Original L48 - keep it stock or ? - Team Camaro Tech
Engine General Engine Discussion.

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post #1 of 9 (permalink) Old Mar 30th, 04, 08:48 AM Thread Starter
Join Date: Aug 2002
Location: Austin, TX
Posts: 18

I'm finally getting to the "fun" part of my '69 Z10 back-to-front mechanical restoration. I'm trying to determine what to do with the original L48. My main question is can I run a stock L48 with 10.25 compression on Texas 93 octane pump gas? I also have other questions added below.

More info: It's a stock L48 62,000 mile engine with 3.07 (open diff) 12 bolt rear, TH400 transmission (non-original) & 14" wheels. Factory AC car with factory exhaust manifolds. I pulled the valve covers and still have the 3947041 heads. Cranking compression comes in at 225psi. Prior owner history shows no engine rebuild.
I want to be able to drive/cruise in this car. No racing.

If I can run the 10.25/1 on 93 octane, should I just have the original 041 heads rebuilt, stick with the original iron intake manifold and Q-jet? Or do I go with a new set of vortec heads, and hope I can find an intake manifold to work with my factory cowl hood clearance? I've also read pdq67's cam suggestions in prior posts and am considering a new cam.

Any prior L48 experience or performance opinions would be appreciated.

69 Z10
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post #2 of 9 (permalink) Old Mar 30th, 04, 09:13 AM
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Join Date: Sep 2000
Location: Shrewsbury, MA, USA
Posts: 6,509

You should set the original engine aside, or send it to me, and then build a replacement engine to whatever performance level you want. The value of the car will be affected by modifying an original matching numbers engine. That may not be an issue to you today, but someday you will be happy to have the original engine. Especially when it adds to the selling price of the car.

Mark Canning
1969 Indy Pace Car
350/300HP RPO Z11

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post #3 of 9 (permalink) Old Mar 30th, 04, 09:16 AM
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Location: Chattanooga, TN, USA
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That's alot of questions......Most can be answered by "what do you want"

If the block is the original L48, and you are doing a restoration, I'd use all the original heads, intake, carb, manifolds, etc. If you are doing a street rod, especially if the block is not original, I'd put whatever performance upgrades you want.

As for the compression, most will say you risk detonation with pump gas for compressions above about 9.5:1. Although you can retard timing to reduce/prevent it.

If I were rebuilding the motor, I'd choose pistons that would allow use of pump gas. If I were not rebuilding, I'd use octane boost or blend a little racing fuel to kick the octane a little. I talked to a guy with a 67 chevelle 396, with 11:1 compression. He kept a coule of those short, square 2 gallon plastic gas cans with racing fuel, in his trunk. He added one can with each fillup of 93. That was enough to raise his octane.

He made an angle iron frame to keep the cans from sliding around in the trunk.
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post #4 of 9 (permalink) Old Mar 31st, 04, 01:59 AM
Join Date: Apr 2000
Posts: 21,341

Imho, you are going to have to decide what you want to do..

A stock engine is only stock once unless put back that way later which is a lot harder to do then one can really imagine..

I wished I had my stock, L-48 with only an L-79 cam in it now like it was when I pulled her out..

But it's long gone now...


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post #5 of 9 (permalink) Old Mar 31st, 04, 04:43 AM
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Location: Winston Salem, NC
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I agree with Mark C. Pull that original puppy out and put it in a nice safe place. It's very valuable of it is a original as you say.

You can get a junkyard 350 for next to nothing and build it how you want.

69 Camaro, 3650lbs., 400ci, TH400, Coan 10" converter, 3.50 gear
D1SC, pump gas, 9:1, 10 PSI, Water/Meth injection
1.325 60', 5.988 @ 115.4 (carb)
Switched to Super Sniper EFI 2019
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post #6 of 9 (permalink) Old Mar 31st, 04, 08:34 AM Thread Starter
Join Date: Aug 2002
Location: Austin, TX
Posts: 18

Thanks guys. Sorry for the pile of questions. I am glad to have the input of folks who have been down that road before. It's really a tough decision. Especially when you factor in cost and the difficulty in making a "new" octane friendly engine work in the AC engine bay with RS components and the factory cowl system clearance. There's lots of stuff under that hood! I've flip-flopped in my mind many times over the last year on this subject. My goal is still to be able to really drive this car in the heat of a Texas summer day and on long road trips. I had hoped to do it with the original engine since it's already there and GM went to the trouble of making everything work and fit together.
But it looks like without driving around with racing fuel or retarding the timing, I risk putting the L48 in detonation at 10.25:1 compression. Do off the shelf bottles of give me any hope?

Pdq67, you have helped me make up my mind that if I'm going to have to modify the original engine to make it octane friendly, then I should just pull it and build another engine/crate motor. (Storage was an issue but it looks like Mark C. is going to take care of that for me!)

Once again, thanks for the experience based inputs.

69 Z10
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post #7 of 9 (permalink) Old Apr 1st, 04, 03:19 PM
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Location: LR AR
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I would upgrade it to use the Corvette L-46 cam and it will run fine on pump gas even with all the accessories. The top of the line Corvette small block got this cam for 69 while the base Corvette engine was the L-48. I am building one myself except it will have aftermarket heads and an ignition recurve. It will run great even with the cast iron manifolds.

The cam is available from Crane under the "Blue Racer" brand name. I have the part number if you need it.

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post #8 of 9 (permalink) Old Apr 1st, 04, 04:16 PM
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Glad I could help..


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post #9 of 9 (permalink) Old Apr 2nd, 04, 05:46 PM
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The 93 octane gas shouldn't be a problem... remember, they played with these #'s just like they played with HP, net vs gross and all that... What says 93 octane is 97-98 in 60's #'s. Just make sure it's tuned good (and I mean dynoed, recurved, and jetted...)and put hardened seats in if you take the heads off. As long as it doesn't lean out and the advance curve is under control, it'll be fine... That black truck below has an 11:1 LS1... the 327-275 in the ragtop's 10.25:1... and my neighbors 327-360 '67 vette runs fine on 93 too...

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