L71 vs. L68 vs. L36
I am interested to know what members think of the 3 different 427 variants in 1967 Corvettes. What opinions do you have of the dependability, reliability, performance, etc. differences of these engines? Is one clearly better or worse for driving around semi-regularly? Thanks for your views, I am trying to decide on which to target for a purchase.
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Big Tanks In the High Mountains of New Mexico -
Re: L71 vs. L68 vs. L36
The 427/390 has better low end torque and driveability than the 427/435, and you only have to deal with one cantankerous, leaky Holley carburator, rather than the three cantankeous, leaky Holleys on the 400 and 435 HP verisons. Most also have taller axles than SHP 427s, so the 390 is a more relaxed highway cruiser. Look for one with a wide-ratio trans and 3.08 or 3.36 axle. And you might even be able to find one with factory A/C that was not available on the 435 HP version.
With some head work a 390/427 will make almost as much top end power as a Tonawanda-built SHP verison with useable power to 6000 plus revs while not disturbing the smooth idle or stump-pulling low end torque.
The SHP 427s aren't that radical, but neither are they as docile or torquey as the 390 HP version. If you absolutely have to have "the fastest Corvette in town", then go with the SHP version, preferably the single 4-bbl. '66 version.
Duke -
Re: L71 vs. L68 vs. L36
My 2 cents; For driveability on the street the oval port big blocks perform much better than the square port motors. Even in NHRA stock classes the oval port heads are the winning ticket.
So if you are concerned with that the L36 or L68 is the way to go. That being said there is the value factor and the Tri-Powers will always carry more value and desirability.
The L68 is the rarest of the Tri Powers as they actually made less 400hp than 435hp motors so the L68 has a unique position as being oval port, lowest production & Tri Power. (I'm biased though as there's an L68 in my garage)
But for bragging rights, value and shear panache the big dog HP 435 will float to the top. It may get walked by a nicely tuned oval port though,,, or even a wicked LT1...Comment
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Re: L71 vs. L68 vs. L36
Thanks, yes many factors to consider I guess. I have a '66 L79, and I must admit I like the lumpy idle sound that comes out of the sidepipes. It sort of says "Covette" to me.Big Tanks In the High Mountains of New MexicoComment
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Re: L71 vs. L68 vs. L36
Interesting, I have always had great luck with Holleys and no luck with Edelbrock/Carter/Rochester carbs. In fact I had a '68 1/2 428 Cobra Jet Mustang that I tried two brand new Edelbrocks on and it would not run until I put a Holley double pumper in. Different experiences.Big Tanks In the High Mountains of New MexicoComment
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Re: L71 vs. L68 vs. L36
The 390 horse has great street manners. Makes loads of low end torque, you only have one carb to mess with and you don't need to adjust the lifters periodically. They went to fuel injection for a reason. One carb under the hood is more than enough to keep you occupied.Comment
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Re: L71 vs. L68 vs. L36
Almost any carburetor can be dialed into what the engine needs as long as you really know what your doing when setting up a carburetor but few do, and buying a "one-size-fits-all" aftermarket carb will usually cause nothing but trouble for the average guy who has no expertise in carb setup and tuning.
The long term problem with Holleys is the "wet gaskets" that ultimately leak. Then there is the warpage problem from guys tightening the fuel bowl attaching screw too tight in an attempt to stop the leaks, delicate power valves subject to failure...
The Carter AFB and Rochester Quadrajet float bowls are integral with the main body castings, so there are no "wet" gaskets to leak. The biggest problem with the AFB is the choke clean air system, which gets dirty, but it's not that hard to take apart and clean, and it can be done without removing the carb from the engine.
The Q-jet is an excellent carburetor. The single fuel bowl is integral with the main housing casting, which means no "wet" gaskets to leak, and the combination of the small primaries with triple booster venturis and large air-valve secondary means you can run these 750 CFM carbs on a small engine for excellent throttle response and decent fuel economy that is no where near flow restricted at the top end.
The early Q-jets even have an adjustable off-idle/transition system that is a real nice thing to have when dialing in the fuel map for a non-OE configuration.
If I was given the task to to specify a carb for some engine configuration, regardless of originality, it would be a Q-jet with electric choke.
DukeComment
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Re: L71 vs. L68 vs. L36
I'll agree I have seen Holleys leak, but none I have had ever did. I dislike the Carter and Rochester accelerator pumps, they are poorly designed, weak, and prone to trouble. That seems to be the common issue on the ones I have had with them, lots of stumbling and stalling, bogging, flat spots and hesitating under hard acceleration. However, if restored and re-engineered by pros like at Pony Carbs, all these things can be fixed and they run great. An electric choke is the way to go for new ones if you don't have to worry about losing points in Flight judging
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Big Tanks In the High Mountains of New MexicoComment
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Re: L71 vs. L68 vs. L36
The 4th variant 427 will always be my favorite. As for carbs, I agree with Duke on the Q-Jet. I have two cars with them. I did a mild tuning of the Q-Jet on my L-82 including bending the tang, jets/rods, and using a rat tail to elongate the slot. Acceleration was much better, no detriment to fuel consumption, it was fully streetable and I have a number of autocross trophies supporting it.Comment
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Re: L71 vs. L68 vs. L36
The OEM Holley on my LT1 leaked from the day I got the car. I "rebuilt" it many, many times with varying degrees of success. I finally got it rebuilt by a former Holley employee -- that finally fixed it. I am convinced it proves one has to know what they are doing, and I don't claim to know squat about Holleys.
The idea of "wet gaskets" as Duke puts it -- is just insane. Then of course there are the leaking plugs in the bottom of the Q-Jet fuel bowls.TerryComment
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Re: L71 vs. L68 vs. L36
There was an article in one of the hot rod Magazine that claimed that a large percentage of Holley carburators have warped metering blocks. Leaks are hard to stop with this condition. Of course the artical was written by a vendor who sells blueprinted carbs.
The professional rebuilders make sure that the metering blocks are flat.Comment
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