96 LT-4 Build Dyno results
#41
I will also admit that I missed the stock intake & heads part as well. I assumed it was blueprinted.
The LT4s have a bad intake to head port mismatch. The engine I worked with had nearly a 1/4" mismatch between the cylinder head and the upper part of the intake port. The intake manifold runner is much smaller and offset down. The old trick was port match both the heads and intake to GMPP gaskets.
GM 12367777
The LT4s have a bad intake to head port mismatch. The engine I worked with had nearly a 1/4" mismatch between the cylinder head and the upper part of the intake port. The intake manifold runner is much smaller and offset down. The old trick was port match both the heads and intake to GMPP gaskets.
GM 12367777
#43
Car sounds great. I would be curious to see if the 52mm TB and the ported MAF ends alone would push it to 400+ HP. Some say the MAF ends are pointless but I put a set on my L31 and gained a few average HP/TQ back when it was a stock engine with headers and a mild cam.
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Gen2-LT4 (11-16-2019)
#45
I was going off memory. Honestly there is ZERO reason GM should have done that other than to purposely choke off the LT4s so they wouldn't be better than the LS1 coming out in the C5 the following year.
GM did the same stupid crap with the 5.7 Vortec in my 99 Tahoe. I compared the spark map from my 99 Tahoe to the one in my 97 Van. The Tahoe had as much as 8° of timing removed in places. Mostly in the high load/lower rpm and midrange. I put the timing map from the Van into the Tahoe. It actually ran like a L31 should after. The lip on the TB was also 2x the size on the Tahoe as it was on the Van. I removed the lip on it. Guess GM didn't want that weak new 99 5.3 Silverado feeling weak next to the old body 99 Tahoe sitting next to it on the lot.
GM did the same stupid crap with the 5.7 Vortec in my 99 Tahoe. I compared the spark map from my 99 Tahoe to the one in my 97 Van. The Tahoe had as much as 8° of timing removed in places. Mostly in the high load/lower rpm and midrange. I put the timing map from the Van into the Tahoe. It actually ran like a L31 should after. The lip on the TB was also 2x the size on the Tahoe as it was on the Van. I removed the lip on it. Guess GM didn't want that weak new 99 5.3 Silverado feeling weak next to the old body 99 Tahoe sitting next to it on the lot.
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Gen2-LT4 (11-16-2019)
#46
Careful mentioning those around here, you'll get your PP smacked! Mine is ported which is pretty much the same thing, it's been that way for 19 years now and I still remember doing it way back when it was a near stock car and it definitely picked up power. Tuners hate them though... Oh well, mine is staying unless I upgrade to a larger meter altogether. I don't see why I can't put a more modern larger meter on the car but I haven't really heard it talked about much.
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Gen2-LT4 (11-16-2019)
#48
Careful mentioning those around here, you'll get your PP smacked! Mine is ported which is pretty much the same thing, it's been that way for 19 years now and I still remember doing it way back when it was a near stock car and it definitely picked up power. Tuners hate them though... Oh well, mine is staying unless I upgrade to a larger meter altogether. I don't see why I can't put a more modern larger meter on the car but I haven't really heard it talked about much.
#49
If I had bought the Tahoe new in 99 after having had the 97 Van, I would have taken it back to GM and told them to fix this POS! The Tahoe felt like it was towing a boat behind it all the time and the fuel mileage SUCKED. The big old heavy van had much better throttle response, alot more off-idle and midrange torque and just flat ran better. They both had the same trans and gears at the time too. Luckily did not take me too much exploration to find out what the problems were.
Normal L31 Vortec TB
The TB that was on my 99 Tahoe L31.
Normal L31 Vortec TB
The TB that was on my 99 Tahoe L31.
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Gen2-LT4 (11-16-2019)
#50
I cut that stupid thing completely off of 4.3 in the ZR2 I used to have. Much better throttle response afterwards. Supposedly GM put it on there to soften the off idle hit and keep people from chirping tires at stop lights.
#51
#52
I intended to put my larger throttle body on and one of those larger MAF housings/honeycomb deletes, before dyno, but when I measured the TB (I've had it for years intended for my '88 Vette with Lingenfelter Super ram) it measured around 58mm which was so big I don't think I could have hogged ot the intake enough, safely, to take advantage of it. So due to time constraints, I ran the stock TB and MAF. So I fell short of my 400 at the wheels goal. But im thinking I could have reached it, IF I did both, what do you guys think? 52mm enough?
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Gen2-LT4 (11-16-2019)
#53
Last edited by Fast355; 11-16-2019 at 10:30 PM.
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Gen2-LT4 (11-16-2019)
#55
At 1.5 in/hg a 3.5" maf with the screen is 759 cfm. At 350 hp and 5,000+ rpm on a 350 I still datalogged a pressure drop of 1 in/hg. At 6,000 rpm that pressure drop had increased to 1.5 in/hg. The MAF was reading a peak of around 340 gms/sec before modification.
Last edited by Fast355; 11-17-2019 at 10:34 AM.
#57
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Gen2-LT4 (11-17-2019)
#58
I thought I seen some company making an adapter to run LS style MAF on the older stuff? I want to say it was analog to digital no?
#59
#60
And this is exactly what I wanted to do. If you figure it out lmk. We are talking about the newer plastic meters, correct? Kinda like the ones used on newer GM trucks. Best I can tell is it reads the MAF and IAT all in one piece vs the two separate sensors used on our cars. That's me speculating though.