Interesting silencer turbo issues at altitude...
 

I had an interesting experience with a silencer in a Apex'i GT spec exhaust when driving a car from <800ft to 5300ft.

I bought a new R1 FD in Indianapolis at the rotary revolution. About 1/5 of the way into my 1100 mi drive home I installed the silencer. To my surprise the silencer really did not effect performance as much as I'd expected. It made revving in the low RMP's easier (as I'd expected) and did not seem to effect top end acceleration much if at all (not what I'd expected).

As I drove home and up in altitude I'd noticed the turbos developed a very heavy transistion (I'd not get full 2ndary boost until almost redline) and produced a squeal at high boost. I thought that i'd developed a boost leak.

After a few days (and removing and reinstalling all intercooler couplings) I removed the silencer... and wham! Full boost - no squeal!

I think what was happening is that the silencer was creating so much backpressure that it was causing a downpipe or exhaust leak somewhere when I came up in altitude.

Anyhow I thought it was interesting how the silencer effected the performance so differently at altitude.

Anyone else had similar experiences?

When I am in Colorado Springs my boost pattern is all screwed up from the altitude. Heck, try driving up in the mountains. Hit about 12,000 feet and my boost pattern goes to something like 6-2-3.

I never had strange exhaust leaks as a result of altitude though, that is pretty weird.

When I lived in the Springs I installed the pre-control adjustment from Rob Robinettes site. I was able to fix my 10-6-13 pattern to something like 11-8-11 with that thing. Well worth the hour of work.

Yea, I think the excessive backpressure was causing the leakage not the thinner air persay.

I though it intersting how dramatic effect the altitude had as I'd not noticed it much otherwise as I've always had a pretty wide open exhaust