IrocZ'85

iTrader: (9)

So i bit the bullet and decided to get some AFR 195s for my 350. They should be impressive over my old swirl port heads. I've got an LO5 350, and I found the volume of the little piston eyebrows by doing a search here on tgo.

So I've been calculating compression ratio, and I was wondering if you guys could recommend some good thin head gaskets to help me achieve somewhere around 10:1. The block and heads don't have anything done to them, so all the measurements should be factory. The 195 heads from AFR are 65cc chamber. AFR recommends FelPro #1003 but I think there are better and thinner ones out there to attain 10:1. Thanks for any recommendations!

Orr89RocZ

iTrader: (20)

Problem with a thin gasket is that it requires a great flat smooth surface to get best sealing. Stock block usually has pistons .020-.025" below block deck. To get a good quench height of around .040 or so, you need around a .015 gasket which is very thin. I wouldnt put that on a factory surfaced block.

Assuming factory pistons are around -12cc dish (my L98 in 89 had 12cc 4 valve relief pistons), best you can get even with the thin gasket is around 9.4 to 1.

I dont see you getting near 10 to 1 without shaving the heads down below 60cc which is possible but extra money and you may also need the intake shaved to fit better. And thats still using a .015-.020 gasket.

Cometic will make MLS gaskets any thickness you want but I dont think they are recommended for factory surfaced blocks, as they like smooth machined decks.

Without knowing exact piston volume and deck height, its hard to say what the compression would be. I believe -7cc to -12cc is a good estimate. Later years had flat tops around -7cc but older cars I believe got -12cc pistons.

IrocZ'85

iTrader: (9)

Thanks for the info Orr! My pistons look to be non-dished and I've read that since it was an LO5 passenger car motor, they were the flat + eyebrow relief type pistons. From another thread on here, someone said "the pistons will have double eyebrow (valve reliefs) that total approx 5 cc per piston".

I'll have to run my calculation for Compression Ratio again. Like you said, I don't think I'd want to mill down the heads to below 65cc stock from AFR anyway. I'll just try and get the safest and best ratio that I can with all these stock components. I've also been reading about quench and I should calculate that as well!

Primetime91

iTrader: (15)

Like you just mentioned, a thinner head gasket will improve your C.R. but will make your quench far from ideal.

Milling your heads down .030" will give you another .50 compression, and is a safe amount in that you don't have to mill the intake gasket surfaces, and won't require shorter length pushrods

Damon

Stock LO5 pistons will be dished design plus 4 valve relief "eyebrows". Except for the outer 1/4" the dish goes all the way across the piston face (although the dish isn't very deep). TRUE flattop pistons will be pool-table flat all the way across except for the valve relief eyebrows.

With stock dished pistons and 65cc heads you will be in the low 9s for compression with any kind of reasonably thick head gasket. True flattops will be up close to 10:1, all else held equal.

The thinnest head gasket I've found that is not just a steel or copper "shim" gasket (which are nightmarish to seal up on block/head surfaces that aren't very close to perfectly flat) is the GMPP .028 compositite head gasket. Fortunately they are quality pieces that are cheap to buy- about $32 a pair from Scoggin Dickey and other sources.

IrocZ'85

iTrader: (9)

ok thank you for that info about the headgasket, i'll definitely check out that GMPP composite gasket. However, from my research i found that non-truck LO5 didn't have the dished pistons. For reference here is a picture of the exact same pistons I have. This pic is NOT my motor, but its from another person's LO5, and this is EXACTLY what my pistons look like:

Damon

Interesting your LO5 would have flattop pistons. I know on TPI engines somewhere around 1990-1991 they switched to flattops (without ever telling anyone and without ever raising the advertised compression ratio of the engine, which it obviously did since the heads were still the same). I wonder if they did that with 350 TBI engines as well.

You'll do fine with the GMPP .028" head gaskets if you decide to get them. I've used several sets now and never had a single problem with them. Even blown up pistons and cracked blocks in the bottom end from severe detonation, but the head gaskets never wimpered.

IROCThe5.7L

I went with these: http://www.summitracing.com/parts/MR...w=1&N=700+150+


So far, so good. Had them on the car with AFR's for about a year and a half.

IrocZ'85

iTrader: (9)

Wow! alrighty then I'll definitely check out the .028" thanks!

Cool! looks like the one Damon was talking about! thanks

IrocZ'85

iTrader: (9)

Alright, I just measured the deck to piston TDC and it looks like on my stock LO5 clearance is around 0.028 in the hole on average. I believe most SBC's came from the factory with .025 deck heigh, so mine might be slightly off.

So, if I were to use the GMPP gasket as listed, that would but me at around .056 quench! I know that between .040 and .045 is the optimal quench. However, a few other sources I've found claim that .040 to .060 is actually a good safe mechanical distance and still claim near the same efficiency as quench areas, with something near .080 being ridiculous and pretty bad.

So, would you guys recommend I do this or is the quench pretty bad @ .056, even if I stick with 93 octane fuel? With the stock setup and 65cc heads I'm really not too worried about compression ratio, I'm just trying to get the quench right. Is there maybe a thinner GMPP composite gasket that would seal well with a stock deck?

RBob

iTrader: (1)

There is also the FelPro 1094 head gasket. Coated steel shim at .015" compressed. Not sure why so many say not to use a steel shim on a stock un-decked block. As Chevy used them for decades in the SBC engines.

I used to run the GM marine steel shim gaskets with nothing more then a coat of aluminum paint. Never had an issue, decked or un-decked.

Note that with the coated gaskets no sealer (aluminum paint, copper coat, etc.) is required. And re-torque the head bolts (cold) after a good heat cycle.

RBob.

IrocZ'85

iTrader: (9)

I ran the numbers again, and using the .015 gasket I would have a quench of .040 which is right on the money, and a static compression ratio of 10.14:1 . I think this will be the way to go considering i would get the most of both worlds! thanks RBob

EvilCartman

iTrader: (1)

I've been using those shim gaskets for I think 4 years now, haven't had a problem. Factory surface on the block and AFR 195 heads. I didn't put anything on them but a friend of mine used copper coat when he did his engine.

IrocZ'85

iTrader: (9)

Alright, I've got the block mating surface all cleaned up now and I'm ready to put the heads on soon. I have read about the old clay method to check valve to piston clearance, but I wanted to ask if anyone has a similar setup, or thinks that I might have any problems with valve to piston clearance.

Setup:
AFR195 heads(#1041) with the normal valves installed.
Head Gasket: fel pro 1094 @ .015 thickness.
Deck clearance: factory deck @ .025 in the hole.
Cam: XFI268 with comp pro magnum 1.6 rockers, specs as follows:
@ 1.6 rockers, the cam has 268 intake/276 exhaust duration,
.570 intake/.565 exhaust lift

just wondering if there was a better way to check valve to piston clearance, or if the numbers work out, I may not even have to worry about it. Thanks!

Atilla the Fun

Looks good, do the claying, no need to torque down the heads with your new gaskets for that. Better to just lightly snug them, then subtract another 0.0050" from your results.

IrocZ'85

iTrader: (9)

Just completed the claying. Looks like the valve reliefs will just barely fit the valve's head, the intake valve seems to have come very close to the tip of the relief. This was also my first time ever doing this, so I'm new and my numbers might not be perfectly accurate, but they should be close.

I don't have vernier calipers, so i had to use a machinist's rule. The width of the reliefs seem to be fine and the valves shouldn't have any problem there. The exhaust valve is about .344in off the relief. The intake valve however is the one I am concerned about. It looks like from the tip of the intake valve down into relief that it has about .078in to .0937in and this is very near the top edge of the relief where it becomes the flat top piston again. Is this alright or should i be more careful and possibly do the test again? Also, I wasn't able to add solid lifters like some how-tos suggest and these numbers are without adding the .0050in.

Atilla the Fun

I suggest your valves are probably 2.05" or larger, while the reliefs may be intended for 2.02" valves. If so, then you can lightly grind the pistons. I don't suggest that. ROL offers some 0.025" steel-shims, at a great price.
The commonly suggested minimum piston-to valve clearance is 0.100" for the intakes.
Your cheapest option, and my personal favorite, is to simply retard the cam.

Orr89RocZ

iTrader: (20)

You sure the cam is in right? Has it been degreed?

IrocZ'85

iTrader: (9)

I believe all we did when installing the cam was line up the sprockets, we didn't degree it. Atilla was right about the valves though, the intake is a 2.05 and the reliefs are just a bit smaller. If anything the intake valve would barely fit or slightly kiss the relief. I have some roloc disks that I might be able to use to radius the relief and get some more clearance. I'd rather not take the motor out of the car again, I need to get it running soon because of time constraints, but isn't that always the case haha.

here are a couple pics of my clay just for reference:

Atilla the Fun

If you're gonna roloc them, get plenty of masking tape, and plenty of tack cloths.
The one you';re about to finesse, bring it to TDC, then tape over the gap between the piston and the deck. Also tape over the other cylinders. do the one, then wipe everything with tack cloths. Repeat 7 more times.

IrocZ'85

iTrader: (9)

Just got back from doing another clay using the new sized reliefs that i widened. The intake is now around .109 and .122in . This seems to fall within the acceptable range, so I will be putting a radius like this on each intake valve relief.

fullsize fun

LOL that is my engine I swapped a set of big valve 305 heads onto . and used a LT1 cam I think, or a zz3 cam , but that ****er even with the stock TBI system and a mail order chip would roast the tires for 2 blocks , that engine was in a 1990 caprice police car .. never was sure why it had flat tops, I had a guy in my area there in va beach that had a tpi Vette and when he went to swap heads his pistons where dished.