Anyone ever dyno test stock GM BB 3 carb set up ?

[oldhead]

Anyone ever dyno test stock GM BB 3 carb set up VS a stock 4 barrel setup ? What about SBC dual 4 barrel VS Single 4.......................Are they worth HP Oldhead

[mag2555]

Like all 3-2bbl dyno test that I have seen , on average they make a bit more top end , but not do that so much due to greater flow levels.
The two end Carbs and the shorter runner lenght they make for shift the TQ peak up higher when they are open.
On the down side of things there's usually a dip in the TQ curve when the outer Carbs tip in.

And in regards to GM trip set ups what a stated above about making some greater power was not with the stock air filter set up as many of them flow wise negate any power gain that could be had with a trip set up!

If I recall right on a built up Pontiac 430 cid motor with a 1966 trip set up the motor made 336 hp on just the center Carb, adding in the two end Carbs added well over 100 hp!

It was very interesting to see that such a large motor could make over 330 hp on just that center Rochester 2 bbl!

[Tuner]

^^^^ Obviously, someone who has never driven the cars. *****

When the tuneup is right there is no "dip in the TQ curve" LOL.

[DaveMcLain]

My friend Bob(Competition Carburetion) told me one time that on the 435 horsepower in the Corvette the quality of the air filter element is very important. If it has more than a few thousand road miles on it then the secondary carburetors will probably not open fully. Its like they built this great big engine and this cool looking swoopy car and then discovered that there was only room for an air filter that was just barely adequate.

[mag2555]

Well Tuner, thanks for taking a stab at what my life has been, but for your info I have owned 3 different GM brand tripowered cars in my 46 years of being old enough to have a drivers license so maybe your experience has been different I guess!

[cpmotors]

Anyone ever dyno test stock GM BB 3 carb set up VS a stock 4 barrel setup ? What about SBC dual 4 barrel VS Single 4.......................Are they worth HP Oldhead

Just this past spring actually. 1969 L71 435hp 427ci (429ci actual @ 4.260" bore)
Started with 825cfm Race Demon and Edelbrock C427X w/o air filter and 2" headers.
Swapped to 3x2 setup and no air filter.
543HP vs 537HP, no tuning on either setup.
Added air filter and tested. This was the original OEM unit and suprisingly killed very little power.
Removed headers and installed stock manifolds with headpipes.

https://www.youtube.com/watch?v=PN6eJnW ... fYWxnZoe35

[pdq67]

It has been said that no more than a cheap set of 4-tube, long tube headers on a high power BBC will produce like 100 hp more power!

I'm talking the big L-88, 430 hp engine here.. From factory 430 to 540 or so hp here!!

And the, "still-born", 454 LS-7 up around 600 hp...

It's a shame that they never put, "trips", on the high hp engines back then.. L-88 and LS-6....

And fwiw, an old 350hp/348, "tripped", "W" engine is a real hoot and will make you a believer in, "trips"!!!

Sucker would rpm to the MOON!!!

I put a hopped up .060" over, 11.5 to 1 CR, 409", tripped, engine in my car back years ago and it was a hoot.

pdq67

[mag2555]

If it where not for GMs foresight and getting there hands on the new Rochester 750 cfm Q-jet in mid 67,GM lines would have had a hard time in keeping there hp numbers up after 1970 when the emissions / fuel mileage crap kicked in.
GM may have been forced into trying to keep some multi Carb set ups I think!

[novadude]

If it where not for GMs foresight and getting there hands on the new Rochester 750 cfm Q-jet in mid 67,

Close. Q-jet was introduced in February of '65 on the all-new 396 ci Chevy, and started making it's way to other GM products and Chevy engines in 1966. It finally got to Pontiac in 1967, and it really didn't give up anything to the 3 x2g Rochester set-up that Pontiac last used in 1966.

It's a shame that Rochester had no aftermarket performance division to promote / market the Q-jet, because people perceptions of this new-fangled funny looking spreadbore carb would have (should have) been much different. Holley would have lost a lot of sales.

[DaveMcLain]

You have to remember that the manufacturers had to be able to meet emission regulations that were coming down in that late 60's and early '70's. This meant total vehicle emissions and not just those from the tailpipe. Having multiple carburetors with multiple fuel bowls sitting on the top of the engine would make meeting evaporate emissions much more difficult.

[pdq67]

Imho, the 750 and 800 Q-Jets are some of the BEST carb's ever made..

I don't know about the 1,000 cfm Thermo-Quad, but I do figure it is a real winner too.

I got a big , "endo", double pumper, "Autolite", off a '58, 430", Merc years ago and didn't realize that it was not a 3310-1 Holley. I didn't even put it back together.....

pdq67

[MadBill]

You have to remember that the manufacturers had to be able to meet emission regulations that were coming down in that late 60's and early '70's. This meant total vehicle emissions and not just those from the tailpipe. Having multiple carburetors with multiple fuel bowls sitting on the top of the engine would make meeting evaporate emissions much more difficult.

I'm suddenly remembering charcoal 'donuts' in the air cleaners from the late seventies until carbs went the way of the dodo ten years later..

[Tuner]

Well Tuner, thanks for taking a stab at what my life has been, but for your info I have owned 3 different GM brand tripowered cars in my 46 years of being old enough to have a drivers license so maybe your experience has been different I guess!

If you owned 3 tripower cars you must have never driven them, otherwise, how or where did you get the idea there is a "dip in the TQ curve when the outer Carbs tip in"??

[dwilliams]

Following an odd thought, I found that Edelbrock still makes brand new 6-carb cross-ram intakes and the matching "94" series carburetors. A manifold and set of six carbs, new, will tap your wallet for $3,000-ish. Not including linkage or fuel logs.

That'd be a big fashion statement on a street rod engine...

[pdq67]

I have always had an itch for the old Holley 3-barrels!

I think they made 4 of them?

Something like 950's and 1050's if not mistaken. Stick and automatic carbs in both sizes??

And the 1,000 cfm Thermo-Quad also trip's my trigger.

pdq67