1979 L48 mods
Thread Starter
Intermediate
Joined: Sep 2003
Posts: 48
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From: Luxembourg europe
1979 L48 mods
Hi
For the moment there already is a Edelbrock performer 600cfm carb and manifold on top, also a new HEI distributor.
I was considering putting new heads on, I was thinking of the Edelbrock ones to match the manifold and also the matching cams ( if they are not in already). Also I still have a set of shorties I want to put on and a full dual exhaust. ( later)
Does this sound ok? what combustion chamber volume do you think is best? 70cc or 64cc? what is stock volume? and what would the compression ratio be of these heads? Considering that the rest is stock ( i think)
Any other suggestions?
thanks
For the moment there already is a Edelbrock performer 600cfm carb and manifold on top, also a new HEI distributor.
I was considering putting new heads on, I was thinking of the Edelbrock ones to match the manifold and also the matching cams ( if they are not in already). Also I still have a set of shorties I want to put on and a full dual exhaust. ( later)
Does this sound ok? what combustion chamber volume do you think is best? 70cc or 64cc? what is stock volume? and what would the compression ratio be of these heads? Considering that the rest is stock ( i think)
Any other suggestions?
thanks
Race Director
Joined: Jan 2003
Posts: 15,176
Likes: 88
From: State of Confusion
I believe the stock '79 L-48 had approx 8-8.2:1 compression, with 76cc chamber heads:
using a 64cc head would bump the squeeze to approx 9.2:1, which'll still run on most pump-fuels.
using a 64cc head would bump the squeeze to approx 9.2:1, which'll still run on most pump-fuels.
Instructor
Joined: Sep 2006
Posts: 154
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From: Upper Darby PA
Glensgages, thanks for bringing up the compression estimate. in David Vizard's book "How to Rebuild Your Small Block Chevy" there is a chart on page 18. it gives compression ratios with the various sizes chamber head volume on common Chevy engines with flat or dished pistons. it shows 64cc heads with dished 350 pistons @ 8.6 compression.
I always take book data with a grain of salt as there is sometimes misinformation and misprints that last forever. I prefer to have the information from real world experience. how did you estimate the compression ratio ? I am ready to do nearly the same mods on an '81 with the stock engine which is basically the same bottom as an L48. I was going to use 64cc heads thinking I would get 8.6-1 compression. I don't want 9.2-1 compression. thanks again, Rich
I always take book data with a grain of salt as there is sometimes misinformation and misprints that last forever. I prefer to have the information from real world experience. how did you estimate the compression ratio ? I am ready to do nearly the same mods on an '81 with the stock engine which is basically the same bottom as an L48. I was going to use 64cc heads thinking I would get 8.6-1 compression. I don't want 9.2-1 compression. thanks again, Rich
Drifting
Joined: Apr 2002
Posts: 1,716
Likes: 4
From: New Baden Illinois
The stock engine had about a 7.9-8.0 CR with the 76cc heads. Going to a 64cc head will bump you up to about 8.8 CR. Here is a link so that you can play around with it.
http://www.kb-silvolite.com/calc.php?action=comp
I used a -15cc piston, 4.100 head gasket bore, 4.000 cylinder bore, .015 head gasket thickness, .045 deck clearance (which is typical for stock cast pistons), and a 3.48 stroke. This will give you about 7.9 with the 76cc heads and 8.8 with the 64cc heads.
http://www.kb-silvolite.com/calc.php?action=comp
I used a -15cc piston, 4.100 head gasket bore, 4.000 cylinder bore, .015 head gasket thickness, .045 deck clearance (which is typical for stock cast pistons), and a 3.48 stroke. This will give you about 7.9 with the 76cc heads and 8.8 with the 64cc heads.
Race Director
Joined: Sep 2004
Posts: 11,874
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
in David Vizard's book "How to Rebuild Your Small Block Chevy" there is a chart on page 18. it gives compression ratios with the various sizes chamber head volume on common Chevy engines with flat or dished pistons. it shows 64cc heads with dished 350 pistons @ 8.6 compression.
I always take book data with a grain of salt as there is sometimes misinformation and misprints that last forever. , Rich
I always take book data with a grain of salt as there is sometimes misinformation and misprints that last forever. , Rich
Le Mans Master
Joined: Apr 2007
Posts: 7,353
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From: Graceland in a Not Correctly Restored Stingray
i.e. the exhaust tube header dimension formula within "How to Build Max Performance Chevy Rat Motors" which appears to be inverse (at best) to the true relationship between displacement and tube size...
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Instructor
Joined: Sep 2006
Posts: 154
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From: Upper Darby PA
DGRUENKE, I am doing mods similiar to heng1, but with a Holley 600 and a RPM. my vette is de-smogged and now has true duals (no cat) with the original manifolds. will be using iron heads. the head work you did sounds like what I want. 8.8 compression would be OK with me. what kind of performance are you getting ? what was your cam choice ? would you do anything different ? thanks, Rich
Le Mans Master
Joined: Sep 2001
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From: Unreconstructed, South Carolina
David Vizard's book "How to Rebuild Your Small Block Chevy" there is a chart on page 18. it gives compression ratios with the various sizes chamber head volume on common Chevy engines with flat or dished pistons. it shows 64cc heads with dished 350 pistons @ 8.6 compression. I always take book data with a grain of salt
Look thru specs of dished 350 replacement pistons ... anything outside 10 - 13 range is RARE. I'm referencing dished ... Not inverse/reverse dome.
Here's a handy, accurate scr calculator from a manufacturer that supplies lots of pistons ... Federal Mogul aka Sealed Power aka Speed Pro aka TRW ... if you KNOW correct data to plug in, it'll match their published piston-specific scr specs.
http://www.21cgt.com/FMWebCatalog/frmConversion4.aspx
Drifting
Joined: Apr 2002
Posts: 1,716
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From: New Baden Illinois
You have a slightly larger selection of heads that come in 64cc. Other than that, you just need to pick the one that works with the rest of your components. You need to sit down and figure out your entire combination of components that you are going to use. If the CR is too high with the 64cc, go with the 70cc. If it is too low with the 70cc, go with the 64cc.
Thread Starter
Intermediate
Joined: Sep 2003
Posts: 48
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From: Luxembourg europe
I was going to go for the Edelbrock performer series, and also matching cams, carb and manifold.
Pistons and rest is stock.
that is why I ask, edelbrock has a 64cc and 70cc head.
Pistons and rest is stock.
that is why I ask, edelbrock has a 64cc and 70cc head.
You have a slightly larger selection of heads that come in 64cc. Other than that, you just need to pick the one that works with the rest of your components. You need to sit down and figure out your entire combination of components that you are going to use. If the CR is too high with the 64cc, go with the 70cc. If it is too low with the 70cc, go with the 64cc.
Thread Starter
Intermediate
Joined: Sep 2003
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From: Luxembourg europe
Drifting
Joined: Apr 2002
Posts: 1,716
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From: New Baden Illinois
That's a relatively small cam. I would recommed something like the Summit 1103 cam. http://store.summitracing.com/partde...3&autoview=sku
The Edelbrock cam that you mentioned is very similar to the Summit 1102.
The Edelbrock cam that you mentioned is very similar to the Summit 1102.
Thread Starter
Intermediate
Joined: Sep 2003
Posts: 48
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From: Luxembourg europe
yes the summit does seem the same.
I am new to all this timing etc..
what would the 1103 do better? more torque more hp?
it says something about RPM range. I guess the max. Power shifts to a higher rpm range?
I am new to all this timing etc..
what would the 1103 do better? more torque more hp?
it says something about RPM range. I guess the max. Power shifts to a higher rpm range?
That's a relatively small cam. I would recommed something like the Summit 1103 cam. http://store.summitracing.com/partde...3&autoview=sku
The Edelbrock cam that you mentioned is very similar to the Summit 1102.
The Edelbrock cam that you mentioned is very similar to the Summit 1102.
Le Mans Master
Joined: May 2002
Posts: 5,086
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From: Lebanon Township New Jersey
Yes. In comparing two cams in the same engine, the cam with more lift and duration will generally make more power and the power peak will be at a higher RPM.
Drifting
Joined: Apr 2002
Posts: 1,716
Likes: 4
From: New Baden Illinois
The 1103 will also give you a later intake closing angle, which will bleed off some of that 9.2:1 CR. This will ensure that you don't have any problems with detonation.
Instructor
Joined: Sep 2006
Posts: 154
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From: Upper Darby PA
this is why I like "real world" knowledge. books are good to a point, but nothing beats current experience. there is no way I could know that 17cc is an uncommon dimension of dished piston volume, and that 10-13cc are most common.
I think heng1 and I are trying to do almost the same mods. I already have my carb(Holley 600), HEI, and Performer intake. I haven't selected the heads yet, but leaning towards Dart Iron Eagles. as you have recommended, I think the 64cc will be best, then go for the cam that puts me at or a little below 9-1 compression. my engine has only 31K on it, but I don't want to put too much strain on 26 year old cast parts. thanks again. CF is the best. Rich
I think heng1 and I are trying to do almost the same mods. I already have my carb(Holley 600), HEI, and Performer intake. I haven't selected the heads yet, but leaning towards Dart Iron Eagles. as you have recommended, I think the 64cc will be best, then go for the cam that puts me at or a little below 9-1 compression. my engine has only 31K on it, but I don't want to put too much strain on 26 year old cast parts. thanks again. CF is the best. Rich