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I have a spare set of backcut intake valves i found.
Not sure if i can find any that arent back cut, ill check tomorrow
No worries, I talked with Brett yesterday. Land Speed is going to help us wring all the goodness out of those GMPP heads. They go to Land Speed Friday. My long term goal is to eventually use these heads in LS2 build for my 02 Z28. Min as well go ahead (no pun) and get them ready now.
Here's the game plan:
Baseline - re flow intake and exhaust as is before starting
Do flow testing on one intake with new valve with several test valves with different back-cut angles and multiple back cuts as well to determine best valve angles.
New 2.04"/1.580" stainless steel valves with Land Speed's custom angles.
Valve job, hand blend also work short turn size.
Rework the intake and exhaust Venturi (bowl)
After the heads are updated, we will flow test the intake's WS6 Store is kindly providing. I still have the LSXRT & 90mm LS6 will probably test them with the revised heads too if there is interest.
The Fast 92 should produce more under the curve power than the 102 based on runner length. The 102 should produce a bit more power at the top. Flow testing won't give you that info but a dyno would.
Makes sense about the runner length, although sorry, I wrote that poorly, I meant ignoring this flow test I had always been interested in the the difference between the "under the curve power" of the LS6 v 92 v 102 on a 5.7 as I've not seen a true dyno comparison of all 3 on the same car under the same conditions. Most discussions in general are about peak power.
People down here rarely change inlet manifolds on 5.7s so even shops can't show you actual evidence. I've seen one person on a forum change from an LS6 to a 102 on a 5.7 and get no increase at all! Most good results seem to be on LS2 with its poor manifold.
People down here rarely change inlet manifolds on 5.7s so even shops can't show you actual evidence. I've seen one person on a forum change from an LS6 to a 102 on a 5.7 and get no increase at all! Most good results seem to be on LS2 with its poor manifold.
No surprises there. For a stock or near stock LS1 or LS6, the LS6 manifold keeps it fed well. Go to big heads/cams, different story. But yeah the OEM LS2 manifold is a dog. The Dorman replacement, however is far better.
No surprises there. For a stock or near stock LS1 or LS6, the LS6 manifold keeps it fed well. Go to big heads/cams, different story. But yeah the OEM LS2 manifold is a dog. The Dorman replacement, however is far better.
I just checked that forum post and that was with a Heads and cam combo and he actually went a bit backwards with the Fast 92 + NW TB but that was coming from a ported LS6 apparently. Interesting result. I cant imagine he would be happy as that's probably over a $2,500 investment down here.
I should add that this may be a one off for this particular car. Some people seem to get good results but they have decent sized cams in their 5.7. Maybe not worth it if you have a small cam? Even with ported heads and the rest of the bolt ons.
It would be my opinion that if you went backwards on any Ls by switching from a Stock ls6 to a fast 92 that something else is wrong and somebody frigged up. Not one single aspect of the fast 92 is inferior to an ls6 for any reason.
Unported LS1< LS6 <TBSS< Fast 90 < Fast 92 <Fast 102 < MSD, with a big cam and lots of rpm I think we agree 100 percent on that. The lines start to blur when porting and tweaking intakes. For example the 90mm TPiS snout on the LS6 picks up enough airflow to put it about on par with an unported Fast 90.
My actual dyno testing results went directly against the conventional wisdom. We dyno tested a tweaked LS6 90mm that Peak Performance ported against a Fast 90 and 102 LSXRT on my 91 RS with a small cam 383 LS1 stroker. The tweaked LS6 made more 2-3 w hp more & ~ 5-8 wtq torque than either Fast intake. The tweaked LS6 had the fatter curve in both hp & tq fr 2,500 rpm to 6,500 rpm.
Peak power was at ~6,000 rpm with the small cam for all the intakes. I think both Fast intakes would have made more power on the top end with a big cam say ~240/250
The tune was optimized for each intake. The RS has an adjustable fuel pressure regulator with gauge to ensure fuel pressure stayed constant. The DynoJet had been calibrated the day before. The coolant temp, air temp & barometric pressure was identical for each test run. Several runs were made with each intake etc.
Up to that point the most an LS1 383 stroker had made on this dyno was 472 whp with aftermarket heads, big cam & Fast 92 intake. I'm happy my car made 465whp and drives like stock.
Last edited by 99 Black Bird T/A; 11-08-2018 at 03:28 AM.
I read in lsxmag the sema article talking about the Holley dual plenum manifold and it mentions lokar has an installation solution for cable throttle bodies. .
It would be my opinion that if you went backwards on any Ls by switching from a Stock ls6 to a fast 92 that something else is wrong and somebody frigged up. Not one single aspect of the fast 92 is inferior to an ls6 for any reason.
As mentioned it was a ported LS6 to Fast 92 + NW TB conversion. No idea if that involved a bigger snout + TB. I've personally not seen that mod done in Australia. He mentioned in a reply that he just felt it was a good combo already with the ported LS6 but regretted the change. In general my reading says that in Aus, the Fast 92 or 102 tends to add nothing to only a handful of kws (so say 10hp). A few people with really big cams in a 5.7 were getting quite solid results though. So it appears to me that if you run a 5.7 with a small cam (say 220/220 and under), even with ported heads etc. it wouldn't be worth ditching the LS6.
However, I have no direct evidence to back this, it probably wouldn't be found in the US either as reading this forum suggests to me that no one uses small cams in 5.7s, these are seen as "truck cams" for smaller capacity LS which we don't have over here. Our LS cars are heavier than F body and Corvettes though so low to mid range power and responsiveness is important for a lot of owners. "Under the curve power". However we don't tend to use low lift cams like trucks in the US do, high 500s to low 600s is pretty standard, even cams under 220/220.
As mentioned it was a ported LS6 to Fast 92 + NW TB conversion. No idea if that involved a bigger snout + TB. I've personally not seen that mod done in Australia. He mentioned in a reply that he just felt it was a good combo already with the ported LS6 but regretted the change. In general my reading says that in Aus, the Fast 92 or 102 tends to add nothing to only a handful of kws (so say 10hp). A few people with really big cams in a 5.7 were getting quite solid results though. So it appears to me that if you run a 5.7 with a small cam (say 220/220 and under), even with ported heads etc. it wouldn't be worth ditching the LS6.
However, I have no direct evidence to back this, it probably wouldn't be found in the US either as reading this forum suggests to me that no one uses small cams in 5.7s, these are seen as "truck cams" for smaller capacity LS which we don't have over here. Our LS cars are heavier than F body and Corvettes though so low to mid range power and responsiveness is important for a lot of owners. "Under the curve power". However we don't tend to use low lift cams like trucks in the US do, high 500s to low 600s is pretty standard, even cams under 220/220.
its been very well documented that the fast makes more power over the ls6, especially the more modded you are.
Lots of people overcam cars in the US. I was talking to the owner of a Mallet Corvette and the 5.7 had a 240 degree intake duration cam in the engine. Back in the day, that was a 30K engine.
Lots of people overcam cars in the US. I was talking to the owner of a Mallet Corvette and the 5.7 had a 240 degree intake duration cam in the engine. Back in the day, that was a 30K engine.
I agree. Big cams only make sense if you also plan to rev. If you plan to stay in stock rpm range, just get a 224-227 and let it ride
I wonder if Performance Design is helping Holley with the intake manifold design . Several new intakes strongman resemble PD products like the Carbon XR & Carbon TR. PD has an excellent background from what I understand.
Warning Intake Manifold **** - Viewing has been proven by the surgeon general to result in 401k loans to feed for whorsepower addiction
The GMPP heads are at Land Speed. Brett said they will be ready in a few weeks. We will have another round of Flow testing with the Land Speed revised GMPP heads.
Update - shipped the 90mm LS6 intake to Peak Speed Shop one of our site sponsors for the "radical" porting. Brent and I discussed the manifold in detail. Very happy with Peak's quality work and fast turn around time. The runners definitely look better now than before.
Here are a few pictures of the Peak Radical ported 90mm LS6 intake. Eventually this intake and the Land Speed Cylinder Heads reworked LPE GMPP 243's heads will go to my 02 Z28.
The 90mm LS6 looks good. For years, people have been saying that porting an LS6 is a lost cause because there’s no power to be had or the gains are so minimal that it’s a not cost effective effort. It’s something I’ve always wondered about. I’d love to see the flow numbers on it so we can compare it to the non-ported 90mm LS6. Did Peak have any thoughts on potential gains or opportunity areas they were able to improve?
Talked with Bret at Land Speed Cylinder Heads and we hope to test the intake this week. Should have some data fairly soon Bret is outstanding to work with on the flow testing and cylinder head tweaks. We will also examine how well the port match is given the heads are on the big side at 250 cc.
Peak asked me why didn't I just get a Fast 92 and have it ported vs all the effort of LS6 + 90mm snout + port work
I told Peak it was a bit of a "science project" for kicks and I'd used a Peak Ported LS6 90 on my 383 small cam LS1 91 RS that worked out to be dyno tested the best intake for my set up. It had also had the best drive ability. He was like most folks wouldn't sink that much effort into using a factory intake. Peak was supportive and did an excellent job.
I think Peak is also interested to see what sort of gains the flow bench will show. The Peak Ported TBSS intake rocked.
I'm sure this isn't the most cost effective set up for the gains. However, it's not always about the $$/hp, great drive ability is important to me, half of the fun for me is doing the testing and research.
Long term goal is with the intake & heads selected to put a suitable short block under the top end if funds allow. Probably a stock displacement LS1 or LS2.
If Santa Claus is good a BES sleeved LS1 block to make a 383 with a 4.125 bore and stock 3.62 crank could make for a lil'hammer
Probably won't have the anywhere close the to the airflow to support an All Bore 383-387. Would probably have to go Tony Mamo / HioSSilver / Peak Speed Shop ported MSD for something like that.
Last edited by 99 Black Bird T/A; 12-07-2018 at 09:48 PM.
Little late to the party on these latest tests. But, the results are consistent with the gains (measured airflow) I saw going from a ported LS6/78mm TB to a ported TBSS intake (90+mm throat)/Warr (92).
11-07-2018, 12:40 PM
Bret is outstanding to work with on the flow testing and cylinder head tweaks. We will also examine how well the port match is given the heads are on the big side at 250 cc.
