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  1. #1
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    Corvette(s)
    1972 Blue T top

    Default L88 engine specs and cam questions

    I am in the early planning stages of my 1968 L88 replica and I need to rub out all the rumors associated with the L88 spec and stuff. JUST HOW POWERFUL IS THIS MOTOR? Some books say its 560 to 600 HP stock. Others say it's 430 HP like it said on the ordering sheet back in 1968. Another thing is how wild is the cam and is it a solid lifter car, or a wild hydraulic pushrod engine? Mine is going to a be a street and strip version of this car. Since you can't get Sunoco 260 fuel I believe is it that the car required to make the L88 engine run with it's 12.5 to 1 compression ratio, is that ratio correct? If so mine will have a 9 to 1 compression ratio so I can run premium gas at the local gas station. I plan on driving this Corvette on the street 65% of the time and 35% on the strip so I hope all 427 Vette owners understand my reasons for limiting the power a little bit. In my opinion all that power is nice, but there is must be some room left over for streetability. To all L88 owners, have I covered all the rumors? If not please let me know on this forum. Thank you and Keep 'em rumbling!

  2. #2
    69 L88 RACER
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    Default L88 Stuff

    I just finished my 69 L88 clone this summer. Its an auto,4.10 rear,Lemans blue. 12.5 to 1 compression is right on for fact specs.The cam is quite wild,would work better on the street with a 4 speed.I had bullett grind mine,I'l give you the specs if you like.I feel the car is quite streetable and I do drive it whenever time permits.I run mostly 110 octane race fuel,but it will run on 92 with some additives.The car was built to compete in the pure stock type classes and has done very well so far,11.99 @ 118.05 in stanton this past Sept.I wish more Vettes would come out to the Pure Stock Drags!!! Its a total blast!!!!!Oh yeah,my motor made 503 hp on the engine dyno @ 6000rpm.485 tq.It went to 575 hp with a cheapo set of headers!! @6900 rpm!

  3. #3
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    Default Re: L88 engine specs and cam questions

    Originally posted by L88 crazy
    I am in the early planning stages of my 1968 L88 replica and I need to rub out all the rumors associated with the L88 spec and stuff. JUST HOW POWERFUL IS THIS MOTOR? Some books say its 560 to 600 HP stock. Others say it's 430 HP like it said on the ordering sheet back in 1968. Another thing is how wild is the cam and is it a solid lifter car, or a wild hydraulic pushrod engine? Mine is going to a be a street and strip version of this car. Since you can't get Sunoco 260 fuel I believe is it that the car required to make the L88 engine run with it's 12.5 to 1 compression ratio, is that ratio correct? If so mine will have a 9 to 1 compression ratio so I can run premium gas at the local gas station. I plan on driving this Corvette on the street 65% of the time and 35% on the strip so I hope all 427 Vette owners understand my reasons for limiting the power a little bit. In my opinion all that power is nice, but there is must be some room left over for streetability. To all L88 owners, have I covered all the rumors? If not please let me know on this forum. Thank you and Keep 'em rumbling!
    What I understand is that they left the factory pretty much at the 430 HP mark, but that was with the factory exhaust - either under car or side exhaust, both were very restrictive. The first thing most people did was ditch the factory exhaust in favor of some heavy-breathing headers and side pipes, and that was supposed to bump the horsepower somewhere around 100 HP. I can let you know for sure in a few weeks. I just pulled the motor out of my L88 for rebuild, and my intent is to build it as close to stock as I can, then run two sets of dyno numbers - one through the factory side pipes and one through a good set of headers and side pipes.

    The factory specs call for a solid lifter cam. The GM part number for the service replacement was 3925535, but it was discontinued several years ago. Crane and Lunati (?) both reproduce the cam, and you can find the specs (which are supposed to match the factory specs) at Crane Cams. Look up Crane part number 968561. It's a pretty wild cam, and they are extremely hard to get through emissions if you happen to live in a state where that would be required. Because of the big cam, it also produces very little vacuum at low RPM, which means that if you have power brakes you may not get alot of assist when you are driving it around town. I get by, but it is something you will always have to keep in mind.

    The compression ratio in 1968 was 12.5 to 1, but that dropped to 12 to 1 in 1969, both are a little high for pump gas without lots of additives as L88 RACER said. I run 110 race fuel in my L88 as well, and buy it by the drum - but that isn't very practical for a street car (and illegal, since it's leaded fuel).

    Enjoy your L88. They're a blast.
    Jon

  4. #4
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    Corvette(s)
    '77 L-82, black on black. Full mod 406 small block

    Default

    correct me if i am wrong, but GM de-rated the L-88 to avoid the corporate mandate against factory racing in the late '60's. from what i have read, the stock L-88's were in the 600hp range on 100 octane fuel. the over lap in the cam dropped the cylinder pressure enough to run 92 coctane without hurting the motor. the "factory numbers" for power were correct at the the given rpm, but the motor made much more power in the higher rpm band than the stat sheet guys knew about, giving berth to the ledend that it is today. if you own one, or even copy one, my hat is off to you!!, Brian

  5. #5
    69 L88 RACER
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    Default L88 power numbers

    The numbers you read about the L88 are likely dynoed with headers. There aint a chance in hell the factory cast iron ones could possibly flow well enough to make 600hp!My engine was all done at 6000 rpm,with stock manifolds.(503hp) We put on cheapo set of headers and it was still pulling hard at 6900,It made 575 then. I could see 600 with good headers and 7200rpm.The factory intake is choking also.It has a stock 850cfm holley carb,we only used 780 cfm at 6900rpm.The cam is perfect for the kind drag racing I do,very little bottom end power,lots on top. We have to run on repo bias ply g-70-15 wide ovals!!
    Wayne Nelson

  6. #6
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    '77 L-82, black on black. Full mod 406 small block

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    only the early proto type production L-88's had iron heads. the mass majority (of the to few engines made), were aluminum heads.

  7. #7
    Member motorman's Avatar
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    the first L-88s were alum heads but roger penske did not trust them for the 1967 24 hours of daytona so traco built the 24 hour engine with iron heads.
    retired race engine builder,former NASCAR tech inspector,corvette owner since 1959, new corvettes owned,59,62,63,64,65,66,97,99,02,05, 2008 is in my garage, 2008 sold and waiting for my C-7

  8. #8
    69 L88 RACER
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    Default iron ex manifolds

    I was talking about iron ex manifolds,not iron heads.

  9. #9
    Scooter76
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    What I have always heard on L88's , ZL1's etc, Gm rated them honestly but quoted the hp #s at diffrent rpm's. I may be silghtly off on the #'s but the L88 was rated at 430 @ 5600 which may have been true, but it also made 550@ 6500 with headers as said above. I think it was "we're only half way lying about the rated hp."

  10. #10
    Member wallyknoch's Avatar
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    Corvette(s)
    One owner unrestored Black 1962 FI Corvette

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    L88`s are a unique engine. All were 427`s. Probably the best single carburator engine built. All of them were solid lifter cams at 560/580 with aluminum closed chamber heads. Naturally a 4 bolt main block. 12.5 compression with forged full floating pistons and special rods. A open plenum dual plain high rise intake and a TI non vacumm distributor. The 1967 engines had 3/8 rod bolts and the later ones were equiped with 7/16 rod bolts. The heads were painted Chevy orange and a lot of overspray on the intake at the mating surfaces. Painted valve covers. The timing chain was nothing special. 3/8 push rods with guide plates opened the valves. Stock rocker arms, oil pump and pickup with a baffeled oil pan. Lightweight 10.5 flywheel and a 10.5 clutch assembly for the high reving engine. The only difference between a L88 and a ZL1 is the latter had an aluminum block. Horsepower was never specifically advertised. All I can tell you is that they are awsome. The only thing comparitable is probably a A990 Race Hemi. I know, I own them both. Built any other way, It`s merely a modified 427 not a L88. Plus you will need an "IT" stamp on the engine number pad.

  11. #11
    Member motorman's Avatar
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    the later 69s came with open chamber heads,#074
    retired race engine builder,former NASCAR tech inspector,corvette owner since 1959, new corvettes owned,59,62,63,64,65,66,97,99,02,05, 2008 is in my garage, 2008 sold and waiting for my C-7

  12. #12
    jfb4548
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    Default

    Originally posted by motorman
    the later 69s came with open chamber heads,#074
    Great thread! The L-88 is a dream Vette for sure! If your looking for heads, I might have some for sale in Closed Chamber and I have atleast 1 bare Open chamber casting as well.

    Peace
    John

    http://corvetteactioncenter.com/specs/l88/

  13. #13
    jdads2
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    Default

    I've finally made a decision to replace the stock engine in my '81 with a clone 427. My greatest concern is hooking the engine up to a reliable auto tranny that can handle the power yet allow it to be streetable. I'd also like to be able to run something more easily obtainable than racing fuel. Are those realistic goals? Will I be taking too much from the romance and mystique of the L-88 by trying to match it to my specific needs?

    Any thoughts or advice on cams to achieve my "Vette Dream"?


    Thanks

  14. #14
    69 L88 RACER
    Guest

    Default L-88

    jdads2
    You can have a 700r4 trans modified to handle the type of power you will be running.That way you have 4th gear (overdrive) to compensate for decent gears.I would suggest a cam no wilder than the 427-435 version,I ran one for years on the street with no problems,I have the L--88 now and still can drive it, but not nearly as streetable.Use the cheapo oval port smog heads,with a little port work they will outperform the rect port heads! Super Chev did a head comparision a few months ago to show what the oval ports can do.Good luck!!

  15. #15
    Member iron cross's Avatar
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    Corvette(s)
    Unrestored one owner 1962 Black FI car

    Default Transmission

    The turbo 400 would be a suitible choice of automatics to handle a ton of HP. A recomended minimum of 3000 stall converter, but dont go overboard with the stall as it will heat up with out a trans cooler. Instead of a L88 cam, the 435 HP 427`s cam will be more practical as others have mentioned. Put a suitable gear as say a 4.10 and you will have a very nice and quick machine.
    Originally posted by jdads2
    I've finally made a decision to replace the stock engine in my '81 with a clone 427 as some other replies have mentioned. . My greatest concern is hooking the engine up to a reliable auto tranny that can handle the power yet allow it to be streetable. I'd also like to be able to run something more easily obtainable than racing fuel. Are those realistic goals? Will I be taking too much from the romance and mystique of the L-88 by trying to match it to my specific needs?

    Any thoughts or advice on cams to achieve my "Vette Dream"?


    Thanks

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