IDAs, CFM, and My Combo

[Chris]

Hello everyone,

I hope this will turn into the end-all, be-all final IDA thread discussing IDAs, their limitations, and what any engine combo really needs.

First, my combo:
351W stroked to 393
12.25:1 c/r
Trickflow Twisted Wedgies flowing 306cfm @ .600
Trickflow Stage 3 cam (Adv Dur 298/325,Lift: .574/.595, Dur @ .050" 236 int./248 exh.)

Let's say it spins to 7k RPM.

So, how do I figure out my CFM needs?

I'm no stranger to IDAs (and no expert) but I'm pretty sure they won't flow enough. I've never flowed mine; however, the numbers I've seen on the internet range from 310-340 @ 20" water with a 44mm vent. That sounds about right.

Finally, I'm really interested in finding a way to make IDAs work. What do you guys think?

My last resort is a 4 barrel...!

Thanks, Chris
​

 

[Terry Oxandale]

Hi Chris,

Welcome to the site!

There are some very good strings related to this very question in the archives (search feature) that debated the individual vs common plenum attributes. To be best of my recollection, the 48 IDA (even with a 44 choke) will be marginal at 7k, even before the stroker is added into it. There was even discussion about fabricating a plate that allowed a narrow common plenum to increase the 'instantaneous' air flow capability per bore.

Terry

 

[Chris]

(search feature)

Hi Terry and thanks for the reply.

I've been lurking here for some time and have used the search feature extensively. I think I've read all the IDA ones; however, I may have missed a thread.

If you know of one that conclusively says how much CFM my engine needs or that an IDA just won't work, I would really appreciate that.

Thanks,
Chris

 

[Jim Rosenthal]

You could look at CB Performance for bigger IDAs; I think they have 52mm or 58mm IDAs. It's hard to imagine that 48MM IDAs wouldn't do it, though, since some really large engines have been set up with Weber IDAs.

 

[Ron Earp]

There are a lot of cars setup for 48mm webers but that doesn't mean they are getting all they can from the motor....because a 48mm Weber has a smaller than 48mm choke.

http://www.gt40s.com/forum/gt40-tec...k-power-choke-size-8-barrel-venturi-size.html

Once the motor gets some cubes and the max RPM goes up the standard weber seems inadequate (from the Weber tuning book and formulas, not me). I just graphed them for ease of visualization.

 

[Ron R.]

I'll keep an eye on this thread, as my set up is not too different from yours, and I've got some decisions to make.

 

[Mike Huddart]

Or you could try one of these.
Photos that Mick Sollis sent me of his Southern GT at the Goodwood track day on Saturday.
In case you're wondering it's our 347 Dynaformance/ Accel EFI motor.
Apparently it went rather well !
Mike

 

[MICK.(southerngt)]

After driving on webbers for many years with the gt40 the change to fuel injection was quite a shock it totally transformed the way the car drives making it so much smoother right through the rev range it also starts easier and the fuel guages dont go from full to empty between petrol stations.Also it went from 450 hp to 490 on the dyno.
regards mick.

 

[Andrew Robertson]

I'm no stranger to IDAs (and no expert) but I'm pretty sure they won't flow enough.​

​

Hi, in my opinion an engine like yours that breathes well probably needs 2 1/4 inches of throttle plate per port in an IR application - and nothing dangling in the airstream - that pretty much rules out IDAs, and I think puts you squarely in the domain of an IR EFI set-up if you want 8 stacks.

I think 48s would compromise your set-up above 5k, and given your cam and intended powerband, that seems quite a limitation.

Cheers, Andrew Robertson

 

[Mike Huddart]

Hello everyone,​

I hope this will turn into the end-all, be-all final IDA thread discussing IDAs, their limitations, and what any engine combo really needs.​

First, my combo:
351W stroked to 393
12.25:1 c/r
Trickflow Twisted Wedgies flowing 306cfm @ .600
Trickflow Stage 3 cam (Adv Dur 298/325,Lift: .574/.595, Dur @ .050" 236 int./248 exh.)​

Let's say it spins to 7k RPM.​

So, how do I figure out my CFM needs?​

I'm no stranger to IDAs (and no expert) but I'm pretty sure they won't flow enough. I've never flowed mine; however, the numbers I've seen on the internet range from 310-340 @ 20" water with a 44mm vent. That sounds about right.​

Finally, I'm really interested in finding a way to make IDAs work. What do you guys think?​

My last resort is a 4 barrel...!​

Thanks, Chris​

I think were all missing something here, have you actually got all these parts for your motor or is it a wish list.
By the flow numbers I take it the heads are something like their 190 cc as cast, these are going to struggle to make big numbers anyway so maybe the Webers WOULD work.
12.25 comp, is this a good idea with small heads on a big motor in a street car AND Webers.
That cam is a Crane 449641 hydraulic roller so it's never going to rev to 7000 anyway and with 110 lobe separation is NOT the cam for Webers on a big motor or ANY motor for that matter. If you want to cover your windscreen (or with a GT40, the exhaust,) with fuel vapour above 5500 then, please, carry on.
If you REALLY DO want to run Webers then you pick the Webers first and build the motor to suit them, not the other way 'round.
Just my two pennerth, Mike

 

[Scott Calabro]

I wish someone would develop and sell a mass airflow setup with the Weber look!

An 8 stack speed density system would seem to be as much trouble to initially set up as the carbs can be, never mind the increased complexity of the overall fuel system for FI.

 

[Mike Huddart]

I wish someone would develop and sell a mass airflow setup with the Weber look!

An 8 stack speed density system would seem to be as much trouble to initially set up as the carbs can be, never mind the increased complexity of the overall fuel system for FI.

Spoken like a true dinosaur, have you tried one, actually very little trouble to set up.
Forget all this Mass Flow self learning crap, you need something that you have total control over.
With gas prices in the UK soon to reach $12.00 a gallon even you might start to think about EFI.
30 MPG, go on, you know you want one !
Mike

 

[Scott Calabro]

Some old dogs really can't learn new tricks.

I don't want or need "Total Control" as far as I'm concerned, the entire reason to have EFI to begin with is so its does not have to be messed with.

Different strokes I guess.

By the way, the cost of fuel should be the last concern when you own a toy like a GT40, and good luck re couping the cost of ANY EFI in fuel savings.

If you cant afford the gas you can't afford the car.

 

[Chris]

Howdy everyone, it looks like we have a good thread going here. Thanks for your useful input.

I think were all missing something here, have you actually got all these parts for your motor or is it a wish list.

No wish list there Mike. I have them all, except the IDA manifold and linkage. I do have the 4 IDAs from back in my VW days- cherry nice sets of Italians that I drilled the 3rd progression circuit and enlarged the float bowls. Since they're sitting on the shelf I am very tempted to try them.

And yes, that cam may not be a great match but it is also sitting on the shelf so I figured "Heck, why not?" I used to run it in a 408W with a Holley (it was a while back and think it was a 950cfm or so). It ran well, I did 6.50-6.70 in a heavy street legal foxbody Mustang.

I am off on my head flow numbers. I don't know what they flow; however, they are off the hook and taken to the max with some very expensive and nice work by Alternative Auto.

EFI is the way to go!

Can anyone recommend a cost-effective EFI TB & manifold setup? I already have the Autronic, a complete Aeromotive fuel system and some injectors lying around. I'm not opposed to going that route...

Thanks all,
Chris