Engine rebuild advice
Thread Starter
Instructor
Joined: Aug 2004
Posts: 103
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From: Alpharetta GA
Engine rebuild advice
So I bought a non-running 72’ project car. Got it home pulled the engine and started disassembling it . I was very hopeful after pulling the intake and seeing how nice the engine looked but then I pulled the heads and three of the cylinders had water and rust. The other five were perfect no ridge hardly any carbon build-up. Such a shame someone let this happen. Anyway this is an L48 with 3973487 heads. I want to rebuild the engine to 300HP and it looks like I will need to bore the block. So I’m looking for head/piston recommendations to get the 300HP. If I change to flat top pistons can I use the same heads and get 300HP?
Drifting
Joined: Apr 2002
Posts: 1,716
Likes: 4
From: New Baden Illinois
Originally Posted by PinHead
So I bought a non-running 72’ project car. Got it home pulled the engine and started disassembling it . I was very hopeful after pulling the intake and seeing how nice the engine looked but then I pulled the heads and three of the cylinders had water and rust. The other five were perfect no ridge hardly any carbon build-up. Such a shame someone let this happen. Anyway this is an L48 with 3973487 heads. I want to rebuild the engine to 300HP and it looks like I will need to bore the block. So I’m looking for head/piston recommendations to get the 300HP. If I change to flat top pistons can I use the same heads and get 300HP?
Melting Slicks
Joined: Aug 2003
Posts: 2,135
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From: Dayton Oh
go with a set of 2 valve relief flat top pistons and heads with 64cc chambers to get your compression ratio up around 9.5:1 and add a Comp Cam XE 262 if an auto or a Comp Cam 268H if a manual. On my 355 I'm using Dart's Iron Eagle 180 heads. This is a good combo that pulls good and no worries on pump gas.
Race Director
Joined: May 2005
Posts: 10,674
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From: Millington Illinois
St. Jude Donor '08-'09
www.ryanscarpage.50megs.com/combos1.html There are over a hundred dyno proven SBC combo's here. A -5 CC flat top piston, 64 CC heads and zero deck with proper quench will be over 11 to 1 comp. I think this is too much for a street engine if you are shooting for 300 HP. Here is a compression ratio calculator. http://www.kb-silvolite.com/calc.php. Compression ratio, Heads, and cam will be the items that will affect your HP and streetability the most. Careful planning to properly match components with consideration for your trans, gearing and your planned use will narrow down your choices. There is a lot of good advice here but be careful who's advice you take. You sound like you want a street engine, in that case don't put full race parts on it. Huge CC runner heads, Heavy valve springs and big duration cams will give you power but you will sacrifice driveability. You can pull 700 HP out of a small block you can't drive except for wide open throttle or you can put together an economical build that will put ou 300 to 350 HP that is a pleasure to drive around in and still has a nice muscle car rumble. There is always someone faster so build it to drive well.
Drifting
Joined: Aug 2003
Posts: 1,424
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From: Lakeland FL
Originally Posted by marshrat99
go with a set of 2 valve relief flat top pistons and heads with 64cc chambers to get your compression ratio up around 9.5:1 and add a Comp Cam XE 262 if an auto or a Comp Cam 268H if a manual. On my 355 I'm using Dart's Iron Eagle 180 heads. This is a good combo that pulls good and no worries on pump gas. I read this article which I found extremely interesting in my search for engine specs. http://www.superchevy.com/technical/...bolt_on_tests/
It supports the CC XE268H theory when used in conjunction with the right heads and other components but will result in about 100 more HP than you are looking at. I like the dyno numbers they came up with and am building about the same engine they did except I'm using Trick Flow heads instead of the Holley's since I already have them.
The best thing you can do is find yourself a lot of reading material and decide what's best for your personal situation.
Last edited by ShinodaVette; Dec 2, 2006 at 10:27 AM.
Thread Starter
Instructor
Joined: Aug 2004
Posts: 103
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From: Alpharetta GA
It seems most people doing a rebuild are looking for 350+ HP and that's not what I want in this engine. I have a 500+HP C5 so I can get my speed fix there. The C3 is really the "looker" but I going to have to rebuild this engine anyways so I thought I would like to get it a little more peppy. I just have not been able to find much info on going with the stock heads and 300 HP. I'm going to talk to the guy at the local machine shop and see what he says. I would really like to freshen the heads replace the pistons and cam and have my 300HP but maybe that's not possable.
Melting Slicks
Joined: Mar 2006
Posts: 2,465
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From: Orange Park Fl
You can probably do what you want with the stock heads, flat tops, a comp XE262 and a mild port and polish. You probably need to work the exhaust also. But I have to agree that a set of Dart Iron Eagle heads would be a good idea. The stock heads are prone to cracking and have old tech (inefficient) combustion chambers. A new set of heads will be less likely to give you problems, give you better fuel efficiency with modern combution chamber design, and all for well under $1K. God bless, Sensei
Drifting
Joined: Apr 2002
Posts: 1,716
Likes: 4
From: New Baden Illinois
Originally Posted by PinHead
It seems most people doing a rebuild are looking for 350+ HP and that's not what I want in this engine. I have a 500+HP C5 so I can get my speed fix there. The C3 is really the "looker" but I going to have to rebuild this engine anyways so I thought I would like to get it a little more peppy. I just have not been able to find much info on going with the stock heads and 300 HP. I'm going to talk to the guy at the local machine shop and see what he says. I would really like to freshen the heads replace the pistons and cam and have my 300HP but maybe that's not possable.
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Burning Brakes
Joined: Apr 2004
Posts: 847
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From: Des Allemands LA
A couple of other things to consider (and you may have) are-
1. Where did the water in the cylinders come from?
2. HP is nice to have, but for street driven vehicles, torque is what gets you moving from red light to red light. When selcting an engine combination a nice flat torque curve is what you want for the street.
ltlevil
1. Where did the water in the cylinders come from?
2. HP is nice to have, but for street driven vehicles, torque is what gets you moving from red light to red light. When selcting an engine combination a nice flat torque curve is what you want for the street.
ltlevil
Le Mans Master
Joined: Jun 2004
Posts: 6,231
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From: Seattle WA
St. Jude Donor '14
I don't have any pushback on the options offered by folks looking for a higher build level, but there's no reason that you couldn't do a performance rebuild and get 300+ HP with the right choices.
Those heads don't suck for the power level and cam lift you're looking at. Agree that aftermarket heads might be cheaper by the time you're done, but have a good overhaul done with larger valves, bowl contouring and a simple pocket port and port match.
MANY piston choices available to give 9+ CR with 75 cc heads.
The cam choice is tough, but something around .450 -.475 lift will get you right to 300 HP. Add headers and see maybe another 20 HP and a very nice burble out the back.
I completely understand the desire for something smoooooth in a daily driver.
Those heads don't suck for the power level and cam lift you're looking at. Agree that aftermarket heads might be cheaper by the time you're done, but have a good overhaul done with larger valves, bowl contouring and a simple pocket port and port match.
MANY piston choices available to give 9+ CR with 75 cc heads.
The cam choice is tough, but something around .450 -.475 lift will get you right to 300 HP. Add headers and see maybe another 20 HP and a very nice burble out the back.
I completely understand the desire for something smoooooth in a daily driver.
Thread Starter
Instructor
Joined: Aug 2004
Posts: 103
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From: Alpharetta GA
Well I took the block to the machine shop and it will require a sleve for one cylinder and the crank will need to be ground. That would be about $500 for that work another $400 for engine kit with pistons. Buy the time I add in the heasds and cam in he reccomended I look into a crate engine. So I guess I'll research that path as well. Lots of good advice on the forum
