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1974 L48 engine specs

V-6 Camaros rule!
Posts: 50
Joined: 07/06
Posted: 07/30/06 10:52 AM


I'm currently in preparation to rebuild the L48 in my 1974 Corvette.  I have no desire to keep the engine stock, but I'm also trying to have the rebuild done on a budget.  That being said, I've already ordered a fully assembled set of modified/ported Vortec heads that have been bench-tested at 500hp that have new roller rocker arms & valve springs rated at .550" lift, and also includes an Edelbrock Performer RPM intake and valve covers, and i'm ready to order a set of forged 4 valve flat head hypereutectic pistons, and a camshaft after I decide on a the ideal size/rating.  What I need to know, that I am thus far unable to find an answer to, is what is the max horsepower that the stock crankshaft & rods can handle, so I know whether to have the existing ones reconditioned or if I should replace them outright.  I also need to know, what is the maximum HP rating of the stock 1974 tach-drive distributor, so I can gauge whether I need to modify the existing distributor or replace it outright with an HEI tach drive model.  My ideal of course is to get as close to the 500hp mark as possible, but as I mentioned I'm trying to do this on a budget and if my stock components are in adequate enough condition and can handle the power, then it could save me quite a bit

Also, I know the larger I go with the camshaft, the more vacuum I could potentially lose.  Would the stock vacuum brake booster be able to pull enough vacuum from the engine with a large cam for the brakes, or may I also be potentially looking at replacing the brake booster as well depending on my camshaft choice?  I would really hate to get the engine rebuilt and then find out my power brakes won't work because I'm not getting enough vacuum...

Any information would be much appreciated.  Thanks!


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Posts: 210
Joined: 07/06
Posted: 08/01/06 06:12 AM

Ok, first, it's not so much the horsepower rating of your rods and crank you need to be concerned with, but the RPM. Cast cranks are generally limited to about 6500 RPM, though some people do run them higher than that, but 6500 is a safe redline. If you're going ot turn the motor harder the 6500 RPM, a forged crank would be a good idea. Same with the rods. A good set of forged rods is what I'd recommend for good piece of mind. On the pistons, make sure you set the ring gaps up correctly with the Hypereutectic pistons, since they "grow" differently than cast or forged aluminum slugs.

On the camshaft, your vaccum loss will be determined more by the overlap ground into the came, lobe seperation angle, and duration. If you have any questions about what camshaft to go with, give the tech line at Comp Cams a call. Before you do, have everything written down on your engine as far as parts go and what you're using, so they can help you pick out a cam that will work best with what you've got. Choosing the wrong camshaft can be all too easy sometimes, and with the wrong cam your motor will never see its full potential. You can go with a good hydraulic roller that'll give you everything you want and still be easy on your wallet. Be aware though, your heads are set up to run at a max of .550" lift, so I'd stick with a cam no large than about .535" for a little extra safety margin so you don't destroy parts.  

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I love my Chevy Chevette!
Posts: 2
Joined: 10/09
Posted: 10/25/09 03:56 AM

OMG!  Smirk How is the manner a piston "grows" affect the id, od or gap of a ring which size would be determined by the cyl wall?  The rings float in the piston groove.  However, I agree with everything else you said. Blush  

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I love my Chevy Chevette!
Posts: 1
Joined: 01/10
Posted: 01/05/10 12:55 PM

It is not so much as to piston "growth" as it is to ring "growth". As metal gets hot it expands, the bore of the engine changes, the outside diameter of the piston changes with temp, and the ring grows as it gets hot. As the metal of the piston rings changes temp, because it is captured between the ring lands of the piston, and contained in the cylinder bore, can only go in one direction. because the cross sexton of the ring is small as comapred to the overall length of the ring (the circumference) it doesn't usually bind in the piston ring groove (abnormal combustion may make it do otherwise). So the way that is most noticable is a decrease in piston ring gap as the ring heats up. The more power your engine is making, the hotter it gets, the more ring gap you need. Certain types of pistons require more end gap than others, but what the pist manufacturer wants is usually included with the piston info. Types, of fuel, blown or nitrous, and how heavy your right foot can all contribute to this. If the gap is to small, the ring ends will butt together possibly breaking the piston ring groove. This is a common problem with some pistons because the person setting the gaps doesn't follow the explict piston directions. Follow directions, no problems, sweet running engine!  

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I love my Chevy Chevette!
Posts: 4
Joined: 03/10
Posted: 03/21/10 03:49 AM

Hi man,If it were me I would buy new to handle the hp/torque you will have with the vortec heads Roller Rockers,ect.You must remember that the engine is only as strong as the weakest part.I wouldnt want to put all of that horsepower and torque on a older crank,bearings,piston rods,ect.But that is just me.I sincerely hope that helps. bmj  

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