3.9L LZ9 engine internal upgrade & performance?

[robertisaar]

you LOST flow at .700 intake session 3?

[mrtohil]

Session 1: stock, no work performed
Session 2: ported, stock hardware
Session 3: re-ported, LS1 valves
Session 4: re-ported & repaired, LS1 vlaves



........................Lift:..........[0.100].........[0.200]........[0.300].......[0.400]........[0.500].......[0.600].......[0.700]...............Average CFM.............Max CFM

Session 1(intake)_________62.40_______128.60____186.80____ _218.90_____232.10_____238.50_____NA____________17 7.88____________238.50
Session 1(exhaust)________52.60_______100.00____138.20____ _150.10_____154.70_____155.80____156.50_________12 9.56____________156.50

Session 2(intake)_________67.10______131.90______191.10___ _236.00______250.00____257.30_____261.10_________1 99.21____________261.10
Session 2(exhaust)________52.60______101.30_____134.10____ _155.70_____166.60____170.30_____172.00_________13 6.09____________172.00

Session 3(intake)_________59.70_______115.30_____169.00___ _217.60______253.30____273.80_____257.90_________1 92.37____________273.80
Session 3(exhaust)_______53.40________102.00_____136.90___ _157.50_____165.50_____169.60_____172.00_________1 36.70____________172.00

Session 4(intake)_________63.30_______125.40______187.20__ __238.70_____263.70____265.10______266.20________2 01.37____________266.20
Session 4(exhaust)________53.60_______105.30_____145.70___ _163.40_____168.90_____171.10_____172.40________14 0.06____________172.40

[mrtohil]

Okay, here's the latest on the project. After careful porting of the seat to eliminate a small step behind the seats, I was able to bring the head back to some good numbers which I will post. I am also working on fitting LS1 roller rockers to the heads.

As was shown on a previous post, the heads can be improved upon with just good port work & stock hardware. And if you choose to leave it at that, is acceptable. But of course, we have to push the envelope (or at least I do because I'm curious). So I stuck LS1 valves. Sent a pair of valves to Ferrea Racing Components to find feasibility of custom valves. And behold... the stems are almost the identical (stock: .313... LS1: intake: .3135 exhaust: .313). The exhaust valve size is almost identical (stock: 1.524.. LS1: 1.550). The difference come in the length (slightly longer, will post exact numbers later) and the intake size (stock: 1.870... LS1: 2.0). Si I decided to try it out. I replaced the seats for the intake and cut both to accept the new valves. I also unshrouded the chamber around both both valves, primarily on the intake side. After initial testing after re-porting to size out the intake port to the new seat, I actually lost flow numbers (Of course I wasn't sure what would happen. I know that bigger is not always better. I knew that there was a possibility that I would have a pair of nice ported paper weights and I might have to start all over, which is still a possibilty). After inspecting the head, it was found that there was a small ridge behind the seat. So the seat was actually just jutting out into the airflow. So I touched up the seat edge to make the transition as smooth as possible. Retested the heads, and much improved numbers.

[mrtohil]

Sorry I haven't been updating more frequently. So far I have reflowed my heads with the new seats and valves. I actually lost flow through most of the valve opening until the top end where I gained significantly, which to be honest was a little disappointing. There is this one area in the seat where we think might be affecting the flow. We'll see after I make some minor changes and reflow the head. I'll try to post actual numbers and pics later.

[SappySE107]

I like those sizes. Got any pics?

[mrtohil]

We have started to cut the angles on the seats to match the new valves. The first valve seat came out alright but the contact point on the valve was a little too close to the edge. We moved the cutting bit in a hair and cut the next seat. This one came out much better, in both the contact point and in the actual cut.

The new valves specs are:

Intake: 2.00in
Exhaust: 1.550in

Stock sizes are:

Intake: 1.87in
Exhaust: 1.525in

New intake valve seats are installed. Pics are in the Photobucket. After I'm done with cutting the seats, I'll flow the heads again and see what was gained/lost. Unfortunately I could only get pics of the new valve on the new seats, and not on the original seats.

What size valves did you use?

[mrtohil]

New intake valve seats are installed. Pics are in the Photobucket. After I'm done with cutting the seats, I'll flow the heads again and see what was gained/lost. Unfortunately I could only get pics of the new valve on the new seats, and not on the original seats.

You didn't need a larger valve for the intake to gain flow, so why would you need a larger exhaust valve when the same pressure increase exists on the exhaust stroke?

It appears more practical to go with a larger exhaust valve being the smaller of the two and space limitations and given your pointing out that the exhaust runner is not optimized to the same extent as the intake, that suggests one more reason to start with that side since it would hinder any further increase on the intake side in its current state.

Desktop Dyno is not state of the art in engine simulation but it does show a significant enough increase in performance for me to make it a worth while consideration provided the size valve I was considering could be made to work. The purpose is to make changes that will improve performance instead of just turning up the boost pressure. Increasing the size of either valve would do this, I chose the exhaust side. The idea never had anything to do with a need.

[SappySE107]

You didn't need a larger valve for the intake to gain flow, so why would you need a larger exhaust valve when the same pressure increase exists on the exhaust stroke?

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.

[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.

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]

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.

[pocket-rocket]

Would like to see more pictures instead of words though.