4bbL vs weber or stack for max hp from 302

Bob

Supporter
My favorite thing about Weber’s is that you can see between them thru rear view mirror.
Know that cameras can accomplish this also but prefer the old mirror.

Have 48 idas bigger chokes on a 427w
with a matched cam pulls hard.
Took a high end fuel injection off can’t say I miss it.
The sound and the way Weber’s run are a good time.
 
I started my SBF conversion in my Lotus esprit with a 4 barrel holley. It was simple and worked fine, and seemed to make pretty big power right out of the gate without a lot of tuning or mucking around with it. I only drove the car maybe 50 miles with the holley.

I got it in my head that it would be nice to see ITB's in the rear view, and also improve the power and driveability of the car. So, I installed ITB's. It runs well, but I don't think there's any more power according to the seat dyno. However, the car starts from cold and idles better and has a dead reliable warm idle and part-throttle smoothness to it now which wasn't the case with the 4 barrel holley.

So, net, my experience has been that the ITB's aren't about making more hp/torque, but rather improving general driveability. The AFR is well controlled across the full range of conditions, which isn't possible with the more static state of tune of the holley.
 

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I don't think you can compare ITB's (EFI) with carbs. ITB's don't have restrictive chokes in them and flow way more cfm compared with IDA's or IDF's in the same size's.
 
Anyone have dyno sheets from before & after?

Torqueband RPM range & BHP range

Weber IDF vs IDA?
Does size matter or hurts.. IDA came in 48, but if you go IDF you could go smaller (44IDF) to get better responce Ill guess, or is bigger better just compansate with smaller chokes..
 
My favorite thing about Weber’s is that you can see between them thru rear view mirror.
Know that cameras can accomplish this also but prefer the old mirror.

Have 48 idas bigger chokes on a 427w
with a matched cam pulls hard.
Took a high end fuel injection off can’t say I miss it.
The sound and the way Weber’s run are a good time.
Be less expensive to get an artist to paint the weber image on rear window then and fit a 4bbl, best of both worlds.
 

Mike Pass

Supporter
I guess it's down to what you want to use it for.
Road, road with a bit of track or track mainly. For track use you want power and it's not too important if it is easy to drive at low speeds. That kind of cammy engine would be a nightmare on the road especially in traffic on a hot day. We used to run a Davrian with an Imp race engine which ran to 10,000rpm but nothing below 5,000rpm. Great on track but otherwise undriveable.
Quad Weber IDAs are very original especially in the "side to side" rather than "back to back" configuration and are more of a race type carb rather than the IDFs. You have one choke to one cylinder which means that at low rpm the carb does not get a good signal and so getting it too give a good fuel/air mix at low rpm small throttle opening takes a bit of fiddling. Also cams with a lot of overlap don't help to get a good signal to the carbs. At wide open throttle and high rpm each cylinder has only one opening to draw from. A 302 would probably have 37mmm venturis so there may be some restriction to air flow depending on what the heads can flow.
A Holley 4 barrel is quite different with one choke per two cylinders. It gets a better low rpm/ small throttle opening signal as there are two cylinders drawing on each choke. Better signal but less flow capacity per cylinder. At higher rpm however each cylinder "sees" four chokes especially with a single plan manifold with a large plenum in the centre of the inlet manifold. This is why the Holley is good at high rpm. The extreme form of this is the tunnel ram which is a tall single plane but is very much a race setup. The dual plane manifold is better at low rpm than a single plane as half the carbs two chokes feed four cylinders (two on one bank and two on the other. The carb is effectively split down the middle with each half feeding two on one side and two on the other. So at low rpm with only the primary chokes open one primary choke is feeding four cylinders and so so there is a good signal flow to the carb so good low rpm performance. A dual plane can be helped at high rpm where each cylinder "sees" only two chokes whereas with a single plane inlet each cylinder "sees" four chokes. The divider between the two sides can be cut down to allow some "single plane effect". The Edelbrock air gap manifold has a piece cut out of the divider as standard. The more that is cut away the more the manifold will behave like single plane. I use a dual plane Edelbrock with a thin open spacer to get the same effect. The inlet runners on a dual plane are longer than on a single plane which is also better for low rpm.
A Holley vacuum secondary has the secondary choke butterflies open ed by a diaphragm system and will open when the inlet manifold pressure reaches a certain value. On the double pumper Holley there is a mechanical linkage from the primary side to the secondary side and the secondaries are opened at a point when the primary side is open at a set amount. The point of secondary opening can be altered. These carbs are called double pumpers because both primary and secondary chokes have an accelerator pump system which sends a shot of fuel as the throttle is snapped open. The vacuum secondary only has pump jets on the primary chokes. The mechanical secondary double pumper types are more responsive to driver input. The double pumpers are more performance orientated and the vacuum secondary types are good for road use. You can juggle the two. I have a vacuum secondary for economical road use and a bigger double pumper when I want a bit more zip. With both piped up ready I can change over in 10 minutes.
The Holley Sniper type of throttle body works like a 4 barrel carb and theoretically should work better as it should meter exactly the right amount of fuel for all circumstances but needs a high pressure fuel setup and some dyno or rolling road time to get the correct setup. The eight stack injection setup has a much bigger actual choke area as it does not need the venturis to create low pressure to drag the fuel into the airstream. It has the same one choke per cylinder as the quad carb setup but the effective choke area is much bigger so the flow is limited by the heads flow ability.
I prefer low and midrange torque rather than high rpm power especially in a road car. My money goes with the double pumper Holley on good dual plane manifold. Cheap, easy to set up, no need for high pressure pumps, swirl pots or ecus, easy to rebuild, lots of spares available, reliable. I buy them used and rebuild them but then again I am a cheapskate!
Cheers
Mike
 

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Neil

Supporter
I agree with Mike except for his choice of a traditional Holley 4-barrel carburetor. In recent years Holley and others have addressed its shortcomings and introduced a more advanced version, a Holley "Ultra". Other companies have upgraded offerings as well. The later versions offer improvements such as a glass window float level indicator (no more unscrewing a brass plug and spilling gas on a hot engine), 4-corner idle adjustment, various replaceable air bleed jets, a machined aluminum body rather than a zinc casting, etc, etc. I investigated the alternative choices and replaced my faulty 850 Holley double-pumper with a Proform 850 "race version" carburetor. It fits in place of a traditional Holley 4 barrel perfectly.
 
I am a carb specialist so know how to handle them all. Did several 48IDA's. IDF's DCOE's DCN-F's etcetera.

In my case, Rover 3500. run-in will be with an Offenhauser Dual Port 360 and a modifiet Holley 390.
Custom grind Compcams 275' intake - 280' exhaust @ .005 lift ( 224 - 230 @ 0.050) with Rhoads lifters.
Compcams did the math for this intake & Rhoads lifters & carb setup.

I do have a brand new Quad Weber IDF set for this engine, with four new 40 IDF carbs just lying around...
 
Richard Holdener has tested a huge bunch of stuff on US V8s (his channel has a wealth of real dyno testing info in it), IR systems among them.

Have a look at this - I think this is a typical set of trends for EFI ITBs vs open plenum short runner. Obviously not relevant to carb'd IR set-ups.


Cheers, Andrew
 

Kevin Box

Supporter
This whole thing about 4 barrel vs IDA vs 4 barrel throttle body with modified 4 barrel intake vs Individual Throttle body injection is all seat of the pants stuff.
There's no doubt a 4 barrel carb on a decent intake will make good power and is easy to get going reasonably well.
Everything from there gets harder
Firstly IDFs or IDAs are only as good as their setup and a lot of guys do not even have the know-how to get them synchronized let alone tuned with their many jetting options and emulsion tube choices. Once setup by someone who knows their stuff they are brilliant but in saying that you need to really look at how big each cylinder is and compare that to the recommended application for IDAs or IDFs as once you get past about 320 Cubic inches they may not be delivering enough air for a high horsepower engine.

Next in line is the 4 Barrel intake with injectors and a huge throttle throttle body. In most cases these come with some form of self tune. With this option you get all the benefits of an EFI with the simplicity in setup of a four barrel (no carb sync issues) and the thing flows as much as you need. It will start nicely when cold and as it warms up it will still behave nicely with no idle issues or stalling. It will make more power than the equivalent 4 barrel since its not fighting with a venturi.

Lastly there is the ITBs in its various forms from slide throttles to 8 individual throttle bodies and everything in between. Just the setup of getting these mechanically operating well is quite daunting to most would be DIYers so lots of rocks get chucked at them as being cranky and fussy to get going probably with just cause for their complexity. However you don't have to go far in motorsport to realize that the people who are enjoying excellent broad torque range motors with high top-end power are running these setups. Examples start top end motorcycles, rally cars, track cars of all types from single seaters to saloon cars, power boats etc etc. I guess what really sums it up is you don see F1 cars or Indy cars running carbs do you????? But make no mistake, the journey to get here is an arduous one compared to the common old 4 barrel. Firstly you need to get the thing mechanically setup with linkages and syncing being being an interesting journey. Next you need a cam that matches your combination. The design of the cam and intake should be melded and take into account the intake volume behind the valve vs RPM & Torque intended. Another detail that is often over looked is idle mechanism with common options being and idle air valve feeding small line to each throat through to idle up solenoids or stepper motors adjusting the mechanical idle point. Assuming you have also sorted out your fuel delivery you can now start tuning and if you are lucky the company who supplied you ECU will give you something reasonable as a set of fuel and ignition maps to start with. You should plan on one day for your first visit to the dyno to get a good tune and then another day once you have driven it a bit to get the dyno man to trim it a bit to suit your driving and sense of how it performs. It may be only am matter of changing the fuel enrichment on acceleration change to make it pull out of corners nicely or a wider tune change to help in other areas but DON'T skip on this visit as it will make the most difference. You may also need some cold engine parameters changed to improve the warm up sequence. Once you're there it will be very rewarding and should stay in tune well.

Something overlooked in the above is mechanical fuel injection such as Hilbourne, Enderle etc. These systems achieve a vary similar result to EFI individual throttle bodies with various bypass valves assisting in matching fuel delivery to RPM but their low end response, idle is no where near as good.

Cheers KevinB
 
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Bill Kearley

Supporter
It took some time but when I chose the Borla 8 stack and Holly HP then used a local shop that had a dyno things worked out well. I made an exhaust deflector and spent some time to sync things. Real world operation on a track, I don't know yet but it works well on the street. First set up and break in was with a Holly 750 then switched to the 8 stack. The end result was 530 HP ( carb ) to over 600 ( 8 stack ) . All that probably a mistake but very drivable.
 
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