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Discussion Starter · #1 ·
I'm going to have my Thermal from my SH and getting a base model so I can't use the entire thing. However I have two questions...not really related. First could I use just the pipe from the cat to the axle back section if the muffler shop cut off the flange and used a slip joint to the new custom rear section?

Next but also an exhaust question, at what point does it make more sense to go 2.5" instead of 2.25"? Initially I'm going to wait on the header but I'm going to put my CAI, and AEM pulleys on right away and do the new exhaust. If I get the entire cat back replaced custom I'd like to think ahead and do the piping accordingly. I'm not sure how far I'll go after I/H/E & pulleys but most likely a little further down the line I'll do some more work. However I'm not going so far as to do cams, head work, or new pistons. Is there any formula for how much hp you can put out before the 2.25" exhaust becomes too restrictive?

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i dont think exhaust diameter REALLY comes into play until you introduce FI. I may be wrong..

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Discussion Starter · #4 ·
So is this the consensus? Normal bolt ons plus a few and your still good with a 2.25" piped exhuast? I figured with our motors and some added power past the normal I/H/E a 2.5" might do you good. Isn't there some type of formula for deciding which diamter is optimal?
 

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May I point out that exhaust systems are indeed "tuned" to the car. Thermal in particular takes pride in their design work.
Have you considered keeping the entire cat-back and only changing the length of the front pipe-from the cat to the resonator. That would resolve the install.

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mark,
my apex exhaust was for the base, i had midas (or meinekee) cut off like 3-4" in order to fit. i will show you where they cut when we meet up next time.
 

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Discussion Starter · #7 ·
I've thought about that too See. I'll check it out next time we meet up.

jc836: No offense but besides putting some "stealth cones" in their muffler what kind of tuning does thermal do on this? They don't have a dyno of a Prelude using it so how do they know it's making the most power? In reality it sounds more like Thermal wanted a low noise system then anything. I like the exhaust but there's some things about it I don't like and I'd like to fix that my next time around. I don't question their piping size but instead the outlets of the muffler. I'd have to say that the actual outlet diamter of each tip is at best 1 1/4" where the pipe from the muffler is closer to 2". I see some people NA are running 2.25" on Integra's...I just figured with a bigger motor I might wind up bottle-necking the power later on with a 2.25" however since nobody seems to know I guess I'll stick with the 2.25" because we do know that works.

I got another month to research this so I'll figure it out by then.
 
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After talking with John at HiTech, a 2.25 exhaust is too restrictive for an H22 with major mods. I don't know about your specific situation, and the only way to really know would be to dyno the same exhausts (just one is 2.25 and one is 2.5) side by side.

Keep in mind that I am going with a full race setup (high compression, ported head, ported single runner intake manifold, etc. etc.), so the engine will breath MUCH better than stock.

I would venture to say that your setup will work fine with a 2.25 exhaust, but if you start to do headwork or other extensive mods, go with a custom 2.5 exhaust.

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North Texas Prelude Owners Group
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Discussion Starter · #9 ·
<font face="Verdana, Arial" size="2">Originally posted by 71dsp:
After talking with John at HiTech, a 2.25 exhaust is too restrictive for an H22 with major mods. I don't know about your specific situation, and the only way to really know would be to dyno the same exhausts (just one is 2.25 and one is 2.5) side by side.

Keep in mind that I am going with a full race setup (high compression, ported head, ported single runner intake manifold, etc. etc.), so the engine will breath MUCH better than stock.

I would venture to say that your setup will work fine with a 2.25 exhaust, but if you start to do headwork or other extensive mods, go with a custom 2.5 exhaust.

</font>

Thanks Billy,

As for mods after the I/H/E & pulleys I'll be doing an APEX-i, and hopefully getting Sun's Endyn worked intake and add a ITR TB to it. The only other thing would be a ECU if anyone ever made a plug in replacement for our cars.
 
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Interested in a semi-complete OBD1 setup? 4Gen ECU that has been reprogrammed?


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Billy
North Texas Prelude Owners Group
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Discussion Starter · #11 ·
<font face="Verdana, Arial" size="2">Originally posted by 71dsp:
Interested in a semi-complete OBD1 setup? 4Gen ECU that has been reprogrammed?


</font>
Well here's the thing with that, could you swap back in the 5th gen ECU for emissions testing? Living in NJ is NOT like living is Texas, state emissions is VERY tough and hard to find shops that simply overlook that stuff. And what else would I need besides what you have? I hate you for even getting me thinking about this
 

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You are correct that Thermal's Dyno was down during the design and tests on the 5th gen system. I also agree that they had to comply with CARB/CHP before they would release a system. Is there an improvement over stock-we both know that only a dyno run will be specific. As to the piping-the power curve will move around with changes in sizes.
I proved it with a silencer for my model airplanes and have also seen changes in performance (perceived) when I did duals on cars.
Guess we should wait for your findings as well. But I repeat that Thermal is very careful with what they do and you can save by either modifying the front of the B-pipe's length or even buying a new one.

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