Can you lose boost with a FMIC????

neverfastenough

Registered User
:(Hey guys some of you have probably seen my post on my recent FMIC project. After it was complete I was really satisfied, and it made a nice difference compared to the old heat soaking with the stock IC. Now heres the deal...when I took the car apart it was making an easy 15psi, before the end of first gear(auto) too. This is on a late model ported blower with a 90 pulley. So after the fmic was complete the car went straight to the drag strip for some testing, after warming it up a few times and snugging the t bolt clamps of course. The car made about 10psi in first and built up to about 14psi dropping to 13 between shifts. I was thinking when then car made its old 15psi it was about 40degrees out and on the day at the track with the FMIC, it was about 70degrees outside. Could just this cause this loss, and a more extended time to max? Ive done many checks and I cant find any leaks and the car makes about 18psi vac in gear. I then thought since it took longer to build it was a slipping belt, so I put a new Gates on from the js to the sc pulley. Could there be a boost leak I'm missing? or is the longer path and way bigger IC core causing the loss. Id really like fine the prob because Im missing some bottem end power that I really enjoyed
 
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40 to 70 WILL show a decrease in boost,
i hit almost 15 PSI on a stock 89 blower one night when it was 0* outside and now im looking at 12 if i stomp on it, which i really dont do


-Tony
 
Well I'd like to get that boost back lol. If its just the OAT causing it mabey Ill throw a 5% OD pulley on it before the dayton meet. Id actually like to get one off a member down there if someone wants to get rid of one to save some shipping costs.
 
I dont know squat

But your new pipes seem a tad bigger then stock and looks like you have added extra length to the system....I would figure the S/C is moving flow at the same pace...Id say your mod might have slowed the flow....I think your right on with a new pulley to spin a bit more..

F1
 
less restiction means less presure but more power. just like when you do ehaust. same amount of air just takes less to push it through.
 
If its the same ammount of air do you think it would be harmful to add back a couple pounds of boost Hg wise? The loss has killed bottem end, thats really the only reason I want it back. The number of psi really means nothing to me as long as it runs right
 
If you lost power then something is wrong. A bigger IC or longer tubes will not affect boost. It is hard to compare a 40 deg day with a 70 deg day though.
 
Dave I cant really say I lost power, it just seems like I lost bottom end power because its building boost slower and slightly less in the long run. Ill probably try 5% more od and see if it feels back to normal on the bottom end.
 
Like I said earlier I know squat on this...

But say the inner diameter of our stock tubes are 2 1/2" with 7' total of tube from the blower exit to intake entrance....I would have thought going to a 3 1/2" tube and 10' of length would lower pressure due to length and width....

Dunno....Im here to learn though....My ears are open..

F1
 
I went to 2.75in tubing and its deffinatly longer. I just dont know enough about this stuff either to really see what that would do to flow.
 
Boost is just compressed air. Bigger pipes, larger exhaust, heads, if any of that stuff is a bottleneck to the system you will lose boost by improving them. You are still moving at least the same amount of air but easier. The fact is you are moving more air faster and cooler.....which is positive! I barely pin my boost gauge with 15% overdrive, but I don't think most people want a piece!
 
If your boost gage is connected to the post on the upper intake like from the factory, an FMIC shouldn't reduce your boost. Any additional backpressure caused from a restrictive IC would only show up before the IC. The air to the upper intake should have the same boost. You may have a boost leak with your new piping. Hows your vacuum? Does the car idle OK?
 
The car idles ok 90% of the time. Its never Idled perfect like a new caddy or somthing though. Vac verys alot its different on different days and OAT's, its usually around 18in in park. I used my air compressor and hooked it to the factory boost location and regulated it to 15psi to check for leaks, but the noise from it leaking from the TB makes it hard to track down anything. By feeling the welds and couplers I coudnt find a leak...any better ways to find a leak?
 
I would think adding a large FMIC on the car will take away a bit how fast boost will build, since obviously you have to "fill up" the IC first before air moves out of it. To get that back you need the blower to push more air...

But here's the caveat. Your only running a 94 blower at 3% with the 90 blower pully. Now say you add a 5% js pully which will net you 8%. That will cause the blower to create ALOT more heat so you could end up being back to square one with a stock IC. The 94 blower's are quite efficient and have been prone to generating alot more heat at higher OD than the older blowers.

It'll be interesting to see where the balance comes in with the above ;). I think its time for you to start saving up for an MPIII or MPX to reap the benefits of that IC.

Frit
 
the front mount will not lower boost per say,
its caused by the air cooling and denser air is compact the boost you seen before was due to expansion of heated air ,

it doestake longer to build boost up more aria to fill but its not a big delay maybe a moment longer, butmost guys with front mount are over driving the blowers so its all good and 12 lbs of cold boost makes more power then 18 lbs of hot air.


just my oppinion
 
But here's the caveat. Your only running a 94 blower at 3% with the 90 blower pully. Now say you add a 5% js pully which will net you 8%. That will cause the blower to create ALOT more heat so you could end up being back to square one with a stock IC. The 94 blower's are quite efficient and have been prone to generating alot more heat at higher OD than the older blowers.

I would definately add the 5% pulley now that you can cool the charge. I ran a 5% jackshaft and a 5% supercharger pulley when I had my 94 blower on (~13% overdrive), it was cooled with a FastFreeddie double IC and a fan. Ran it like that for 2 years, no problems and made 250/365. BUT I also had 36lb. injectors and a tune.
 
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