How much boost?

sleepydsm · 10-23-2005

I FINALLY got my car working perfect, and I tuned for 21psi on 92 oct. It doesn't knock at all, and I've got plenty of injector left.

Mods:
20g
ported 2g mani
hks external wg
fmic
3"turbo back
2.5"tubular o2
660cc
255hp
afpr
afc
maft
3"gm maf
greddy type rs
copper sprayed mitsu metal MLS HG
arp headstuds
rebuilt motor
rebuilt head

If I remember correctly, I read something about the 1G ECUs having too much timing that it can be dangerous with "high boost"

I am curious as to what PSI I could run on a) 92 pump b)100 oct c)110+

Kath is by my house, and there is a few smaller gas stations with 100 oct near by.

**Shane@DBPerformance** · 10-24-2005

The timing is mainly a problem when raise the compression to 8.5:1 or 9:1 or whatever and don't change the ECU.

**Kracka** · 10-24-2005

I personally ran about 17-18 with my 20G on pump gas (BP 92) and that seemed to work fine. You could probably go higher, but I decided it wasn't worth the risks and tended to stay more on the conservative side.

**JET** · 10-24-2005

21 psi is probalby pushing it. I wouldn't go any higher than that without better fuel/timing control (dsmlink or AEM). 100 octane should get you to 26 or so with a good quality 110 getting you to 30-32, depending on the gas. 110 around here can be hit or miss.

sleepydsm · 10-24-2005

Thanks for the info. So what negative things are happening at the higher boosts (20+) when it is not knocking?

**JET** · 10-24-2005

The problem is that you really don't know if it is knocking or not. The knock sensors are extremely picky on the torque settings. Since you had yours rebuilt, it has been out and probably not torqued back in properly. DSMlink and the AEM allow you to calibrate the knock sensor and make sure it is reading correctly.

You could possibly be running high EGT's if you are running too much timing, but that would be the only negative effect if you truly aren't knocking.

sleepydsm · 10-24-2005

I actually installed a new knock sensor before I put my new head/turbo on. I finger tightened it, and then using an adjustable wrench I tightened it a little more. I couldn't get a torque wrench on there, and I read what other people have done.

**scheides** · 11-10-2005

I ran 20-22psi with my 20g on 92 octane w/ no problems or knock either. JET is right though--the knock sensor is a very picky piece, too much or too little torque and it may not be reading correctly. What did you tune it with? Might want to get some wideband action and make sure it's tuned a little conservatively, that will help prevent problems in the future.

The problem is that once you finish tuning & go about your merry way, one day you might get some bad gas, be boosting along like everything is fine, but your egt's spike through the roof b/c you're detonating like crazy. Of course, you don' t notice b/c you've had it tuned the same way for the last six months, you boost on it regularly, and might not notice!

So, feeling lucky? I ended up turning the boost down a bit, kept it at 18-19 because I'd rather be a few HP short and a be a bit more on the safe side than a sad punk w/ holes in my pistons.

**Shane@DBPerformance** · 11-10-2005

Quote:

Originally Posted by scheides

but your egt's spike through the roof b/c you're detonating like crazy.

The only reason your EGTs go up on a DSM when you knock/detonate a lot is because the knock sensor/ECU sees it happening and retards the timing a lot. Low timing = High EGTs. With no active knock sensor, it will just continue knock away.

sleepydsm · 11-10-2005

I might as well just buy a wideband to play it safe. Sound like a good idea?