Generation IV External Engine - 402ci w/LQ9 6.0 heads/FAST ported 90. Switching to LS3 top end worth a damn?

I've got a 402 with PRC stage 2.5 317 casting 6.0 LQ9 heads and a ported FAST 90. I am considering switching to ported L92 heads and a ported LS3 intake.

What could I expect in gains if any?

I guess I have my answer...

Yes, I have be using the search and researching BTW.




Thanks for nothing :rolleyes:

someone needs to switch to heavy flow pads ;)

according to tests by gmhtp theres not a big difference in flow when youre talking about comprably ported heads, around 15 hp in favor of the rectangular ports vs cathedral on the topend while the cathedral ports held some more power down low in the rpms. that was also with fast 102s on each set of heads however.

i went from afr 205s with a fast 90 90 to ported ls3 setup when i switched from a 346 to a 402. power went from 430/405 to 505/480

now cheer up

All I wanted was a response. Over 24 hours and nothing. I'm used to the appearance section where things are a bit quicker.


Looks like I'll hold out for some TEA ported 225cc TrickFlow heads and a FAST 102

Everybody saw that you think 317 heads are LS2 heads and decided factual conversation was a waste anyway..

Everybody saw that you think 317 heads are LS2 heads and decided factual conversation was a waste anyway..

Good catch and way to be an ass.

6.0 LQ9 heads


It's been a long time since I've paid any attention to heads.

FWIW...there are people making 500 at the wheels with a stock ls3 top end and decent cam in otherwise stock ls2's.

FWIW...there are people making 500 at the wheels with a stock ls3 top end and decent cam in otherwise stock ls2's.

Yea that's what I don't get. I'm not seeing a whole lot of 402's putting out 500 RWHP. Most that are seem to have gone all out.

i personally dont see spending the extra money for a new top end and more on the tune... id say its worth a a few more hp, keep in mind the valve shrouding on the smaller bore creates turbulance, and all... ported 317s will probably flow 310 or so... rectangle ports also like a different cam due to the size difference in the valves... they dont need the longer intake duration. afrs and tfs are great due to the larger 2.08 valves that are associated with them... id look for other areas to improve...