Can't get top end boost with stock air box
 

Hey

Does the stock air box restrict boost at top end with a 3" dowpipe, midpipe and catback? Car is very quick off the line but lags in boost at top end, and i'm thinking it's the stock air box restricting it. Would intake help keep the turbo's running strong at top end?

ps. mods in the signiture.

-Marshall

you have no ecu? I think the marvelspeed port will probably require one unless they told you otherwise. And yeah I think an intake will make a fair amount of difference just watch the boost levels. Your car with the port and exhaust should be pulling harder and boost increasing if anything at higher rpms.

The stock intake is the only thing keeping you from badly overboosting.

Intakes will make the difference but don't put them unless you have an aftermarket ECU first.

what kind of plug in play ecu would yall recogmend?

http://www.rx7store.net/product.asp?0=208&1=297&3=632

The stock intake is very restrictive. I suggest that you install a boost controller before you open up the intake. With a boost controller, you can limit your boost to 10, and keep your stock ECU. Here is a thread on a nice mod to the stock airbox.

https://www.rx7club.com/forum/showth...hreadid=121491

The kind everyone recommends the most, which you have undoubtedly seen posted about 100 times, judging from your post count. The initials are APFC.

Now, this is kind of a touchy situation.

What I have found, on more than one system, is the fact that the primary intake elbow closes up when it gets hot and the turbo spools up.

Some people have gone through $1000's trying to correct a problem which isn't. My advice to you is go through the engine comp. and make sure everything is to spec. After that, then look at your mods to see if correct installation has been done.

You might just find you have a leaking one way valve or split hose.

Just my 2 cents.

Adam

I don't understand how the elbow can "close up". Please explain.

The rubber elbow on the stock primary turbo will collaps at times when the elbow gets hot and the turbo is pulling a large ammount of air. Kind of like drinking a milkshake through a soda straw. Try to drink too fast and the straw collapses.

more like a straw with the far end half closed. stock intake box has a severe restriction at inlet elbo, so 1-2 psi vacuum at the turbo inlet can occur.

for rubber 'pipes' that will not collapse (or heatsoak), with full flow area:

mcmaster carr 53335K12 metal reinforced hose, 60mm.
$4 per foot.

When you said "elbow", I thought you were referring to the plastic elbow from the intercooler to the throttle body. I was wondering how you were going to explain that one:)

I designed a nice mod for the stock airbox, that will eliminate that situation you described:

https://www.rx7club.com/forum/showth...hreadid=121491

the "elbow" he refers to is known as an intake pipe or hard pipe. connects the airbox to the turbo.

it is doubtful that your boost situation is being caused by the stock airbox.

what do you mean by "lags in boost"? what is your boost pattern? you do have a boost gauge don't you?