2-barrel Roch Only Questions
 

For any of you 2-barrel GM racers who have experience with and/or know a lot about Stock racing with 2-barrel Roch combinations, I have questions.

By now, most everybody here knows, I'm a Pontiac Freek. So, what sparked my interest in this subject is the fact that I don't know of a single Pontiac Stocker, with a 350 or larger cube Pontiac engine, that has run a 2-barrel combo in national competition.

IIRC, it was Billy Nees who posted that there are lots of different sizes of the Roch 2-barrel, & most 2-barrel Pontiacs had the small ones, making them bad combos, at current hp factors. I think he also mentioned that Don Himes ran a 2-barrel Pontiac wagon, in a Pure Stock class maybe, many years ago.

Anyhow, there were lots of 350 & 400 cube Pontiacs that came with a 2-barrel Roch. Even a GTO came with one ! And, a few 455's came with one. I bought a '71 wagon 455 that still had one on it, still running.

So, I'm investigating to see if there were any of the 2-barrel Pontiacs, mid-'70's & older, 350 cube & larger, that might have a carb size & hp factor that would make a decent combo for a Stocker build. To make it clear, I am NOT building such a car. I'm investigating the possibilities of a competitive 2-barrel Pontiac combo. Lets confine the year models to '67-'76.

1st possibility I see is a '67 GTO, 255hp 400 cube. hp factor is still 255hp. Don't know if anybody has ever tried to run one, in serious national competition. There is no venturi size listed. But there is a carb number listed. "...2GC-7027061..."

So, for you Roch 2-barrel experts, what is the venturi size of that carb ?

http://www.classracerinfo.com/Engine...8&MAKE=Pontiac

At the current 255hp factor, a '67 GTO would have to run K,L or M Stock. Would need to run mid 12's, or slightly slower, to run under the index. Obviously, the 2-barrel would be the limiting factor. Don't know if that combo could run that quick. What do you 2-barrel experts think ?

I'm not familiar with the popular competitive sbc 2-barrel combos. So, what are the popular years & combos ? What classes are they doing well in ? What is the venturi size for the competitive combo's ? Sorry for all the dummy questions. But I'll have to plead almost complete ignorance of this subject. :o

Re: 2-barrel Roch Only Questions
 

OK, here's another possibility to consider.

'73/'74 Pontiac 350 2-barrel. 210hp factor

http://www.classracerinfo.com/Engine...3&MAKE=Pontiac

Venturi size 1.186. I assume that is a "small" one ?

Looks like it would have to run the 16lbs/hp class. So, with the current 13.45 index, it would need to run low 13.40's, on a bad day/slow track. IMO, that's a tall order for a 2-barrel low compression 350 Pontiac.

What do you 2-barrel experts think ? :confused:

Just for kicks, I looked up the '73 Chevy 350 2-barrel. It has a 230hp factor & needs to run real high 12's. But, it also has a bigger carb, 1.250 venturi size, and more compression.

I just don't know how to estimate probable power output & ET's for the Pontiac, considering the smaller carb & less compression. There is only 20hp difference in the 2 hp factors. So, would the bigger carb & more compression give the sbc more than 20hp advantage ?

Just looked on Class Racer Info. Seems that for '67-'73 400 & larger cubes, there are no venturi sizes listed for any 2-barrel. Are they listed on the official NHRA site ?

Re: 2-barrel Roch Only Questions
 

Stan

Re: 2-barrel Roch Only Questions
 

Hey looks like I've already visited this subject.

Oh well, it seems that the same subjects keep coming up, over & over. They are argued about, then dropped, then later, somebody else will start another thread on exactly the same subject.

I suppose it happens on all car forums.

Some will say just "Do a search". But, I've found that on this site, it does absolutely no good to do a search. I've tried many times. Get mostly stuff that has absolutely nothing to do with the subject I'm lookin for. :(

Just noticed that the '74 2-barrel 400 also can use 88.9cc heads, as well as the 1.25" venturi carb. So, it can have a bigger carb & more compression than the '74 350. MIGHT be a better combo ? But, would need a lower hp factor, than 255, to really be a good combo.

http://www.classracerinfo.com/Engine...6&MAKE=Pontiac

Re: 2-barrel Roch Only Questions
 

1.18 carb is the same size as the 305s ..Some of them are under 180 hp. In U/SA , a Pontiac would have to weigh 600+ pounds more, in the same class.. No thanks..
I didn't even mention the 302 FFFFFFords.

The big inch Pontiacs had a 1,250 carb, I believe. Same as the smog 350 Chevys.
The 69-70 350 Chevys have the big 1.375 carb. That's the one that the restricted circle burners use.
69 Chev 350 2v is good. The 70 is even better... 70 4 dr. Nova should run low 12's in N/SA, with no roll bar , belts ,and monkey suit requirements..
One of the best 2V deals is of the blue oval persuasion, but is stick shift only, and we now know it's harder to win with that extra pedal. ;-)

Re: 2-barrel Roch Only Questions
 

69 and 70 SBC used the 1.375 x 1.686 Rochester. This I believe is the largest Rochester 2 GC .
Some Pontiac's used 1.312 x 1.686 Rochester's. I'm not a Pontiac guy so I can not tell you the motors or years these 2 GCs were used.
I would suggest limiting engine cubic inches to the 350's if using a 2 barrel.
2 barrels are adversely effected ( more so than four barrels) by Altitude and temperatures. Making them more difficult to predict an accurate run completion number, has been my experience.
They can be Fast as many have soft HP ratings by NHRA. But they are way different than running a 4 barrel combo in what they like or don't like.

Good Luck.
Steve Teeter STK/SS # 620
70 Camaro M/SA 350 2 barrel.

Re: 2-barrel Roch Only Questions
 

The 350 ci 2 bbl Ventura has been campaigned by Ron Thorne in D3 …I have not seen him run the car in years ..
.He does visit this site so MAYBE he can give YOU some insight regarding the combination..……………

Re: 2-barrel Roch Only Questions
 

Originally Posted by Danny Ashley View Post
Back in the late 80's when I had my 1974 GTO I considered the 2-bbl. because that body was a one engine combination for a 4-bbl. I obtained a manifold and carburetor and knowing that the late W.A.Lee worked on 2-bbl's, I sent it to him. He called me up and said they had tried it already and that the carb was too small and it would slow the car one and a half seconds. I had looked at Allen Peters at the time and made my decision off him but W.A. informed me that the '69 Chevy had a much larger venturi. He didn't want to do it because he felt I was wasting my time and sent it back. I really didn't think it would kill it that much so I decided to try it anyway.
It was in the fall and we had decent air but nothing like I had just ran at the Keystones where I was no.1 qualifier and ran 11.97 in L/SA which was really quick for that time. The car at that time with the 2 bbl. was P/SA and the index was an odd number for some reason of 13.54. My first pass was 13.53 followed by a 13.52. The car had no power. I had to almost floor it to do a burnout. I came back and installed the 4-bbl. set-up which is quick to do on a Pontiac and went right back up and went 12.22. I'll admit that the car could go quicker with maybe more gear, smaller headers, cam change, etc. but it didn't look worth the time and money to flogg it out especially when the 4bbl. was so good.
One last thought. Please don't base the 2bbl. combination off of Bill Rink's car. Bill is a good friend and carburetor customer and I can tell you that his engine is a "Top Shelf" Parson & Meyers piece as is everything else on the car. Definitely not a "Dime Rocket". Just a "Rocket" in it's day.

Re: 2-barrel Roch Only Questions
 

" The big inch Pontiacs had a 1,250 carb, I believe..."

When you say "big inch", do you mean the 455, or does that also include the 400's, as opposed to the 350's using a smaller carb ?

Don't mean to be picky. But I've always thought of the 421, 428, & 455 as the "big inch" Pontiac motors. But obviously, a 400 is bigger than a 301, 326, & 350.


"...Ron Thorne...He does visit this site...MAYBE he can give YOU some insight regarding the combination."

Thanks for that info ! Do you know if he goes by that name here, or something else ?


"...My first pass was 13.53 followed by a 13.52..."

Well, without trying to improve that combo, he ran low 13.50's, back in the 1980's. The 16lb/hp auto class index is 13.45.

So, here's some questions for you guys who were doing this back in the '80's & are still doing it, or at least still keeping up with the changing technology.

(1) How much more power can be made with this engine today, than back in the '80's ? I'm assuming that the current cam/spring rules should allow for at least a small power improvement, even with the small carb limitation. But, I have no way of knowing that. Just going by the fact that most all popular combos are now much quicker than they were 30+ years ago.

(2) How much quicker would a good TH200 trans be, than the TH350 that was required in the '80's ?

(3) Are today's available converters quicker than those of the '80's ? If so, by aprox how much, for a combo like this one ?

(4) Considering Danny's times, plus the use of currently available quicker parts, what ET do ya'll think this combo would be capable of.

I realize this is not a good combo. There are LOTS of better Pontiac combos. BUT, there are a LOT of guys racing combos that are not good. And, they are doin so for various reasons. I suppose some are doin it just because they've been racing the same car for a long time, & wanna keep racing it.

Some probably just don't have the money to buy or build what they'd really like to have. Some probably figure that since they can't buy or build what they'd prefer, then since what they have will run under the index, it'll do just as well as any other combo they could afford. So, they just stay with what they have & know.

I'm just guessing about a Pontiac Stock racer. He has a '69 Bird. He was running a RAIV engine. As the story goes, one of the heads got messed up. So, he switched over to the legal D-port engine for the car. It runs good, in the mid 10's. But, almost the same engine has a lower hp factor, in a '68 Bird. That has been a popular combo since the cars were new. I'm assuming this guy keeps running his '69 because he has it, knows it, & likes it, not because he thinks it's the best combo.

That's sorta my reason for digging around in this 2-barrel deal. These old Pontiacs are getting a lot harder to find, & more expensive, for anything decent. But, from what I've seen, in recent years, a '73-'74 Ventura would be a lot cheaper than a Bird, in similar condition. So, if starting from scratch, a guy could probably build a Ventura a lot cheaper than a Bird.

I suppose this might be considered a possible "dime rocket" build, tho it wouldn't exactly be a rocket. It would be more of an " I can build this car fairly cheap & it will run the index" type build.

Then there is the '67 2-barrel GTO build I mentioned. Even if it would be a better combo, a good '67 body won't come cheap. But, I'd still like to get opinions from you guys with 2-barrel experience, as to the potential of these 2-barrel Pontiac combos, or other 2-barrel Pontiac combos that you think might be better.

Hey, since VERY few examples exist, all this is mere speculation on my part. Guys with experience can provide more accurate info.

The only 2-barrel racing experience I've had was on a Pontiac powered dirt tracker. I did win a feature, a heat race, a trohpy dash, & had some other top 5 finishes, but that don't provide any answers to the drag racing questions I have.

Thanks to all you guys who have & will try to help me find answers to my 2-barrel Pontiac questions ! :)

Re: 2-barrel Roch Only Questions
 

He goes by the name Ron Thorne ….I believe he lives in the Evansville, Indiana area …

Re: 2-barrel Roch Only Questions
 

Thanks !

I just sent him a PM.

Re: 2-barrel Roch Only Questions
 

Didn't the 305 in a 76'-77' Camaro run the 1.375 2-barrel?

Re: 2-barrel Roch Only Questions
 

NO.
Well probably lots of year cars run them but only legal on two years of 350s ;-)

Re: 2-barrel Roch Only Questions
 

How about the 2 barrel 265 horse 396?

Re: 2-barrel Roch Only Questions
 

1.25...Same as the 327/ 235.
Also same as the 71 and newer 350

Re: 2-barrel Roch Only Questions
 

I tested the difference/gain between the 1.186" 1.250" on my 305 Nova, and on the 75 350 Nova combo. Was only worth a tenth on both combo's.

Re: 2-barrel Roch Only Questions
 

Now there's some useful info !

Thanks for posting it ! :)

Now, for some of you serious 2-barrel Roch racers. Who are some of the best 2-barrel roch carb builders who are CURRENTLY building them ?

Don't need the names of those who use to build 'em & are no longer doing it.

What is the aprox cost of a 1.186 & a 1.25 nowadays, including the core ?

Don't have to be for a class winning record holder. Just a good competitive carb to run just under the index of an average combo.

These may seem like REAL dummy questions. But, if I knew the answers, I wouldn't ask the questions.

(1) Is a good 2-barrel Roch any more consistent than a Q-jet ?

(2) Is it easy to get a 2-barrel Roch to launch(start the timers) consistently, so that you can dial in your RT, pretty close, on the tree.

You can compare it to a Q-jet, which is what I've always used. Have no idea how much different running a 2-barrel is. :o

Re: 2-barrel Roch Only Questions
 

I've been doing the 2-bll. Rochesters for the c/track guy's here in the southwest for several years. Lil known secret to make them run is not necessarily in the venturi housing but in the
booster cluster, float prep., and proper jetting.

Oh, and were at 4000 ft. Above sea level with a air density altitude
of 6500/7000 ft. On race day..

Re: 2-barrel Roch Only Questions
 

Now that brings up more questions.

(1) So, as long as the holes(throttle/venturi) aren't bigger than legal size, are these dirt track mods you mention legal for NHRA Stock class ?

(2) I'm assuming that the initial pump shot is not near as critical for dirt racing as for drag racing. I'm basing that on the fact that the engine rpm are already up, coming off the corners.

I remember how I had to modify the Q-jets to get our bracket cars to leave the line from an 800 rpm idle, running a stock converter. Had to get a full pump shot. And the rear flap had to open at just the right speed, to avoid a bog.

I'm assuming that when using a current Stocker converter, your launch rpm will be high enuff so that the pump shot will not be near as critical as it would if launching from an idle, with a stock/low stall converter.

But, I've never used a high stall converter. Our '75 Stocker had a Vitar(you old guys will remember them) 9", which would only stall about 3000.

I assume that a current converter for a 350 cube Stocker would have a much higher stall speed ?

For a Pontiac 350, with a 2-barrel, what would the aprox converter specs look like ?

Aprox what would be the launch rpm ?

Since the Pontiac 350 has a longer stroke than the Chevy 350, I assume you'd need to run less gear to reduce big end rpm & keep it more down in it's power range. Anybody reading this know enuff about a Pontiac 350 to figure aprox best converter specs & rear gear to choose, for a 2-barrel 350 combo ?

I assume the best trans would be a 200, with the lowest 1st gear available, or at least a low gear TH350, OR ? :confused:

Just trying to get a good recipe for a good base setup. I realize that every combo has to be thrashed out, beat on, tuned, or whatever term is used. But, it would be very helpful to anyone building a new car to get opinions from experienced racers that might help them get the correct parts, to begin with, rather than discovering they'd tried the wrong parts & had to spend extra money & work changing to what they really needed.

For example: If the Pontiac needed a 5000 stall converter & the builder went with a 4000, that would be extra time & expense, to correct the mistake. Same with the rear gear. If it needed 5.13's & he went with 4.88's, that would be more time & expense. I just pulled these numbers out of the hat. Don't know what would be best. Our '68 400 Bird Stocker needed 4.56 gears. That's about all the rpm it could stand on the big end. But it was stone stock, compared to Stocker engines today. And I don't know how a 2-barrel would affect the needed rear gear.