Custom IC tubes and rediculous boost

plev72

Registered User
Hey all, I've got custom 3" Mandrel IC tubes (I'm putting pics on the non-tech board), a custom intake, a 10% pulley, and a 3/4 top spacer. I don't believe that there are any leaks. I'm pegging 14+ PSI on the stock boost gauge which is causing the spark to retard after a few seconds at max boost. My intercooler is stock. I expect that at least for the short term I'm going to have to pull the 10% pulley in order to reduce the amount of boost. Can someone give me the technical explanation for what is going on? Am I just trying to run too much air and the stock IC is unable to cool it all?

Thanks,
Paul
 
That sounds right. Air id so hot that your getting detonation and your knock sensor is pulling some timing. You could probably go with a %5 pulley or you could go to a double IC or something bigger and not have the detenation problem. Just my .02
 
Throw some alcohol into the mix and that should take care of the detonation.
Regards,
TBSCoupe
 
pics..........

Any pics of the tubes? Did you make them or have someone? How much did you pay to have them made and will they be making more?
 
Logic doesn't fit with bigger pipes making more boost. It's that 10% pulley that's pegging your boost gauge. These are positive displacement super chargers. They just pump air. Bigger tubes after the SC just allow for more capacity for the air.

More space, more turns of the pump to fill the space with the equivalent pressure. If anything, the bigger pipes decreased your total boost.

But turning that SC so fast will certainly raise intake temperatures, and it will increase drag on the crankshaft as well.

Detonation at that pressure could also be due to too lean of a mixture. You're adding a lot more air with that 10% pulley and your pipes are ensuring that as much as possible is getting into the cylinder. But if the injectors can't support that much air, you could be leaning out, causing the timing to be retarded.

Make sure the Exhuast is opened up as much as possible as well.
 
Stock exhaust with that pulley is a no no if thast the case..Also..Your lower IC tube..Is it close to the manifold??..If so some header wrap would keep heat from soaking into it...One last thing..WHat plugs and what is the gap?
 
Looks like consensus is leaning towards the 10% pulley being the root of all evil... I have a custom mandrel 3" into dual 2 1/2" with deleted center cat and a glass pack equivalent (ish) instead of a resonator into two dynomax mufflers. I've got the exhaust pics up here somewhere, I'll see if I can find them to give you a link. All the other pics are posted on the non-technical forum. The lower IC does not run very close to the exhaust now... think I have another picture of that that didn't get posted yet. As for whether he is making more, I can ask, don't know if he'd be willing to without actually having a car to work on though, the margins are pretty close and mine are moved a bit outboard (towards the battery) due to the oversized radiator.
Paul
 

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Ditch the 10% pully before you burn holes in the pistons. You should only run autolite or motorcraft plugs. I had the same problem. I resolved it by installing the stock pully from my 93.
 
Spacer?

It may not be related to your problem but from your picture, it appears that your spacer is just that, a spacer placed between the blower and the stock top. If this is the case, you still have the stock restriction, it's just mounted higher. A true raised top opens up this restriction by adding material where the restriction exists and then boring out the opening. Or, in the case of the MP unit, it's just cast that way.
 
Here is the deal.

There is absolutly nothing wrong with a 10% pulley as long as you can maintain a sufficient Air/Fuel ratio. Because you are having detonation now, I'd try throwing the stock pulley back on for now. If the detonation comes under control, then plan on making a trip to for a test and tune day at a dyno that has a wide band oxygen sensor.

then test with the10% and find out what your true A/F ratio is at. I'm guessing pretty lean and that is very..very..very bad for your engine.

A adjustable fuel pressure regulator cranked up may be able to compensate enough but you won't know unless you test.

But again... This is all conjecture. You should be able to pull your plugs to also look for signs of a lean condition. Validate everything so you don't just end up wasting your time.
 
Love those pipes. They look just like mine! 'Cept I have them connected to a FMIC, but the routing is the same. The work great on my combo. Don' t know why you are pegging the boost gauge though. Is that a late model or ported blower? Even if that is just a spacer under the stock top, I'd not worry too much, I made 300+rwhp with just a spacer. I don't make that much boost, but then again I have ported heads.
 
Yeah, for the moment it is just a spacer. Think I'm going to drop the big bucks though and get the top done (opened up and welded), as well as getting my supercharger rebuilt and done as a magnaport, the highflow plenum, and an 85mm TB. Wish I'd seen the info on the pulley before I bought mine, probably would have gone with the 5% instead. Oh well, may pick up a 5% and hold on to the 10% for when I've managed to put on upgrades that can take advantage of it. From what the guy who did the work says, I won't be able to fit a double IC due to the radiator being wider. My IC is actually moved slightly closer to the battery area for clearance. Looks like we'd have to move a major computer wiring harness in order to fit the double IC and we are obviously wary about doing that. Might have to at some point, that and perhaps pulling the battery and battery tray and going with that solid gelpack type... maybe turned sideways so that the + and - terminals are perpendicular to the front of the car, thus making more room. I need to move the winshield washer resevoir from in front of the IC as well. Probably move that over to where the stock airbox used to be, I think there is room to mount it at that end.
 
Maybe I can help you out some Plev. In the summer I had a dyno pull with the 10% on my car, got high #'s but the "spikes" in the curves was bad. So 2 weeks ago, I go for some test & tune time, I had my 10% removed and installed a '90 stock pulley. With the car being a '95 the blower is still overdriven about 3%. Well the curves where much better. Nice and smooth. I have a O2 bung being put in my car, so next time I go(to the Dyno) I'll have the air/fuel hooked up. Then I'll test the pulleis back to back.

As the for the 10% yeah, it seems to heat up the air too much with a stock IC, so I'm getting a double HI-PO welded up by T1Bird. Nice unit, no spaces or %hitty top cuts. I'll post pics when it's ready.

Good luck Plev.
 
Haven't rotated the MAF yet, think I did a pretty good number on the supercharger though. Pulled the 10% pulley, but tore the old belt trying to put stock back on... now I'm running superchargerless... no boost, no detonation ;-)

Still get the 'check engine' light erratically though.

Think I'm going to 42lb injectors... hopefully then I can go back to the 10% pulley :)

Oh yeah... and a magnaport and rebuild ;-)
 
RE

Just courious is that a spacer that I sold you? It looks so.
If you want it modified for max performance let me know.
Nows the time to get it completed.




Chris Lazzo
 
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