heads question from a novice
Thread Starter
Burning Brakes
Joined: Nov 2002
Posts: 952
Likes: 44
From: NC
heads question from a novice
I have a 73 L-48 and have toyed with the idea of getting a different set of heads. The ones I have on the car are the stock low compression heads 8.5:1 I think. Now im not sure what that means, but know that is low compression as opposed to the high compression L-79 327 that has like 11:1 compression ratio. So i guess my first question is, what determines your compression ratio. Is it the space between the piston at top dead center and the head during combustion?
Also, I see heads advertiesed with 2.02/ 1.60 valves. Is that the diameter of the valve? the 2.02 being intake and the 1.6 being exhaust?
Also, heads are advertised at different cc...such as 64cc and 76cc. I have no idea what this means. Is it how much fuel flows per minute or something?
Thanks for the input
James
Also, I see heads advertiesed with 2.02/ 1.60 valves. Is that the diameter of the valve? the 2.02 being intake and the 1.6 being exhaust?
Also, heads are advertised at different cc...such as 64cc and 76cc. I have no idea what this means. Is it how much fuel flows per minute or something?
Thanks for the input
James
Drifting
Joined: Jan 2002
Posts: 1,645
Likes: 11
From: Schaumburg IL
Heads
James,
Briefly, The CR is a function of the total area in a cylinder being compressed between the piston top and the heads combustion chamber. For all purposes the design of the piston will control the CR. For iron heads a safe number without concern about detoniation is 9.5:1 with today's octance rating and quality of fuel.
If you up the CR, change the cam also to a more agressive type, add a new intake manifold and it will wake up the engine.
Yes, the 2.02 is the size of the intake valve. Hope that helps.
Briefly, The CR is a function of the total area in a cylinder being compressed between the piston top and the heads combustion chamber. For all purposes the design of the piston will control the CR. For iron heads a safe number without concern about detoniation is 9.5:1 with today's octance rating and quality of fuel.
If you up the CR, change the cam also to a more agressive type, add a new intake manifold and it will wake up the engine.
Yes, the 2.02 is the size of the intake valve. Hope that helps.
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
Compression ratio is the difference in the size of the space between the piston and the head when the piston is at the bottom and top of it's stroke. When the piston is at the bottom of it's stroke the space above it is a given value. When said piston is at the top of it's stroke this space will be somewhere between 8 and 14 times smaller. This gives you the term 8 to 1 compression. The higher the compression the higher the power level if the engine.
Yes, 2.02 and 1.6 refer to the valve head sizes.
The 76cc or 64cc refers to the size of the combustion chamber in the heads. Putting a 64cc head on your engine will raise the compression about 1 point. Maybe a little more.
Also you may see heads listed by their intake runner or port size. Something like a 200cc intake port. DO NOT put anything like this on your engine because they are too big for your camshaft and compression. You should stick to something under 170cc.
BigBlockk
Later.....
Yes, 2.02 and 1.6 refer to the valve head sizes.
The 76cc or 64cc refers to the size of the combustion chamber in the heads. Putting a 64cc head on your engine will raise the compression about 1 point. Maybe a little more.
Also you may see heads listed by their intake runner or port size. Something like a 200cc intake port. DO NOT put anything like this on your engine because they are too big for your camshaft and compression. You should stick to something under 170cc.
BigBlockk
Later.....
Race Director
Joined: Jun 2000
Posts: 10,046
Likes: 675
From: FL
Originally Posted by James B
So do bigger valves mean better flow which means more power?
This is an incredibly complex issue. A good idea is head down to your local library (or bookstore if you want to start building a library) and check out some books on rebuilding small block Chevrolets and building high performance engines. There are some good ones out there. One respected name is David Vizard and you can't do wrong with his books.
Here are a couple of his:
http://search.barnesandnoble.com/boo...84089348&itm=1
http://search.barnesandnoble.com/boo...57880298&itm=2
http://search.barnesandnoble.com/boo...31472245&itm=4
http://search.barnesandnoble.com/boo...84089143&itm=3I am also very partial to Chevy High Perfomance magazine for good general performance information.
Good luck. This is a fun hobby. You can do almost anything on these cars yourself if you have time, patience, and are willing to invest a little in getting smart.
Last edited by SteveG75; Jul 2, 2005 at 01:26 PM. Reason: My spelling sucks....
Burning Brakes
Joined: Oct 2002
Posts: 1,040
Likes: 109
what is the intended purpose of the car ?
daily driver ?
track car only?
it seems like you want the big valves on your motor,which will most likely run worse ,since you will be velocity thru the ports.
just my opinion, i am sure i have stepped on toes again today with this answer ,so all the engineers need to step in and point the gentleman in the right direction.
daily driver ?
track car only?
it seems like you want the big valves on your motor,which will most likely run worse ,since you will be velocity thru the ports.
just my opinion, i am sure i have stepped on toes again today with this answer ,so all the engineers need to step in and point the gentleman in the right direction.
Thread Starter
Burning Brakes
Joined: Nov 2002
Posts: 952
Likes: 44
From: NC
Originally Posted by 1971corvette
what is the intended purpose of the car ?
daily driver ?
track car only?
daily driver ?
track car only?
Ultimately, like I said, id like to either beef up my L-48, or buy something like an L-82 short block and find some good heads and build the top end. I have a lot to learn, but I don't think it will be to hard, and it will be fun as well. I also need to learn more about solid lifters
i heard they provide some high revving fun.
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Instructor
Joined: Oct 2004
Posts: 173
Likes: 0
From: Hattiesburg MS
Going to put a set of vortec heads on mine within the next week or so with a new manifold. According to Dave Vizard's flow tests, these heads have very good flow. I have a post out asking if anyone has tried these but have not seen any response yet, will post on the results after all the new parts are installed. This info may help you since I have a L-48 too.
Burning Brakes
Joined: Oct 2002
Posts: 1,040
Likes: 109
Originally Posted by Mr Fanuc
Going to put a set of vortec heads on mine within the next week or so with a new manifold. According to Dave Vizard's flow tests, these heads have very good flow. I have a post out asking if anyone has tried these but have not seen any response yet, will post on the results after all the new parts are installed. This info may help you since I have a L-48 too.
jamesb follow above advice and you should be happy,and not have spent money foolishly
you need a good strong bottom end if you want to build the top of the motor,so go slow ,do research, (read some books unlike some people here ) concentrate on getting the tolerances on bearings,rings gaps,and having a leak free motor (oil,coolant)
you will get many OPINIONS from this site,
some good,some
I'll stop now,I have stepped on more toes !!
