2.76 swap, only up 11hp!!??

[mikeshimek]

so i did a 2.76 pulley swap this weekend and went in for a dyno tune. Car was running great and felt real strong. made 422 rwhp and 444 rwtq, compared to 411 and 392 before the pulley swap. Pulls were made on a mustang dyno and it was a cold night. Im wondering if the 2.76 can overspin the stock blower and maybe i need a 2.93??? car made 16#'s at 2500 and then dropped to a hair over 11#'s at the end of my run. Tuner said I made over 40whp "average" but really only 11 at the top end. any ideas on how i can get some more top end hp? thanks!

 

[Posi]

Sounds like a loose belt.

What was the peak timing up in the rpm's on these runs compared to the first ones?

 

[mikeshimek]

damn, i dont have timing on my graph he printed for me. i can call him tomorrow and get that. i thought beltslip would show on your graph via distortions or funny looking curves?? i did a quick install im now wondering if my buddies and i put the stock belt on or the 74.5 i have!! i do have the BF idlers and snub as well

 

[64T-bolt]

that sounds like belt slip to me, thatas really the only real reason boost would decrease as rpm increases. you made a s*it bag of torque. curious about timing as well.

tighten/shorten the belt and let her eat. If your still not happy, have a competent tuner pull a little timing, add some octane and she'll talk to you. . (just keep a close eye on AFR obviously). honestly though if you would have held 16# til the end you would have seen 460/500 ish. .

it's not overspin. .

 

[Posi]

Is the belt relatively easy to put on or a pain for one person? Chances are if it's really easy for one person then it's to loose.

 

[lx347cid]

well with the 4 pulley idlers and snub Billet Flow shows to use the 75.1" which is the stock size belt.

what plugs are you using?

 

[Dynotune04]

what kind of intake are you running on the car? intake might not be flowing enough to feed the blower in the upper rpm's. i ran into that problem a while ago. abviously check for belt slip as well.

 

[mikeshimek]

tr6 plugs and stock intake. belt was a bitch to put on and now i looked and we did use the stock belt. one person held the tensioner and it took 2 of us to slip the belt on. any other signs of belt slip? noise?

 

[mikeshimek]

that sounds like belt slip to me, thatas really the only real reason boost would decrease as rpm increases. you made a s*it bag of torque. curious about timing as well.

tighten/shorten the belt and let her eat. If your still not happy, have a competent tuner pull a little timing, add some octane and she'll talk to you. . (just keep a close eye on AFR obviously). honestly though if you would have held 16# til the end you would have seen 460/500 ish. .

it's not overspin. .

yeah i was hoping for about 450ish whp! will a stock eaton hold 16#'s up high?

 

[bigdog93lx]

Get an intake setup. Wouldn't have thought you would be running a stock intake unit.

 

[mikeshimek]

duh! my bad....i have a JLT rai, i was thinking tb and plenum. yeah rai, mafia is hooked up on #2, and a catback. seems like same setup as your car and you made way more hp

 

[Robertp]

well guys this is on a mustang dyno reading on what the op said above, and if its not a ported blower, the numbers arent gonna be in the 450-460 range without a ported blower on a mustang dyno unless im reading something wrong i know must guys with this setup make between 450-460 on a dynojet and with the conversion he is prolly right in line but that is just my 2 cents

Robert

 

[bigdog93lx]

Hard to tell. My car was dynoed on a dynojet, mustang dynos read alot lower. Stock eaton isn't going to hold the same PSI across the board. With my Long tubes i peaked at 14.2psi but then it tapered down to 12psi in the higher rpm. Did you happen to see how much boost your car was making in the higher rpms? I would get a good belt (Gates or Goodyear) and do a quick swap, it only takes a minute and is relatively cheap. Make sure its the right size and if it still doen't seem to be running right. What did you gap the plugs at?

 

[mikeshimek]

yeah i will check the belt, my peak psi was 16.5 at about 4000 rpm, and it steadily fell off all the way till 6300 where it ended up at 11.1. thats why im wondering if a bigger pulley will drop the midrange boost a little and let me carry it into the upper rpms?

 

[dynobobstieg]

Were your test comparisons done on the same dyno and same weather conditions? Does sound like you may have belt slip. You got a tune also or just dynoed the car?
Stiegemeier:burnout:
StiegeSplash
636-949-2275
636-925-1656
[email protected]

 

[03cobra#694]

I`d like to know the timing and a/f.
Curious about belt slip also.Was there alot of dust on the pulleys?

 

[SVTDom]

thats weird, 422 is really low power. its prolly belt slip. Buy a 74" belt and throw it on. You may have to grind the stop off the tentioner pulley bracket thou. Pretty easy and now my belt goes on easy, and is super tight.

im curious about your AFR's and timing also, you have them?

 

[Robertp]

wow o thought the mustang dyno read about 15 percent lower thats what i was always told and if thats the case on a dyno jet he should be in the 480 range, i know what my cobra made on a mustang dyno and its like yours seems low but at the track it lays down just over 122 mph maybe im missing soming in this post

Robert

 

[4.6snakedoc]

May I ask what size pulley you swapped from?

 

[mikeshimek]

Were your test comparisons done on the same dyno and same weather conditions? Does sound like you may have belt slip. You got a tune also or just dynoed the car?
Stiegemeier:burnout:
StiegeSplash
636-949-2275
636-925-1656
[email protected]

yes same dyno and same tuner and it was exactly a year to the date so condtitions should have been similar. and yes i did get a tune done.