I have a few questions on their templates... for the exhaust templates, what all is the difference between streetable and race templates? Is the porting worth any noticable hp vs noise? I am assuming the race template will make the most hp, but the noise level will be outrageous, correct?

Race exhaust template part number: 22211
Street exhaust template part number: 22210

I am looking at their Bridge and J porting. Dont you also have to do some grinding on the rotor itself on the J bridge or am I going crazy?

 

Just looked around their site some more, and noticed that they cut the HOUSINGS and not the rotors... Silly me. I guess they just put the Iron next to the housing and cut away some of the housing where the bridge is at? This is judging from their pictures. I dont want to spend money when I can do it myself, as I am on a tight budget.

 

If you're going BP, you need the race exhaust templates. Street ported exhaust isn't enough for a BP.

 

Now that you got me thinking about the porting being enough for the exhaust gas to flow through, would the streetable RB header still be good for the BP or am I going to have to opt for the road race?

 

The street header will work, but the road race setup would be better.
The key to making the street header work best, is using 2.5" pipe behind it. A long primary exhaust is still the best way to go, but if you already have the street header, you can make it work.

 

Cool, I have 2.50 from header to presilencer, then 2.25 from presilencer to rear muffler. Wont be that hard to change.

 

That will work, but will rob a little bit of the power potential, but only up high in RPM range, where BP's are golden.

 

I dont plan on spinning more than 8k anyways.

 

my understanding is:

BP starts putting out big time HP.... the more HP the more exhaust gas volume per unit time. The exhaust gas must exit through the exhaust system as unrestricted as possible and at a fast rate to help scavenge upstream back to the engine exhaust chamber.
what this points to is the following:

There is a way to calculate the exhaust gas volume generated by the hp devoloped. Knowing the exhuast pipe cross sectional diameter ( or diameters ) will give you the velocity of the exhaust gas. This process allows for the selection of the proper cross sectional exhaust pipe diameter for the application your working on.

I will have to look this up and get back to you if you want to know the specifics on how to do this.

The simple answer is full road race exhaust system for BP.

also there is a sizable improvement if you bench flow your porting progress.
I have not done this yet but I understand the basic idea....bournolli principle of pressure and velocity.
set up adjustable air flow through the port you are working on and measure it with a monometer. adjust port shape form and size to be optimal...see Paul Yaws site.

hope this helps

regards
two79rx7's

 

I have a lot of charts and exhaust books I am looking at right now. It says that for 200HP I shoudl run 2 1/6" pipes for optimal flow, but this is basing on maximum velocity of 250 ft/sec. Lots of math to go through, but I think I should be fine with 2.50 single with straight through mufflers like I have now. Stockport motors run the best with 1 7/8" if I remember correctly.

 

A = pi x (RxR) RxR is r squared, no way to write it properly here.

" for 200HP I shoudl run 2 1/6" pipes ( 2 1/16"? )"

A = 3.14 x 1 1/32 sq = 3.339 sq inches per pipe
"pipes" as you wrote above means 6.68 sq inches for two pipes

For one 2 1/2" pipe
A = 3.14 x 1 1/4" sq = 7.85 sq inches

Do you want more than what is recommended by using the 2 1/2" pipe?

 

A=pi x r²

I understand the volume and area, but I am more concerned with velocity. I am still researching and reading

 

"There is probably a magic number that airflow velocity in a tube should not exceed, for reasons of rapidly increasing drag and consequent flow losses. I suspect this number is around Mach .4, or about 450 feet per second, since drag, and therefore flow loss, increases significantly after this. Tube size can easily be checked by calculating the maximum airflow attainable, dividing by the area of the tube in square feet, and dividing again by 6 to convert to feet per second. An approximate value for maximum airflow can be obtained by multiplying the desired bhp by 1.5"



"Thus, the 2.5 inch diameter tube will be adequate to flow 600 cfm without unreasonable drag.
Resist the temptation to use larger diameter tubes than necessary, an as little drag is created in smooth tubes with gentle bends. Larger tubes will only add to the volume, and that is not a good thing to do."

Corkey Bell, Maximum Boost

 

That took me forever to do in MSPaint, and I hope that has some relevance to the topic at hand.

 

Back to your original question.

The specific difference between the two templates is that the race template closes the port about 4mm later (moves the port closing like up) than the street template. Opening stays the same. This will increase overlap and provide greater gains at high RPM at the expense of a little rougher idle. If you're going NA BP or HPB I'd go with the race port.

There is a great thread on calculating exhaust primary length on the board already. Includes discussion of both intake runner and exhaust primary length.

https://www.rx7club.com/showthread.p...ning+resonance

 

If I had to get templates I think Pineapple Racings new templates would be the way to go. For the price and selection you cant go wrong.

 

I was thinking of RB bridgeport plates and PR exhaust plates. Actually, looking back at PR's templates, they do not have bridgeport plates for the 12a. They supply an aligning jig with their templates, which RB doesnt, or they do not say they do.