metalliman

I noticed on my '83 12a the intake ports on the intermediate housing are far larger than the ports on my Dellorto intake manifold. I know for a stock ported engine, that you're supposed to leave the ports alone, but my engine is street ported, should I open up the ports on the Dellorto intake, or will this leave me with an un-streetable engine?

WackyRotary

There are made that way intentionally. Otherwise the maker of the intake would make them match.

peejay

The port runners in the manifold cannot be opened up to even remotely match the engine's runners for the center two ports because the port cannot turn and open up at the same time. If it did, it would result in hellacious turbulence.

Also, port mismatch is GOOD when the mismatch gets larger downstream - this acts as a kind of check valve.

Project84

do a search for turbulence. Someone explained all the details about what creates turbulence in the intake manifold and how it is bad.

MattG

iTrader: (2)

I just ran into this same problem on my intake and engine, but I dont see how my ports being huge on my engine and little ports on my intake would be ok. Wouldnt it want more fuel to flow but with the smaller hole it couldnt feed its need, thus causing less power.

OR

Does it do good because it pulls more fuel through the intake at a higher speed because it needs more fuel, kinda like forced induction.

Im stumped. Ive been searchin, and will continue too.

Where is rx7carl when you need him? Airflow is his life!

Or PeeJay cant forget about him

MattG

iTrader: (2)

Ok I think im getting it! Its blowing my mind really all this talk about airflow!

ARGGGGGH

MattG

iTrader: (2)

Ok I think I got it now.

I will not touch the center ports. Every thread I have read has peejay saying dont touch the center intake ports on the manifold. So im going to stay the F away!

But I have looked at streetport templates and none of them touch the intake ports on the outside.



Only the exhaust and intake port on the inside of the engine.



So I think ima leave it alone! If they were ment to be ported out I think RB would sell it.
Gosh

j9fd3s

iTrader: (3)

i got to see a renisis 4 port motor and the port openings inside the motor are HUGE and the runners are teeny compared to the older engines.

DriveFast7

iTrader: (1)

how much smaller should the mainfold's center runners be?

MattG

iTrader: (2)

Let me go take a picture becuase mine is a huge gap.

MattG

iTrader: (2)

Ok

here is the pic of the intake I am talking about.


Here is the size of the gasket and the hole on the intake manifold I have


This is the size of the intake ports on the engine Look at the huge difference