racedriver

Anyone open up the sides of the exhaust ports when doing the street port. I did and i am wondering if it is the cause of a lot of turbo lag with stock twins compared to before. Like 10 pounds at 4500 rpm? Anyone with a port job or experience please respond

RICE RACING

Yes completley, open it up to the limit of the sleeve and beyond by tapering it IE: a reverse funnel if you get what I mean, this helps flow.

I take the sleeves out in some engines and finish the sides flush with the inner edge of the exhaust port minus the sleeve (this is very wide !)

Stock turbos though I would not open up the port too much (in height) as the extra overlap will have a negative effect in power...but once you run a larger turbine section you will pick up a big increase in volumetric efficiency.

If you do a search under my name you will find a photo of the exhaust porting, if not drop me an email.

riceracing@ozemail.com.au

And I will send you a photo.

regards.

jspecracer7

Hey R Racing...Post a pic! I've seen a few exhaust ports, but I'd like to see what you use.

RICE RACING

here you go

I cannot double post images already on here so you will find it in here, I think?

https://www.rx7club.com/forum/attach...=&postid=91840

https://www.rx7club.com/forum/showth...threadid=14131

racedriver

Thanks for all the info. With a T78 single turbo would it spool up quicker than the stock twins?

jspecracer7

Damn Man!!! That's a HUGE exhaust port!!! The primary isn't "small" either!

I've found that the exhaust port is what gets you more top end power than the intake ports. You agree?

RICE RACING

100% bro !

It was a thing that I could not get enough "courage" to open the ports as much as I did in my last build (version of my street engine) ..... You cannot make the port any wider/higher/lower than what I am running now without having the seals fall out or water leak into the exhaust port !

When you combine this philosophy with a tuned length big diameter exhaust manifold and non restrictive turbine section, you get excellent mid/top end power, from 5k to 8.5k when combined with street porting. The only range that is afected badly is 700rpm to around 2000rpm where the power produced is a little low due to low gas speed mainly and the idle is a bit more unstable "lumpy" with the large exhaust porting and circuit racing flywheel I have to increase my idle speed to 1100rpm. Also if doing a back to back run with a less agresivly ported engine under 4k rpm you will find that it will be slower again due to non ideal port size for this rpm range.

However.

These are small negative things which are more than offset by the higher peak rpm range and power spread (band) gained through this style of porting when matched with correct bolt on's.