Hi,
I have a 1980 SA with:
stock engine
Holley HP 4150
RB Intake

My concern is that I bought:
RB's Road Race Header 79-85 RX-7 (12A)
ISC's IT7 Front Section
ISC's IT7 Mid Pipe
Flowmaster 70 series muffler
This stull is huge!(3"OD)

ISC said it was a perfect match to the RB head and if you look a the sweeped area I would agree- It would not make sence to put smaller pipes after the RB header.
But my concern is that my stock engine already has a narrow power band, so will this stuff make my power band extremely small?

I'm having a very hard time fitting the exhaust components to my SA. I'm sure I can do it but is it worth it if my power band shrinks in half? Maybe my peak torque will even be hurt!?

Dyno gurus please help,
Vin

 

Bumped

 

Narrow power band...? On a rotary? It should have a WIDER power band than most engines...
It should start making decent power aound 2500rpm and pull nicely up to the redline...

Anyways, I wouldn't go with a 3" pipe on a stock motor. The exhaust velocities will be WAY low. I would say 2.5" on a stockport 12A

The racing exhaust was designed for modded engines making more power, and pushing more exhaust...
Even then, on my streetport 13B, I only used 2.5"...

 

I agree with you.
Now that I have the parts I'm not sure what to do.
The RB Header has about the same cross-sectional area as the 3" pipe so if I where to go to a smaller system I should get a smaller header to.

ISC racing said that the system was designed for a stock (un-ported) 12A and would make more torque at 4000rpm and above than all the other exhausts they tested.
Torque coming in at 4000rpm would be OK but I would prefer 3000rpm.

Thanks,
Vin

 

Really? They reccomend 3" for an un-ported 12A?

I'm quite supprised!

As I said, I only ran 2.5" on my ported 13B and it was probably making 160~ish hp at the flywheel.

I had a cone-intake, but figure the intake was still more restrictive than the exhaust at that point.

 

I hear ya,
I'm guess going to finish it and see what happens

SCI said that a great deal of time was spent on the dyno to tune the chamber. I have my fingers crossed. The owner of SCI seems like a strait-up sort.

I just wish installing was a little easyer.

Thanks for all the help,
Vin

 

Let me know how it turns out...

 

Wow!
With the Flowmaster 70 series on the exhaust sounds sweet.
Low throaty purr.
I like quite cars but this is not too bad there either.

BUT, I have not driven the car yet due to fitment issues with the Flowmaster.
I'm hoping to finish today. I don't expect good results in power or torque but I have my fingers crossed

Vin

 

I'll keep mine crossed for you too...

 

Dude, compared to a stock exhaust, thats going to scream! Don't think its going to LOOSE anything compared to other systems, because ISC has their **** together big time. I used to have a series 40 flowmaster, and that what pretty sick loud, good luck.

 

Sounds like good news to me!
Still have my fingers crossed,
Vin

ps. love the Flowmater!

 

alot of times when you go to the track, the rotary guys run straight header.... i wonder why this is? because it initially does give you more power. 3" on a stock port 12a is not stupid, in fact you will get the most power. these aren't honda engines and exhaust scaveging isnt the deal. you need less pressure. yes your low end grunt may be lost.... but who cares!!!!! aahahhahaha if it still bothers you put a turbo on there i think you will be happy. ISC is the JAM!


edit: what size holley you running? double pumper right? i'm proud of you

 

Ummm... I think you missed the whole point of his post...

He's concerned about low end, and keeping a usable power band.
Since he's got a muffler, I'm assuming this is a street car, so your track comparisons are meaningless...

OBVIOUSLY 3" is gonna make more top end. Nobody is arguing that.
And nobody mentioned exhaust scavenging...???

 

Hey Vin, I just noticed the RB website lists the Road Race header as having 2" O.D.

http://www.racingbeat.com/resultset....rtNumber=16125

 

Yes "ISC is the JAM!".

Yes "RB website lists the Road Race header as having 2" O.D". Good point.
But there are two of those pipes leaving the engine so it would not make sense to have them go into a single 2" O.D. pipe. Although I'm no expert.

Yes to the Holley double pumper!
HP 4150 with no choke horn.
BUT it is rated as 390CFM , actually it flows about 500CFM and gives VERY crisp responce.

It is a street car but I want to use it in Solo II, just for fun.

The Flowmaster 70 series is just cut and pasted from the "Scientific Design of Exhaust & Intake Systems" by Philip H. Smith and John C. Morrison. I like it

TURBO? Anyone want to help?

Thanks for all the help.
I still have my fingers crossed,
Vin

 

My final guess befor I run it is that SMNC is right and I will have to go to something below 2.5" O.D.

 

Car running nice, but Holley 4150HP (390CFM) NOT dialed in yet and the snorkel is not finished. Power is up everywhere but not buy a huge amount.
The wide band O2 sensor is in and I'll update after tuning the carb is done.
Thanks,
Vin
ps. I have a smaller exhaust coming to see the difference in low end torque- thanks Mr Project!

 

How did you do with the holley?

 

I love the Holley, but I havn't dialed it in yet