'75 L48 heads question.
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Pro
Joined: Jul 2000
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'75 L48 heads question.
After I get new duel exaust without cats and intake manifold. Will I get improved performance if I have the heads rebuilt with roller rockers, port them and 3 angle velve job? How much performance can I expect? Can I get away without changing my cam?
Race Director
Joined: Apr 1999
Posts: 15,146
Likes: 477
From: NM
Re: '75 L48 heads question. (Racer-X)
The L48 is the basic passanger car engine, very tame. If you want performance I do not see how you can get by with the stock cam. I would also go with aftermarket alumn heads.
tom...
tom...
Racer
Joined: Jan 2000
Posts: 386
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From: Lewiston ID
Re: '75 L48 heads question. (Racer-X)
A Good cam and set of lifters will do more for you than a set of roller rockers, but you need to be very realistic about what you want from the modifications, as everything involves compromise. Think it through befroe you buy, or you can chase changing objectives with lotsa $$$$$.
Hope this helps!
Hope this helps!
Burning Brakes
Joined: Dec 2000
Posts: 1,183
Likes: 2
From: Des Moines Iowa
Re: '75 L48 heads question. (JerryM)
Agree that cam, lifters and headers are far better bang for the $ than roller rockers. Been said many times in the past, that for anything but an all out race motor, all you need is a good set (like comp cams) roller tip rocker arms. Plus, in most cases, you must use non-stock tall valve covers to provide necessary clearance for full roller rocker arms.
Instructor
Joined: Sep 2001
Posts: 204
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From: winston salem nc
Re: '75 L48 heads question. (JerryM)
Dump the l48 heads! Simply replacing with a pair edelbrock Performer 70cc heads and a thin felpro gasket will bump you up 1 whole compression point.
You can keep the stock cam and bump the rocker arms up to 1.6 and get roller rockers, to get a little more out of your cam.
You could easily replace top end parts and get around 70hp gross and run a stock cam/carb
70cc heads - anything less will degrade performance on a stock cam.
1.6 Rocker Arms & roller rockers - Adds a little more lift to your cam.
Intake - A performer dual plane intake (w/gr if needed)
These will give you a realistic boost of maybe 50hp or so on a stock engine. Toss in headers and a better ignition and you might be 70-80hp on a stock bottom ended engine.
This is not the prefered way, but is the budget way to boost a l48. Your looking at under $1500.00 to do this route and can be done in a weekend alone.
[Modified by 1976C3, 1:51 PM 9/12/2001]
You can keep the stock cam and bump the rocker arms up to 1.6 and get roller rockers, to get a little more out of your cam.
You could easily replace top end parts and get around 70hp gross and run a stock cam/carb
70cc heads - anything less will degrade performance on a stock cam.
1.6 Rocker Arms & roller rockers - Adds a little more lift to your cam.
Intake - A performer dual plane intake (w/gr if needed)
These will give you a realistic boost of maybe 50hp or so on a stock engine. Toss in headers and a better ignition and you might be 70-80hp on a stock bottom ended engine.
This is not the prefered way, but is the budget way to boost a l48. Your looking at under $1500.00 to do this route and can be done in a weekend alone.
[Modified by 1976C3, 1:51 PM 9/12/2001]
Racer
Joined: Mar 2001
Posts: 326
Likes: 44
From: Newberg,Oregon,U.S.A.
Re: '75 L48 heads question. (Racer-X)
carefull with 1.6:1 rockers, you may need to obround the push rod hole in the head! You can purchess a pair of vortec heads from jegs or summit for around $420.00 and you will need a vortec manifold also, check the local wrecking yard, definitly change cam & lifters,a comp cam xe258 is the hot ticket for the 8.5-1 engine, at least keep the max. int. duration @214deg and exh. @ 224deg.I to have been looking to wake my stock L-48 up, untill I rebuild it!! :yesnod:
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Drifting
Joined: Nov 2000
Posts: 1,428
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Re: '75 L48 heads question. (jdunne)
IMHHO: A good Comp Cam & Lifters will set ya back less than $150...Is that too much of an expense for all the other good things that you have planned? All I've added so far to my '76 L-48 was a Comp 260H (VERY Mild Cam) and chambered pipes and noticed a H*ll of a difference. To each his own but you're missing a golden opportunity here since you're already gonna rip your motor apart... :seeya
Race Director
Joined: Dec 2000
Posts: 10,896
Likes: 2
From: CO
Re: '75 L48 heads question. (Racer-X)
I haven't ever done it... but you would have to pull the top half of the engine apart I would guess.... Not to mention the timnig , and lifters. Pull the radiator, alt. waterpump... hum... might have to do alot. Im suprised that someone who has done it hasn't stepped in yet. I would bet its not brain surgery , but a pain in the **** :yesnod:
Instructor
Joined: Sep 2001
Posts: 204
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From: winston salem nc
Re: '75 L48 heads question. (flood)
How difficult?
Drain radiator
remove radiator/shroud
loosen alt/ac belts
remove waterpump
remove timing cover/timing gear
remove intake manifold
remove valve covers
loosen rockers and remove rods/lifters carefully
remove cam carefully
And much more I am sure but that is just a simple breakdown.
Alot of ppl on here say its a snap but they are looking back on the event after they have done it once at least.
I would consider it a time consuming endevour, I was going to do mine at one time but opted to wait until I decided to rebuild or upgrade engines. It just made sense to me to do it this way. Yeah replacing cam/lifters is alot cheaper than rebuild engine, but if you goof and smash a cam bearing your looking at a mess of work to fix, and you would most likely just rebuild it then.
*shrug*
Drain radiator
remove radiator/shroud
loosen alt/ac belts
remove waterpump
remove timing cover/timing gear
remove intake manifold
remove valve covers
loosen rockers and remove rods/lifters carefully
remove cam carefully
And much more I am sure but that is just a simple breakdown.
Alot of ppl on here say its a snap but they are looking back on the event after they have done it once at least.
I would consider it a time consuming endevour, I was going to do mine at one time but opted to wait until I decided to rebuild or upgrade engines. It just made sense to me to do it this way. Yeah replacing cam/lifters is alot cheaper than rebuild engine, but if you goof and smash a cam bearing your looking at a mess of work to fix, and you would most likely just rebuild it then.
*shrug*
Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,987
From: Connecticut, USA
Re: '75 L48 heads question. (tnt76vette)
TNT76 - I bought a 260H cam based on various recommendations here for my 72 350 8.5:1 engine. Just how mild is it? I'm going to retain the TH400 add a B&M shift kit and keep the 3:08's. I was planning on keeeping the stock heads too but don't know the # of them. I am looking for low end power with this combo, not drag strip performance but it's still in a vette.
Gary
Gary
Safety Car
Joined: Aug 2001
Posts: 3,685
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From: Waterford Mi
Re: '75 L48 heads question. (gtr1999)
Don't play around! Pull the motor out and do it right. I have found that short-cuts cause more problems and end up costing BIG mney. No mater what you choose to do to the motor you will not be Happy with the 0-60 Times with a 3.08 rear end. I've been there. Keep you expectations real and work it in to your budget.
Have fun.
73 L-48 th400, 3.55 gear(3200 rpm@70mph), Flat top pistons, Crane Cam #114132, Performer #2105 Manifold, Holley Carb. #4175 Spreadbore
Have fun.
73 L-48 th400, 3.55 gear(3200 rpm@70mph), Flat top pistons, Crane Cam #114132, Performer #2105 Manifold, Holley Carb. #4175 Spreadbore
