Why is my 2001 ACR so slow?

[Supercharged Vipermad]

Does anybody really know what engine changes there were between the 2000 & 2001 model year. At first I thought the motors were identical, then the window sticker had me wondering. The hp rating on the ACR was 450 and torque was 490 (down from 460/500). The gas mileage in the city went from 20 to 21 (from 2000 to 2001).

It didn't seem like a big deal, but after I put 1000 miles on the car (finally broke a car in properly!) and ran it ******* the street it felt slow. I thought it was because my '98 had headers and my sense of speed was warped, but my mechanic, David Jenkins who drives these cars all day long, felt that it was slow too.

I took my car this weekend to RTG Dyno and ran it with Chris Costa's '97 GTS. His car is IDENTICAL, modification-wise, to my 2001 ACR (K&Ns & smooth tubes ONLY). My car pulled a best of 379hp in 3rd gear (I know 4th is 1:1, but the dyno compensates)! Then I ran it in 4th gear and the best I got was 394 horsepower and 430 lb/ft of torque! I was hoping the dyno was just calibrated low until 10 minutes later Chris pulled up and dropped a 422 horsepower/450 lb/ft Scud on me. The ONLY difference other than year is the fact that his car has 12,000 miles to my car's 1,000 miles.

I know the car will gain a couple of hp with time, but 28-43 horsepower is absurd! What gives? I've heard people say they think the cam is different, but does anybody really know why the rating dropped and mpg went up? I can't imagine that normal tolerances would allow me to have such a drastic difference (you can TOTALLY feel it).

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[Mamba man steve]

I am with you, I hope to have my RT next month. D.C. is now only giving us the rated HP. Everyone before us had a bonus, you might try speaking to a higher authority Jon B. might have some inside dope. So now we must go inside the engine to be even with our fellow Viper owners. Does not make me happy at all!

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[Fred(DrivingSchool)Kinder]

Milder Cam reduced NRG which so many have complained about. Emissions were likely an issue. All speculation.

 

[Joseph Houss]

Jon B will probably respond to you with some technical highlights but until then:

394 x 1.15 (driveline loss) = 453 HP just about perfect! (especially for a brand new Snake)

Chris' car is either hiding some upgrades (headers? exhaust?) or is one quick snake!

Jon and others have mentioned that it really takes 2,000 miles before our motors are "loose"...so be patient, replace that cat back, and enjoy.

By the way..."feeling fast" has a lot to do with sound...and the 2000+ Snakes are definitely much quieter, which could be one of the factors contributing to your belief. Snake Oyl, Sean Roe, Mike Adams, Borla, Corsa, and all our aftermarket suppliers can help 'ya "feel fast".

 

[luc]

My understanding of the certified HP and torque rating on the ACR is that it always has been the same than the regular Viper(450 and 490).
That is due to the fact that DC didn't wanted/want to spend the extra $ for the certification of an different engine with the EPA and the CARB.
Regarding your 2001 low dyno #.
1000 miles is very low to have full power on an engine.
Assuming that the engine is the same than the 2000,easy to check with a comparison of parts # between 2000 and 2001,I will suspect the PCM, part # for a 2000 is 4865 406 AA and 4865 413 AA for export.
I have a Mopar race PCM that I could loan you to see if indeed the power loss come from the 2001 PCM.
Luc.

 

[jcaspar1]

Your engine may just need more time to break in. Chris's car is right on as I have a 97 GTS with tubes/K&N's and 12k miles that dynoed at exactly 422 SAE also. I would expect you to see some more HP with time.

 

[Steve-Indy]

You make GREAT points, Joe! I do wonder what DODGE says about the drive line loss and therefore what THEY say (IN PRINT ) the conversion factor really is...I have seen MULTIPLE posts here by honest folks, all using different numbers in the .12-.17 range...again, it would be HIGHLY DESIRABLE to know a VALIDATED, REPRODUCIBLE, DOCCUMENTED reference FROM DODGE for the various years of Vipers...Can anyone point me in that direction?? Happy Holidays to All !

 

[Venom Lover]

Paul,
That *****. I didn't realize Dodge de-rated the ACR from 460 to 450 fwhp. I agree, I can't see your car picking up 25 hp just from break-in, but perhaps we'll be surprised.

Joe,
453 fwhp might feel "perfect", except that many of us with "older" Vipers far exceeded the factory claim of 450 fwhp. My car dyno'd at 424 rwhp when it was bone stock (SAE corrected on a Dynojet 248C at R&D Dyno in Gardena, CA). With your 1.15 factor, that's 487 fwhp. You can easily see why Paul might not feel that 453 fwhp is perfect when he was driving around with 30-40 hp more in his previous ACR! Also, I know Chris's car, and he's not hiding anything.

Steve,
I have no idea what DC actually claims, but you know there is an area in the VCA FAQ that discusses this issue. I don't know where the numbers come from or how accurate they are, but they say 13-15% driveline loss. (E.g., rwhp=(1-.13)*fwhp)
www.viperclub.org/faq/powerfaq.html

 

[David Jenkins]

hey guys, first off, the car IS soft. it's down on power for sure. that's the first thing i noticed when i drove it. joe, it doesn't just "sound" slow, it is slow. just gutless. we've got plenty of parts to get it up where it should be, but the bottom line is that the car is about 20 hp short of chris'. his car only has k&n's.( i work on his car too) i know it's stock. thank's for the pcm offer luc, i've got a couple different pcms to try. fred, are you for certain the cam is different? i've changed a couple of things on the car, so we'll see how she pulls again.dj

 

[Leonard Knight]

Hey Paul. Sorry to hear about the new car. I just got back to town and am trying to get some miles on my 01 so I can dyno it. I know it feels slower than my 96 but I have a lot of mods on that one. As soon as I can get to at least 1000 miles I will dyno it as well and let you know.

Hope all is well and look foward to seeing you soon.

Leonard

 

[Steve Ferguson]

Paul, give me a call and I will try and make a call for you today.

(Personally, I think all the Guys who run at Viper Days called the factory and asked that they de-tune your car. That is the rumors I keep hearing.)

Best,

Steve Ferguson
800-448-6248
ex. 172

 

[K Adelberg]

Do you want some cheese with your "whine"? Just face it, this year you are going down! Pinouch

 

[2charmed]

Jon B,
Correct as usual. (I think it's spelled differantly though)
Ahcums (sp?)Razor "all things being equal the simplest solution is the most probable" for exact quote see the movie "contact" with Jodie Foster.
And I hope they didn't detune all the blue ACR's because of Mumford. I have one comming so they tell me and I hope it's fast as he!!.

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Happy Holidays,
Steve

 

[David Jenkins]

I wonder how fast Money will be with the brakes, flywheel, exhaust and suspension? Gee............. I hope he can keep up.
We gotta' get one of those shift knobs.

 

[Joseph Houss]

I can't believe that we've first discovered now that every older coupe is underated...it's just not true. We've been on this site for how many years...and occasionally, yes, someone states that there Viper pulled 460...maybe 470 (although I don't recall) total HP...most pull within a 5-7 HP range.

I do believe there could be a problem with Paul's car...(did you try resetting the computer?...just a thought, it still might be assuming you have a "break-in" driving style), but I don't think my '96 was "up" much HP from my 2000...and with some of the posts from 2000's on the dyno...it looks like the 2000's (and I'm just assuming 2001's) will be "up" from the earlier Snakes.

I'm interested in finding out everything you learn about this.

By the way, I'd be glad to swap my 2000 (non-ABS, non-ACR ...but real pretty!) for your 2001 (down on HP..but I'll live with it!)

LOL... I'm sure all will be well!

 

[Mike Brunton]

Paul,

I hate to give you more data to confirm your suspicions, but my '98 with only K&N's and smoothies with 20k miles put 415hp down at the wheels - corrected. BUT, the big number is the torque - it put down 462lb-ft at the wheels, corrected. That's more than 15hp and more than 30lb-ft over your car and yours comes from the factory with the same mods I did.

I don't think you're down on power enough to where Dodge is going to investigate this - 397RWHP is reasonable, although I'd have hoped for more.

FYI, Motor Trend dynoed a '00 RT/10 and got 424RWHP, and a guy in my area dynoed his '00 RT/10 the same day as me and got 415.2RWHP and 456RWTQ (corrected of course).

I wouldn't be surprised if you pick up 10hp from break in, but if you can FEEL the difference in power, then that's not a good thing. I bet you're feeling the loss of torque.

Oh, and one more thing... the correct way to get from RWHP to FWHP is to DIVIDE by the remaining power at the wheels - as a percentage. You don't multiply by 1.15, you divide by 0.85. So 397RWHP would come out to 467RWHP with a 15% loss - and 459RWHP with a 13.5% loss. You're right there as far as #'s go, but it does **** that you're down on power.

Maybe someone else with an '01 Viper can dyno it for us?

 

[Steve-Indy]

I LOVE this Board...Many thanks for all the fine answers, insights, and suggestions. I will TRY to track this " official " drive-line loss in the Viper through Dodge/Team Viper...if any one else gets Dodge's info on this, please POST same. May be time to visit the GOOD FOLKS at Kenny Brown's place here in Indy to test our Vipers just to see " what's happenin' " ! Happy Holidays to ALL.

 

[Bob Woodhouse]

Paul, You have recieved stellar advice from your Viper brethren here, especially Joe H. and Jon B. I have little to add, but think we need to approach this with a well thought out plan. Yes a power test at 1000 miles is potential for a low number. On 00 and 01 engines the piston to wall tolerance is much closer, friction loss will be higher at the outset. Ring packages are different.
All this discussion about the cam, I doubt you will find the specifications are the culprit. To put the record straight, the camshaft lift is the same on 96 model and up, duration is the same, the lobe centers were modified on the 00 and 01 engines, the overlap went from 60 to 66 degrees, meaning both valves are open together a bit longer. This will change torque rpm slightly. Idle quality did improve, yes, but much of that came from the lifter. In the 00 engines and going forward the lifter was changed. In the old days we called them "Rhoades" lifters, or pump up lifters. Probably should call them leak down lifters, but they reduce the valve event at slower speeds to improve idle and off idle torque. Good for 20 ft lbs max. but am unaware of their relationship with the newer camshaft.
I am hesitant to conclude we have anything defective. Keep a couple things in your thoughts, all dyno's have a small amount of variance. There are variances in other measurements as well: ie barometric pressure, engine operating and oil temperature on the pull compared to others.
What is the oil? Original I assume, viscosity differences can bring 7hp. The engine has a learning curve and if the computer or battery was recently disconnected or doing something out of the ordinary the spark and fuel curves may have needed time to normalize. Where did the fuel come from that was in the tank? Was it measured for specific gravity? Fuel can effect horsepower BIG. Hope this helps.

 

[LTHL VPR]

Paul-
As soon as my 2001 yellow ACR is broken in, I will be going to the dyno too. Only 84 miles now. I know what you mean by the 'feeling', but I think it is just that; a hunch/feeling. I don't think these cars are any slower, just quieter.

I have done about 20+ pulls in my 98 GTS, and here is what I found:
1) The Viper and heat are a bad combo. I have done 5 back 2 back passes, and I found a variance of up to 10hp/12ft lbs as the engine sits and heats up and cools down so make sure the engine temp is the same for all runs.
2) How many runs in 4th gear did you do? I would do at least 3 or until you get some consistency and build a baseline.
3) My 98 GTS gained over 10hp between 1500 miles and 4k miles, and it had the older forgesd pistons.
4) I think your numbers aren't bad all things considered.
5) With 1k miles on my 98 GTS I was only able to pull 404hp (best) with a couple runs in the high 300s. Smooth tubes and K & Ns only. However after more miles of break-in, with only headers and exhaust (no cats) I was making 458hp and 495ft./lbs which is more than most other cars with the same setup.
6) Are you more concerned that Dave's car had more hp or that you thought you should have more hp? Remember dynos are very sensitive devices. If the pressure and temp. are not measured properly you can have strange dyno results. The dyno shop I used for years was able to make my 98 GTS go up and down up to 15hp by measuring temp and pressure in different areas of the shop. They claim this is how aftermarket tuners in the car industry give outrageous claims for how much power their components make.
7) My suggestion: At 2k miles go to a different dyno and run your car again. Do 6 runs . Make sure they are consistent. Hopefully you will bemore satisfied with the results.

Good luck! I will post my results after mine has about 1500 miles.
-

 

[kverges]

JonB and others

Not sure I follow the duration figures you give. My understanding is that cam duration is usually in degrees, complicated by whether it is an "advertised" or at .050 lift of the valve with a given rocker arm ratio.

In addition, a shorter duration cam typically has MORE low rpm torque and LESS high rpm torque. I also thought overlap was very significant in both "lope" and where the torque peak occurs. Then there is cam timing . . . . Bottom line is that, traditionally, a better-idling cam usually makes less power. This is much less true these days due to EFI, as low vacuum at idle is not as detrimental as it once was. So I presume a smoother idle is unlikely to increase horsepower. At least my limited knowledge makes me think this way.

As for tighter-fitting cast pistons and break-in, you are still talking at least .002 piston-wall clearance, I would assume, and an extra .001 should not make much frictional difference, would it? I instead assume the ring-bore fit "smooths out" with break-in, reducing the sliding friction of the ring in the bore. This sliding friction should be at least 10X that of the piston alone, I would expect. I would hope that power goes up some with more miles, and would not be surprised to see improved power to 10,000 miles and beyond.

I still think Paul is down on power. My '98 dyno'd at 404 rwhp and 460 torque bone stock and gained about 7 hp with smooth tubes and K&N filters, so Paul seems down about 15-20 rwhp. Chris' car is pretty darn strong for a stocker, that's all I can say.

I only wish the reduced power would make a difference for Paul; I say give him more power but bolt on 4 space-saver spares for the track.

 

[Supercharged Vipermad]

Thanks for the tips, what really bugs me is that there is no way the car will pick up that kind of hp over the next few thousand miles. When I got my new '98 motor (the old one blew up on the freeway, sir) it was noticably faster from the get-go.

Also, the torque is 430, not 453 (as in Chris') and why would Chris lie about his mods? Dave Jenkins put Hennessey headers, pulled the cats and put a Borla cat-back on it, so I'll run it again. The car is obviously faster now, but still noticably slower than the '98 was with the same mods.

I would've thought that with a milder cam I would've made more torque than the '97. But the 2001 was slower everywhere. I just don't get it. Also, the dyno guy said that the 379hp in 3rd gear could be the computer giving it a different map...I don't know why that's different. I know I can get the first 30 hp back quickly (with headers), but after that the law of diminishing returns sets in pretty quickly.

Hopefully, when Leonard's is broken in we can dyno them on the same dyno to see if my car is the problem. I'll also run the '98 when it's in the same stock condition just to see.

I appreciate the help.

 

[Jay Herbert]

This may sound silly, but it is possible the exhaust header gaskets and or throttle body gaskets are installed such that they limit flow.... the latter is a lot easier to check than the former.... these are likely are some of the things that account for variability people see.......

 

[Mike H]

Paul, I heard rumors that adelberg snuke into your garage and added 87 octane gas before the test....thats what I heard..