Compression Ratio Calculation - 1969 L36
Burning Brakes
Joined: Feb 2005
Posts: 894
Likes: 91
Does anybody have an opinion on these heads? ProComp castings. Looks like they use good valves, etc.http://vi.raptor.ebaydesc.com/ws/eBa...=0&cspheader=1
I would want Ferrea's valves for a minimum, the +.250" long intakes may just give the assembler a rocker/pushrod issue.
I have no issue with the "Pro-Comp" heads but he should buy "blanks" and have a shop put a set together, usually saves time, money, and aggravation! You don't want Chrome-moly retainers any more, you really want L/W tool-steel!
Thanks, Gary in N.Y.
P.S. He may also have an issue with the larger intake valves (2.250") clearing the existing valve pockets??
Thread Starter
Instructor
Joined: Feb 2014
Posts: 154
Likes: 1
From: Irvine CA
The former owner did put a hot cam in the motor. I don't know exactly what's in it as I was never given documentation on the rebuild when I bought the car. People who are well versed in motors and have driven the car have told me it's in the realm of 240 degrees at .050 lift.
Last edited by Dammakins; May 16, 2018 at 08:01 PM.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
Are the pistons staying in the block? Is the block deck ok where head gasket let go? Get a timing tape and harbor freight dial indicator and you can figure out what you have for a cam and whether or not it is acceptable or part of the problem.
Thread Starter
Instructor
Joined: Feb 2014
Posts: 154
Likes: 1
From: Irvine CA
Yes - Piston at TDC is still inside the block. I'm assuming it's the .025" deck clearance that Speed Pro recommends for the pistons that are in the car. The area where the head gasket blew is a little discolored. The surface is a bit gritty in comparison to the same location in other cylinders.
Thread Starter
Instructor
Joined: Feb 2014
Posts: 154
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From: Irvine CA
Safety Car
Joined: Nov 2008
Posts: 3,709
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From: Seattle Washington
I think You are making a classic mistake of using compression calculators, part numbers and manuals to get a compression ratio. There are two many unknowns. What is the Bore of the block ? When the Pistons were installed were they left at stock height or was some of the Dome machined off ? What's the deck height ? How much has been machined off the Heads ? Were they angle milled ? What is the Cam Shaft Specs ? The only way to find out what You have is to measure what You have. A compression ratio measuring kit is easy to make and probably easy to buy from people like Summit Racing. You will also need a caliper or some other method of determining when the piston is 1" down the bore.
Thread Starter
Instructor
Joined: Feb 2014
Posts: 154
Likes: 1
From: Irvine CA
I think You are making a classic mistake of using compression calculators, part numbers and manuals to get a compression ratio. There are two many unknowns. What is the Bore of the block ? When the Pistons were installed were they left at stock height or was some of the Dome machined off ? What's the deck height ? How much has been machined off the Heads ? Were they angle milled ? What is the Cam Shaft Specs ? The only way to find out what You have is to measure what You have. A compression ratio measuring kit is easy to make and probably easy to buy from people like Summit Racing. You will also need a caliper or some other method of determining when the piston is 1" down the bore.
Last edited by Dammakins; May 17, 2018 at 12:40 PM.
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Race Director
Joined: Jul 2015
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From: SW Florida.
No, you can degree your cam in place with a timing tape and a 25 buck harbor freight dial indicator and vise-grip base. And check cyl head and piston dime volume with piece of plexi and a graduated cylinder or Walmart flavor shooter. Accurate little 25 cc syringe.
Race Director
Joined: Jul 2015
Posts: 13,082
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From: SW Florida.
I think a set of heads with 119 cc chambers would put you where you want to be. Bout 10.1. Then degree your can and measure the lift and you will know if you need a cam too. Dropping pan to do timing cover is not a rough job at all. Those heads are already too small. You shave them to remove that flame cut, they are smaller. They are good to liven up a flat piston engine. Measure those valves. If somebody put 2.19 or .25's in it, you may be able to get them installed in the set of 049 or 781 heads you scare up. Or spend 1400 on up for new heads.
Thread Starter
Instructor
Joined: Feb 2014
Posts: 154
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From: Irvine CA
Ok - So here’s my next big question. Let’s say I pull this motor in my garage and disassemble the whole block and get a stand for her. If I buy the correct pistons and rods to work (AKA to get my CR where it should be) and provide those to my machinist along with crank and fly wheel for balancing, would it be a monumental task to reassemble the motor in my garage? I’ve got a friend who’s built these motors before and is walking me through all of this - he helped me tear the heads off and is very knowledgeable. Basically what I’m trying to say is it reasonable to think an average guy like myself could rebuild the motor myself once I get all the new parts balanced and verified by my machinist - including cam selection and all confirming the new parts will work. I’d love to learn how to do this and would feel super accomplishing. However, if there’s a ton of expensive tools, etc. then I want to know if I’m dreaming and being unrealistic.
Had a 1976 L-82, 4-sp
Joined: Mar 2011
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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
There's no reason why you can't assemble the engine yourself. You don't need a ton of expensive tools - just a few pounds worth. You will get all the help you need from your contacts and the folks in here.
Race Director
Joined: Jul 2015
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From: SW Florida.
I don't see a reason to remove the pistons, unless necessary. That is a rebuilt short block with forged pistons in it. Too much dome for those small chambered heads but heads would be an easier, quicker, way to get the compression you want. With a big improvement in flow and horsepower, at least if you go aftermarket.
Team Owner
Joined: Jan 2007
Posts: 53,648
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From: Southern Cal Ca
St. Jude Donor '22
ring pliers to install rings on piston
ring compression sleeve to put pistons in bore
snap ring pliers if your pistons to rods are full floating
torque wrench to tighten caps, heads, manifold bolts.
various sockets and extentions
some guidance about seals, glue, and assembly lube
strong back for lifting.
all doable with check twice and do once thinking.
ring compression sleeve to put pistons in bore
snap ring pliers if your pistons to rods are full floating
torque wrench to tighten caps, heads, manifold bolts.
various sockets and extentions
some guidance about seals, glue, and assembly lube
strong back for lifting.
all doable with check twice and do once thinking.
Dr. Detroit
Joined: Mar 2012
Posts: 10,091
Likes: 4,016
From: New Braunfels Texas
I would put the correct pistons in it.......they are cheap enough. Do your research and find the right ones.
You can hone it while it is out and new rings/bearings......I bet you could get out of it for less than $500 if you do not come across any issues.
Jebby
You can hone it while it is out and new rings/bearings......I bet you could get out of it for less than $500 if you do not come across any issues.
Jebby
Thread Starter
Instructor
Joined: Feb 2014
Posts: 154
Likes: 1
From: Irvine CA
I don't see a reason to remove the pistons, unless necessary. That is a rebuilt short block with forged pistons in it. Too much dome for those small chambered heads but heads would be an easier, quicker, way to get the compression you want. With a big improvement in flow and horsepower, at least if you go aftermarket.
Last edited by Dammakins; May 20, 2018 at 08:58 PM.
Thread Starter
Instructor
Joined: Feb 2014
Posts: 154
Likes: 1
From: Irvine CA
Hi Jebby - An engine rebuild kit with the pistons I would need (Speed Pro L2300F) is around $700 at SummitRacing and that includes a ton of stuff. I think honing the motor is not necessary - There are very clear cross-hatching patterns in all the cylinders which I've been told is indicative of a fresh rebuild. I wouldn't want to bore the motor over again if I don't have to.
Last edited by Dammakins; May 20, 2018 at 09:07 PM.
Dr. Detroit
Joined: Mar 2012
Posts: 10,091
Likes: 4,016
From: New Braunfels Texas
Hi Jebby - An engine rebuild kit with the pistons I would need (Speed Pro L2300F) is around $700 at SummitRacing and that includes a ton of stuff. I think honing the motor is not necessary - There are very clear cross-hatching patterns in all the cylinders which I've been told is indicative of a fresh rebuild. I wouldn't want to bore the motor over again if I don't have to.
Those Speed Pro kits are a bargain for a street deal. You are on the right track....pistons are a little heavy but like half of a Top Shelf deal....
Make sure you weigh everything to see if you need balancing....
Yes, yes....you need to hone.....find a good machine shop and have them run a “ten pass” home on a Sunnen....this may remove a thou....not much.
New rings simply will not seat on a run bore.
You can get out of this very cheap....and less than the cost of tossing some heads on it....more labor intensive....but you KNOW what you have when you are done.....document and write everything down.
You and the next guy will thank you later
Jebby
Last edited by Jebbysan; May 20, 2018 at 09:18 PM.
Safety Car
Joined: Nov 2008
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From: Seattle Washington
There is probably no reason you can't machine some of the dome off the pistons you have now. But there isn't any point thinking about that yet because you don't know what compression you have now.
Race Director
Joined: Jul 2015
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From: SW Florida.
How period-correct are you going for? Any oval MK-4 head can not be distinguished from another, from 65 to 89. Not until you pull valve cover and read casting number and date code. So a set of 049's or 781's will fit that bill. Unless those are the original heads to that engine, which is possible. In which case we are discussing numbers-matching not period-correct. And THAT trumps a LOT.