Thermal Cat Installed, new boost reading question

[lundgren]

TITLE WRONG! - I meant Random Tech Cat

I removed the 'generic' cat I had, and replaced it with a random tech cat. It should flow better, and outside of materials, the inlet and outlet seem to be better matched size wise.

I notice that in 4th gear, if I WOT to redline, from 7-8 k rpm, the boost falls of 1 psi. I don't think I noticed it before I installed the new cat.

Here is my question. Do you think my belts are loose (they don't feel loose), or that the new cat simply lets the air flow out so much better, that the boost falls off up top. With the kazi header, thermal 3'' exhaust, and now a better cat, I can see this could occur, but before I over tighten the belts, I thought it would be easy to simply ask what you guys have seen.


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http://www.groupbuycenter.com/

[This message has been edited by lundgren (edited May 19, 2001).]

[strng1dah]

I could see that being a result of the new cat.

ps How do you like that setp, with the Kamakaze, cat and Thermal?

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SC'd GSR
www.Strng1dah.Homestead.com

[lundgren]

I like it a lot. The exhaust is loud (and mine has been modified), but it's clean, deap, and it makes power.

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http://www.groupbuycenter.com/

[JASONS]

I Like that header. do you have ceramic or stainless.how much did it cost and did you notice a differance .the better tune I get my car the less boost it shows.

[This message has been edited by JASONS (edited May 19, 2001).]

[rjaffey]

Did you figure this out yet? Somehow it doesn't sound right. I wouldn't expect boost to drop off at the high end unless there's an intake restriction or a slipping belt.

[johnyew]

It is normal for boost reading to drop as the exhaust side of the engine is made to flow better as there is less backpressure. There is a 'solution' suggested by someone looking to show a completely clueless person on how to increase boost by plugging the exhaust end with a potato.

[rjaffey]

Unless I'm misunderstanding something, it sounds like Jeff is saying that the boost drops off by 1psi in the 7 to 8K range when compared to what he's seeing below that range.

I'd expect intake manifold pressure to drop as exhaust restriction is removed, but I wouldn't expect it to drop more at the top end than anywhere else. This is where the volumetric efficiency of the engine is dropping off, while volumetric efficiency of the blower is higher as are the temperatures. I'd expect the manifold pressure to be higher there than anywhere else.

[lundgren]

I'll try to adjust the belts, and make them a bit higher, and we'll see what happends.

[VTeCno Geek]

I thought Lundgren would know better, but I highly recommend "not" getting the Random Tech Cat (he probably got an awesome deal through GroupBuyCenter). The only reason I say this is I, like many others, have had the Cat material break loose in mine and rattle around like crazy. The Random Tech Cat seems poorly built. I am not sure if any other aftermarket Cat is any better, but I definately didn't like the Random one.

[rjaffey]

Carsound!