Topic: 4bbl or 2bbl

So the Cordoba is running pretty well but of course it needs to go faster because it just does. Currently it is a stock low compression smog 400 Mopar big block with about 190 net rated HP. The cam is the mildest street cam I could buy for it from Crane.  I have a large 500 cfm Holley 2bbl on it and it has been very reliable with no performance issues. No hesitation or driving issues at all.

My team and I have discussed installing a 4bbl on it to get some more HP. (would that be maybe 25 add’l hp?)
However, when I use the carburetor calculator formula that I found .

CFM = Cubic Inches x RPM x Volumetric Efficiency ÷ 3456.

and I put in the max rpm of 4600 ( I have a Rev limiter on it ) and I use .85 efficiency  ( which I think is optimistic ) it computes to only needing  452 CFM

452 CFM = 400 x 4600 x.85 / 3456


Using this math, I would only need a bigger carb if she runs faster than 5000 rpm.

So….My question to Lemons World is …..  Do you agree…am I missing something?  This stuff is way above my pay grade.

Cordoba

2 (edited by chaase 2022-04-20 10:46 AM)

Re: 4bbl or 2bbl

Carb sizing is basically voodoo/magic. There are a lot of factors including the use,500CFM is probably sufficient at those RPM but I have seen some articles saying go a little on the higher side for race situations. Street cars don't end up running high RPM for as long as we do on the track so some argument can be made for going up a little bit.

In that respect, what are you using for an exhaust? The cars from that era had terribly restrictive manifolds and you would need to replace that with headers to even be able to use the extra CFM.  If you haven't done so, you can also hook up a wide band 02 setup pretty easily and run a gauge to see what your A/F ratio look like on the track.


EDIT: We use a 650 4 BBL on the AMC 360 in the Javelin but that can run at higher peak RPM if we want to (We just don't). We use a more aggressive cam and rocker ratio in our setup though,

1992 Saturn SL2 (retired) - Elmo's Revenge -  Class B winner, Heroic Fix winner x2
1969 Rover P6B 3500S(sold) - Super G-Rover - I.O.E Winner, Class C Winner
1996 Saturn SW2 - Elmo's Revenge (reborn!), Saturn SL1  Dazzleshipm Class C winner
1974 AMC Javelin - Oscar's Trash heap - IOE,”Organizer's Choice" and "I got Screwed" award winner

Re: 4bbl or 2bbl

Jimmy wrote:

So the Cordoba is running pretty well [snip].

Currently it is a stock low compression smog 400 Mopar big block [snip]

and it has been very reliable with no performance issues. No hesitation or driving issues at all.
[snip]

I think it needs a turbo.

Re: 4bbl or 2bbl

Lemon_Newton-Metre wrote:
Jimmy wrote:

So the Cordoba is running pretty well [snip].

Currently it is a stock low compression smog 400 Mopar big block [snip]

and it has been very reliable with no performance issues. No hesitation or driving issues at all.
[snip]

I think it needs a turbo.

You can't go wrong with a turbo

1992 Saturn SL2 (retired) - Elmo's Revenge -  Class B winner, Heroic Fix winner x2
1969 Rover P6B 3500S(sold) - Super G-Rover - I.O.E Winner, Class C Winner
1996 Saturn SW2 - Elmo's Revenge (reborn!), Saturn SL1  Dazzleshipm Class C winner
1974 AMC Javelin - Oscar's Trash heap - IOE,”Organizer's Choice" and "I got Screwed" award winner

Re: 4bbl or 2bbl

Three votes for turbo.

Eric Rood
Everything Bagel, 24 Hours of Lemons
eric@24hoursoflemons.com

Re: 4bbl or 2bbl

chaase wrote:

Carb sizing is basically voodoo/magic. There are a lot of factors including the use,500CFM is probably sufficient at those RPM but I have seen some articles saying go a little on the higher side for race situations. Street cars don't end up running high RPM for as long as we do on the track so some argument can be made for going up a little bit.

In that respect, what are you using for an exhaust? The cars from that era had terribly restrictive manifolds and you would need to replace that with headers to even be able to use the extra CFM.  If you haven't done so, you can also hook up a wide band 02 setup pretty easily and run a gauge to see what your fuel trims look like on the track.



It has the factory exhaust manifolds but does have back yard bubblegum welded / pieced together 2 1/4" duals going thru turbo style mufflers.

Good thinking on the fuel ratio - That would be a very good indicator if the carb was too small, . .  . I do have an AEM 02 sensor.  I try to keep an eye on it. . Its hard to look at that while racing but the fuel ratio is normally between 12 and 13.  That’s with whatever jets the carb came with.  I did adjust the idle screws a little to fatten it up

The plugs look good after a few races - grayish black ...Not super white or dry .  I don’t think its running lean. (also -the car does stay cool - almost never runs hotter than 190 degrees)

The way I am thinking is  - a 4bbl probably won’t help much ...maybe a little, but I could also be opening up pandoras box for over fueling or stumbling or some other gremlin. And I guess at partial throttle the 2bbls might actually have more cfm avail before the secondaries open on a comparative 4bbl. That where I get confused - and like you said the voodoo comes into play. Really Appreciate the input.

Cordoba

Re: 4bbl or 2bbl

therood wrote:

Three votes for turbo.


Turbo…. really ……Turbo? ….. I can barely gap a spark plug correctly and you all suggest a Turbo. 

But …. It would be magnificent.

Cordoba

8 (edited by chaase 2022-04-20 12:15 PM)

Re: 4bbl or 2bbl

Jimmy wrote:

It has the factory exhaust manifolds but does have back yard bubblegum welded / pieced together 2 1/4" duals going thru turbo style mufflers.

Good thinking on the fuel ratio - That would be a very good indicator if the carb was too small, . .  . I do have an AEM 02 sensor.  I try to keep an eye on it. . Its hard to look at that while racing but the fuel ratio is normally between 12 and 13.  That’s with whatever jets the carb came with.  I did adjust the idle screws a little to fatten it up

The plugs look good after a few races - grayish black ...Not super white or dry .  I don’t think its running lean. (also -the car does stay cool - almost never runs hotter than 190 degrees)

The way I am thinking is  - a 4bbl probably won’t help much ...maybe a little, but I could also be opening up pandoras box for over fueling or stumbling or some other gremlin. And I guess at partial throttle the 2bbls might actually have more cfm avail before the secondaries open on a comparative 4bbl. That where I get confused - and like you said the voodoo comes into play. Really Appreciate the input.

I would investigate the exhaust manifolds and see what info you can find. The mid-late 70s were notorious for heavy exhaust restrictions. Anything you do for extra power will require that the exhaust be able to handle the flow out. Bigger carb, cam, turbo charger, etc won't do squat if the exhaust doesn't flow properly.

EDIT: If the exhaust is flowing properly, I can see a 4 bbl manifold and carb helping get some more oomph into it. It will be more on the top end so you may not want or need it. One other thing to check is what other vehicles in that era had the 400 as an option. If they had 2 and 4 BBL choices that will give you an indication of what gains are to be had moving to a 4 BBL setup.

1992 Saturn SL2 (retired) - Elmo's Revenge -  Class B winner, Heroic Fix winner x2
1969 Rover P6B 3500S(sold) - Super G-Rover - I.O.E Winner, Class C Winner
1996 Saturn SW2 - Elmo's Revenge (reborn!), Saturn SL1  Dazzleshipm Class C winner
1974 AMC Javelin - Oscar's Trash heap - IOE,”Organizer's Choice" and "I got Screwed" award winner

Re: 4bbl or 2bbl

Jimmy wrote:
therood wrote:

Three votes for turbo.


Turbo…. really ……Turbo? ….. I can barely gap a spark plug correctly and you all suggest a Turbo. 

But …. It would be magnificent.

A low pressure turbo would be glorious!

1992 Saturn SL2 (retired) - Elmo's Revenge -  Class B winner, Heroic Fix winner x2
1969 Rover P6B 3500S(sold) - Super G-Rover - I.O.E Winner, Class C Winner
1996 Saturn SW2 - Elmo's Revenge (reborn!), Saturn SL1  Dazzleshipm Class C winner
1974 AMC Javelin - Oscar's Trash heap - IOE,”Organizer's Choice" and "I got Screwed" award winner

Re: 4bbl or 2bbl

Jimmy wrote:

I can barely gap a spark plug correctly and you all suggest a Turbo.

The beauty of this plan is that when the turbo tears itself apart, the proper plug gap won't really matter.

1982 MG Metro 1300: IOE 2015 Pacific Northworst GP, Longest Distance 2010 Cd'L Box Wine Country Classic
1980 KV Mini 1: Worst of Show and Fright Pig Supremo 2009 Concours d'Lemons
1978 H Special: Second-Round Elimination 2010 Lemons Pinewood Derby at Sears Pointless
1967 SAAB 96: IOE 2012 Pacific Northworst GP, Organizer's Choice 2022 Hell on Wheels California Rally

Re: 4bbl or 2bbl

chaase wrote:
Jimmy wrote:
therood wrote:

Three votes for turbo.


Turbo…. really ……Turbo? ….. I can barely gap a spark plug correctly and you all suggest a Turbo. 

But …. It would be magnificent.

A low pressure turbo would be glorious!

I have an extra turbo from a GM 6.5l Tdi; just sayin' ...

Re: 4bbl or 2bbl

There's gotta be some weight reduction somewhere in all that rich corinthian leather... Talk to Pagel about what constitutes crash structure and what doesn't and start cutting.

World record simca driver, kei car owner, zymurgist
1989 Merkur XR4Ti - Project Merkur Space Program - Winner "Halloween Meets Gasoline" The Pitt Maneuver 2022
1980 Dodge Challenger: Most Extreme eLemonAtion Challenger (Rust Belt Ramble 2021 Dishonorable Mention)

Re: 4bbl or 2bbl

Jimmy wrote:

Good thinking on the fuel ratio - That would be a very good indicator if the carb was too small, . .  . I do have an AEM 02 sensor.  I try to keep an eye on it. . Its hard to look at that while racing but the fuel ratio is normally between 12 and 13.

The plugs look good after a few races - grayish black ...Not super white or dry .  I don’t think its running lean. (also -the car does stay cool - almost never runs hotter than 190 degrees)

The way I am thinking is  - a 4bbl probably won’t help much ...maybe a little, but I could also be opening up pandoras box for over fueling or stumbling or some other gremlin. And I guess at partial throttle the 2bbls might actually have more cfm avail before the secondaries open on a comparative 4bbl.


AFR is important to know, but it won't tell you if the carb is too small. All it lets you know is if you have the correct amount of fuel for the air flowing through the carb to achieve your desired AFR.

Sadly, your AEM O2S is a narrow band sensor, and provides about the same level of information as looking up into the sky to place the Sun for determining time of day. You get a general idea of AFR, but the narrow band sensors bounce around a lot.

Looking at your plugs is a good way to get closer to proper AFR for the situation, but you have to be careful about how loaded the engine was before you shut it down. If it idles for a while and your idle AFR is lean the plugs will be cleaner than when it's loaded, and vice versa.

Now on to the meat...If you ran a 500 CFM 2BBL and a 500 CFM 4BBL at WOT they should come close to making the same level of power. However, manifold accommodations made to fit each one can change the power level somewhat. Where the 4BBL is superior, all other things being equal, is how fast the air flows through the primaries to feed the engine. Smaller diameter primaries of the 4BBL mean that the air has to move faster to get the same volume through. Higher air velocity means more inertia, and better air/fuel mixing. This means that the engine is more efficient, with a bit more cylinder filling at part-throttle. That means more torque at lower engine speeds, and better acceleration out of the corners. Opening the secondaries would then provide the max power available with 500 CFM.

You will notice a more responsive throttle with a 600 CFM 4BBL over a 500 CFM 2BBL, AND you can control when and how fast the secondaries open.

Another benefit is somewhat better fuel economy, due to the greater efficiency of the smaller primaries.
Quite literally, YMMV.

(If I have made any errors in the above reasoning, would someone with greater knowledge please correct me. I don't want to propagate "bad" information.)

Capt. Delinquent Racing
RUST-TITE XR4Ti - '21 ARSE-FREEZE-APALOOZA  I Got Screwed
The One & Only Taurus V8 SHO #31(now moved on to another OG Delinquent)
'17 Vodden the Hell - (No) Hope for the Future Award, '08 AMP Survivor, '08 ARSE-FREEZE-APALOOZA Mega-Cheater

Re: 4bbl or 2bbl

I think all the turbo folks got it wrong.  You need a supercharger and throttle body fuel injection.  I mean TBI is basically just carb with the jets removed and "fuel dribblers" set on top of each barrel.

15 (edited by Jimmy 2022-04-21 07:10 AM)

Re: 4bbl or 2bbl

Preach on!

I knew I would get good Ideas and discussion from this forum. I can’t tell you how much I appreciate it.  Building these cars is a lot of fun and this makes it all the more so.



BTW - Instead of counting sheep last night ....... I was thinking on how to plumb a turbo.

Cordoba

Re: 4bbl or 2bbl

Jimmy wrote:

[snip]
BTW - Instead of counting sheep last night ....... I was thinking on how to plumb a turbo.

The piece I have is sitting in climate controlled storage about 10 minutes from Collegeville, in case you'd like to eyeball it for fit...

Yes, it's a relatively low pressure turbo.

No, the way I earn a living does not include "The first one is free" as a marketing strategy.

Re: 4bbl or 2bbl

Turbo would be cool. Supercharger neat too.
Probably will gain a lot more with Intake manifold and headers. 500cfm carb for those rpms is totally fine.

https://www.facebook.com/greatglobsofoil/
This car....Is said to have a will of it's Own. Twisting its own body in rage...It accelerates on.
1978 Opel/Buick Isuzu(C>B>C>B) 1996 Ford Probe GT(B), 1996 Nissan Maxima OnlyFans (B)

Re: 4bbl or 2bbl

We played around with various carbs on a Ford 5.0 and wound up with a relatively high-CFM two-barrel.  I don't recall the numbers, but I want to say it was a circle-track part,

We wound up two-barrel for driveability reasons.  We couldn't tune around the lump in power delivery that occurred when the secondaries on the four-barrel opened, and the two-barrel was nice and linear.

Other than yellow flags we didn't spend much time at steady-state part throttle, so the economy advantages of the four-barrel weren't really relevant. 

Power numbers were pretty much the same.

Steering the car on the throttle through corner exit was much more predictable on the two-barrel.

Re: 4bbl or 2bbl

hoverducky wrote:

We wound up two-barrel for driveability reasons.  We couldn't tune around the lump in power delivery that occurred when the secondaries on the four-barrel opened, and the two-barrel was nice and linear.

Was the above carb vacuum secondary or double pumper?
The 650 DP on our 5.0L is very predictable and linear.
I set it up so that the secondaries open later, but more quickly.

I agree that the 500 CFM is adequate for what the OP is doing.
It may also prevent over-revving the engine as it strangles the
engine above 5000 RPM.

Capt. Delinquent Racing
RUST-TITE XR4Ti - '21 ARSE-FREEZE-APALOOZA  I Got Screwed
The One & Only Taurus V8 SHO #31(now moved on to another OG Delinquent)
'17 Vodden the Hell - (No) Hope for the Future Award, '08 AMP Survivor, '08 ARSE-FREEZE-APALOOZA Mega-Cheater

Re: 4bbl or 2bbl

You're not going to get any more power out of a 4bbl over your current 2bbl aside from some small induction efficiencies. Definitely not 25 more HP.

That's going to require real work on the rotating assembly. to get more out of the 4600 RPM and or bringing that RPM up to 6000 with all the fancy $$ needed to keep it in one piece spinning that fast.

190 NET is pretty damn bad. As deeply indivisible as it is. That jank turbo is probably a legit option short of decking and stroking the thing to a 440 and a new cam.

At which point an engine swap may be just as easy because the 400 is not a Summit Racing golden child engine.

Mistake By The Lake Racing (MBTL)
88 Thunderbird "THUNDERBIRDS ARE GO!", Ex Astris, Rubigo / Semper Fracti
A&D: 2014 Sebrings at Sebring (NSF), 2014 NJMP2 Jurassic Park (SpeedyCop), 2012 Summit Point J30 (PiNuts)
2018 Route Sucky-Suck Rally Miata, 2019 World Tour Of Texas 64 Newport

Re: 4bbl or 2bbl

Unless you are going to swap the intake, go with headers, I see no reason to go to a 4bbl. Not a chance you pick up 25hp from a carb swap. If you want 25+ swap the intake and mani's out.

"get up and get your grandma outta here"

Re: 4bbl or 2bbl

I would recommend 8 SU carbs sticking up through the hood.  Definitely slower, but just think about how cool it'd look!

1977 Lancia Scorpion

Re: 4bbl or 2bbl

box the frame rails, then pressurize the frame and cage with NAWWWWSSSSSSSSSSS.

Re: 4bbl or 2bbl

Mr.Yuck wrote:

Unless you are going to swap the intake, go with headers, I see no reason to go to a 4bbl. Not a chance you pick up 25hp from a carb swap. If you want 25+ swap the intake and mani's out.

I would do all three. Headers, 4 BBL intake and 4 BBL carb.It's a Cordoba so its not like it's going to get laps in BS.

1992 Saturn SL2 (retired) - Elmo's Revenge -  Class B winner, Heroic Fix winner x2
1969 Rover P6B 3500S(sold) - Super G-Rover - I.O.E Winner, Class C Winner
1996 Saturn SW2 - Elmo's Revenge (reborn!), Saturn SL1  Dazzleshipm Class C winner
1974 AMC Javelin - Oscar's Trash heap - IOE,”Organizer's Choice" and "I got Screwed" award winner

25 (edited by Lemon_Newton-Metre 2022-04-27 07:38 AM)

Re: 4bbl or 2bbl

chaase wrote:

I would do all three. Headers, 4 BBL intake and 4 BBL carb.It's a Cordoba so its not like it's going to get laps in BS

.

chaase wrote:
Lemon_Newton-Metre wrote:
Jimmy wrote:

So the Cordoba is running pretty well [snip].

Currently it is a stock low compression smog 400 Mopar big block [snip]

and it has been very reliable with no performance issues. No hesitation or driving issues at all.
[snip]

I think it needs a turbo.

You can't go wrong with a turbo

And a turbo...

;-)