So I am building a 383, as probably most of you know now. I have aluminum heads and a iron block bored out to 4.030 and the piston 0.012 in the hole. I am shopping for the right head gasket now. The felpro MLS look good because I have heard it works well. But then again others say a plain old felpro gasket will work fine.
What are your suggestions?

Also, should I shoot for a 4.100 bore?

TIA

 

I've been a copper head gasket person for years because of dissimular blocks and head metals.

I've also tried for 4.060 gaskets on 4.030 bores and .034 -.042 quench.

If your -.012 down in the bore you should be shopping for a gasket in the .028 thickness. I have not heard of one. So something like a .030 would be next best.

 

Select a thickness that achieves your target compression ratio.

Here's a good online CR calculator.

http://www.csgnetwork.com/compcalc.html

Duke

 

However, bear in mind that reducing the compression ratio, a small amount, at the expense of a proper and tight quench distance, can be counterproductive.

RACE ON!!!

 

What constitutes a proper and tight quench?

Let's say you are building for a particular CR and you know your combustion chamber sizes along with what piston style you will be choosing. Then assuming your block is square, ready to build and you have a particular rod stroke length chosen, how is quench adjusted? I guess if the block has been decked this could affect what would have been a "standard" quench, is there is such a thing. Can pistons be ordered to achieve a particular quench?

Thanks for sharing your knowledge. That goes for Duke and averyone else, too.

 

Another option - cometic offers a .031 thk gasket. I had pistons .010 down in my cylinders after decking and got the quench I wanted with the cometic gaskets. They are a quality piece although a little expensive. CV products carries them in stock.

 

The tighter, the "more proper". One CF member had an engine, that when disassembled, he found the piston part number that was stamped into the piston top, was embossed into the cylinder head. The engine never made any noise or indicated that the pistons were hitting the heads. THAT is a proper quench.



At this point, about all you can do is select a gasket that will give you the closest to what you want. Ideally, the quench and compression ratio will be factored into the original planning and parts selection. It can cause some real hair pulling if left for the last moment. It can even make one to ask, "Head gasket recommendations?"

RACE ON!!!

 

Ouch CFI, that hurts....

The reason I asked, was not about quench, but actually about bore and more specifically what brand/style. I had read about cometic and fel-pro mls gaskets and I wanted to see if their advertisements read as good as their feedback does.



Thanks everybody, I am thinking Cometic or Copper, as I haven't been able to find the MLS in less than a .041 and that doesn't fit the plans.
So in this sense which is more "idiot proof" copper or cometic. I would think cometic, but in all honesty, I just want something that will last.
Input?

Thanks again!

 

The remark that bothered you was directed to Solid327 as indicated by my quotes and follow up comments. Sorry. However, if the shoe fits...

The smaller the bore the better, until it starts to encroach into the cylinder. It is best to keep crevice and end gases to a minimum. The smallest, popular, Fel-Pro high perf gasket, shows a 4.166" bore...really not that small for a 4.030" cylinder.

Neither is cheap. Cometic will make up just about any thickness you specify...for a price. That is why I commented to Solid327, "Ideally, the quench and compression ratio will be factored into the original planning and parts selection. It can cause some real hair pulling if left for the last moment.". I should have included, and extra expense.

RACE ON!!!

 

I appreciate it CFI, I just thought it was funny either way.
Thanks for the advice, I'm leaning towards copper...until my next annoying simple engine post!

And I will second the hair pulling, I had everything laid out, even had head gaskets ordered ( ) and everything was pieced together to build a 383 using different heads, but I changed plans completely midway and I've been pulling out hair since!

Thanks again everyone!

 

Thanks CFI-EFI, I think I'm getting a better grasp. Okay, so I understand that the desired quench should be determined during the planning process and that it should be "tight" as possible for whatever CR and operation you are building for. I can "see" the benefits of a tight quench in maximizing cylinder pressure and turbulence BUT a piston collision with the head?, that can't be good can it? Which leads me to another question. Would there be a different "ideal" quench for a high rpm race engine vs. an engine built for towing, or for an RV? I'd guess yes, thinking a 13.1 race engine spinning at 10,000 rpms would need a looser quench. I don't see quench as a totally static number, once the engine is hot and spinning at the maximum rpm.

So let's say we are planning to rebuild a Gen I 350. I'll use my truck as an example, as I am considering a 383 stroker converstion. As part of the rebuild I will be doing a head swap. The new heads will have a smaller CC than the stock heads BUT I want to keep the same CR, or nearly so, OR whatever is the maximum ideal for the end goal. Should the stock quench be measured before the short block is disassembled? And does this have any bearing on the final build, since decking may or may not be required and the rotating assembly is going to be different. The combustion chamber being smaller on the new heads will obviously affect the CR, so the pistons will be different from stock to end up with the same CR. Is there a specific number in mind as the ideal quench for a particular build, and if so how do you get there?

I'd like to have a better understanding of the correct planning process and sequence. I see where there is a HUGE difference in just overhauling vs. purpose building a motor to maximize performance and efficiency, whatever the intended use.

Once again thanks for the insight. I'm sure it's helping more than just myself. (others may not want to admit it tho').

 

For quench height just shoot for .040 that is enough gap to allow for piston rock and rod stretch. A couple of years back in the highest hp small block shoot out. Where all these engine builders were competing within set rules. The motor that won had a quench height of something .026. But I think that it also had some kind of offset piston pin. So even with a very light weight short skirt piston, they had very little piston rock.

With a small squish area, you create more turbulence and can get away with higher compression with a given octane of fuel.

I’ve had good luck with silicone coated copper head gaskets from Flat-out. They are about $124 delivered. My present ones are .021 thick and my pistons are .020 down in the hole. I also in my last 4-5 motors used ARP head studs and retorq them after a few heat cycles

 

If you are upset with me only wanting to discuss bore and gasket type, you should try starting your own thread...

As for being ungrateful to those that did answer me...

 

Gkull, thanks I will check out flat-out. I was also looking at http://store.summitracing.com/defaul...=KeywordSearch

Well looks like this is one of the ones "summit doesn't carry" but does.
FOG-900134060

This should be it, and it sort of shows up on the search, thanks Gkull, you just saved me some bucks!
http://store.summitracing.com/defaul...2.asp&N=400422

 

I have used a detroit gasket that measures .028. I can check the bore size if need be. The gasket cc's is 8.0. They are very inexpensive and work well for myself and many friends. Cost was $40 for the pair if I recall correctly.

 

Thanks Pete, if you can get me some more info, I'd really appreciate it!

 

USAsOnlyWay,
You are absolutely correct. It is your thread and it was hijacked. I bought into the superfluous questions and that makes me as guilty as the perpetrator. My apologies.

One quick note to Solid327. The Chevrolet Power Book recommends a piston to cylinder head clearance of .035" to .040", minimum. There are no qualifications as the the components used or the engine usage.

BTW, USAsOnlyWay, although I did not acknowledge the original "thank you", it was duly noted. And for my smart assed participation, you are welcome, for whatever it is worth.

RACE ON!!!

 

I've had trouble trying to find these specs for gaskets. Is that about the norm? That's screwed up! Will I need to go with Cometic or something like them to get something tighter?
Yes, I DO like that calculator, saved it.

 

The Summit catalog shows the gasket bore diameter, the compressed thickness and the compressed volume for the high performance Fel Pro head gaskets. Those gaskets listed are for the Gen I engines. Since the Gen II engines were never made with a bore larger than 4.00", the gaskets you need for your LT, may have smaller bores.

RACE ON!!!

 

I have the Felpro embossed shims, p/n 375-1094. 4.100" bore x .015" thick. This is what Felpro recommends for aluminum heads as they will not cause any brinneling (sp?) of the surface. Rebuilt my engine 5 years ago & car sits months at a time - no issues.