RX200013B

has anyone used 1 3/4 tube for headers before?, or 2" only

s4 6port stock ports

have 1 3/4 mandrel bender availible but not 2"

what performance will i loose with the 1 3/4 tube?

ultimatejay

iTrader: (1)

With the stock porting, you should be fine with the 1 3/4. It actually might be better than the 2" for stock porting.

rotarygod

iTrader: (1)

The stock ports have the same area as a 1-5/8" hole. The sleeves however expand to nearly 2" which is why we see 2" being common. The sleeves I machined kept the port profile all the way through to the header. I then shaped a 1-3/4" pipe so that there was a very slight lip for anti-reversion purposes. Works great. Pipe size isn't the problem. It's the turbulence in the stock exhaust sleeves that is. If your pipe is smaller than your exhaust sleeve, just radius the inlet to the header to help flow. This will work fine.

RX200013B

rotary god, when using the 1 3/4 tube and using your math(here's how to figure runner lenght) would the tube need to be shorter or longer with the smaller dia tube?

rotarygod

iTrader: (1)

Don't use that formula exactly as is. The speed of sound number is way wrong. It is close for intakes though.

A larger diameter pipe will generally move the powerband up.

RX200013B

would you have a better # to go off of? i wanting to make a short primary system

plans before you said (Don't use that formula exactly as is) was a 21" primary to a 2.5" collector and 2.5" all the way out. 1 muffler

any comments on that set-up?

rotarygod

iTrader: (1)

That actually should work just fine. Since I wrote that, I've learned alot more about intake and exhaust tuning and now I look back and realize I only knew about half of what I could have. In other words not all of the info is there and what is there isn't quite correct although the general premise is correct. It comes down to a couple of small errors in the calculations which don't mean a whole lot but still matter. There is also a much simpler way to explain things. I actually need to write separate articles for both intakes and exhausts and even then they should probably be broken down into chapters. This isn't quick or easy to do but one day I'll get around to it.

The biggest mistake I see is that many people want to plug a target hp peak into a formula and then build the intake or exhaust system exactly to that number and then expect to see it work exactly as predicted. It's not that easy. They are meant as a general guideline. Someone who lives in Miami will get different results on their car than the same part would on a car in Denver. It would also change based on temperature. They do anyways. There is far more to it and it needs to be written as almost a book. There are many of them that exist but it needs to be rotary specific so people understand it better and even then it needs to be made as simple to understand as possible. Another issue that I've seen in threads like that is that many people try to over think things and make a big deal out of something that doesn't matter. Case in point, I've heard people try to argue that a single exhaust flows better than the dual exhaust in the 2nd gen as the y-pipe is a zone of turbulence and affects tuning. What is technically true and what is noticable in the real world are 2 different things.

For now, just go by that general design. It'll be fine. Is there a better design out there? Probably. If you want to experiment, build it in a way that you can change the header length or the collector.

diabolical1

iTrader: (3)

i have probably fallen into that category more times than i can remember, but i think it's natural for people to try to apply the new things they learn, though it may occasionally be inappropriate. at any rate, truer words are seldom spoken - and i especially like that you are one of the few people to take the time to correct himself/herself for the benefit of a future audience.

lonetlan

you two should write a book.