Hi ,

I want to make my '74 L48 sound and run more like my '80 L82.  The '74 has an original 115,00 miles on it and a 4 speed, not an option on the '80.  After this summer I will probably spring for a rebuild of the L48 and I am researching options.  One is to go with an Edelbrock top end package, another is with a mild Thumper cam, 2000-5800 RP and a Summit engine rebuild kit.  I intend to store the stock parts in grease and plastic in case I ever want to rebuild to stock,but for now, I would like a bit more "show and go".  I really would like about a 50 HP boost, but don't want to go with headers if possible.  I now have wide open dual exhaust.  I would like to increase compression to about 9.0/1 but not go crazy.  Some of the rebuild kits are closer to 10/1.

If any one has experience with either of these or another option I would appreciate the input.  The car already has a 750 cfm
Edelbrock carb, non stock GM intake and low profile air cleaner.  Everything else original.

Thanks for any input,

Ray

I am new to this site and haven't figured out how to post photos under the message.  Something I should click on?

Quite a few might think I'm nuts but I would pull the engine and replace with a crate motor and keep the stock motor stock.  I would do this if I had space for the old engine and if the rebuild includes machining.  Of the 3 stock engines I have considered rebuilding('67 camaro 327, '79 Z28 350 and the '81 Vette 350) none were close to the cost of dropping a crate motor in once I got through the machining bills.  The only one I kept the original engine for was the '67 because of potential resale value.  The vette I'll never sell (just ask my head mechanic/daughter Sara) so I wasn't concerned about keeping it original.

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Dave C..........My mantra: I can not be bought!!      Long and short term leases available.

Thanks for the idea, Dave.  I poked around online and foumd crate engines running from $2100 which actually had a bit more horsepower than I was thinking about to $6000, which is a lot more than a rebuild.  The best price was from Summit.  I will certainly keep this in mind and store the stock engine.  I honestly don't know if a matching numbers engine would make the "74 that much  more valuabl, but it would be an ace in the hole.  I am trying to keep the car looking original, but after driving the L82 the performance seems dogged.

Where did you find your crate for the '82?

Ray

My Car


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|UPDATED|4/25/2013 10:14:28 AM (AZT)|/UPDATED|

Well I don't have any direct experience with the Comp Cams Thumper, but when I researched a cam choice for my engine I was interested in the Thumper cam too. I called Summit's tech line and spoke with a very knowledgeable person who told me that cam needs 9.5:1 compression ration to do any good and would not be a good choice for a near stock engine. The Thumper cam profile is more or less for the sound and not for power.  He advised me to go Comp Cams High Energy cam. He said the engine will run much better with that cam and he was right. The High Energy cam has a choppy idle that sounds good and runs good. I would call Summit and talk to someone about your plans for the engine and what they would recommend, they will be happy to do this for you. 

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DanT

I originally was only thinking camshaft.  Don't have resources to do the work myself.  A mechanic I trust somewhat told me labor would be around $700.  Add $300 for parts.  I am wondering if it might lead to failure of my older engine .  The mechanic says it should be OK.  This is why I am looking for experienced opinions. 

Can you tell me what kind of performance increase you got with the new cam.  The '74 engine only has 8.25 or 8.5 to 1 compression.  You did not say which year engine you modified for a comparison.  Also,did you make other changes with the cam?

All opinions appreciated.

Thanks,

Ray

I purchased a slightly used (750 miles) rebuilt engine for my 74. In the process of working on the engine I discovered it over bored .040 with flat top pistons. Internally, that is about the extent of mods. Along with the cam, lifter, and valve spring kit, I installed an Edelbrock Performer intake, Summit Racing 600 cfm carb, high performance HEI tach drive distributor, aluminum water pump and headers. Unfortunately I have not had the engine dyno tested so I don't know horsepower, but it runs great. I would definitely get Summit's recommendations for a cam with stock internals or advice on a crate motor. That might be the best way to go, a lot less hassles.

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DanT

 Seems to me that rpm range is a tad rad for the street, when we mostly use power between off idle to maybe 4000 rpm's. I never rev past that, but then I'm a little conservative. And keep in mind, the higher the lift on that cam, the worse the fuel milage. Those crate motors are very respectable runners and Summit does have some of the best pricing on GM crates. Keep us posted on what you decide.

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Jimmy B.
Just can't wait to get on the road again.

 
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Thanks for the input.  The nice thing about the L82 is the idle, the frustration is that you have to be in second gear to use the power curve, even on the 2 lane highways.  4 speeds not available in the year I have.  A power curve from 2000 to 5000 would be a lot more usable with the 4 speed Stingray. 

Now that the sun is about to shine, raining today, I won't lay the car away for improvements until the good  season is over.  We are lucky to have 6 good months here.  I will keep researching and thinking about things for a while yet.  Putting in about 300 HP of crate engine and storing the original is an idea I had not considered.  I will have to chat with Summit
Thanks,  Ray

Stock CR on the L-48 is 8.5.1
The only way to increase the CR to 9 or more is with new pistons. Any good cam is goin to need at least 9-9.5 to actually work right. Anything less, the engine will sound good at idle, but "won't pull a cork out of a broken wine bottle", so they saying goes.
You can get a really good "RV" cam, that will idle smooth, and give you goo-gobs(hi-tech term) of low end torque, but will fall on it's face above 3000rpm. Not a good choice, either.
The best money spent will be on a crate engine, in the long run, unless you have access to a machine shop, and can do the work yourself. Back in the day, we could build KILLER engines for $600....that won't even pay for machine work these days....that's what make crate engines so popular, annnnnd....they come with a warranty!


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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

I think putting a high performance cam in an old engine will probably be a waste of money.  Trying to get that tired engine to make power will likely cause lots of blowby and you'll start seeing oil puking into your air cleaner via the PCV pipe.

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1973 BB 4-Speed Coupe Project Car

Considering the crate engines I see run from 290 to 335 horsepower and up,  how much power can the stock 4 speed handle? I believe it is the standard Muncie.Has the transmission been downsized from the higher horsepower "Vettes of previous years?  My understanding is that the engine isn't that different from the previous versions, just lowewer compression heads.

Any experience with the GM performance 290 HP 350.  Does it really have 95 hp more than the stock L48, or is it dyno power?  That seems to be the bottom of the performance crate ladder and more than I would expect from a rebuild.

All input appreciated before I explore options with the mechanic.  He personally used to build racing engines, but labor rates aren't what they used to be.  If I could get 50 hp more at the rear wheels with a moderately rough  idle, I would be happy.  I really doubt if I would use it except for highway passing.  I don't rally want to upgrade the transmission.

Thanks,  Ray

The stock trans will handle the extra torque/hp....unless you get plumb silly with it, that is. It will handle up to around 400ft/lbs with the stock driveline/tire sizes. Put slicks on it, and launch at 6000rpm.....might be an issue then.

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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

I got my engine from Phoenix engines...go for the turn key.  When you get a crate engine make sure you check on the break-in procedures.  Some can be more elaborate than others.  You should also check with local shops.  Go to local car shows and talk to some of the folks there.  There are three things car people love to do, talk cars, drive cars, work on there cars...maybe not in that order but you get the idea.  Going with a local shop can make things a little easier.  They might do the install as well.  That makes for a nice smooth transplant.

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Dave C..........My mantra: I can not be bought!!      Long and short term leases available.

Thanks for the input. Sounds like an entire summers worth of research ahead of me.

Ray

I have had all the above, first I had a 383 stroker with the big mother thumper cam it sounds good but!! no vacume and you need a canistrer. I took it out and put an extreme energy 268 which was far better and gave me about 75 more HP with my build.

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My motor: although I agree that a crate motor is the better choice for the vast majority of us, for some reason I went the other way and built my original block.  Found a good machinist that was willing to work with me - he bought all the parts and did the work, but I put it together.  (He built the heads).  I think it was a good choice for me because I enjoyed doing it and I got exactly what I wanted, but I don't think it saved me any money and it certainly didn't save time!!  I'd only recommend it if all that time sounds like fun, not work.  

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