I have the 3.4 pulley which is suppose to give me 9 1/2 lbs of boost, but most of the time I only get 7 1/2 lbs. Is it because of this hot weather here in Iowa or is it some other restriction?

 

Heat plays a big role. Remember that your computer pulls timing under a lot of different circumstances besides just knock. One of those is IAT's (intake air temps) - when the IAT's reach a certain level, the car will retard the timing no matter tune is in there.


It's easy to find out if this is what your issue is. Just drive it at night when it's nice and cold and see what you've got. If you're making 1-2 psi more than this is what it is (IAT overheat during the day)

If you don't make any more psi at night running ice cold, then it is something else that could be a million things as simple as your compression and air flow in your heads is limiting your psi production.

My bet is it's just the heat. Look into a larger intercooler resevoir (icebox) and that will help you out quite a bit.

 

Also remember that with the air flowing through anintercooler, you will loose a certain amount of psi. It's usually no more than .5 to 2 psi, but depending on how efficent the intercooler is that could be the reason for it dropping.

I don't understand how timing will effect his boost pressure. I'm not saying your wrong or incorrect, I just don't understand it. Please explain. I know boost is created through the pulley system, which depends on engine rpms. I'm not sure how that connects timing to boost pressure. A reduction in timing will almost always create a reduction of power. The hotter your engine is, the more your engine will pull out timing, thus loosing precious power. I understand all that, just not the boost/timing issue.

Now I'm confused. .

 

I was going to pose the same question in regards to heat. I have noticed a huge difference when driving the car in very hot temps....been high 90's here in Maryland for several weeks....and thought something was wrong with the car/tune/supercharger. Now the evenings are cooling off and I can tell a huge difference in power. I don't have the guages yet to tell for sure but can tell by seat of the pants feel. Got on it hard last night and it jumped and went sideways shifting into 2nd gear!

 

Don't be confused...lol I bolded your comment that explains it all. The s/c itself is irrelevant. Doesn't matter if you are pushing 24 psi through it - if the computer retards the timing, the power is cut...period. To put is simply, take a look at the placement of your meter and how and where it reads and this should help you understand.

You guys with a s/c just get a larger resevior and you will notice a big performance difference in the heat. You don't have to fill it with ice on the street. Just having the extra water helps greatly. Take a look at your current resevior and I garuntee you it holds now no more than a couple CUPS of water. Now replace that with a resevoir that holds around 3-5 GALLONS and it's a big difference. Fill that baby with ice at the track and you can carry 24º of timing all the way down the track. Heat is your enemy...period.

The S/c itself also is prone to heat. The hotter the charger gets, the less efficent it is and the less boost it will create. This is all drag racing 101 - heat = bad.

 

I always thought it was the actual act of the air having to pass through the intercooler that caused a drop in psi, but after getting an email reply from whipple I now see that the cooling of the air lowers the psi. I was asking about why they didn't move the IAT sensor to after the intercooler. In one of the emails they said that if your intercooler wasn't working for some reason you'd see a 1-2 psi increase in max boost.

Do you guys running a 10psi pulley ever see 10psi of boost? I'd expect 9.5 max right?

 

Where do I get one of those bigger intercooler resevoirs? Can someone post a link?

 

Sounds like a heat issue to me, I make 6.5psi with the 3.8 pulley.

 

There is a note in the Whipple Install manual that says a lot of modifications to the exhaust system (less backpressure) can cause a drop in boost pressure.
They said that a pulley change would bring the boost levels back up.

I didn't see any headers, etc on the original poster's sig though...

 

Wow... how about the simplest of answers... Maybe your guage is wrong?

On a turbo Supra, I've tested 4 different guages in however long it took to swap from one to the next, all the exact same guage from one manufacturer and no two of them read the same. Readings ranged from 1.5 psi low, to .75 psi high.