First off, let me apologize, as I hate asking someone's advice and then not taking it.

I just found that Lunati makes an equivalent cam for the LT1, which works in the L98 if you cut the opti-spark pin shorter.

Since I now know that I don't have to find a different grind, I'm going to stick with the 262/270. Any bigger and I might not pass smog, smaller and I'd have higher dynamic compression.

 

no apologies necessary; just want to see you back on the road

 

Ok looking back at your engine pix i see the spider retainer and the dog bones. JFYI, something that GM changed in their roller cams over the years - 'bout '96 - was the cam pin became longer and the center hole became larger and deeper. GM made a revised Opti distributor in '96. But if your pin is too long it is easiest to shorten it with a hack saw and clean it up with a file. If going the other way (which i doubt) u have to install a longer pin and may have to drill out the center hole (maybe).

Did u consider "degreeing" the new cam? Or just install it "straight up" (line up the gear dots/marks)? Best power maybe 4 degrees advanced but to reduce the DCR u can install the cam a little retarded. Retarding the intake centerline delays closing the intake vlv and reduces DCR. This works well and moves the power band to higher RPM but loses on max torque. BTW this has nothing to do with ignition timing so dont worry over that issue by retarding the cam.

And i recall u had a struggle with removing the head or was that the intake also? Maybe a hint the last owner just bolted everything down to force it to fit. U could easily just do a trial fit up once the heads are finally bolted down.

Sorry but there are so many head gaskets for the sbc it makes me dizzy to try searching them. But your getting good at this very fast and im sure u will sort this all out and be the happiest for doing it yourself.

 

Thanks for the info. Let's hope the pin isn't too short.

I was planning on installing it straight up. I've heard mixed results from either advancing or retarding it so I figured I would leave it as Lunati intended. Good to know that I can retard it to drop DCR if I need to, but I don't want to lose low-end if I don't have to.

I did have issues removing it, but that was because it just had a lot of sealant. Once I chiseled through the sealant (very carefully) with a putty knife, the intake base came right off. That being said, I'll make sure everything lines up well when I put it back together.

Tell me about it! When I initially started looking at head gaskets I had no idea where to start. Summit's search filters really helped, but they don't carry anywhere close to all of the head gaskets on the market.

What thickness do you recommend? Here's a basic comparison. The last is the Fel-Pro 1044, which came with the engine. I'm assuming a 4.1" bore for the other two because that seems to be a common size.

 

Okay, finished my college apps so I have some time to work on my car again.

What do you guys think? Should I use the .051" gasket I have or get a different one for a more optimal compression ratio?

 

If a composition gasket is your current intent & IIRC your slugs are .017(?) in the hole suggest Felpro perma torque head gaskets.
they are .039 compressed.

 

Yes, I want a composition gasket since I have aluminum heads, and my pistons are .02" on average in the hole.

How much difference should I expect by going with a .039" gasket instead of .051"? 5-10 more horsepower? Do you think both options would need the same gas, or would the .039" require a higher grade?

Thanks again for the help.

 

90's are 10.5 CR from the factory you can get by with poor/sub standard fuel due to the knock sensor. Do not lug the engine in the upper gears.

Your call on what you wan to run, I use the following links for DCR & static CR.

DCR & compression calculator link
https://www.uempistons.com/index.php...ge=calculators

 

Thanks.
Wish I would have known to be careful in the upper gears before--I think I was lugging it unknowingly until recently when I decided that's what I had been doing. This was my first manual and neither parent commented, so I figured I was good. Oh well, I'm replacing the engine anyway.

I'm thinking I'll stick with the .051" gasket. Going to .039" only gives .24 higher SCR (9.5 vs 9.74). I've heard as a very general rule of thumb each point gives 3% power, so I'd be looking at a difference of only a couple horsepower.

 

Churchkey had a good idea for gasket. U will still get some quench effect below 0.060" but nothing above that. 0.039" + your 0.018" deck height should still see some quench effect - and i think u need it now. I would choose the thinner 0.039" gasket with a large bore to keep compression in check.


BTW i thought we had nailed your s.c.r. at 10.5. Where do u get 9.5 and 9.74 now? Also i still think u should look at DCR with a few degrees of cam/intake retard.

I thought u had a good handle on all this now. It read like u were ready to be the next forum expert on compression ratio. Where are u going now?

Just trying to help, not harass.

 

Thanks for the help.

Any idea how much power I'd get from a quarter point of compression?

Well, I did have it nailed down, not considering the possibility that my heads had been milled. Once I cc'd the heads, I found out that compression would be higher from a lower than expected combustion chamber volume.

I thought I had a handle on it too. But I guess then I didn't know what I didn't know. Once I figure out the head gasket, I'll be ready to reassemble my new engine and start the swap.

 

Tried to find the numbers you posted but they seem to be spread over 4 pages.
Please post the particulars again I'll run the #'s for you & suggest a part # for head gaskets.

Bore, stroke, Combustion chamber CC, piston CC, deck height + degrees that the intake valve closes ABDC.

 

Bore: 4.032"
Stroke: 3.75"
Combustion chamber volume: 61.6cc
Piston volume (including volume of cylinder above piston at TDC): 15.8cc
Deck height: I believe it's irrelevant using my piston volume measurement, but approximately 9.020"
Intake closing point: 57 degrees ABDC (using the calculation here)

Since new head gaskets are likely going to cost me $60 or so, return on investment will be a major factor in whether or not I replace the gaskets. The two things I'm most interested in is approximately how much power I'd gain from whichever gaskets your recommend and whether thinner gaskets would require higher octane gas. I know both of these things are hard to estimate, so I'm just looking for your opinion.

On a related note, I finally installed my new cam. It went fairly smoothly, with one hiccup. When I installed the cam sprocket and timing chain, I remembered to align the mark on the cam sprocket with the mark on the crank sprocket. Each sprocket had an apparent mark: a circle and a triangle. I put it all together, Loctite and all, but noticed that the crank wouldn't rotate all the way around. After quite a bit of head scratching, I noticed that the crank sprocket had *two* markings, an easily-discernible triangle, and a nearly invisible circle. Turns out I lined up the dot on the cam sprocket with the wrong marking, the triangle, so the cam was about 40 degrees off causing a clearance issue. Live and learn. Anyway, it's in now so the next step is figuring out this head gasket situation.

 

Crank gear should have 3 keyway slots & 3 line up marks. The marks are located 3 sprocket teeth counter clockwise of each key slot.
Rectangular mark = 2* cam retard
Zero mark = cam is straight up
Triangle mark = cam is 2* advanced

Check each con rod to cam lobe for clearance. More often than not stroker motors require a small base circle cam.

Need the intake ABDC from your cam card + con rod length.

 

So that's what the other markings were for! Now that I think about it, I remember seeing the rectangle too. I thought they were way more than 3 teeth apart, but I guess not. Anyway, I have it on the zero mark so I'm good.

I rotated the engine around several times (more than twice) so I know there aren't any clearance issues. Or is there a specific way to check clearances? Plus, this cam is smaller in every aspect than the one that was in the engine already.

Duh, why didn't I think of just checking the cam card? It's 31.5 degrees ABDC. Apparently either I can't do math or the formula was wrong.

I have 5.7" rods.

 

Learning by hands on is the most effective - now u will know how to set the timing gears forever. But if u are calculating the DCR u should look at DCR with 2 degrees of cam retard JRYI before u button things up. It only takes moments to calc.

As far as cam clearance the best idea i have heard of is to find a long strip of plastic 0.050" thick to slip between the cam lobe(s) and the rods when rotating the crank - yes quite and awkward position. But cam clearance is problem with much higher lift cams than yours and greater stroke cranks. I would be surprised if u dont have good clearance.

BTW, are u planning on checking main bearing clearance and thrust? So far it looks like the machine shop was doing correct work on the block. Thrust is easy with the crank as is. Main bearings u would have to pop a cap and use some "fresh" plastigage. Actually much more work than that but dont know what your plans are here.

 

I'll run the numbers with 2 degrees of retard. That would shift my torque curve higher in the RPMs, right?

The cam I installed is smaller than the one installed by the machine shop, so I shouldn't have a problem. I'll check to be sure.

Yeah, I'm going to plastigage the main bearings before I put it back together. I don't expect to find a problem, but better safe than sorry.

 

Well 2 degrees of retard will shift the power higher but makes more rpm than power - actually the peak torque will be less. But 2 degrees should not have that big of an effect - u may need more retard. U need to do your DCR calcs first to see what the retard gives u.

The smaller cam will actually raise the DCR as the intake vlv closes earlier trapping more fuel/air charge. yes a larger cam still makes more pwr but its at higher rpm where the overlap pulls more fuel/air into cyl (rather than low rpm reversion).

That is your choice but to check the brg clearances u need to wipe all the brgs dry before placing the plastigauge under the brg then torque the bolts to full spec (but in steps/increments). Unless u know how to roll out a brg then i expect u do all the brgs at same time. And u should do the crank in 2 positions too - but not at the same time - use only 1 piece of plastigauge at a time. Sorry but i warned u its alot of work. Im thinking a good machine shop that does alot of engine overhauls should have nailed this already. do u know the shop that assembled the motor? This is definitely your choice and i in no way would try to make it for u.

Good luck.

 

Some figures based on the cam card you posted in this thread post #55.
Kind of ironic, 55 is/was my track car #

With Fel Pro 7733PT2 (no lock wire) 4.125 X .039 Cost 13.00 ea.
Static = 10.13
DCR = 8.56

With your .051 gaskets
if 4.125 bore
Static= 9.86
DCR = 8.338

if 4.200 bore
Static = 9.82
DCR = 8.3

Since this is a street build recommend using your .051 gaskets.

As far as ideal quench: IMHO GM has zero concerns about quench. Stock engines have slugs .030 in the hole + .050 something gasket thickness = .080 or better quench.

Keep on trucking young man & good luck.

 

Thanks for the calculations and advice! I'll put the heads back on with the .051" gaskets as soon as I can, probably next week sometime.