BSB67
Well-Known Member
Not all 950s are the same. The small venturi Holley (80496) flows like 840 cfm. With tuning it can be pretty decent down low
What Carb to Run on my 408 Stroker Duster.
- Thread starter TimS
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B3422w5
Well-Known Member
Yep.
The HP 950 has smaller Venturi and the booster signal is much stronger than on an ultra 950.
To me, the hp 950 is the best of both worlds in the 750-950 arena.
Those two carbs are quite different, and the hp 950 is more than capable of supporting most any NA small block this side of exotic.
BSB67
Well-Known Member
I call the small 950 the 850 that drives like a 750. I’ll probably get flamed for that statement.
I did a season of flip-flop testing between my 4781 850 DP and small Venturi 950. Probably 15-20 passes on each. Despite the 60’ and mph being nearly identical between the two, the 330’ and 660’ data and et were better with the 950. Not what I expected.
That said, I find that the small venturi 950s require more tuning for the street than the 850. This was two different 950s on two different motors. The idle and transition were very fat in both cases. Again, kinda the opposite of what I expected.
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I second the Holley Sniper suggestion. I was running an F1 Procharged 416 at 18-20lbs of boost. For years I struggled with blow through carbs. I never could get it to run that great. If I got one parameter dialed in, it would give me an issue somewhere else. Get it running good at idle and low rpms, and it would die out on the top end. Get it to scream at the top end and it would wouldn’t want to start cold or hot start, or would stumble when you stabbed the throttle or whatever. It was a constant tweak and tune to try and nail the perfect tune and it was never great.
I finally decided to swap to the Sniper and it was different car. Just reach in and turn the key and it would fire right up and idle smooth as day. Cut the fumes smell down by a lot too, throttle responded throughout the power band and it didn’t die out even up to 7000+rpms with full boost.
I’ve been an old school Motörhead forever. But I don’t think I’d ever go back to a carb again. Actually, I’m going even more modern. I’m in the process of swapping that Procharged 416 for a 426 Gen 3 Hemi with a 3.0 L Whipple Supercharger.
I finally decided to swap to the Sniper and it was different car. Just reach in and turn the key and it would fire right up and idle smooth as day. Cut the fumes smell down by a lot too, throttle responded throughout the power band and it didn’t die out even up to 7000+rpms with full boost.
I’ve been an old school Motörhead forever. But I don’t think I’d ever go back to a carb again. Actually, I’m going even more modern. I’m in the process of swapping that Procharged 416 for a 426 Gen 3 Hemi with a 3.0 L Whipple Supercharger.
MobileCustoms
You can twist perceptions, reality won't budge
Well for whatever it's worth, I brought my 530 horse 340/416 Barracuda to the strip for the first time last weekend at the Mopar showdown. At the last minute, I had a fuel issue with my 750 Brawler that I couldn't sort out in time, so I swapped it for my my spare 600cfm Holley and ran it just so I could make the event that I already paid for and rented a trailer for.
I didn't expect much at all out of it and was pleasantly surprised when it ran a 12.85@104.5mph with 4.10 gears. Still very fun! It also surprised the other racer friends that were there.
I don't even remember what jets are in it but I had it setup for my old van 6 or 7 years ago and hadn't used it since then. My afr gauge showed it wasn't running lean throughout the runs.
I didn't expect much at all out of it and was pleasantly surprised when it ran a 12.85@104.5mph with 4.10 gears. Still very fun! It also surprised the other racer friends that were there.
I don't even remember what jets are in it but I had it setup for my old van 6 or 7 years ago and hadn't used it since then. My afr gauge showed it wasn't running lean throughout the runs.
I haven't seen one of those in years.
I had one in the late 80s, and wanted to try one again. I had a small block Mopar in a '61 F100. This one is in my '67 D100. The MSD box in the picture is the same one that was in the F100 way back when.
mygasser
Well-Known Member
i would have said the same dan, but i recently did some work on a late 30's nash lafayette gasser that had a 454 bbc with a tunnel ram and 2 of those predators. a pretty oddball combination for sure.
neil.
Sounds like a oddball combination.
We had a Henry J gasser roaming the streets in the early 80's here in LC Valley that sported a 454 bbc with a pair of predators, actually there was a few guys using them.
There's a guy with a 68 Buick GS stilling using the same predator he had in the 80's.
Gator
Mopar or No Car
In my 408 SB Stroker I am running a 750 Holley DP along with an electric pump and psi regulator set at 6psi. Runs great.
MidnightSwinger
Well-Known Member
My MP crate 408 loved the 800 avs2 on the street. Excellent street manners and nasty when opened up.
TimS
Well-Known Member
The 750 Holley and AVS2 sound like good options?
Thanks.
Thanks.
RAMM
Well-Known Member
You are no dummy. It's all about signal. J.Rob
RAMM
Well-Known Member
It depends on the booster. Booster technology has gotten better in the last five years or so.
I don’t do pump gas engines without them any more. The only exception is the 395 that came off the dyno a few months ago.
It was a 650 and he wanted to keep the carb. It’s too small for that many inches so I didn’t change the boosters.
A good annular booster will not reduce airflow 1 CFM.
RAMM
Well-Known Member
You guys need to grab some calipers and study, venturi/size/exit/entry. .I've said too much. EFI is not the way....too keep your man card. J.Rob
I agree with this^^^
Icetech
Well-Known Member
TimS
Well-Known Member
I’m running a Weiand Stealth intake.
Also due to the lack of vacuum, the original power brake booster was removed and is running manual brakes now.
If I want to swap to an AVS 2 will this lack of vacuum effect secondary opening carb performance?
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There are some who understand the need for "idle bypass air" when your Hg starts getting below 15 inches and you want to tune a clean transition from idle circuit to transfer slot. The Carter and carter copy is not user friendly in this situation, but it can be done. I'm at 4700 altitude and opened the air bleed a couple of thou in the primary air horn for my sons 360 with some luck.
Attached is a video on secondary air valve adjustment. If you want to understand idle bypass and air bleed affect on tuning get Cliff Ruggles quadrajet book from amazon. All carbonators hav ethe same circuits in different configurations, but Ruggles explains the effect of low vacuum and the calibration need to maintain proper afr though idle/transfer and main circuit load.
Perhaps there is a good Holley or Carter book out by now, but there are few carb shops who publish their carter air bleed and idle down channel tuning on the net. Its there, but the information is often on message boards in closed groups.
Good luck!
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Tim.
Idle vacuum, high or low, does not affect the operation of the sec air valve. Air speed [ engine rpm ] in the secondary barrels create suction [ vacuum ] on the air valve as rpm increases. When that is high enough, it overcomes the AV spring & opens the AV. You are good to go.
Idle vacuum, high or low, does not affect the operation of the sec air valve. Air speed [ engine rpm ] in the secondary barrels create suction [ vacuum ] on the air valve as rpm increases. When that is high enough, it overcomes the AV spring & opens the AV. You are good to go.
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