3800 Disappointing Dyno Run - Need Advice

[markymarc]

Back in the Spring of 03, I dyno'd my car with a 3.5 pulley, Thrasher intake, and RT downpipe. I had these results:

218 whp
240 wtq
12:1 a/f

In the last year I have added the following:

Ceramic TOG's
Intense 1.9's
DHP
ZZP MPS 3.25
180 stat
MSD Wires

Last night I showed the follwing dissapointing numbers:

238 whp
247 wtq

I was looking at the graph telling myself that this cannot be correct. I was expecting somewhere in the neighborhood of 255 whp and 265 wtq. As it turns out, I am getting around 6-8* of knock and my air/fuel seems to be the real culprit here. It was 15:1, obviously a problem. I need some assistance on what to do to alleviate the lean condition. I am thinking about adding an APC, seeing Charles for some tuning, colder range plugs (currently stock), and possibly bigger injectors. I need some advice, as I am severely disappointed with the results last night. The car pulls way to hard to only be putting out these numbers.

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[J.E.T.]

<Rainman>

Definately colder plugs, colder plugs, definately colder plugs.

Thats a start. I dont think you need bigger injectors just yet. Tune it with what you have first - then see if you are maxing your injector pulse width #'s - then determine if you need bigger injectors.

Heh, Im trying to give advice when I need advice myself! :lolsign:


J.E.T.

 

[alexgtp]

TUNE TUNE and TUNE again.


Did you do a wideband run?

Did you have a chance to log the runs?

What are your O2's? what are your ltrims? what was your timing advance? What gear did you dyno in?

 

[markymarc]

Can Charles help me tune? Or anyone with scanning ability? I am not well versed in the science of tuning by any means.

 

[sr71_rgl]

Stock plugs cause KR on a stock motor...you could easily go 2 ranges colder and kill almost all that KR. As far as your A/F you might want to invest in a AFC2.

 

[beyerch]

they must not have relayed the message...

i was talking to the dyno guy last night.

I think you really need to check your FUEL PRESSURE. There's no way you should be that lean if everything was working A OK.

Our fuel regulator is a boost referenced system.

Stock Pressure is ~52PSI

for each PSI of boost increase, the FP should increase.

So if you have 10 PSI of boost, your fuel pressure should be 62 PSI.

You need to verify that this is in fact happening. IF it is not, then you will run very lean.

This is the best guess I have as to why you were that lean.

You will need to put a pressure gauge on the test rail and monitor it.

charles

 

[CoolGTX]

you can lead him to water, you can stroke his throat, but you cant make him drink.

 

[beyerch]

^^^ ????

I"m just saying J/O that the most likely culprit will be Fuel Pressure. Thats really lean and usually that is the cause when its that lean. I don't know if the jimmhy or the dyno operator told marc to check that out or not as i didn't talk to mark directly.

Either way, I'd drive the car nice until you can verify the fuel system. That is pretty lean and you don't want your car to mimic that song by saliva ... 'click , click, booooom!'

 

[markymarc]

Thanks Charles. My plan is to do the following

1) Colder plugs this weekend. (Pepboys claims they can't order autolites though?)
2) Throw the 3.4 MPS on for the time being. At least that should improve the ratio.
3) Scan, etc.
4) Adjustments to fuel somehow after the scan.

Am I correct in thinking that the 3.4 will lessen the lean condition?

 

[sr71_rgl]

Originally posted by markymarc@Dec 10 2004, 08:07 AM
Thanks Charles.  My plan is to do the following

1) Colder plugs this weekend.  (Pepboys claims they can't order autolites though?)
2) Throw the 3.4 MPS on for the time being.  At least that should improve the ratio.
3) Scan, etc.
4) Adjustments to fuel somehow after the scan.

Am I correct in thinking that the 3.4 will lessen the lean condition?

[snapback]63405[/snapback]​

Napa sells AL104/103 coppers. I buy mine in West Chicago on Roosevelt if you're near there. A 3.4" pulley is smaller (if only slightly) than the 3.5 which means it'll spin more rpms (aka faster) than the 3.5". This is gonna pull more air into the motor (*beavis* kick ass!) and will make your car run leaner...you don't want this. Leave the 3.5 on, hook up a fpr to the test port on the rail, tape the fpr to your windshield and do some wot runs making sure it fuel pres climbs from 51psi to 51 plus however much boost you get. If frp goes up just buy a afc2, they're good for tuning A/F on a budget and get some AL104s @ .050 in there. GL

 

[markymarc]

I have a 3.25 on currently. Not a 3.5. So the 3.4 should assist.