3.9L LZ9 engine internal upgrade & performance?

[torq455]

i thought they were 1.6.

[robertisaar]

they might be, but for some reason i remember them being higher ratio than a 1.6....

[torq455]

when i think about it...that sounds familiar.

[robertisaar]

http://60degreev6.com/forum/showpost.php?p=333209&postcount=9

1.7 according to that...

[gectek]

they are def 1.7.

[mrtohil]

Does anyone know if the OEM cam bearings are similiar to another GM engine? For example, the 3.1L cam bearings can be replaced with SBC cam bearings which are wider.

[gectek]

cam journal is alot larger....answer = no. just get the oem ones.

[mrtohil]

Hey everyone. Started another quarter. Well, here's the latest developments (issues).
I am going to try to fit the LS1 valves into the heads. This in turn will means I have more than likely have to replace the valve seats. And also widen/unshroud the combustion chamber around the intake valve, especially on the outer edge of the chamber.
Also, discovered that the current LS1 pistons will work for four of the six cylinders. Due to the fact that the other two cylinders have the intake and exhaust places swapped. So, we're going to have to cut the reliefs by hand (not literally, but you know what I mean) onto the non-cut side of the pistons (since I have to match all). But that will have to wait until I have the valve fitting resolved.

[SappySE107]

Why are you going to use LS1 valves?

[Joseph Upson]

Why are you going to use LS1 valves?

My guess is the larger valves, didn't see any in the store for the 3900 and I'd like to go larger on the exhaust valve, looks like there may be just enough room for 1.7". Would like to see more pictures instead of words though.

[pocket-rocket]

Would like to see more pictures instead of words though.

[SappySE107]

I have not found any benefit to larger valves in any of the splayed 60V6 heads I have done research on. The 3900 may be different, but I wouldn't hold my breath on it.

[Joseph Upson]

I have not found any benefit to larger valves in any of the splayed 60V6 heads I have done research on. The 3900 may be different, but I wouldn't hold my breath on it.

I'm turbocharged and that should make some difference in that unlike naturally aspirated engines I can build enough pressure to start overwhelming the ehaust gas exit capacity at some point. From what I've read the greatest exhaust flow occurs as the valve lifts off the seat and then starts to slow down as pressure immediately starts to drop, just the opposite of the intake valve where velocity is increasing as the valve lifts further away from the seat.

Desktop Dyno shows greater benefit for an increase in exhaust valve diameter than intake. It's not a necessity but I want to make the engine perform maximally without having to rely so heavily on high boost.

[SappySE107]

Interesting fact, the 3400 and 3900 have the exact same exhaust port runner, with the bowl opened up to accomodate the larger valve.

When you don't gain flow with larger valves, I don't know how boosted vs NA is going to change that fact.

[Joseph Upson]

Interesting fact, the 3400 and 3900 have the exact same exhaust port runner, with the bowl opened up to accomodate the larger valve.
When you don't gain flow with larger valves, I don't know how boosted vs NA is going to change that fact.

You didn't state that fact previously and I was not aware of it. Obviously a larger valve will not be of any value without addressing the remainder of the runner.

We may disagree on this but a larger valve than stock in a system that flows considerably more air than stock should make a difference provided the rest of the path is addressed. I'd have to ignore some common laws of physics to accept otherwise.

If the stock size is more than sufficient for natural aspiration then I agree a larger valve is not going to help much if at all if there is no additional flow to justify the additional area. Just keeping in touch with the production trend, larger engine getting larger valves.

Just in case I misunderstood what you were saying, my rational is I'm moving 5.7L or greater exhaust volume so I should be able to benefit from 5.7L valve size with the additional equivalents in port volume.