cdscarab

TomZ,
I've been reading about building 383/400ci motors and there has been a consistent warning about rod to cam clearances. That is with the 5.7" rod of course. Have you had this problem or how did you avoid it? How big a cam can you go before encountering it?
Thanks Chuck

traviss

for the rod to cam clearances, you can have a small base circle cam ground, or have the rods stroker clearanced... you need a minunum of .050" between the two.. I am buying the eagle h beam 3D rods that are already clearanced for a 3.8" stroke.

TomZ

The rods were clearanced to work with the block and a reasonably sized cam. Because the motor was built with a marine-type cam in mind the clearance issue is not as big a deal as it would have been had this been going into a car... where I would have been running a very BIG cam and more compression to crest the 500 HP mark ...so it should not be an issue. The motor is not in the boat at the moment so I can easily check the clearance and I will, though I don't see any problem with a cam that is still below .500" lift, which is where I plan to be. If I do find a problem I'll switch to smaller base-circle grind which will definitely clear it up (though cost will be greater).

Good point though.

Now... I wonder how they do it with the new HT383s that GM is producing? They use a 4" bore with a 3.80" stroke to reach 383 CID. There was an article on it in Hot Rod or Car Craft this month. Guess I'll have to see what they used in terms of a different cam and the effects on rod/cam clearance (this motor uses a 5.7 rod as well).

Tom

jr

I didn't have problems with my cam/rod clearance, but when I put in a new crank into one engine I had to clearance the block for the counterweight. That kind of suprised me.

Iggy

I've got that issue of Hot Rod here in front of me.

There's no mention of any clearance work on the block or rods.

The cam in the engine as supplied by GM is 196/207 @ .050 duration with .431/.451 lift, LSA not specified.
Peak HP: 338.1 @ 4400 and peak torge: 444.3 @ 3400 using a 625cfm carb and hedders.

Swapped carb for 750cfm, 1.6 ratio rockers, RPM Air Gap intake and Comp Cams XE282HR (230/236 dur, .510/.520 lift, 110 LSA) and a thinner head gasket raising comp ration from 9.1 to 9.6.
Peak HP: 455.3 @ 5600 and peak torque: 493.0 @ 4200.

Sound lik a good deal for a little extra work.

After all the work they changed the oil over to Royal Purple.
Peak HP: 463.1 @ 5600 and peak toeque: 502.9 @ 4200

[ 02-12-2002: Message edited by: Iggy ]

TomZ

Ahhh... the benefits of a roller. If I didn't have to come up with $1400 in Fed taxes this year I might have gone that way instead. (Homer Simpson voince on) Stupid IRS...

How much would a 2* drop in lobe separation angle effect reversion? I was looking into some of the split pattern Xtreme Energy cams (basically a 270/280 type grind) but all of the automotive grinds are based around a 110* LSA. I think there was something on it in the Dennis Moore book but I can't find it right now (buried in the office).

Any thoughts?

blue thunder

ttt

TomZ

Found the book... 109* according to Dennis Moore is the sweet spot. Anything shorter is looking for trouble with reversion and driveability.

Now I jus thave to choose a grind.

TomZ

I'm going to run the Xtreme Energy XE-274-H. These are the specs:

Adv- 274*/286*, 230*/236* @ .050, Lft- .487/.490, 110* LSA

Any thoughts? Anyone have a desktop dyno that they could run the numbers through? 383 CID, 10.1:1, Vortec heads (not sure of what the numbers are but they have 2.02/1.60 and a fair amount of porting), Performer Vortec, 750 CFM quadrajetc, center-riser manifolds (Barr, better than the Mercs).

Thanks!
Tom

jr

Tom, I'll run it tonight. I'll insert your cam against my engine and look for the changes. It should be pretty close to yours since we're running almost the same except for heads and cubes. It will get you into the ball park. You can compare the increases or decreases against your numbers on the engine you dyno'd. The big thing would be the flow of the heads, I have info on stock Vortec's but not ported with 2.02's