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exhaust port size
sammundo - 12/12/20 at 02:23 PM

hi folks. Quick question. I have a standard 1300 crossflow going in my locost with 30mm exhaust ports. I have the standard manifold but i have found a 4-2-1 with 34mm ports for pretty cheap. Will it work well without porting the head? Or should i stick with the original.
cheers

Deckman001 - 12/12/20 at 02:34 PM

Hi ya, the slightly larger exhaust shouldn't affect your 1300 xflow, it lets the exhaust escape quicker that normal so if you have a big valve head, it'll be even better. I have a larger than normal exhaust on my 1600, it allows the gases to escape better.

Jason

gremlin1234 - 12/12/20 at 04:45 PM

mismatched pipes can/will cause turbulence, think of the exhaust as a tuned musical instrument.
but just go for it, gives you an excuse to 'port' the head later too

steve m - 12/12/20 at 05:48 PM

I would fettle the head to match the headers, its an easy but time consuming job,
You will also need the larger exhaust gaskets

But in reality a 1300 xflow, even in a locost/lightweight car will be like driving a Nissan Micra

Shooter63 - 12/12/20 at 07:49 PM

Just to go against the grain here, don't match the port to the manifold, mismatch is a good thing as long as the manifold is bigger, what it does is help stop the pulse going back into the chamber and pushing the new inlet charge out.

Shooter

snapper - 13/12/20 at 08:01 AM

quote:
Originally posted by Shooter63
Just to go against the grain here, don't match the port to the manifold, mismatch is a good thing as long as the manifold is bigger, what it does is help stop the pulse going back into the chamber and pushing the new inlet charge out.

Shooter


Shooter is sort of right but the professional way is to use anti reversion stubs which are short tubes welded on to the manifold plate that are port matched then a much larger primary pipe welded over that.
In reality only any good for a drag racer.

You 4 branch manifold will be better than the cast original by a long chalk and work well on a 1600 if you ever swap it out.

Fit it and enjoy

jelly head - 13/12/20 at 08:27 AM

Smooth flow on the exhaust side is not quite as importand as such as don't forget you have a piston pushing the exhaust gasses out, depends if you're after every HP in which case you'd be doing the head anyway.

sammundo - 13/12/20 at 05:48 PM

thanks for the replys guys. I think i'll go for it. I am liking the simplicity of the xflow so maybe a 1600 will come in down the line.

steve m - 13/12/20 at 06:56 PM

You wont regret going up to 1600, its 7/8" taller,
and then you may progress to a 1700 (1696)

coyoteboy - 15/12/20 at 12:41 PM

It's 2mm on the radius, you won't see any difference without back to back dyno runs. If it had been 5mm I'd be much more worried, but I've still seen OEM manifolds worse.