Changing valve springs on GN1s

[bison]

Typically with valve float the fuel consumption will drop off rapidly within a couple hundred rpm.

 

[toomanymodz]

Duty cycle went from 67% down to 62% Not a huge change, but it was within 1.2 seconds (I don't want to be into float for much longer than that, assuming this is indeed float)

 

[bison]

Duty cycle went from 67% down to 62% Not a huge change, but it was within 1.2 seconds (I don't want to be into float for much longer than that, assuming this is indeed float)

That doesn't indicate float based on what ive seen. It would go a lot lower than that. Try dropping boost way down and see if you pick up a couple hundred rpm. When I saw float on the dyno the power would drop off over 100whp within a few hundred rpm and the curve would become a downward pointing squiggly line with a/f going very rich

 

[toomanymodz]

Interesting observation. A/F stays about the same. I'll try the low-boost experiment and report back.

 

[toomanymodz]

Ok, I lowered the boost from 19 psi down to 14 psi and held 2nd gear. I held 2nd gear for several seconds this time to get a good graph. The car pulled hard and the RPMs climbed nicely until around 5650, where it started climbing slower. Then at 5750 it stayed there for about 1 1/2 seconds then climbed a bit more to around 5900. I felt a little stuttering too. Vehicle speed at that moment was 86 MPH on the powerlogger, so about 92 MPH in reality (my speedometer is off slightly). It seems that lowering the boost had no effect on the RPM limit. I will say that even at only 14 psi boost, this thing absolutely flies. I bet that it can run 11.70's at that low boost level!

This engine runs so well (11.18 sec at 19psi shifting at 5300 RPM, straight 93 octane, no alky) that I may just leave it be. I am very happy with how strong it runs! The tranny shifts before 5600 anyways. The engine makes so much darn torque that my drag radials don't have a chance. On the street I can lay rubber 'till over 80 MPH. At the track, it can do a 1.57 sixty foot at 4psi and anything above a 4psi launch ends up being a 'John Force'.

I spoke with Weber today, and as always, they were very helpful. I'm running more than enough spring pressure, so it's clearly not a valve spring issue they said. They had an interesting hypothesis... It's a possibility that it could be related to exhaust pressure, or more specifically the ratio of the exhaust pressure to boost pressure, possibly exceeding 2:1 ratio. I hadn't thought of this before. I wish I had a pressure gauge on the exhaust side! Bison, any thoughts on this?

 

[bison]

Ok, I lowered the boost from 19 psi down to 14 psi and held 2nd gear. I held 2nd gear for several seconds this time to get a good graph. The car pulled hard and the RPMs climbed nicely until around 5650, where it started climbing slower. Then at 5750 it stayed there for about 1 1/2 seconds then climbed a bit more to around 5900. I felt a little stuttering too. Vehicle speed at that moment was 86 MPH on the powerlogger, so about 92 MPH in reality (my speedometer is off slightly). It seems that lowering the boost had no effect on the RPM limit. I will say that even at only 14 psi boost, this thing absolutely flies. I bet that it can run 11.70's at that low boost level!

This engine runs so well (11.18 sec at 19psi shifting at 5300 RPM, straight 93 octane, no alky) that I may just leave it be. I am very happy with how strong it runs! The tranny shifts before 5600 anyways. The engine makes so much darn torque that my drag radials don't have a chance. On the street I can lay rubber 'till over 80 MPH. At the track, it can do a 1.57 sixty foot at 4psi and anything above a 4psi launch ends up being a 'John Force'.

I spoke with Weber today, and as always, they were very helpful. I'm running more than enough spring pressure, so it's clearly not a valve spring issue they said. They had an interesting hypothesis... It's a possibility that it could be related to exhaust pressure, or more specifically the ratio of the exhaust pressure to boost pressure, possibly exceeding 2:1 ratio. I hadn't thought of this before. I wish I had a pressure gauge on the exhaust side! Bison, any thoughts on this?

There's no way it's ex pressure related. It wouldn't just fall off like that. Top Tsm runs close to 3:1. Anything that spools decently and makes over 600whp with a 3 bolt ex housing will be at 2:1 or more.

 

[bison]

Ok, I lowered the boost from 19 psi down to 14 psi and held 2nd gear. I held 2nd gear for several seconds this time to get a good graph. The car pulled hard and the RPMs climbed nicely until around 5650, where it started climbing slower. Then at 5750 it stayed there for about 1 1/2 seconds then climbed a bit more to around 5900. I felt a little stuttering too. Vehicle speed at that moment was 86 MPH on the powerlogger, so about 92 MPH in reality (my speedom

 

[toomanymodz]

I'd like to slap on a different turbo to do some more experiments. I have a billet 6262 with the ported S cover laying around, but unfortunately it won't bolt up to my existing piping, which is setup for an E cover. Wish I could get my greedy hands on one of the new 6266CEA turbos.

 

[toomanymodz]

This thread doesn't have a single pic. So here is one... closest to the camera is a billet wheel 6765 E cover, and behind it is a billet 6262 ported S cover.

 

[DCVING 6]

is the 62 for sale

 

[toomanymodz]

Ha ha. Maybe. It has less than 2k street miles on it. Zero track time. PM me an offer. If I get a good offer I'll sell it.