max boost question

bumpskier45

Registered User
as some of you know I just had my fmic installed,after we did everything checked the vacuum at idle it was at 21 which is very good,and at wot it was pushing 13-14 lbs max boost. prior to that it was only boosting 8 lbs but that was due to my bypass not closing all the way,we felt we got it to close all the way by the fact that is pushed good max boost. well now it max's 11 lbs boost. So is there still something wrong with my bypass. figured it was highly unlikely with 21 at idle that I had a vacuum leak. any idea's or do most of you feel I still have a leak?
 
I have a spare here we could put on and try to see what happens. While we are at it you can help me put the trans back in mine. :)
 
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just installed magnum powers springs,so I would have to say probably not slipping no. the bypass shuts down all the way on that stopper that is on the plentum when we had the return off we could see it close when it hit that stopper it looked to be fully closed,but that was initially the original problem when I was only getting the 8lbs of boost which is why I am leaning towards it still being an issue but keep shooting other things though.it was an all of a sudden thing to not gradual,before I left from getting the fmic on it was boosting 14lbs at about 4k rpms I was on a rural road at the time so I didn't take it further but im sure if I gave her more rpm's I could have easily pegged he gauge. it is a late model s ported blower with coated roter packs done from Charles at magnum powers so it should be pushing more than the 11lbs I would say.
 
Might be a leak in the hose for the boost gauge, cold weather vs warm weather or several other things. Check your tensioners to see how much travel is remaining. Belts may have stretched and are now slipping. Does it feel like it's running just as strong ?

David
 
actually it feels just strong hard to tell if its exactly the same but feels about as strong,I installed new belts when I installed the tensioners.I am wondering if the vacuum line to the bypass is making it shut all the way,it shuts all the way when I inspect it but that is with the engine off in order to see if it closes all the way would have to be under wot. would a leak in that line show up when I am idleing?
 
am wondering if the vacuum line to the bypass is making it shut all the way,it shuts all the way when I inspect it but that is with the engine off in order to see if it closes all the way would have to be under wot. would a leak in that line show up when I am idleing?

Vacuum pulls/makes the bypass open...that's when boost is allowed to bypass. No vacuum, such as when under WOT, means the vacuum drops and the spring closes the plate and the bypass is blocked.

You can check it (a) engine off it should be closed by the spring (b) with the engine running at idle to see if it is pulled open (c) blip the engine quickly and watch to see if it moves shut again.
 
Quick redneck check, ty-rap it shut, quick drive, see what your boost is. With the bypass shut you will heat the blower up in a hurry at idle/cruise, don't drive it much like that, but for a quick test it ought to be OK

Adam
 
Boost gauge may be the culprit! I thought I had a boost leak and showed good idle at vacuum and the crappy plastic line for the boost gauge was cracked
 
I test drove it last night,it sure does feel like its pulling pretty hard.I have done the checks you have all suggested the bypass appears to be working perfectly pehaps it is the gauge,I need two other gauges to go in the three pack thing along the window with my wideband perhaps boost gauge will be one of them.ooops sorry didn't finish my thought,coming out of 2nd gear I was able to push about 13lbs right at 5k rpms maby I am just expecting to much from that blower and its really ok.
 
If this happened just after you changed from a stock to an FMIC it could be that nothing is wrong. It's just that the new FMIC flows so much better that you've reduced cavitation in the super charger and back pressure in the system because of poor flow thru the stock IC. Even if it was a double IC it probably stills flows so much better now.
 
I am starting to think nothing is wrong,the bypass passes all the tests a spraying of all connections reveals no vacuum leak "no surprise there" and I have ran it several times and the boost gauge may say one thing but she is really pulling hard. I am going to a dyno day up in louiville with dave clark,jacob royer,etc will have my quaterhorse running by then so we shall see what the data loging tells me.
 
It's good that you rig passed all those tests, however the spraying "stuff" to check for vacume leaks is old skool carb thinking. It DOES NOT WORK on fuel injected cars. The computer controls idle with timing (as well as IAC air control), near to instantly. If the vacume leak at any one point is not massive, it will NOT change the idle because the computer will adjust it. A smoke test is the only real way to find a vacume leak on these cars. I agree with the previous posts that you don't have any "problems", just changes in the entire "system" which changes the readings (boost gage). Your last post is the one that I like. Data logging and learning how your car responds and what works/doesn't is where it's at.

Adam
 
ordered my dongle last night,so my quarterhorse will be ready.And a after market boost gauge,the thing that did it for me is how hard it pulled and I thought to myself at one point I don't care what you say boost gauge that was a hard pull LOL. thanks for all the posts though its good to learn what makes these cars tick even when nothing is wrong.
 
I do have one thought, which is that it the IC tube connections may possibly be leaking only under boost. Maybe when the engine leans against the mounts on hard acceleration, something pulls a little?

Spraying propane may not work for every leak on fuel injected cars, but I find it usually tells you something. If the car has to cut timing to slow the idle speed, you can hear a change in the quality of the engine sound. If you pull the nozzle away and it goes back the way it was, repeatedly, then you have found your leak. But maybe for the little ones, it's not quite enough.
 
going off your suggestion I examined the fmic lines one more time,and low and behold I found one that joint that looks like a tiny bit of oil has leaked down it,and one of the lines looks like it may have moved slightly from where we put it,so im positioning it back in place and tightening again that may have been it I think.
 
replaced my IAC and I am still having an issue with my idle,I think the idle issue and my max boost issue are one and the same. someplace there is a vacuum leak,I thought the system was tight but apparently not. So a smoke test is in order,what is the going rate for that so I will know if the price is to high.
 
Try doing a google search, I know there r lots of people who have made their own testers. Most r some variation of a pressurized can with a little baby oil in the bottom and a soldering iron to create the smoke. There was a thread by a member here too a while back, he used a 1liter pop bottle with a bicycle tire valve in the cap and the bottom cut out stuck in the inlet tube and a "smoke bomb" for testing HVAC systems. I'm planning on building one when I get some free time:rolleyes:, I think its a good tool to have in the box if ur gonna mess with SCs, rather than pay someone else every time a vacume leak question comes up

Adam
 
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