What Head Gasket Do You Suggest?
Thread Starter
Burning Brakes
Joined: Feb 2004
Posts: 924
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From: Kearneysville West Virginia
What Head Gasket Do You Suggest?
I am rebuilding my stock 70 350/350 and need to purchase head gaskets. What gasket do you suggest? I have been looking at Fel Pro gaskets on the Summit site, but I am not certain which would be best, and the price range is quite wide.
Thanks.
Thanks.
Le Mans Master
Joined: Mar 2008
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From: Oxford MA-----You just lost the game!!!!
Doe your engine still have the stock pistons? That engine has an 11:1 static compression ratio, so I'd go with the thickest gasket I could find, to try to lessen it just a bit.
Scott
Scott
Thread Starter
Burning Brakes
Joined: Feb 2004
Posts: 924
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From: Kearneysville West Virginia
Yes, it still has the stock pistons, but why drop the compression? When I got the car, it had the wrong heads on it and they were low compression 76cc heads that had been on there since the mid 70's. I am taking it back to stock, with the correct 186 heads.
Le Mans Master
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From: Oxford MA-----You just lost the game!!!!
Scott
Le Mans Master
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From: Seattle WA
St. Jude Donor '14
Ideal quench (distance between the piston top and the head deck) is around .040 - anything more than that dramatically increases detonation sensitivity - the last thing you want, especially with high CR.
Measure how far down the pistons are in the hole, subtract that measurement from .040 and there's your recommended gasket thickness...or as close to that number as you can get. You'll likely be at a fairly thin steel shim-type gasket.
You will have some real challenges regardless running 11:1+ on the street...you might want to rethink your design a bit
Measure how far down the pistons are in the hole, subtract that measurement from .040 and there's your recommended gasket thickness...or as close to that number as you can get. You'll likely be at a fairly thin steel shim-type gasket.
You will have some real challenges regardless running 11:1+ on the street...you might want to rethink your design a bit
Last edited by billla; Jan 16, 2012 at 05:43 PM.
Race Director
Joined: Nov 2002
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From: Taylor Michigan
if you want to keep the compression up, use a steel shim which can be purchased at a dealer....otherwise a Felpro 7733PT-2 is a good choice to replace the shim....most parts places will push the 7733PT-2...I forgot the part number for the shim
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Cometic can make a 3 layer MLS gasket any thickness you want for $100 a side a little pricey but that's what I have, if it's iron heads 11:1 might run you into problems. Quench distance should be determined when you are buying parts for a new motor, sometimes it is hard to get it where you want, my 406ci made 550HP ran on 91 octane, I could run 40 degrees advance and it had 55 thou. quench which in my opinion is one of the most overrated measurements you can make on a motor for example it was near impossible ( or very expensive ) for me to get my 427ci under 50 thou and it also runs on 91 octane and have had the timing at 40 degrees advanced and still makes plenty of power and no detonation
I have yet to see a comparison of the same motor with 40thou quench and 60thou seems easy enough to do. Every small block every made by GM in the 60's-80's had 60-80 thou quench or 60 on one side and 70 on the other
I have yet to see a comparison of the same motor with 40thou quench and 60thou seems easy enough to do. Every small block every made by GM in the 60's-80's had 60-80 thou quench or 60 on one side and 70 on the other
Last edited by MotorHead; Jan 16, 2012 at 05:55 PM.
Le Mans Master
Joined: Mar 2008
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From: Oxford MA-----You just lost the game!!!!
Ideal quench (distance between the piston top and the head deck) is around .040 - anything more than that dramatically increases detonation sensitivity - the last thing you want, especially with high CR.
Measure how far down the pistons are in the hole, subtract that measurement from .040 and there's your recommended gasket thickness...or as close to that number as you can get. You'll likely be at a fairly thin steel shim-type gasket.
You will have some real challenges regardless running 11:1+ on the street...you might want to rethink your design a bit
Measure how far down the pistons are in the hole, subtract that measurement from .040 and there's your recommended gasket thickness...or as close to that number as you can get. You'll likely be at a fairly thin steel shim-type gasket.
You will have some real challenges regardless running 11:1+ on the street...you might want to rethink your design a bit
If your pistons are flat-tops, and .025" down in the cylinder at TDC, then a .015" thick gasket like this one,
http://www.summitracing.com/parts/FEL-1094/
would give you a quench of .040". If you are not familiar with what quench is, here is a good article about it:
http://kb-silvolite.com/article.php?action=read&A_id=35
Scott
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Le Mans Master
Joined: Jun 2004
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From: Seattle WA
St. Jude Donor '14
Lots of good reading on quench so readers can determine for themselves if it's important for their build It's definitely tough on a "top" to balance CR and quench. I've linked just one article below; many others out there!
http://www.popularhotrodding.com/tec...ech/index.html
"As far as power is concerned, an associate of mine ran some tests in a nominally 450-horse 350 and found that each 10 thousandths of quench reduction was worth approximately 7hp. If you are building from scratch, make maximizing the quench your number one priority toward achieving compression and avoiding detonation."
It's definitely tough on a "top" to balance CR and quench. I've linked just one article below; many others out there!http://www.popularhotrodding.com/tec...ech/index.html
"As far as power is concerned, an associate of mine ran some tests in a nominally 450-horse 350 and found that each 10 thousandths of quench reduction was worth approximately 7hp. If you are building from scratch, make maximizing the quench your number one priority toward achieving compression and avoiding detonation."
Thread Starter
Burning Brakes
Joined: Feb 2004
Posts: 924
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From: Kearneysville West Virginia
WOW! I did not expect this thread to get so complicated and so technical so quickly, but it is all good. Thanks so much for the great information.
This is not a new engine. It is a car that was in storage for 20 years and the original engine was stuck. It is completely stock, with the original bore, original domed pistons, and original crank. etc. The only thing that was not original was the low compression heads mentioned above. I am not building a new engine, I am just refeshing an old original engine, so I was expecting the head gasket selection to be pretty simple. I know the original head gaskets were thin steel, but I won't go with that because of concerns about sealing, since the block surface has not been machined. So, I guess I am just looking for suggestions for a Fel Pro gasket that will seal well and not be expensive.
I can measure the piston to deck distance and such, but I am not convined this is all needed. There are plenty of these 350/350 engines running around currently and using pump gas I expect, and I am sure there are plenty of these 350/350 engines that have just been freshened up like mine. I am just wondering what head gasket they used for a stock rebuild. I hope this helps.
This is not a new engine. It is a car that was in storage for 20 years and the original engine was stuck. It is completely stock, with the original bore, original domed pistons, and original crank. etc. The only thing that was not original was the low compression heads mentioned above. I am not building a new engine, I am just refeshing an old original engine, so I was expecting the head gasket selection to be pretty simple. I know the original head gaskets were thin steel, but I won't go with that because of concerns about sealing, since the block surface has not been machined. So, I guess I am just looking for suggestions for a Fel Pro gasket that will seal well and not be expensive.
I can measure the piston to deck distance and such, but I am not convined this is all needed. There are plenty of these 350/350 engines running around currently and using pump gas I expect, and I am sure there are plenty of these 350/350 engines that have just been freshened up like mine. I am just wondering what head gasket they used for a stock rebuild. I hope this helps.
Last edited by longbros; Jan 16, 2012 at 07:01 PM. Reason: text
Le Mans Master
Joined: Jun 2004
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From: Seattle WA
St. Jude Donor '14
Making the gasket change is a chance to maximize the engine's potential and minimize the impact of your choice to run 11:1 on the street. There are a bunch of L-46's running around at 11:1 (including my old '69 L-46 Roadster 
) but even at 92 octane it can get interesting trying to run full ignition advance.
There are no issues with sealing with an MLS, especially the new rubber-coated ones.
So simple answer - Fel-Pro 1094 would be the way I would go. I still worry about CR, but there you go
http://www.summitracing.com/parts/FEL-1094/
) but even at 92 octane it can get interesting trying to run full ignition advance. There are no issues with sealing with an MLS, especially the new rubber-coated ones.
So simple answer - Fel-Pro 1094 would be the way I would go. I still worry about CR, but there you go
http://www.summitracing.com/parts/FEL-1094/
Thread Starter
Burning Brakes
Joined: Feb 2004
Posts: 924
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From: Kearneysville West Virginia
Okay. I have been reading a lot of articles about quench, etc. As you have pointed out, roughly .040 is ideal for the sbc, and I am guessing that is pretty close to what it had from the factory.
My question is, is .040 a little too tight for my old engine using the original stock forged pistons, and stock rods? I would not want the piston to hit the head because it rocked in the bore a bit or some other reason.
I don't plan on racing this engine. It will be more of a driver, cruise-in car that I might take on a long trip from time to time. It will most likely never see 6000rpm.
I will measure how far the piston is down in the bore and report back. My guess is it is going to be somewhere around the normal .025, so as you pointed out, the FelPro 1094 with a compressed thickness of .015 puts me right at .040.
My question is, is .040 a little too tight for my old engine using the original stock forged pistons, and stock rods? I would not want the piston to hit the head because it rocked in the bore a bit or some other reason.
I don't plan on racing this engine. It will be more of a driver, cruise-in car that I might take on a long trip from time to time. It will most likely never see 6000rpm.
I will measure how far the piston is down in the bore and report back. My guess is it is going to be somewhere around the normal .025, so as you pointed out, the FelPro 1094 with a compressed thickness of .015 puts me right at .040.
Thread Starter
Burning Brakes
Joined: Feb 2004
Posts: 924
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From: Kearneysville West Virginia
So, I did some measuring today and learned some things. It appears that the pistons in my engine are about .032 below the top of the block. If I do the math that Billla suggested, that would mean I would need a gasket thickness of .008 to get the ideal .040 quench. If I go with the Fel Pro 1094, that would put me at about .047, which I am thinking is pretty good. If I go with the Fel Pro 7733pt-2, it puts me at roughly .072 which appears to be a bit on the high side.
The low compression 76cc heads that came off this engine had the Fel Pro 7733pt-2 gasket, crushed down to .039, the advertised crush thickness.
The low compression 76cc heads that came off this engine had the Fel Pro 7733pt-2 gasket, crushed down to .039, the advertised crush thickness.
Thread Starter
Burning Brakes
Joined: Feb 2004
Posts: 924
Likes: 2
From: Kearneysville West Virginia
A couple more questions. Do you know what thickness the factory gasket was? Also, should I be concerend about any sealing issues with the 1094, since the block has not been surfaced? The 7733 would seal fine I am sure, but is it your opinion that the 7733 is too thick? Just don't want any trouble sealing, parts bumping together, or increased detonation. This is some fine tuning here.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
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From: Seattle WA
St. Jude Donor '14
No concerns with sealing issues - again, it's important to differentiate between the old steel shim gaskets and the newer rubber-coated MLS gaskets that have no issues at all with a rougher block or head deck.
I can't think of a reason to use the other gasket referenced, but if you're concerned there is middle ground with an .028 compressed gasket. I'd stick with the 1094, but it's your call
I can't think of a reason to use the other gasket referenced, but if you're concerned there is middle ground with an .028 compressed gasket. I'd stick with the 1094, but it's your call
Thread Starter
Burning Brakes
Joined: Feb 2004
Posts: 924
Likes: 2
From: Kearneysville West Virginia
Thread Starter
Burning Brakes
Joined: Feb 2004
Posts: 924
Likes: 2
From: Kearneysville West Virginia
No concerns with sealing issues - again, it's important to differentiate between the old steel shim gaskets and the newer rubber-coated MLS gaskets that have no issues at all with a rougher block or head deck.
I can't think of a reason to use the other gasket referenced, but if you're concerned there is middle ground with an .028 compressed gasket. I'd stick with the 1094, but it's your call
I can't think of a reason to use the other gasket referenced, but if you're concerned there is middle ground with an .028 compressed gasket. I'd stick with the 1094, but it's your call
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
You can get the 1094 gasket pretty reasonably priced here:
http://www.northernautoparts.com/Pro...tModelId=22765
It gives you a nice little sales pitch, too. Enjoy!
Scott
http://www.northernautoparts.com/Pro...tModelId=22765
It gives you a nice little sales pitch, too. Enjoy!
Scott