Holley 3811 67 390hp

[Roy S.]

What CFM was the subject carburetor?

[Leif A.]

Re: Holley 3811 67 390hp

what cfm was the subject carburetor?

585 cfm...

[Duke W.]

Re: Holley 3811 67 390hp

It's the same basic Holley 4160 as used on the 300 and 350 HP small blocks, but specifically calibrated to the L-36. It's slightly undersize for a big block, but gives it excellent throttle response. A Q-jet (either the 750 or 800 CFM version... not sure which) replaced the Holley for the '68 model year.

BTW. flow ratings without specifying the test depression are MEANINGLESS, but at least in the case of 4-bbl. carbs the "industry standard" is 1.5" Hg. Two-barrel carbs are rated at 3", so you can't compare two and four barrels directly, but since flow is proportional to the square root of depression, you can convert the two barrel flow measured at 3" to 1,5" by dividing the 3" rate by the square root of two.

For example, if you add the flow ratings for the L-71 triple two barrels you get about 1281 CFM, but that's at 3", so converting it to 1.5" yields 906 CFM, which is a bit more than the L-72s 800 CFM rating, but the 3 x 2 manifold is somewhat compromised so it's probably a wash as far as power is concerned. In fact, my bet is that back to back testing of the same engine with both induction systems would show the 4-bbl. induction system to be slightly better.

Duke

[Joe L.]

Re: Holley 3811 67 390hp

In fact, my bet is that back to back testing of the same engine with both induction systems would show the 4-bbl. induction system to be slightly better.

Duke[/QUOTE]

Duke------


You'll note that GM only used the 3X2 set-up on L-68 and L-71 big blocks. For the L-88 and ZL-1, a single 4 barrel was used. The 3X2 set-up was all about "bling". As I've said many times before, if I ever bought a Corvette with a 3X2 system, the very first thing I'd do is remove it and replace it with a 4BBL. I HATE 3X2.

[Mark F.]

Re: Holley 3811 67 390hp

You'll note that GM only used the 3X2 set-up on L-68 and L-71 big blocks. For the L-88 and ZL-1, a single 4 barrel was used. The 3X2 set-up was all about "bling". As I've said many times before, if I ever bought a Corvette with a 3X2 system, the very first thing I'd do is remove it and replace it with a 4BBL. I HATE 3X2.[/QUOTE]

Hi Joe,

Well said...and I agree, GM must have figured out the setup was more trouble than it was worth (or didn't generate enough profit for them).

That being said, I have only owned 1 Corvette and it's a '67 3x2 L-68 400HP. After 23+ years, I still like him ...he pushes me back in my seat and helps me enjoy a few lateral G's on twisty windy roads here in western PA.

In the early 2000's as part of restoring the "top end" of the engine (intake and up), I will admit I spent a few days with potty mouth mumbling around trying to get it to run right after all the "restoration" activities.

One of my favorite Holley quotes is from Terry McManmon (makes me LOL every time I see it):
"The only thing worse than one Holley is three ! "

If I were to get a 2nd C2 Corvette, it would be a '67 L-79 SB Convertible...no garage space, so that probably won't happen...

Happy Holidays !

Prep in progress for Regional 2-1-03 shot 1.jpg

[Duke W.]

Re: Holley 3811 67 390hp

Duke------


You'll note that GM only used the 3X2 set-up on L-68 and L-71 big blocks. For the L-88 and ZL-1, a single 4 barrel was used. The 3X2 set-up was all about "bling". As I've said many times before, if I ever bought a Corvette with a 3X2 system, the very first thing I'd do is remove it and replace it with a 4BBL. I HATE 3X2.

Yup! The only thing worse than one Holley carburetor that the late Dale Pearman often described as a "package leak" is THREE Holly carburetors!

Duke

[Ray K.]

Re: Holley 3811 67 390hp

My opinion is that the 3 X 2 Holleys as used on the L-68 and L-71 427 motors was a throwback to the 3 X 2 carbs available on the 348 motors of 1958 - 1961 era, although the carburetor's were Rochester vintage. As referenced above -- this was about bling. Some one at GM said ( lets bring back the 3 x 2's ) and so they did. The 409 motors never used the 3 x 2 setup, a 4BC or dual 4BC was only offered. Have never owned a Holley 3 X 2 427 motor but concur with the Joe's comment - I would pretty quickly remove it.

Ray

[Michael J.]

Re: Holley 3811 67 390hp

It seems every Corvette person needs to experience an L71 once. Then you learn your lesson, satisfy the "gold chain" phase of your mid-life crisis, and move on to the really good engines for C2s, the L36 and L79.

[Keith B.]

Re: Holley 3811 67 390hp

My opinion is that the 3 X 2 Holleys as used on the L-68 and L-71 427 motors was a throwback to the 3 X 2 carbs available on the 348 motors of 1958 - 1961 era, although the carburetor's were Rochester vintage. As referenced above -- this was about bling. Some one at GM said ( lets bring back the 3 x 2's ) and so they did. The 409 motors never used the 3 x 2 setup, a 4BC or dual 4BC was only offered. Have never owned a Holley 3 X 2 427 motor but concur with the Joe's comment - I would pretty quickly remove it.

Ray

I think its more that Deloren got tri power on GTO's in 66

[Tim G.]

Re: Holley 3811 67 390hp

I've had more than my share of tir-Power setups on Corvettes and I love/hate them. I've got the set up on "Elkie" (Elkhart Blue '67) working quite well now. No leaks and the end carbs come on nice and smooth with the 4.11 gears. That being said, I've also had my share of problems with tri-power setups.

[Chris H.]

[Timothy B.]

Re: Holley 3811 67 390hp

They are basically all the same, once you understand the workings of a Holley. Biggest problem I have experienced is the modular surfaces not flat.

[Lawrence S.]

Re: Holley 3811 67 390hp

During Covid I rebuilt the carbs on my 69 L71. So over two years ago. So far so good. No leaks, car starts up great, end carbs come in as they are supposed to. The car has a 4.11 rear end. I have not had any problems. I also have a 70 AAR Cuda with the same setup. Same story, rebuilt during Covid and so far so good.

[Kenneth B.]

Re: Holley 3811 67 390hp

I think its more that Deloren got tri power on GTO's in 66

The 65 GTO I bought new had tri power.