Whats better, larger valves or better ports?

[Adam]

As above.
I've got the choice of using either a cathedral port head(as i already have one spare), or a square port head(1.6i) which has larger valves than 1200/1400SPI heads.

What would be better, good flowing ports but usual nova size valves, or bad ports but big valves?

Im thinking good ports, as big valves are still going to restricted by the square ports.

Any opinions?

[Stuart]

imho PORTS are key then valves.....

best of both worlds is the 1.4/1.6 MPI heads ;)

[beavy69]

I'd say if it was two standard heads I'd go for the bigger valves if they are original as the head is designed to handle more fuel+air. and you can help it with some really easy basic home porting. i.e matching the inlet manifold - don't try and put a square peg in a round hole lol

If its aftermarket valves I wouldn't bother untill you can have ports that can use the increase in volume.

[Adam]

Ok cheers Stu and beavy.

Looks like i'll mod an inlet then to run SPI on a 14se head.

[beavy69]

Here are some useful links for porting that may help you(I looked into in debth a short while ago):

http://www.sa-motorsports.com/diyport.shtm
http://www.chevyhiperformance.com/techarticles/95518/
http://www.mondellotwister.com/ArtHeadPort.htm

good luck

[Stuart]

the dave andrews site is good too. google it i cba to be THAT helpfull lol


WHY oh WHY bother keeping the SPI crap on a good head... just retrofit the MPI setup on there!

[beavy69]

What dumb GM fool came up with the idea of square ports anyway? lol Is there any other car company that use them?

[Stuart]

chevvy ;)

[Adam]

WHY oh WHY bother keeping the SPI crap on a good head... just retrofit the MPI setup on there! Whats the point of fitting MPI, when i'll need MPI inlet,loom,bottom pulley,ecu etc, and bumps my insurance up by 4extra groups.

When a 1.4spi is one group more than my current 1.2spi, and the 1400 should end up with more power than the MPI engine, plus i find SPI easier to work with, less stuff to break,Lol. :thumb:

Unless someone has a MPI top end that there willing give me? Lol

SPI in its self is not a poor fueling system.

Beavy-I think the square ports were done for a reason, something do with small ports=greater gas speed, giving more torque or something. WHich is why SPI engines are town driving engines, not BHP monsters,Lol.

[mikey14sr]

I recently got hold of an almost complete mpi wiring loom and engine, I shall be keeping the head, but you're welcome to offer some cash for the inlet manifold, exhaust manifold, and the loom, the only bits I don't have are the map sensor and fuel pump/tank/lines.

[Adam]

Got a few map sensors matey, and a MPI pump for my tank so i wouldn't need those bits.

Do you have the ECU, wiring loom,inlet, fuel rail etc?

I'll pm you.

[womble sri]

Unless someone has a MPI top end that there willing give me? Lol
.
or swell? i got an sri for spares let me know

[Adam]

I'll PM you too lol