Looking for a better Carburetor

55C150

55C150

Well-Known Member
I checked the minimum intake vacuum at hard acceleration when I made a pass at the "Strip" (it is a closed road, nearly 2 miles long). So the minimum is 1.47 in HG.
What I know is, if the vacuum is between 1-1.5 at this test, the carb is too small.
Now the facts.
- 1955 chevrolet 150, weight with me and full tank = 3527 pounds.
- Muncie 4 speed manual trans (1967 Version)
- 3.55 Posi Trac rear end (1960), with Cal Tracs on leaf spring
- car has new suspension at standard hight, with Ridetech RQ Shocks
- front sway bar
- PU bushings everywhere
- 355 cui Sbc, 10.0:1 compression, 1.6 ex / 2.02 in valves polished, Aluminum Head, flat tapped cam 229 in / 230 ex @.050, Edelbrock Performer RPM intake (I will switch soon to a Air Gap RPM)
- Carb is a Holley 4160 / 1850-14 600cfm, main jets 64, blue acceleration pump cam, .37 nozzle, vac, 6.5 power valve, secondary with Quick Fuel adjustable diagraphm, manual choke
- AFR at idle = 12.8-13.2, AFR at WOT = 12.3, at some faster cruising speeds (between 50-60 mph) the AFR is 15.8 sometimes 16.1
- when I accelerate in traffic the off idle is terrible, it leans out at AFR = 19.5-20.1, the engine struggles for a second or two, I tried to compensate it with the blue acc pump cam and the .37 nozzle but no luck
- vacuum at idle is 13.3 in HG at 850 rpm

I also tried a 600cfm double pumper for one day, the feeling was that this carb performed better. The acceleration was more direct and straight forward, the idle was better too. But I don't know if this carb had changes from his standard jetting etc. I have no numbers on AFR or vacuum. I didn't installed the O2 sensor at this time and forgot to take the vacuum gauge with me.

Quick Fuel carbs seems to be popular today, I looked at the recommendation, the 650 Street Q came out. But the carb has no choke and I need one. So I will not buy it.

After a research for a carb with choke the Speed Demon 650 came my way. But I don't know if I would buy a vac secondary or double pumper version. I think the I will take one with annular boosters for better streetablity. The car drives more on the street (80%), ok a bit road racing and some 1/8 and 1/4 mile events. We have many Highways with no speed limit, so I can race there too.

What you think?
 
https://www.summitracing.com/parts/dem-1903/overview/

https://www.summitracing.com/parts/dem-1901/overview/

Ive seen several people have very good results from these carburetors in similar engine combos


dem-1903.jpg




http://documents.holley.com/streetdemonarticle.pdf




pressuregag.jpg

http://www.hotrod.com/articles/carburetor-dyno-testing-flowing-results/

http://garage.grumpysperformance.com/index.php?threads/carb-tuning-info-and-links.109/

http://garage.grumpysperformance.com/index.php?threads/setting-up-your-fuel-system.211/

http://garage.grumpysperformance.com/index.php?threads/fuel-pressure-regulators.635/

http://garage.grumpysperformance.com/index.php?threads/cooler-denser-air.8961/
 
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please let us know what you find out!
and your experience with what you buy!
 
Physically look and measure the intake port locations on that RPM air gap.
Compared to the regular Performer RPM, I have found the ports to be raised.
That might cause a port mismatch with your heads.
 
its ALWAYS a good Idea to get your questions answered from several sources
(especially the component manufacturers )
and thank you for posting that linked info

remember that an experienced mechanic / engine tuner can generally recognize ,
test, and verify and tweak /tune an engine to maximize results,
and its rare for any carburetor to be perfectly set up out of the box
 
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Ok Proform didn't answered. I talked to a buddy here and he has a 750cfm double pumper style Quick Fuel SS carb on a 327 with similar items like my 355. He made good experiences with the carb, it runs well and he has no drivability problem at off idle or part throttle. He want to give me his carb for a few days, so I can see how this carb work on my engine.
 
having a buddy let you borrow and test out that carb.,
would certainly be informative and help you make an intelligent decision,
based on facts and actual hands on, experience
 
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Have you given thought to an EFI system? I’m very happy with mine and I don’t think I will ever go back to a traditional carburetor unless I was doing a restoration.
The market prices are falling like a stone and they are stone simple to get going “if “ your system is in good health.
No vacuum leaks, no exhaust leaks and enough fuel “pressure” to feed the EFI.
 
Look at Holley Sniper and the FiTech units. Summit Racing also sells a modified FiTech branded as Summit although it uses an external ECU.
 
Here in germany it is not allowed to put an EFI on a vintage car that it never had at the time the car was build. If I do I will lost my historical car registration and will rise the tax for the car 10 times. So EFI is no option for me. The only fuel injection system that is allowed is a mechanical version like the Bosch tronic or the one that came out 1957 from chevrolet.
 
OK i did a test with the 750cfm dp Quick Fuel carb. It was not bad. No off idle stumble. It got richer at low end and mid range rpm. At the top end it was very similar. The carb was tuned, but my friend forget the jet and air bleed numbers. I think it is a bit too big, the acceleration was not so fast like with the 600 dp.

I wrote AED and John answered quick (1/2 hour after sending the mail). He recommend his 650 HO carb without choke. He told me I can use a choke if I have to use it, but I will lost a bit top end and the distribution of air and fuel is not so good. John told that customers from canada has no problems with the no choke version. He wrote that I have only wait 30 seconds at idle before I start driving it.

I found some interesting articles

http://www.hotrod.com/articles/carburetor-dyno-testing-flowing-results/

http://www.hotrod.com/articles/tuning-with-air-bleeds/
 
first, thank you for providing related links
now I've tuned more than a few cars, over the decades and a 600cfm, to 650 cfm carb on a 350 is as you say generally a good fit and once tuned they usually perform well,
that being stated Ive also used more than a few 750 cfm carbs and have gotten good results, naturally the results vary and the engine under the carbs configuration,
the cars weight and gearing and exhaust scavenging, compression, and obviously the owners ability to tune or tweak the combo for the best results,
and other factors like engine,exhaust and drive train,components being used, have an effect on what works best,
thats one major reason why its rather difficult to suggest that only lets say a 650 cfm carb , vs a 750 cfm, carb, is the best potential match to any 350-355 sbc.
 
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If I had enough money I would like to try a 650 and 750 of the same model (like AED HO or Speed Demon) to find out which works really better.
I would like to do a chassis dyno test to see how the whole car reacts to these carbs.

I gave John from AED the same information like here at the top of this thread.

The 750 I tried is a good carb. But the time was to short and I couldn't do any changes to the carb to tune it for my engine. The owner tuned it for his 327 in his '65 El Camino with a modified TH350 and 2500 stall converter, he eliminated the choke and did some jet changes but couldn't remember his final jetting.

Last night I found an enigne dyno test of a similar 355 engine like mine, the 750 picked up only 1.5 hp and 3 lbs torque in the comparison to a similar 650 model. I can't remember on which website it was, damn.

But in my opinion the smaller carb is the better choice. I also like to add a 1/2" 4 hole spacer under the carb.
I calculated so much things, like the air cleaner size, exhaust pipe size, the rear wheel dia and some more. I checked the position for the H pipe in the exhaust and now stumbling at the carb.
Sometimes I think it would be better to reset my carb thinking and hear what my stomach says.

We have a saying here "probieren geht über studieren" that means "testing is better than studying". Many times I did this, but it got expensive.
 
The more you learn, the more there is to question.
That's why IGNORANCE IS BLISS. Which might be where the term, "fat dumb & happy" comes from.
 
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