New all time high boost in second gear - musings as to why

Q&A regarding engines, turbos, and intercoolers and power upgrades

New all time high boost in second gear - musings as to why

Postby Griffin » Fri Oct 29, 2004 2:39 pm

So I finished putting the car back together from the new clutch, P/S pump and P/S rack last night. Rear diff cushion still needs to be replaced (its pretty bad) but I'll get to that next week.

Anyways - I took her out of the neighborhood to try just one pass under high boost. Went from about a 25 MPH roll in second, lifted before I got to redline (not sure of Revs, but I'm thinking it was about 6K maybe 6500) Anyways my fiend who had been watching the laptop for me says "wow" I assumed he meant that it was pulling well, and I said yeah - feels pretty good, probably shouldn't have got on it that hard so soon after the new clutch, but what the hell. He says "no, it not that - you just hit 27 PSI" I was surprised to say the least - the highest I had gotten on the old clutch was 24 PSI and that was under serious load in 4th. I'm pretty sure I haven't seen anything over maybe 21 PSI in second before, Its bizzare. The only thing I did differently that I can think of was I made VERY sure my pipes on my DP to MP connection were exactly lined up this time around (last time I was having to wresle with the MP due to some VERY tired hangers and I settled for a slight misalignment).

Now to me a gain of about 5 - 6 PSI in single gear seems a bit much for a minor correction, but I can't imagine what else it could be. I did remove and reattch all the FMIC piping but its positioning is pretty static... The only other possibility I can think of is that I had a boost leak somewhere that I fixed when I put everything back together.

Anyways I'm happy with the new development, but I am a bit perplexed as to where all the extra boost came from. I'll do more in depth testing as soon as I get my diff cusion replaced and the wheels aligned. (the fronts are a bit off from the rack and tie rod ends getting replaced and I don't really care to burn off my tires.)

Curious if anyone has had a similar experience and what your thoughts are.
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Postby alltrac4life » Fri Oct 29, 2004 8:00 pm

Did the old clutch slip?
If so, then it might have relesed some load and the turbo didnt hit max boost. kinda like when you boost in first gear.
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Postby BraveUlysses » Fri Oct 29, 2004 9:37 pm

27psi on a ct26?!

Are ya sure that boost gauge is right?
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Postby furpo » Sat Oct 30, 2004 11:16 pm

my guess is you have a leak somewhere in your wastegate or wastegate hose.

good luck
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Postby Zeus » Sun Oct 31, 2004 1:39 am

alltrac4life wrote:Did the old clutch slip?
If so, then it might have relesed some load and the turbo didnt hit max boost. kinda like when you boost in first gear.


that would be my guess too
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Postby Terboman » Sun Oct 31, 2004 3:19 pm

BraveUlysses wrote:27psi on a ct26?!

Are ya sure that boost gauge is right?


Wow, 27 psi on a CT26 is right! Hot damn. :shock:

I don't think he is reading a boost gauge. I'm sure he is saying that is what the AEM software is telling him (via AEM Map Sensor...which is very accurate).
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Postby Griffin » Sun Oct 31, 2004 4:36 pm

yes, I am reading that off my AEM, which is using a Kavilco 5 bar Map sensor which is about the best one money can buy. No, I don't have a boost leak at my wastegate actuator - doublechecked that on Thursday - was thinking the same thing.

And yeah, 27 PSI is pretty high for a CT26 :D Those shims behind the wastegate actuator are working like a champ. I may actually take one shim out after the IDRC races on the 13th though.

The cluch MAY have been slipping all the time, its hard to say - it didn't feel like it at all, but it would definitely slip on a hard launch. Then again, I would have expected it to burn away to nothing if it was constantly slipping under boost for 3000 miles. The pucks actually had most of the meat left on them.

This is actually the first true winter weather I have had my car running for, It was about 50 that night, I'm thinking maybe it was a combination of that and the pipe alignment.
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Postby MrWOT » Sun Oct 31, 2004 5:16 pm

Hey Griffen, since you seem to be looking for serious performance, have you considered having a cast iron tounge welded into the turbine housing so you can run a seperate wg pipe? You mentioned racing and I've found that better wg control will ALWAYS lead to lower laps times. :)
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Postby Griffin » Mon Nov 01, 2004 5:51 am

Its just drag racing - I don't need CONTROL so much as a closed WG :D

Anyways next turbo will have an external WG
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