Good heads on low compression ---good idea?
Thread Starter
Melting Slicks
Joined: Sep 2002
Posts: 2,783
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From: Engineers do it better.
Good heads on low compression ---good idea?
I have the original heads (L48) on the car at the moment along with headers, intake, cam and chambered exhaust (going in soon). And since Lars worked his magic on the carb and dist., the car runs great.
I want to replace the heads with the Sportsman II heads (200cc) without changing to flat top pistons. I think the compression is around 8.5 form the factory.
Can just slapping on the new heads hurt anything? Bottom end is stock. I am going to do a compression test before changing heads.
Will just changing to good quality head help much or do I have to swap pistons as well?
Thanks guys
I want to replace the heads with the Sportsman II heads (200cc) without changing to flat top pistons. I think the compression is around 8.5 form the factory.
Can just slapping on the new heads hurt anything? Bottom end is stock. I am going to do a compression test before changing heads.
Will just changing to good quality head help much or do I have to swap pistons as well?
Thanks guys
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Depending on your long term goals they will be fine esp if you get 64cc version although that runner size might be a bit large and hurt your low end torq. If you are shooting for 400hp or close you might want to look at the L98 alum vette heads, can be had cheap on e-bay and will also bump your compression even more since they are 58cc heads (what are used on the ZZ4 crate motor as a matter of fact).
Race Director
Joined: May 2003
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From: Science Bitch! Mississauga, Ontario
Canadian Events Coordinator
So Fevre, what you're saying is that he could run the heads for now without any problems.
I don't mean to hijack the thread, but I was considering getting the Dart Iron Eagle 64cc heads, but don't think I'll be changing the pistons yet.
I don't mean to hijack the thread, but I was considering getting the Dart Iron Eagle 64cc heads, but don't think I'll be changing the pistons yet.
Race Director
Joined: Mar 2001
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From: Living in the Hartland
I have ran some 64 cc cnc'd Trickflow heads on a 350 LM1 crate eng, pretty much a L48, with pretty good results using a 224/232 duration roller cam. As long as your low end is good and you aren't going to rev it past 5500 or so (I have taken mine to 6300 
) you should be fine. Cast parts (crank/pistons) like what is used in the L48 and LM1 are not the best for high performance or long duration but if treated with some respect can last a good while.
) you should be fine. Cast parts (crank/pistons) like what is used in the L48 and LM1 are not the best for high performance or long duration but if treated with some respect can last a good while.
Thread Starter
Melting Slicks
Joined: Sep 2002
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From: Engineers do it better.
I am running HE260H, low end could be better but otherwise happy with it.
I am worried about the stock bottom end. It's the original block. I shift at around 5300 rpm when floored without any problems all the time....no issues there.
And yes these are 64cc heads.
I also have a 400 block machined and ready to go with some light weight Al piston, but if I am happy with the 350 I will not build it at all. My target is to get around 350 hp out of the old 350 without pulling the block.
I am worried about the stock bottom end. It's the original block. I shift at around 5300 rpm when floored without any problems all the time....no issues there.
And yes these are 64cc heads.
I also have a 400 block machined and ready to go with some light weight Al piston, but if I am happy with the 350 I will not build it at all. My target is to get around 350 hp out of the old 350 without pulling the block.
Safety Car
Joined: May 2001
Posts: 3,758
Likes: 3
From: Surrey
Originally Posted by desi
I have the original heads (L48) on the car at the moment along with headers, intake, cam and chambered exhaust (going in soon). And since Lars worked his magic on the carb and dist., the car runs great.
Le Mans Master
Joined: Jul 2001
Posts: 9,622
Likes: 16
From: absecon nj
I also have the sportsman 2 heads and like said above pulls hard mid to top end with 3 different motors ive run them with,from stock piston motor,to forged11.1 motor to the flat top hyper. i have now.
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Race Director
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From: CORVETTE 77 385 C.I. TEXAS
Originally Posted by desi
I am running HE260H, low end could be better but otherwise happy with it.
Thread Starter
Melting Slicks
Joined: Sep 2002
Posts: 2,783
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From: Engineers do it better.
I know the heads are great. I have seen 296.4 RWhp out of these ones.
Here is another question: Do I have to get the cylinders bored if I decide to change the pistons or could they be just swapped with flat tops?
Here is another question: Do I have to get the cylinders bored if I decide to change the pistons or could they be just swapped with flat tops?
Safety Car
Joined: May 2001
Posts: 3,758
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From: Surrey
Hi Ganey,
What are the advantages of a rebore? If the bores have low wear then wouldn't a light hone be better ie. saves the block for a rebore at a later date (extending service life), less work & a lot cheaper?
What are the advantages of a rebore? If the bores have low wear then wouldn't a light hone be better ie. saves the block for a rebore at a later date (extending service life), less work & a lot cheaper?
Instructor
Joined: Jul 2004
Posts: 210
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From: Missouri
Originally Posted by UKPaul
Hi Ganey,
What are the advantages of a rebore? If the bores have low wear then wouldn't a light hone be better ie. saves the block for a rebore at a later date (extending service life), less work & a lot cheaper?
What are the advantages of a rebore? If the bores have low wear then wouldn't a light hone be better ie. saves the block for a rebore at a later date (extending service life), less work & a lot cheaper?
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Slap those Sportsmans on they will really wake the 'ol L48 up, while your at it you can upgrade to Harland Sharp full roller rockers, a CC 282 solid cam and some cool looking polished aluminum valve covers like the ones below 
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Originally Posted by Ganey
If you are concerned w/ low end, then you probably want about 170 ports which is the size on Edelbrock, S/R Torquer & Vortec heads.
Largest stock Chevy sb runner size (even hi-po engines) was only 161cc for a reason. cardo0
Pro
Joined: Jan 2004
Posts: 653
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From: TX
Originally Posted by desi
I have the original heads (L48) on the car at the moment along with headers, intake, cam and chambered exhaust (going in soon). And since Lars worked his magic on the carb and dist., the car runs great.
I want to replace the heads with the Sportsman II heads (200cc) without changing to flat top pistons. I think the compression is around 8.5 form the factory.
Can just slapping on the new heads hurt anything? Bottom end is stock. I am going to do a compression test before changing heads.
Will just changing to good quality head help much or do I have to swap pistons as well?
Thanks guys
I want to replace the heads with the Sportsman II heads (200cc) without changing to flat top pistons. I think the compression is around 8.5 form the factory.
Can just slapping on the new heads hurt anything? Bottom end is stock. I am going to do a compression test before changing heads.
Will just changing to good quality head help much or do I have to swap pistons as well?
Thanks guys
A swap to 64cc heads should give you about 9.5:1 over the current 8.5:1. 9.5:1 is still well within what cast iron heads can and do run. I'm going to differ from others and throw out another option to consider: flat tops w/ reliefs and mildly pocket port the existing heads - they actually do flow pretty well and can easily flow better. But I'm sure those alum heads will slap on just fine and work well. If you are not after high RPMs your bottom end is fine but may benefit from an overhaul w/ all the other changes being thrown at it.
Thread Starter
Melting Slicks
Joined: Sep 2002
Posts: 2,783
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From: Engineers do it better.
Thanks for the info guys. I was just trying to avoid pulling the engine. If I can slap on new heads and make respectable power (around 350), then I will not swap the pistons.
My concern is just that the crank and rods might not hold up. But again, I won't know until I try. The only draw back is that if I damage the block, there goes the original number matching car.
My concern is just that the crank and rods might not hold up. But again, I won't know until I try. The only draw back is that if I damage the block, there goes the original number matching car.