I have a Honda Prelude 95 Vtec H22A and occasionally take it to our track for racing. I have upgraded the intake manifold - Skunk2 - and headers -replica Hytech Tri-y. The cat has been removed. I use slicks and have been dropping the exhaust but I am getting two trains of thought on that. Which is better - and why?

 

need more clarification... do you mean you are taking the exhaust off at the track? is that what you mean by "dropping the exhaust"??

 

From what point are you removing the exhaust? header back? If so, is there anything holding the header to the bottom of the engine? We definitely need more details.

 

We take the exhaust off at the track at the point of the flange ring where the headers down pipe meet the exhaust. The exhaust isn't removed completely, just disconnected from the headers and tied down. I am told that this would improve the airflow, but I am also told that Honda engines run more effectively with the back pressure, which supposedly isn't there when the exhaust is disconnected. I did ask the question about what is holding up the headers, I can't recall what the answer was to that.

 

Don't drop your exhaust! Generally, all engines need backpressure for the sake of vacuum to pull in a fresh charge and to keep up air flow inertia. I can't believe so many people are naive enough to buy and bolt on aftermarket parts. Do you really think that car manufacturers spend millions to research and build cars with parts that are inferior to poorly made aftermarket brands? When a car engine produces a lot of punch for its size, things have been engineered correctly (like the Prelude). If you’re going to change, add, or remove something, you better do your research and compliment everything else, or you’re going to waste your money!

 

Really noob? You believe that? Have you ever see a dyno?

 

ok i dont know where you got that info because every dyno i have seen has has better numbers OPEN HEADER. it work fine just make sure that you have it dynoed that way cause your car might act differently being open header

 

We don't have dyno facilities here on this little island. Please bear that in mind. My question is : open header or not? And why (not)?

 

open header runs better because the motor is less restricted... the trade off is the added noise and the "illegal for street use aspect" they make switches that do exactly what you are trying to accomplish, like a Y right after your down pipe (I am racking my brain trying to remember what the F its called)

 

Wildhoney, my "noob" questions were directed at Needy4Speed. His comments were ignorant.

I ran open header (not by choice) for about 3 days. I also have the Tri-Y and it banged on the crossmember everytime the engine torqued. However, if you make a bracket that bolts it to the bottom of the engine block (like the stocker) I think you'll get good results.

 

I thought I might get some flak for that. Maybe I came across as too harsh, but I stand by my words.

I don’t know what your numbers were before your bolt-ons, but I bet you didn’t get much bang for your buck. If you had your car dynode between each mod, I’m sure you’d see trade-offs. Maybe you gained a couple of peak ponies, but you probably lost some too.

Take off your header if you want too. You might gain some horse power near the redline, but your torque curve will probably look like $h*!

P.S. I’m not ignorant. I might not be a pro, but I have more experience than you know.

Also, some bolt-ons are worth it for Preludes. I went to 11:1 comp, intake, cams, and some slight porting. The next thing might be a VTEC controller.

 

There are thousands of people with dynos showing open header makes more power. The difference between open header and full exhaust is usually ~5whp. I don't think it's enough to bother with, but it's still a benefit.

As for when the power comes in....95% of racing is done between 5k and 8k RPMs. So the down-low effects are irrelevant.

Actually, I know pretty much everything there is to know about this particular subject. I'll just let you see the dyno:

 

i'm willing to bet you dont

 

So you ARE alive. Any chance in getting a response to the PM?

 

He's probably been hiding in the All-motor forum of FI forum

 

I don’t believe any charts unless I witness the dyno making them. Magazines have it in with the aftermarket companies, and people are byes about everything.

 

That must be how you got so knowledgeable. You only believe what you want to believe, because everyone else is BIASED.

As for the dyno, it's mine. I witnessed it. It's real. Backpressure isn't needed.

 

Thanks for this information. The header doesn't appear to be banging anywhere, but I'll recommend that it be bolted down. There was some vibration initially, but the exhaust was tied down differently after I mentioned that, it appears to have gone away. I still wonder about the comments I have heard about Honda engines and back pressure, but if the dynos shows better performance with open header then that's the way to go. And yes, the noise is quite something

 

[QUOTE=Needy4Speed;39503795]

Take off your header if you want too.
/QUOTE]

You mean exhaust ?

 

Any idea what 5whp equates to in time elapsed over 1000 ft or 1/4 mile? (More or less). And just for my information what is VAFC Tuned please ?

 

^probably negligible at best. Concentrate on driving consistently.

VAFC is an air/fuel/vtec controller. It allows tuning on a minor level

 

No backpressure means his, presumably stock, injectors and ECU won’t be able to compensate. He’ll be running lean and possibly burn his valves. Also, without adjusting his cam and ignition timing, I’d be surprised if his numbers didn’t drop.

 

please stop posting.

thanks.

 

Very correct, every dyno chart I've ever seen in magazines the torque curve looked like crap after an exhaust upgrade, all for a couple horses up top. And as a matter of fact, whoever said that most of racing is done between 5-8k, you're right, but you neglect that fact that every 1/10th off your 60' time equates to about 2/10ths off your quarter, so the torque curve is very important when drag racing.

And it's not back-pressure that we want, it's the velocity that's created by back pressure. That's why with n/a's you want a very tuned exhaust system, but with cars like my dsm the turbo creates all the back-pressure needed, so anything after the turbo, the bigger the better.

 

so back pressure creates velocity now?