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4.8 lsa head swap test

 
Old 01-14-2019, 01:51 PM
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Default 4.8 lsa head swap test

I did a head swap from what most people would consider a really good cyl head, the stock 799's as they had exhaust valve seat pitting, wich is fairly common, to some dirty old 862 heads from 2002 4.8 i had laying around.

dropped them on and picked up almost 40whp up top. funny considering the intake valve is smaller, but the head chamber is also smaller

it raised my compression from 8.8:1 to 9.53:1

it was an interesting experiment to see if it would be a push or worth it.





food for thought a hellcat makes 640whp on my dyno
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Old 01-14-2019, 02:07 PM
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I've been trying to tell people for years that head flow on a boosted 4.8 or 5.3 is completely irrelevant. Thanks for this.
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Old 01-15-2019, 09:57 AM
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Not busting your chops. I really appreciate what you have done for the automotive community. But that test isn't very accurate. The"good" heads had leaking valves. And you said it makes another 1-2psi of boost as a result of the changes. But we always appreciate the honest data anyhow!
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Old 01-15-2019, 11:05 AM
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Originally Posted by JoeNova View Post
I've been trying to tell people for years that head flow on a boosted 4.8 or 5.3 is completely irrelevant. Thanks for this.
At relatively low power or a setup that's not maxed out I agree 100%, under 1000hp on most setups you can easily turn up the boost and save the money. But when you're already at 35+psi on the largest S400 offered and you are looking for a few more MPH aftermarket heads are a viable option if you don't want to completely rework the turbo kit or build another engine. You can take that 1200 hp or so limit of stock heads chucking gaskets and bump it up to 1400hp or more keeping the heads down. Between a turbo upgrade to S500 or GT55, bigger engine, or better flowing heads in some cases a set of TFS heads is the cheapest option and we did see them perform, easily picked up MPH on less boost.

That said I too went from 317's to 862's on the same setup and picked up a few MPH on the same boost, but was still 5-6MPH down from the aftermarket heads.
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Old 01-15-2019, 11:36 AM
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Extremes always create exceptions.
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Old 01-15-2019, 11:55 AM
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That car turned out really nice Matt! You should run it at a half mile or mile race, perfect for it! I ran my bike at the Texas Mile last year and while the turbo blew up and took a dump and never got a good result it was a lot of fun and very laid back.
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Old 01-15-2019, 01:10 PM
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Have you driven this combo on the street yet? I am curious to see if you have an issue with lean tip in as some have reported.

Also, Was it actually pitting on the valve seats or cracked in between the seats?

Last edited by 1FastBrick; 01-15-2019 at 01:18 PM.
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Old 01-15-2019, 05:26 PM
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I went and watched your youtube video on this... I'm shocked that the 862 heads actually made slightly less down low, but made a lot more up top. Can someone explain how this happened? Maybe the 799's with issues actually are what caused them not to perform as well up top? Not a criticism at all as no one is really doing these type of comparisons, but I'm seriously interested in learning.
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Old 01-15-2019, 07:00 PM
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Its called coefficient of discharge. Flow numbers are down the list for importance of cylinder heads even though thats the first thing everyone looks at.
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Old 01-15-2019, 10:06 PM
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Hey Denmah, do us a all a favor and notch the bores like the BBC did next time you throw big chambers/valves on a small bore.
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Old 01-15-2019, 10:49 PM
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Originally Posted by SLOW SEDAN View Post
At relatively low power or a setup that's not maxed out I agree 100%, under 1000hp on most setups you can easily turn up the boost and save the money. But when you're already at 35+psi on the largest S400 offered and you are looking for a few more MPH aftermarket heads are a viable option if you don't want to completely rework the turbo kit or build another engine. You can take that 1200 hp or so limit of stock heads chucking gaskets and bump it up to 1400hp or more keeping the heads down. Between a turbo upgrade to S500 or GT55, bigger engine, or better flowing heads in some cases a set of TFS heads is the cheapest option and we did see them perform, easily picked up MPH on less boost.

That said I too went from 317's to 862's on the same setup and picked up a few MPH on the same boost, but was still 5-6MPH down from the aftermarket heads.
I agree but the majority of the people are not shooting for 1000+hp , yet on this forum everybody always recommend to swap to 799 heads to gain that extra '50hp' on sub 600-700 hp setups and ditch the garbage 862s .
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Old 01-15-2019, 10:50 PM
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Those are some really good numbers for such a basic and daily driveable setup
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Old 01-16-2019, 03:52 AM
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This video shows it isn't a fair comparison because there were obviously issues with the 799's...

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Old 01-16-2019, 08:30 AM
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Not to mention adding compression does the same as adding boost.
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Old 01-16-2019, 08:49 AM
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Originally Posted by badass68 View Post
Not to mention adding compression does the same as adding boost.
I bet you add a lot of compression when you canít see day light between your exhaust valve and the seat...lol
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Old 01-16-2019, 09:46 AM
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Originally Posted by BCNUL8R View Post
I bet you add a lot of compression when you canít see day light between your exhaust valve and the seat...lol
Right! lol

Originally Posted by Lsx Rubi View Post
I agree but the majority of the people are not shooting for 1000+hp , yet on this forum everybody always recommend to swap to 799 heads to gain that extra '50hp' on sub 600-700 hp setups and ditch the garbage 862s .
Agree, zero reason not to use 862's at that level or higher. I've given the 862's hell and they took it all. I ran 8's on 862's they still looked perfect so slapped them on another engine to do it again. I did try some ported 799 heads which worked well but basically it was just the same power at slightly lower boost, I dont care about boost level so didn't mean much to me. To do it again I'd skip the ported stock head step and go straight to TFS with a thicker deck, only a $500-600 difference that will take you much further.

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Old 01-16-2019, 11:06 AM
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How is this even a valid comparison? leaky valve heads vs a non leaking valve head. Am i missing something?
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Old 01-16-2019, 11:31 AM
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maybe the part where his compression tester died and was giving him the same 50psi on the new heads?
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Old 01-16-2019, 11:56 AM
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Lol what about the part where he said he could see daylight between the valve and valve seat?

edit. This video. Fast forward to 1:16


Last edited by Kfxguy; 01-16-2019 at 12:11 PM.
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Old 01-16-2019, 11:58 AM
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Originally Posted by Kfxguy View Post
How is this even a valid comparison? leaky valve heads vs a non leaking valve head. Am i missing something?
Itís not and youíre not.
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