Dyno Run - Low #s For Current Mods

[Todd Richmond]

I finally had my 97 GTS Dyno tested and the #s are low for the mods on the car (most were put on before I bought it). Peak Hp was 418@5500 and torque was 465@3700 with an A/F ratio starting at 13.5-14 @ 2500 and dropping to 12.4 by 5000. These don't seem dramatically improved from stock

My current engine mod list includes K&N airbox, SVSi headers, Snake-Oyl muffler delete, high flow cats, T&D rockers, BPE heads and extrude-honed intake. The car drives ok with the only minor irritations being soot on the back bumber (seemingly common) and bucking in low rpm traffic. The mechanic checked out vacuum, fuel pressure, throttle bodies but didn't see anything obviously wrong

Any ideas on what to look into next and roughly what #s should I be seeing?

Thanks...

 

[fe155]

I called the company that sells the headers you have , which ive seen it posted that these alone can ad 40hp , anyway he said because of the collector type on them that in California it would run too lean on a stock car . I have a s/c and can adjust the fuel and timing and am waiting for the Belanger headers to arrive. My A/F is starts at 13 and then down to 11 . I think with all your mods and your timing and fuel are stock that may be your problem. To me it looks a little lean .

 

[fe155]

Also check the "FAQ" under the "how to" it list various mods and the increase in power they give .

 

[Todd Richmond]

If I am comparing correctly, it looks like I am down around 100 hp from similar setups! Can A/F being off by about 1 full point make that much difference? Someone mentioned about possibly blocked cats and I have a pair of open pipe replacements I could try, but that is a bit of work
Thanks again...

 

[utahviper]

What is your A/F at peak HP? I don't think your A/F is that bad. Mine was much worse with my 650R.

With the mod's you listed you should have between 475-500RWHP and more than 500RWTQ. Are BPE heads ported and polished with bigger valves?

My 97 with K&N air filter only gave me 414RWHP/459RWTQ. Mod's on 97's give a ton of HP. I would say that Headers/exhaust would give 35-45RWHP alone.

Anyway, check your compression! Very easy to do with a $20 compression gauge, change the sparks while you have them out with the stock champions. Check the CATS to make sure they are in good condition(free flowing). Can you verify that all of these mods are done to your car? Do you have your baffles in your valve covers? If not, then take the oil cap off and look to see if you have T&D's. Also, did you check the A/F on both sides? Next time your at the dyno check both sides. Do you have a friendly viper tech in your area? Have him hook up his OBD2 tool to see if all of the long/short term adaptives are within a normal range. Finally, if you have buddle with a viper in your area, preferable a 96-99 viper, see if they will let you try their PCM in your car. 96-97 PCM are very similar and the 98-99 are okay to try but not as aggressive on the timing curve. Another possiblity is that you have the wrong year PCM in there. You should be able to write down the part number and call a dodge dealer to look it up. Another possiblity is that you have the mopar pcm ( a pile of junk IMHO). I actually lost ~30RWHP with it on my 650R, couldn't even crack 500RWHP with it.

There are many other things to try but my guess is that you will find your problem or at least something that is causing the problem will show up in one of these tests.

Good luck!

Make sure you write everything down and the associated results good or bad.
Post or email me the results and we will go from there. I am not an expert but I have learned a few things from the experiences I have had with my 2 vipers.

 

[Marv S]

Does the car have a sticker for this TSB being done?

PCM - Erratic Rpm Drop/Perceived Misfire
TSB NO: 18-32-97
GROUP: Vehicle Performance
DATE: Dec. 12, 1997
SUBJECT:
Drop in Power / RPM/Perceived Misfire

MODELS: 1997 (SR) Viper Roadster/Coupe

SYMPTOM/CONDITION:Erratic drop in engine RPM or perceived misfire at approximately 5500 RPM.

DIAGNOSIS:
Using the Mopar Diagnostic System (MDS) or the Diagnostic Scan Tool (DRB III) with the appropriate Diagnostic Procedures Manual, verify all engine/transmission systems are functioning as designed. If Diagnostic Trouble Codes (DTC's) are present, record them on the repair order and repair as necessary before proceeding further with this bulletin. If no DTC's are present, perform the Repair Procedure.

NOTE : WHENEVER A POWERTRAIN CONTROL MODULE (PCM) IS REPLACED DUE TO FAILURE, THE SOFTWARE OF THE REPLACEMENT PCM SHOULD BE VERIFIED FOR THE LATEST REVISION LEVEL.

EQUIPMENT/PARTS REQUIRED:

1 CH6000 Scan Tool (DRB III)
1 CH7035 General Purpose Interface Bus Cable (GPIB)
1 CH7000/7001 J1962 Cable
1 04669020 Label - Authorized Software Update
1 04275086 Label - Authorized Modification

NOTE : THE MDS AND DRB III ARE REQUIRED TO PERFORM PART OF THIS REPAIR AND THE SYSTEM MUST BE OPERATING WITH RELEASE 21 OR HIGHER AND TIL CD RELEASE 1146 OR HIGHER MUST BE INSTALLED.

REPAIR PROCEDURE:

This bulletin involves selectively erasing and reprogramming the Powertrain Control Module (PCM) with new software (calibration changes).

1. Connect the MDS (Mopar Diagnostic System) and DRB III (Scan Tool) to the vehicle and power them up.

NOTE : THE FOLLOWING STEPS ARE REQUIRED BY LAW.

9. Type the necessary information on the "Authorized Software Update Label" p/n 04669020 (Figure 1). Attach the label to the PCM and cover the label with the clear plastic overlay.

10. Type the necessary information on the Authorized Modification Label p/n 04275086 and attach the label near the VECI Label
FAILURE CODE: FM - Flash Module

 

[utahviper]

Gears can also affect RWHP on a dyno. I am not an expert so I do not know by how much, I will let the experts explain.

 

[KenH]

Another factor to consider is whether the dyno was a Mustang Dyno or a DynoJet. Most people use and publish the DynoJet numbers, but the Mustang numbers tend to be quite abit lower, perhaps 8% or so.

In either case, you numbers seem low, even for a Mustang. Not sure what the BPE heads are, but assuming some type of ported head, you should be north of 500RWHP with those mods.

--- Ken

 

[pjb]

for reference my 97 gts before/after exhaust mods:

before: 423rwhp/446rwtq (filters-only)
after: 446rwhp/486rwtq (see sig)

i would guess you should be a bit higher as well with your addnl mods.

 

[Bugeater]

I would guess with ported heads and intake you should have at least another 50 rwhp, if parts and installation was done right.

What are "BPE heads"?

 

[Mike Adams]

oops

 

[Mike Adams]

My suggestion would suggest checking the 02 sensors. I have seen where the front 02 sensor doesn't switch, and no check engine light comes on. If nothing wrong check the compression to make sure nothing is hanging a valve open.

 

[Todd Richmond]

Thanks for the info! Here is more data

1) I pulled 5 Champion RC12LYC plugs and they are all white and 2 were undergapped at just over .025 instead of .035. I'll put the rest later but it looks like low A/F. A/F at peak HP is 12.4(5500 RPM). The plugs and Mopar wires have about 1000-1500 miles on them. What do you recommend to lower A/F ratios? VEC1?

2) Before making a dyno run the mechanic noticed that the O2 sensor wires were 3 feet too long and so toggled very slowly. New O2 sensors were installed in the proper location before the test

3) BPE heads have larger Mopar valves with mild porting/polishing but stock compression. They were supposedly designed for broad, but slightly lower improvement instead of high RPM peak power

4) My ECU was a replacement I bought off the net for the [******] that came w/ the car(drove poorly and not recommended) and I can't remember if it is a 97 or 98 so it may not match. Chrysler part # is P04848 702AD with 702AF "authorized software update" and also a "TEM3447PD0Q5" number and "R Code 39842" along with 11/98 on the update tag

5) I can't determine what TSBs were performed. The software update on this ECU does not match the post above. When I bought the ECU last year a few people said anything under 2000 should work so I did not make sure it was 96-97

6) I can replace my cats with open pipes in a couple of weeks and try that too(more work). How do you determine if they are "free flowing"?

 

[Todd Richmond]

I tracked down the online Mopar catalog and PCM #4848702Ax is for a 97 - 98 is 4854704Ax so this shouldn't be the problem

 

[utahviper]

Quote
4) My ECU was a replacement I bought off the net for the [******] that came w/ the car(drove poorly and not recommended) and I can't remember if it is a 97 or 98 so it may not match. Chrysler part # is P04848 702AD with 702AF "authorized software update" and also a "TEM3447PD0Q5" number and "R Code 39842" along with 11/98 on the update tag

---What are the stars? H M S?

 

[WCKDVPR]

Todd,

Looks like you have a similar setup to my car. I have a '96 GTS with BPE heads (fully worked, slight compression bump), extrude honed intake, TNT headers, T&Ds, no cats, Borla cat-back, 65mm TB's, and an upgraded fuel pump/system. My car made 536 hp/540 tq at the wheels, SAE corrected on a dynojet. That is with the stock '96 cam.

You are local, go see Ted May at Valaya 408-448-8811 (San Jose), he did the work on my car, has a bunch of computers to try (we did this at the dyno), etc.

Your numbers are way low!

Good luck,

 

[treynor]

Hey Todd - long time no see. I'll similarly recommend Ted May, he's done some good work on my other cars. Your #s are definitely low, and offhand I would guess O2 sensors or slipping clutch. However, I'll be happy *ahem* to give it a spin for you and provide a more accurate diagnosis

 

[Todd Richmond]

Thanks - Ted has done quite a bit for me but he didn't have dyno facilities back then - I'll probably have to ping him again soon

Ben - driving my car would be like going for a spin in a civic for you - nice looking car, but the throttle won't seem connected. I do have a nice 500HP 428CJ short wheelbase Cobra replica with crappy Radial TAs that might give a little scare though It also makes the Viper seem like a quiet, fuel efficient econobox with a clutch for babies

 

[SSNAKE]

Todd - My mods were similar to yours, but with a gen1, '94. After dynoing, I pulled only a sad 411hp. The garage that performed the job was unfamiliar with vipers. I went home & checked everything over. Finally, I resynched the throttle cables & took her for a test run. There was about 1/2" play in each cable. It now screams unlike before. I have not yet had the opportunity to dyno.