need advice on how to get to 550whp

[AIllick]

Hi all.

I need to get the motor in my autocross car to at least 550whp. I need as broad and flat of a torque curve as possible for really good digs out of corners in 2nd gear. I need a really good bang for the buck option here. I'm open to the idea of converting the car to flex fuel and running a E85 tune for when I'm at the track racing.

Here's what's in the car now.

Fresh gen 2 creampuff short block
Bellanger headers
Open 3" sidepipes
Gen 1 airbox with K&N filters and smooth tubes
Stock gen 2 intake manifold
Unknown tune
93 pump gas and E85 easily available

Stock gen 2 heads with:
Fresh valve job with new guides and seats
Stock valve sizes
Stock rockers
Stock compression
LS valve spring conversion
Pocket port

I have access to a good engine builder and machine shop that's eager to develop a Viper porting program, but not sure if the gen 2 heads can get me there. I'm local to Houston TX, but not willing to do any work with Greg Good, too many horror stories about him and HPC.

Will roller rockers, porting the gen 2 heads, and an E85 tune get me there with the stock cam? Or do I need to look at a gen 3 head swap with maybe a custom autox grind cam. I really need a brutal low end pull from this motor.

Thanks for any advice

[Martyb]

Stock cam will not get you where you want to be. I had Dan Cragin do a custom cam and port my heads last year, ended up with 562rwhp and 592rwtq. Car runs very well! It’s a 98 GTS.

[Aevus]

You need a cam.

[Aevus]

Will roller rockers, porting the gen 2 heads, and an E85 tune get me there with the stock cam? Or do I need to look at a gen 3 head swap with maybe a custom autox grind cam. I really need a brutal low end pull from this motor.

Waiting for my race engine to be ready on my gen 3 and I'll be lucky if I get anywhere near 620-640whp... That's with a lot $$ / time invested and sacrifices in the low-end torque (rev limit 6,800-7,000rpm). You might want to consider 3.91 or 4.10 gears as well. Ported head + camshaft might not be sufficient... Valvetrain upgrade unavoidable if it's a moderate/big camshaft.

Also, dyno tune obviously. And don't forget oiling/cooling systems.

[GTS Dean]

For Auto-X, here's an entirely different perspective to consider:

The Belanger headers will work extremely well for your low end torque requirement. Keep the pickles. You specifically want a smooth torque/HP cam grind for control of torque delivery to the rear tires. I did pocket porting and 1.7 rockers on my mostly stock rebuild and the bottom end is gone - but on a big track, I'm almost always over 3500 rpm max torque peak anyway. More rear gear will help with driveability and modulation.

If I were you, I would spend engine money on SUSPENSION instead.

[TKO MOTORSPORTS TEAM]

Have you baselined car yet at an autocross event?

[JonB ~ PartsRack]

Hi all.

I need to get the motor in my [G2] autocross car to at least 550whp. I need as broad and flat of a torque curve as possible for really good digs out of corners in 2nd gear.
I really need a brutal low end pull from this motor.

I agree with suspension Dean3

First make it TURN better.
Then make it BRAKE better.
Then add Power.... or re-gear the HP you have?

Could be as simple as a 3:55 Ring/Pinion. The OE 3:07 is NOT doing you any favors other than longer pulls. NOT "Brutal." Vipers get 'penalized' by shorter courses......

[AIllick]

For Auto-X, here's an entirely different perspective to consider:

The Belanger headers will work extremely well for your low end torque requirement. Keep the pickles. You specifically want a smooth torque/HP cam grind for control of torque delivery to the rear tires. I did pocket porting and 1.7 rockers on my mostly stock rebuild and the bottom end is gone - but on a big track, I'm almost always over 3500 rpm max torque peak anyway. More rear gear will help with driveability and modulation.

If I were you, I would spend engine money on SUSPENSION instead.

Have you baselined car yet at an autocross event?

I agree with suspension Dean3

First make it TURN better.
Then make it BRAKE better.
Then add Power.... or re-gear the HP you have?

Could be as simple as a 3:55 Ring/Pinion. The OE 3:07 is NOT doing you any favors other than longer pulls. NOT "Brutal." Vipers get 'penalized' by shorter courses......

I completely agree that suspension, brakes, etc comes before power. What I didn't mention is the car started it's life as an SCCA road race car. It's fully modified for autox, Moton shocks, adjustable swaybars, StopTech big brakes, roll cage, custom wheels, Quaife diff, autocross spoiler and splitter, and lots of weight reduction getting the car to 3040lbs, etc etc.

I took this car to SCCA autocross nationals in Lincoln Nebraska a few weeks ago and placed 10th in class, and that's with having a broken front swaybar link the first of two days. If it wasn't for the broken sway bar link, the car would have trophied making it the third Viper to ever have done so. I do my own alignments on the car, and have spent a lot of time tuning it to work at autox.

The goal for this car is to score the first SCCA National title in a Viper. The car can do it, but it just needs more power to be competitive in it's class.

The car currently has the stock 3.07 ring gear, but here's the thing.. regearing to 3.55 will reduce the mph at the top of 2nd gear to an unfavorable spot for autox. As some of you guys know, most of the driving in autox is 2nd gear, and the proper mph is really critical. The only option to make the 3.55 work is to swap gear ratios in the T56, or to swap to the 6060.

Maybe that's a solution then. 6060 swap and a rear gear. Anyone know if the 6060 is lighter than the T56?

[AIllick]

Here's the car.

Sasca C5's

Beeville Divisional 4

[AIllick]

Stock cam will not get you where you want to be. I had Dan Cragin do a custom cam and port my heads last year, ended up with 562rwhp and 592rwtq. Car runs very well! It’s a 98 GTS.

Can you tell me more about your setup? That sounds like exactly where I need to be.

What heads did you use, and what work was done to them?

What intake did you use, and what work was done to it?

Who did the tune? What software was used?

Stock pistons? What compression ratio?

Thanks for the info!

[GTS Dean]

I completely agree that suspension, brakes, etc comes before power. What I didn't mention is the car started it's life as an SCCA road race car.

regearing to 3.55 will reduce the mph at the top of 2nd gear to an unfavorable spot for autox. As some of you guys know, most of the driving in autox is 2nd gear, and the proper mph is really critical. The only option to make the 3.55 work is to swap gear ratios in the T56, or to swap to the 6060.

Maybe that's a solution then. 6060 swap and a rear gear. Anyone know if the 6060 is lighter than the T56?

That is the backstory we need to help you. You have a a laudable goal, with a solid chassis and experience-based foundation to build upon. I ran with SASCA back in '94-'95 with my brand new '93 RT. Once I found the Coastal Bend Porsche region and Cabaniss NAS, I practically never did another parking lot again - I think only once with my GTS.

Shifting is definitely a time killer. What I think you might need is a wider power band (more rpm) in a more tailored second gear. Adding more power may allow better acceleration within that rev range and reduce times. OTOH, it might just get you to your next shift point earlier. What you don't want is excessive wheel spin. There used to be a 3:31 gear set for the Super 44 Dana that was shared with the Vette. I've not heard of anyone running that any more.

I would suspect that nearly all of the cars you compete against have ABS, with some even having a TC system. Running a Zero-Nannies Viper is a tough assignment, but I applaud you for the effort!

[Martyb]

Can you tell me more about your setup? That sounds like exactly where I need to be.

What heads did you use, and what work was done to them?
Factory heads ported by Exotic Engines, custom ground cam, 1.7 rockers, bellanger headers, 3” catless Corsa exhaust.

What intake did you use, and what work was done to it?
Stock Gen 2 intake, not modified at all

Who did the tune? What software was used?
Dan and his team at SPT did the tune, and it’s absolutely perfect. The car drives better than when it was stock.

Stock pistons? What compression ratio?
Stock pistons, 10.5:1

Thanks for the info!

Anytime! Give Dan a call, he will custom build to meet your exact needs.

[AIllick]

Shifting is definitely a time killer. What I think you might need is a wider power band (more rpm) in a more tailored second gear. Adding more power may allow better acceleration within that rev range and reduce times. OTOH, it might just get you to your next shift point earlier. What you don't want is excessive wheel spin. There used to be a 3:31 gear set for the Super 44 Dana that was shared with the Vette. I've not heard of anyone running that any more.

I would suspect that nearly all of the cars you compete against have ABS, with some even having a TC system. Running a Zero-Nannies Viper is a tough assignment, but I applaud you for the effort!

Two very good points.

I rechecked mph at 6k rpm in 2nd, and the 3.07 gets me to 83mph. I really need to be around 75mph. The 3.55 gets me to 73, so that's ideal. Plus, the car has the valve train to sing past 6k, so I could tune the limiter to get a few more mph.

The competition in my class are the C5, C6 and C7 Corvette, so I'm definitely battling the abs in those cars. But, I've never actually autocrossed a car with abs, so the instinct is there at least.

I've thought about adding abs to the car, but I'm not sure how competent the gen 2 abs controller is. The last thing I need is to have the ice mode issues that the Corvette guys are always belly aching about. The next step up is standalone abs from a BMW, which may cause more issues than solving.

The key for non abs is to get the right pedal feel for modulation. The pedal feel in the car now is extremely light, so there not enough pedal modulation to really dance on the threshold, plus I can get into lock up before the nose has time to setup on the front tires. I need to find a smaller bore master for the car, and possibly even convert the car to manual brakes. Most of the racing I've done has been with manual brakes, so I know I can get it to work.

[Aevus]

Two very good points.

I rechecked mph at 6k rpm in 2nd, and the 3.07 gets me to 83mph. I really need to be around 75mph. The 3.55 gets me to 73, so that's ideal. Plus, the car has the valve train to sing past 6k, so I could tune the limiter to get a few more mph.

You can use that tool, it's very useful and precise:

https://xse.com/leres/bin/gearratio?...le=30&wheel=19

Make sure to have the actual rear tire height (including wear) and each gear ratio...

If you have an upgraded valvetrain, you can probably bump rev limiter by 100 or 200rpm to get 2-3mph extra in 2nd gear... But it's a bit pointless if the engine cannot deliver more power, not to mention the added stress on oiling/cooling systems.

another solution would be to get slightly bigger rear tire (actual measurement)

[AIllick]

You can use that tool, it's very useful and precise:

https://xse.com/leres/bin/gearratio?...le=30&wheel=19

Make sure to have the actual rear tire height (including wear) and each gear ratio...

If you have an upgraded valvetrain, you can probably bump rev limiter by 100 or 200rpm to get 2-3mph extra in 2nd gear... But it's a bit pointless if the engine cannot deliver more power, not to mention the added stress on oiling/cooling systems.

another solution would be to get slightly bigger rear tire (actual measurement)

Thanks for the link. I usually use the gear calculator on Tremec's website because it has all of the T56 ratios available. Unfortunately I'm stuck to a very specific tire for the kind of racing I do. The car is actually 315 square on a set of custom built 18x11.5 wheels. Probably the only Viper setup that way.

Here's an interesting concept in regard to building some overrev into a motor. 600cc sport bikes typically rev to about 15k rpm or so, but peak power is down around 12k, with the idea that it's better to allow some overrev instead of upsetting the bike midcorner with a shift.

Same idea works in autox where every foot on course counts. The guys who run data will tell you shifting costs about .300 seconds, so it's usually faster to just bang the rev limiter at the very end of a straight. Allowing some overrev is even better even if the motor is nosing over on power.

[usmcfieldmp]

The guys who run data will tell you shifting costs about .300 seconds, so it's usually faster to just bang the rev limiter at the very end of a straight.

If my memory serves me well, you can see this in action during the Gen 4 ACR Nurburgring run. I remember a bunch of people getting their panties in a bunch wondering why the driver was running on the rev limiter like he was when approaching corners.

[Aevus]

Thanks for the link. I usually use the gear calculator on Tremec's website because it has all of the T56 ratios available. Unfortunately I'm stuck to a very specific tire for the kind of racing I do. The car is actually 315 square on a set of custom built 18x11.5 wheels. Probably the only Viper setup that way.

Here's an interesting concept in regard to building some overrev into a motor. 600cc sport bikes typically rev to about 15k rpm or so, but peak power is down around 12k, with the idea that it's better to allow some overrev instead of upsetting the bike midcorner with a shift.

Same idea works in autox where every foot on course counts. The guys who run data will tell you shifting costs about .300 seconds, so it's usually faster to just bang the rev limiter at the very end of a straight. Allowing some overrev is even better even if the motor is nosing over on power.

Correct me if I'm wrong but gen 2 and 3 have the same T56 ratios: 1st 2.66, 2nd 1.78, 3rd 1.30 ?

If you're ready to overrev or rev higher (bigger cam) maybe you should consider 3.73 instead of 3.55. If you already have an upgraded valvetrain (what is upgraded?) the cam would be the best route I think, and 6,300-6,400 shouldnt be much of an issue.

I'm not autocrossing or tracking my car so I'm confortable with my 7,000 rpm target but now I'm thinking to switch from 3.73 to 4.10

(3.73 gears) 74.5 / 102 mph in 2nd / 3rd @ 6,250 rpm
(4.10 gears) 75.9 / 103.9 mph in 2nd / 3rd @ 7,000rpm

[TKO MOTORSPORTS TEAM]

Correct me if I'm wrong but gen 2 and 3 have the same T56 ratios: 1st 2.66, 2nd 1.78, 3rd 1.30 ?

If you're ready to overrev or rev higher (bigger cam) maybe you should consider 3.73 instead of 3.55. If you already have an upgraded valvetrain (what is upgraded?) the cam would be the best route I think, and 6,300-6,400 shouldnt be much of an issue.

I'm not autocrossing or tracking my car so I'm confortable with my 7,000 rpm target but now I'm thinking to switch from 3.73 to 4.10

(3.73 gears) 74.5 / 102 mph in 2nd / 3rd @ 6,250 rpm
(4.10 gears) 75.9 / 103.9 mph in 2nd / 3rd @ 7,000rpm

7000rpm can get a little dicey on a hydraulic viper motor.
Gear ratio calculators and simulators are just references never absolutes since most of them don't account for all variables unfortunately. Alot of the time the actual RPM when running is lower then what was calculated. You have to add in your own correction factors if you want more accurate numbers;
Nothing wrong with staying in it and bumping of the chip for a second if motor is under load. It takes more time to shift up and then shift back down then it does to stay in it and carry it in. The only trade off is the cars dynamics will be compliant in a more balanced load condition then if she's completely wound tight coming into a corner.

[Aevus]

7000rpm can get a little dicey on a hydraulic viper motor.

Yes it is. Will be the guinea pig in few weeks...

Doing pretty much everything I could:

- high duration custom camshaft
- ported heads
- 3.5'' high flow exhaust + headers
- oversized valves and pushrods
- lightweight conical springs + titanium retainers
- Prefix hyd lifters w/Truarc
- forged pistons lightweight 4032 alloy
- forged rods
- 11.5:1 compression
- overbalanced and machined crankshaft
- oversized oil pump rotor

Will minimize preload on the hydraulic lifters:
https://www.motortrend.com/how-to/ad...e-top-end-rpm/

Valvetrain should be perfectly fine. Not 50k miles fine but at least 2-3 years, oiling shouldnt be an issue, especially since I won't track the car very often or at all. Same for cooling.

7,000 rpm is the target but 6,800 would be satisfying.

[TKO MOTORSPORTS TEAM]

Yes it is. Will be the guinea pig in few weeks...

Doing pretty much everything I could:

- high duration custom camshaft
- ported heads
- 3.5'' high flow exhaust + headers
- oversized valves and pushrods
- lightweight conical springs + titanium retainers
- Prefix hyd lifters w/Truarc
- forged pistons lightweight 4032 alloy
- forged rods
- 11.5:1 compression
- overbalanced and machined crankshaft
- oversized oil pump rotor

Will minimize preload on the hydraulic lifters:
https://www.motortrend.com/how-to/ad...e-top-end-rpm/

Valvetrain should be perfectly fine. Not 50k miles fine but at least 2-3 years, oiling shouldnt be an issue, especially since I won't track the car very often or at all. Same for cooling.

7,000 rpm is the target but 6,800 would be satisfying.

Why be a guinea pig; We have been there done that learn from our expensive mistakes. Rev limiter at 6800rpm you should be ok with hydraulic on track. Its not the lifter thats the problem its the oil galley feeding the lifter. The lifter passes by the hole so quickly at 7K the lifter wont stay pumped up. After having problems we now only install Kevin Singleton's ( exotic engine) de-stroked solid motors in our more aggressive street and track cars. 8k rpm not a problem with these motors if you need to carry RPM. Little more work running a solid motor for sure but well worth the piece of mind, longevity and in the long run cheaper.

[Aevus]

Why be a guinea pig; We have been there done that learn from our expensive mistakes. Rev limiter at 6800rpm you should be ok with hydraulic on track. Its not the lifter thats the problem its the oil galley feeding the lifter. The lifter passes by the hole so quickly at 7K the lifter wont stay pumped up. After having problems we now only install Kevin Singleton's ( exotic engine) de-stroked solid motors in our more aggressive street and track cars. 8k rpm not a problem with these motors if you need to carry RPM. Little more work running a solid motor for sure but well worth the piece of mind, longevity and in the long run cheaper.

I won't be pushing that engine 7,000rpm on the track. In fact, I wouldnt be confortable with anything north of 6,600-6,700 except for street/drag. It's a roadster anyway, born for street use...

I sure won't be dogmatic about the 7krpm mark. We'll see on the dyno, if it doesnt pull beyond 6,500 I see no reason to set the rev limiter higher, it's not like AIllick who needs a certain speed in 2nd gear for autocross.

[Aevus]

... also I only have compe coupe's swing arm oil pan and Prefix's oil pump rotor... but with suspension/tires that can generate some serious G's. Sure not drysump's safe here.

TBH I'll buy another 981 GTS or GT4 if I ever want to seriously track again

[Aevus]

Gear ratio calculators and simulators are just references never absolutes since most of them don't account for all variables unfortunately. Alot of the time the actual RPM when running is lower then what was calculated. You have to add in your own correction factors if you want more accurate numbers;

You were right TKO, gear ratio calculator was off.

Yesterday I used a GPS speedometer and matched it with 1,500rpm in 6th gear (67mph) + 2,500rpm in 5th gear (74mph), assuming the rpm gauge is accurate...
Since I don't know if it's the gears or the tire that are off, I decided to just change the tire diameter (Kumho ACR 355-30-19, 50% wear) to 27.88'', while it says 27.4'' brand new...

Now it matches reality-simulation.

[TKO MOTORSPORTS TEAM]

You were right TKO, gear ratio calculator was off.

Yesterday I used a GPS speedometer and matched it with 1,500rpm in 6th gear (67mph) + 2,500rpm in 5th gear (74mph), assuming the rpm gauge is accurate...
Since I don't know if it's the gears or the tire that are off, I decided to just change the tire diameter (Kumho ACR 355-30-19, 50% wear) to 27.88'', while it says 27.4'' brand new...

Now it matches reality-simulation.

As long as you know calculators and simulators are just to get you in the ball park they are great tools. Solid parts like gears are pretty dang accurate for the most part; Soft parts like tires are where the most inconsistences hide. Tire growth, mfg inconsistences, tire deflection to a certain degree will all throw your numbers off ; so you have to find your correction factors. Of course this all depends on how far down the rabbit hole you want or need to go.

[Aevus]

As long as you know calculators and simulators are just to get you in the ball park they are great tools. Solid parts like gears are pretty dang accurate for the most part; Soft parts like tires are where the most inconsistences hide. Tire growth, mfg inconsistences, tire deflection to a certain degree will all throw your numbers off ; so you have to find your correction factors. Of course this all depends on how far down the rabbit hole you want or need to go.

I took for granted the 0.75 ratio on the gen 3's 5th gear but it seems to be 0.74, which makes more sense now. My ''tire correction factor'' is now 27.52'' for that 355 ACR tire 50% wear. I triple-checked with the 4th gear and it matches almost perfectly (66mph @ 3,000rpm).

The only thing left that is a little off is the top speed at rev limit (6,250): on the simulator its 77.1 mph @ 2nd gear while I get constant 79mph GPS reading. So either the rev limiter is not precise or the car continues to accelerate a little after cut off...

But anyways, I placed the order for the 4.10 gears to go along my high-rev engine and on the simulator I get 76.3mph @ 6,800rpm, so very similar... And max of 135.8 mph in 4th gear, which is about the max trap speed on 1/4 mile I will be able to go. If I'm lucky, I will be able to set the rev limiter to 7,000rpm for 140mph. I'm not building a drag car at all, but would be interesting to give it a try.
Also, on my local racetrack the maximum I would be able to go on the stretch is about 135-138mph, which is perfect as I will use mostly 3rd and 4th gears.