NOT the usual cam advice...
I didn't get the ECU with the motor or any of the wiring. So my initial start up will be with proven carbs that I have. I had a bad experience with after market F.I. so I'll go with a carb for now......
:thumbsup: Agree 150%! I can take a well sorted out carburettor / intake and distributor and make same (or more) power than EFI any day of the year...... And at 1/3 of the price of aftermarket EFI (4bbl TBI) changeover parts even if I must buy carb, intake and distributor new.
This is what we are doing with my son's engine. Its a 350 Chevy TBI truck engine and we are replacing it with a fresh 350 truck engine (warmed over slightly) with a carburettor and reworked distributor (breaker points distributor recurved and changed over to magnetic pickup) running early '80s vintage NOS MSD 6A ignition box and late '60s vintage Mallory oil filled Voltmaster II coil.
My youngest son is putting together what started out as a '96 - 2000 GM L31 (Vortec) crate engine for his '92 Camaro. He bought the engine back in '98 for his previous '88 Camaro whilst serving in the Navy. As he worked his way through college, began a family and career, the L31 engine has sat sealed and covered in my garage on the shipping pallet since '98. The '88 Camaro long ago gave up the ghost and he bought the '92 about 10 years ago. Youngest son is in his mid-40s and is a grandpa now and we are finally getting around to putting the top end of his engine together for the '92 Camaro.
Some years back, I sold the L31 Vortec heads to some circle track guys. He bought this engine from Sallee Chevrolet (no longer in business) and they installed ZZ4 timing gears and chain along with a mild CompCams RV type roller cam to boost low and mid-range power. A couple weeks ago, we bolted on a set of AFR 180 heads and when he can get down here next, we will finish installing the valve train and setting valve lash.
I might add that like the 5.9 litre / 360 Dodge truck engines of the late '90s, the L31 GM 350 truck engine suffers from low static compression. These engines are supposed to have 9.0:1 static compression (advertised), but due to having dished top pistons that sit down in the hole a bit at TDC...... If you pull one apart and actually measure them....... Most will fall short of that, coming in with only 7.5 to 7.75:1 static compression (actual).
This being a new engine and not wanting to disassemble the short block, bore it, install new flat top pistons and have the block decked so new pistons are at zero deck at TDC...... I got the cam specs from CompCams (intake closing angle in degrees is what I needed most), cc'd the dish top pistons and calculated DCR and thought about what we could do to optimize compression ratio without disassembling the short block. Ideally, we needed between 9.0:1 and 9.25:1 static compression ratio with this cam to optimize DCR.
What we did was this...... When we ordered his AFR heads, aside from a spring upgrade, we had AFR flat mill them to reduce chamber volume from 64cc to 60cc. Then we brought a piston up to TDC, laid a metal straight edge across it and used a feeler gauge to measure how far down in the hole (how short of zero deck) it was. The flat part around the circumference, not the dished portion.
The dished portion will have no quench anyway (too far below flat part of cylinder head). We only needed this measurement to maintain adequate piston to head clearance and calculate DCR.
Ideally, if pistons were at zero deck, we could have used a head gasket having 0.045" compressed thickness to set quench and distance to bottom of head (excluding combustion chamber). 0.040" to 0.050" will give good quench and its wise not to go closer than 0.040" to avoid piston coming in contact with head once engine reaches operating temps. So I like to set this at 0.045" when I can.
In this case though...... The flat part of his piston head was 0.024" below deck at TDC. Now GM and Fel-Pro both make head gaskets having 0.026" thickness and there are steel shim head gaskets 0.018" thick as well. I have used them all and they are good so long as you prep everything properly. Yes, I'm old enough to remember factory steel shim head gaskets. If both surfaces are absolutely flat and true and you torque them down just so, they seal well. Otherwise, a good quality composite gasket is better at sealing. First engine I ever built when I was a kid was a '53 DeSoto hemi. When I disassembled it, I saw that it had steel shim head gaskets and it looked as if the gaskets had been painted (both sides) with aluminum paint when installed at the factory. I always brushed KopperKoat on the steel shim type gaskets, though.
Anyway...... Last thing we want is to blow a head gasket on this engine, so I contacted Cometic. They can do one of their MLS (multi-layer steel) head gaskets as thin as 0.027" compressed thickness. These are viton coated and seal well. Also allow for movement as aluminum head and cast-iron block have differing rates of expansion and contraction whilst heating and cooling. I custom ordered a set and had Cometic make bore exactly 4.00" in order to pick up the small amount of static compression lost when gaskets having larger bore size than engine allow some compression to be lost in the crevice between head and block before reaching gasket bore size. Not the cheapest way to go, but by doing all of what is mentioned above, we were able to bump true static compression from 7.5:1 to 9.2:1. Piston to head clearance (and what little quench is present due to dished piston design) came out at 0.051". Close enough.
Only reason I mention this is the same can be done with MOPAR engines so long as pistons are not too far down in the hole at TDC. Otherwise, its necessary to disassemble engine, bore and deck block and buy new pistons, rings and gaskets. Or if not decking block...... Order custom pistons having compression height adjusted to reach zero deck.
Another way to go...... With a really low compression engine and short duration cam, you can get a noticeable power boost at lower RPMs by tightening up LSA and installed centerline as Hughes have done with their 'Whiplash' cams. If you are interested in boosting power from off idle through low to moderate engine speeds...... This will make a noticeable difference. Yes, tightening LSA will increase overlap a few degrees and cam may have a very slight lope at idle. But that is no reason to do it. Tighten LSA only if it will pick up power in the RPM range where you need it.
Tightening LSA with a short duration cam will also narrow your powerband and favour power at those lower engine speeds, but if you are cruising at seriously low engine speeds (2,000 RPMs or less) at highway speeds, you don't need max power at higher revs your engine will never see anyway. Your main concern at that point (heavy vehicle turning low RPMs with lock-up converter or manual transmission at highway speeds) is not lugging your engine under load and beating the main bearings out of it.
And then there are Rhoads lifters (think of them in terms of variable valve timing without the complication of computer controls and added moving parts as today's more modern engine designs have for the same purpose). They will broaden your power band whilst decreasing effective duration and valve lift at lower engine speeds. But they won't fully restore duration and lift until engine speed exceeds 3,000 to 4,000 RPMs depending on which of their lifters you use. And some guys dislike the 'solid lifter' sound they make at idle. So probably not what you need to boost off idle power when you will not be turning the engine fast enough to actually 'use' the duration and lift specs ground into your cam. In those instances, its better to begin with a cam specifically designed for what you are doing.
Hope this gives you some ideas,
Harry
