14BFF

hi

I am considering changing the cam or heads in my truck to improve the performance as it is lazy on low RPM but it loves to rev high. the truck is used in sand dunes and I am using around 93 octane fuel.

what step do you suggest to start with:
- milling the heads and install thinner gaskets to raise the compression
- change the cam (any suggestions?)
- change to CNC ported cathedral 799 heads

below are the specs:
1986 GMC K15 4x4 short-bed pickup
6.0 LQ9 block bored to 6.2
6.2 L92 stock pistons
821 LS3 heads ported by Lloyd Elliot + milled 0.020"
GM MLS 0.051 head Gaskets
CR around 10.7
222/230 .598"/.598" 112 LSA custom camshaft
PSI1511 Springs
L92 6.2 Stock intake manifold
92mm DBC WARR throttle body
1 7/8 long tube headers
3 inch dual exhaust w. H-pipe
SM465 manual gear
3.73 differentials
33" mud tires

thx

Tuskyz28

I would try these. They seem to be cheap as CNC 243 heads.

G Atsma

Are these heads something new?

grubinski

Be aware that changing to Cathedral from LS3 heads drives a lot of extra expense. You'll have to source an intake manifold if you don't already have one from before your LS3 heads went on, and perhaps different injectors. It adds up quick.

lazerlemonta

With that tall of tire and missing your low end grunt, you could swap gears in the rears and likely leave your engine alone. Edited (looked up your transmission gearing and see you should be pulling stumps at idle lol) 26mph in 1st @ 6500!

DualQuadDave

iTrader: (6)

You need 3 things:

-Bump the compression to about 11.2-11.3:1. Thinner gasket and cut the head some more. It'll make the whole combo better and torque everywhere.

- More lift, I think the cam is ok, but those heads need more lift to make them effective. 1.8 rockers, probably non-adj Yella Terra's will help. Probably 15-20hp right there.

- 3.73's and 33's is killing the whole combo. I would go straight to 4.30's and maybe 4.56's. No matter what you do motor wise, this will always hold you back, especially if you have less than a 3000rpm stall.

EDIT: Rod mod your intake also. You may even consider a ported L92 Intake, just for the longer runner to help the low/mid range. I would do everything else first and then try that.

Summitracing

OP,

Some great advice you're getting from the community.

We like your idea of going with cathedrals for the use of this combo. Rectangle port heads are great for flow but less efficient below peak torque. They're not a good match for trucks used as trucks. As Grabinski said with switching to cathedral there will be added costs. Obviously, those could be offset some by selling the ported LS3 heads.

Compression is your friend here. You could mill the current heads more and get a thinner head gasket to boost compression. Usually, once you start getting around .030" milled or more the intake will start needing to be angle milled as well. Just going with some .040" compressed thickness head gaskets should put you right around 11:1.

We also like the idea of a gear change. If this is just being used in the dunes some 4:30-4:56 gears like DualQuadDave mentioned would help. That would surely make it more responsive for off idle and part throttle response.

The cam specs look pretty good. If you had the ICL or how much advance is ground in that would be helpful to see where the valve events are at.

Depending on your budget and how far you want to take this build you could change up the rotating assembly. More specifically going to a 4" stroker assembly. Something we have in mind for this would be our Pro LS SUM-R58400656 rotating assembly. All forged rotating components with a 6cc dished piston. With a stock head gasket and your milled heads, you should be right around 11:1. Drop to a .040" gasket and bump it up a little more. This would give you that low-end grunt you're looking for as well as improve power and torque across the board.

RonSSNova

iTrader: (3)

People trying to spend your money.
Big *** rig, wrong gear to tire ratio, and fat port no torque heads till past 5000...
Stock cathedral 799’s, Truck or TBSS intake, stock throttle body. Purdy cheap.
With those tires, 4.56.

DavidBoren

Some gear would definitely help... I would also go with 4.56 gears, as others have mentioned.

Cam is good, but could use some more lift... some 1.8 rockers will probably be enough to get you there without changing too much else.

IF, and I mean IF, you want to change your heads, I would go with cathedral ports. TBSS intake.

But I would try gears first, then higher ratio rockers, before changing anything else.

RonSSNova

iTrader: (3)

Kinda what I just said

14BFF

thanks a lot for your opinions
I think that I will start by changing the gearing or tires before touching the motor and see how that works

then I might keep the LS3 heads mill them, use thinner 0.040 gasket to gain more compression, install 1.8 rocker arms

in the same time will evaluate going with cathedrals if I can sell the LS3 stuff (heads, trionion rockers, L92 intake)
- 799 heads already available
- CNC porting (around $500 for a local shop but I need to see their flow charts)
- new cam suitable for cathedrals (another $500)
- NNBS or dorman intake, fuel rails( $100 - 360 used or new)

showdog75

iTrader: (8)

Consider total engine airflow for cnc porting. They seem to be at the top of the game.

64post

iTrader: (5)

Those AFR Enforcer heads are cheap because they are not CNC’d, they’re meant to be as cast replacement heads and in no way do they perform like AFRs CNC performance offerings. Great way to go if you don’t already have of 243 heads and don’t want to spend the money for rebuilding heads. RHS is making as cast LS3 heads for replacement heads in the way, no extra big flow, just heads.

RonSSNova

iTrader: (3)

Be interesting to see just how much those new AFR heads would benefit from some hand porting in the right hands.

Gears will help a ton. 33’s and 3.55 are more suited to a turbo car looking for max 1/4 mile performance. 😊

lazerlemonta

https://en.wikipedia.org/wiki/Muncie_SM465_transmission
That is a link to his transmission. You put 4.56 in this thing it will be like granny gears. First gear with 3.73 and 33" tire @ 6500 rpm 26 MPH Second 48 MPH and third is 101 MPH. With 4.56 @ 6500 its 21 MPH 39 MPH and 82 MPH

old motorhead

iTrader: (10)

Should he ever need to pull a plow...there's that.

Stampede4ever

Do you have any pics or vids of the truck?

Thanks.