I just came from the dyno hoping to finally put down the big numbers, but once agian I was stumped by a hardware issue and I would like some suggestions.

You can see the car in the sig. Here is the story. The car pulls quite nicely to 4500 rpms and then the power dips, recovers and by about 5100 sinks quickly into the sunset. The strange thing is that the air / fuel ratio stays at about 12.6 - 12.7 throughout. The log on the FAST gives no hint as to the problem.

When I was street driving I would feel this stumble and attributed it to detonation and indeed one of the reasons to go to the dyno was to get my timing fixed up.

However, I'm assurred by those in attendance that it is not detonation. Currently it would seem that it is either coil, MSD or opti. The opti is three years old, the coil is 6 years old and the MSD 3 - 4 years old. To test the MSD we unplugged it but the same thing happened and abotu 600 rpms earlier which does not surprise me. Chances are the spark was being blown out.

Anyone have any experience with this syptom?

Thanks

 

97TA, you give me very little to go on, but my first guess would be spark plugs, after that valve springs!

 

Yeah valves have come up as an idea but I have all the parts and that should not be a problem. The other thing we did was to unplug the MSD to see if things changed but baseically the same thing happened and except at a lower rpm. I figure it has to be a coil or the MSD box. At worst, the opti.

Hopefully someone can lend me these parts to test things before I have to buy one.The plugs are basically new.

 

What were the numbers? What kind fo dyno?

 

12.6 is a little lean for a hi po blower setup IMO. I am running less boost and was happy to see my A/F down around 12.2.

My setup stumbles horribly at 5500+ rpm. I doubt it's detonation though, and I doubt it's my plugs since they are quite cold with small gap. Maybe both our coils are going out since I am still running the original stocker. Bad coils are known to give high rpm stumbles, and we need a LOT of juice to ignite the amount of air/fuel we are forcing into the cylinders.

Another thing to consider might be timing. I would think you would want to be running around 30-32 degrees timing if your IATs are staying nice and low (since you are intercooled). What are you running?

Let's see your numbers! Post a dyno plot if you can, it might help us diagnose.

 

My timing numbers are VERY conservative. Indeed that is why I went to the dyno. At WOT I'm only at 22 degrees in the high rpm / high MAP area.

Power peaked at 4800 and 481 torque was 535 @ 4700. Actually I'm disappointed in those numbers. They are the same as last years but now I have the AFR's and the FAST. THAT being said, last years numbers had the car running with an air fuel ratio of 15:1 plus. Can I asume that a 15.:1 afr with generate more power then an 12.8:1?

Mustang Dyno.

Anyone have a newer coil I could borrow? lets start there.

 

remove blower
sell blower
add nitrous

 

Tune blower
Pulley up blower
Add Nitrous

 

damn 22 degrees of total timing is low.... I run about 26 degrees without an intercooler and 100+ degree celsius IATs. You are losing a LOT of power there.

that doesnt explain your stumble tho - definitely try a fresh coil!

 

Wait, this was on a mustang Dyno????? Ok I hope you know that it will show something like 10% less power or something rediculous like that then the dyno jet. whatever either way, go back to a MAF system.

 

Or be like me & acctually put the money into what counts, convert to LS1 Coils & be done with the opti!!!

 

Matt

I may consider that option but first.......

Can anyone lend me an MSD box and / or a coil so I can test these parts first.

Also, I was mistaken. It IS a Dynojet.

Craig, what base timing do you have? Again, I went to the dyno to play with timing but with this apparant ignition issue the opportunity did not come up. Would too little timing cause the car to loose power badly and stumble?

 

The thing about timing is that the further you are away from "optimal", the more rapidly you lose power as you move away from the optimal mark. Basicaly that means if you cut 2 degrees from optimal, you wont lose much power. But it you are already 8 degrees from optimal and cut 2 more degrees, the power loss will be much more significant.

Shaun do you have LT1_edit? if you do I can send you my tune and you can see my timing curve. Mind you I cut a couple extra degrees of timing so that I can run Nitrous . If not I will send you my timing marks at the RPM intervals in my file.

Low timing could *possibly* cause a stumble since it may result in incomplete ignition of the fuel mixture (i.e. the flame front doesn't propagate far enough by the time the piston is moving back down towards bottom dead center. I bet you are having ignition problems tho, and I bet I am too up top.

One thing you can do is go for a hard run (causing a stumble), then immediately shut your motor off and pull a plug to see if you are fouling them at WOT. You will have to do this at the roadside tho (or at the end of the 1/4 mile track) because you cant wait to drive home or to your spot in the pits to check them since this will clear any fouling.

 

So your power drops off after 5100 your saying basically.

Maybe opti but people have made way more without.

I would not do the LTcc thing for your setup IMO. I would have a distributor put into your intake and run that will eliminate all problems with ignition. I have a stock coil i think if you want to test with it.

I would honestly look at your intercooler setup imo. On a dyno it doesn't cool and that is a restriction in your blower. If you ever get the energy and want to make some ducting and try one of my intercoolers while dynoing just shout. *just need to setup a pump and i have a tank for water. Just an idea but i think you are held up cause of the intercoolers some.

I would not go back to a maf system though NOT IN A MILLION YEARS.

Another thing if you haven't addressed is the exhaust that will hold you up granted i don't know if you are really worried about that or not cause i know you want to keep the borla system etc...

 

LTCC. I have seen that before. Is that the LS1 conversion?

Borla: Well I definately DO want to go to true duals but cash is short right now.

IAT: temps were pretty good at about 85 - 90 degrees. They had a huge blower for the front and ALSO a huge fan - about 4 feet - at the back sucking air.

I also played with the timing. I increased the timing. I only have had ONE opportunity to 'test' and that was in second gear. Now the rpms and speed rise at a VERY quick rate in second gear BUT for the fractions of a second I was over 5000 I did NOT sense the stumble problem. I'm going to play with the tuning a bit more. of course that is why I went to the dyno to begin with. *sigh*