TWM/Weber manifold flow

[Mike]

Help. Does anyone have any flow numbers (CFM) for the TWM set up on Weber manifold combination, either in total or per throat? I'm getting the idea they may be limiting my motor. My TFS heads flow 306 CFM at .600 lift, but it doesn't seem to be coming out the RWHP pipe.
Also, any good or bad comments on Desktop Dyno advanced sim?
Thanks.

 

[Bob Putnam]

Weber 48s are rated at 340cfm for each barrel.

 

[Mike]

Thanks, Bob.

 

[Ron Earp]

Bob, is that with 44mm chokes, the largest that fit in the IDAs?

I'm interested in this too and have bought it up on a couple of threads. One fellow sent calculations for a particular motor/cam I was doing and indicated I'd be out of luck with Weber 48s above around 6700 RPM or so. And, I've seen a couple of articles with Webers and 4bbls with some interesting conclusions (I know about 289s comparison on this site, but some more detail is needed there and it is only one data point).

Some questions and issues - do you want the head flow so close to the max flow of the venturi? Or, would it be much better to have the carb flow a max of say 500 cfm per barrel while the head flows a percentage of that, maybe 70% or so?

Does a 4bbl have an advantage - a 4bbl carb might flow 850 cfm on a built motor, but, on a single plane intake the cylinder that is opening "sees" a large percentage of that flow and it is flow more than 850 cfm divided by 8. Reason is that only one cylinder will be drawing an intake charge from the manifold and carb at a particular instant, compared to a weber setup in which one cylinder can only "see" a maximum flow of what one weber barrel will produce, in this example 340 cfm.

There have been numerous people on the board that have experienced "choked" motors with various EFI induction setups. Hershal, Jerry, Mark, and some others all experiened it with some systems at bore sizes ranging from 40-44mm. Some went to carb systems and whammo - car ran like a bat out of hell claiming the flow did it for them. I think Paul Thompson has 58mm bore on their EFI setup on their stroker motor for flow reasons. They don't have flow problems on theirs, but 58mm is 42% larger in area than a 44mm bore and would flow accordingly.

Mike G, what sorts of rwhp numbers on a Dynojet are you seeing on that 347? Would also be useful to have cam specs. Flowing 305cfm at 0.600" lift is fine, but if you aren't at that lift but for a short time it doesn't mean much. I'm interested since I want to run webers for sure, but I don't want issues with choking my high RPM motor.

Ron

 

[Al Wohlstrom]

Mike, What size (mm) throttle bodies do you have? I'll find out what the flow is.

 

[Paul Thompson 'Hooligan']

Hi all

Came across this when browsing -

"2 pics of Modified Weber throttle shafts. Increased flow by 14 cfm with stock 36mm. venturis. With 42mm. chokes, the flow increase was nearly 30 cfm over stock shafts."

Unfortunately the site did'nt quote actual measured cfm, but interesting all the same..

The site can be seen at http://www.yawpower.com/

here are the modified throttle assemblies..

 

[Mike]

Ron, the Dynojet numbers (17" pin drives/11" rims/315 BFGs-they tell me this makes a difference in the numbers?)are:
3000/185HP, 4000/250, 5000/325, 5500/340, 6000/350, 6200/345 and we quit the pull.
Comp. cam 236/242, 112 LDA, .55/.57" roller lifters, 2.02/1.6 valves.
Head flow #s: .4"lift/248cfm, .5"/285, .6"/306, .7"/308.
Given the theory that IR manifolds give midrange torque at the expense of high RPM HP, it still seems to me the engine quits pulling too early, hence the question re. TWM (48mm IDF type) throat/Weber manifold combination. As you said, the cylinder doesn't have the 'plenum' to draw from, just the 330/340 cfm throat. Also, why would the Weber carb. do better, with a venturi, unless it's flow velocity, in which case why didn't TWM just do the same????
I'm confused. Maybe we should invent variable geometry inlets, as in 'real' jets
Mike

 

[Neal]

I have IDAs with a similar combo
4200/355, 5000/425, 5500/443, 6000/456 at the flywheel
Isky. cam 238/248, 110 LDA, .544/.573" roller lifters,
TEA Trickflow 2.02/1.6 valves.
Head flow #s: .4"lift/265cfm, .5"/286, .6"/300

Did you check our EGTs?

 

[Sandy]

I have the 50mm IDA TWM bodies and matching manifold, has anyone run that on a dyno to see what that will do? I had the same concerns that on a high hp motor that it will not do as well as the carb. Once I get the RCR40 rolling it will hit the chassis dyno before I do the TWM EFI, and see how bad the hit is once I decide to to the switch.

Maybe a better question is who made 500-600hp with the TWM/Injection, and I'm sure others would also be interested in seeing similar Weber number.

Sandy

 

[Ron Earp]

Mike,

With your cam/heads you might not be that far off. 345 at the wheel, add 10% (or whatever your favorite loss percentage is) and you'd be around 345 + 34 = 379 fwhp. Not as much as you'd like, but in the neighborhood. What is the compression ratio? Timing, fuel, etc. might pick the rest "missing" up - has that been extensively optimized or did you folks stop after a pull or two?

If you want more RPM out of it, that is, power at higher RPM you might need a different cam and go to solid lifters if you wish to be turning 7k+, and of course that could necessitate other changes in the engine with crank/rods/pistons etc. depending on what is in there now.

Ron

 

[Mike]

Ron, originally, with a 241/248 cam,.57" lift, we pulled 420 FWHP at 6200. (11.8/116 in the 1/4 implies about 290 RWHP, I believe, but the Kluts who built it burned a piston (unbeknownst to me) before delivery...long story).
The 'new' rebuild has all the goodies, 10.3+CR, JE/SRP flat top pistons, Eagle forged crank and H-beam rods, Isky dual springs etc. The recent rebuild was not on a budget, with a target max/limiter set at a conservative 7000.
The A/F ratios etc. are fine (12.9 > 4500/85% MAP). The power curve just starts to fall past about 6200??? Fooling with Desktop Dyno's sim. suggests a big jump with a single plane manifold and a 4 barrel, hence the concern re. the TWM/Weber set up.
I get the idea the ZF-2 tansaxle eats up more than 10%, but tough to pin down. Come summer, a trip to the drag strip might give a clue, in comparison to the previous time slips.
Can't quite make sense of all this.
Mike

 

[Mike]

Oops. I forgot. 37 deg advance.
Mike

 

[Ron Earp]

Mike,

Sounds like you've got the bases covered and have done the detail work. I would expect more hp out of it too and I am seriously interested - I'm getting ready to select a manifold/carb setup for my 342 that is similar to yours, just a larger cam, compression, and a little higher target RPM capability.

I am thinking that a single plane intake with a Demon carb is going to be the trick for power, but I don't like how it looks. I want to find a solution involving webers, or weber EFI setup, but want to do it right and do it once. I am afriad that 48s won't get the job done with the 44mm chokes and larger webers are really costly.

 

[Russ Noble]

If you want the looks and the performance, has anyone ever tried running Webers (or injection) grafted onto a single plane manifold? If it worked I'm sure there would be scope for a casting run. Just a thought, but what would I know. Now shoot that one down in flames!! /ubbthreads/images/graemlins/flamer.gif There must be all sorts of reasons why it won't work, or it would have been done before, surely. Maybe it has been done before and doesn't work. Does anyone know anyone who might have tried this?

Regards

 

[Mike]

Hi, all. Standing by for a response from Gary at TWM re. flow and other TWM customer experience/results. I'll post the answer as soon as I get it. I'd like to know how to get peak power up around the high sixes to 7000 from the Weber type FI. (evidently, Weber carbs work a little better than the FI, but still confirm the IR 'mid range' characteristic). I too want the 8 stack look vs. a 4 barrel.
Mike

 

[Ron Earp]

Hi Mike,

A buddy of mine that does a lot of Porsche stuff just came in with some documentation from Weber regarding venturi diamter and engine size/RPM. To calculate the size it says to use this formula:

Venturi size in mm can be found with:

20 * SQRT ( (V/1000) * (N/1000))

Where V is the volume of one cylinder in mm and N is the RPM where the engine makes peak horsepower.

I ran this formula for my engine, 5.6L (342) and 7500 RPM peak power and came up with 45.85mm.

It also goes on to say that Weber suggests that the throttle bores be larger than the venturi by 10 to 25 percent. So, a 44mm choke in a 48mm IDA would be as big as it could get.

 

[Ron Earp]

If you take that formula and plot venturi size vs. peak RPM, for a 342 inch motor, this is what you get.

I did it in a spreadsheet so I can vary engine displacement easily and the results are telling. A 289 is very happy with 44mm venturis since it'll go to over 7800, while 347 is not and will peak about 6700 RPM.

 

[Sandy]

Ron - I think your axis are backwards.

Sandy

 

[Ron Earp]

Opps - the axis is okay, the labels are screwed up. RPM is on the Y axis, venturi size in mm on the bottom. Plot is correct, labels are not. Sorry, was in a hurry at coffee break!

Mike, what is the bore diameter on yours?

 

[Mike]

Ron, your plot seems to verify the Individual runner characteristic, i.e. MID range performance. In fact, there seems to be an almost linear relationship between RPM and displacement/cyl. volume. The 289 is about 8.5% smaller than the 342, and the 7800 or so peak is roughly8.5% more than the 6700 peak on the 342.
I remembered my Daytona Ferrari (1970) produced 385HP at around 7500 RPM) with 6 twin-choke Webers (45mm??) from 4.4 liters, i.e.367 cc/cyl. The 342/5.6L has 700cc/cyl, damn near double.
The TWM Guru, Gary Williams, said Rousch and the high power guys use the 50mm units to produce 5-600 HP, but he didn't know at what RPM. That was all I could get. He's not an engine guy.
Comp. Cams tech help said my cam should peak at 65-6600. I'm seeing 6200, so if my 48's aren't perfectly set up, I may be looking at about all there is (I run 8 K&N air cleaners on straight stacks). He had no clue why the engine wouldn't pull higher.
Finally, found an interesting web site (Brit):
http://www.jenvey.co.uk/~Tech_QA.htm
They have an excellent overview on exactly what we've been discussing, and they make the point that Weber CARBS. are not the same as FI throttle bodies.
My current thought is to try air horns (TWM has some choices, but so does Jenvey) to see if they increase the flow. Seems a cheap way to prove or disprove the theory. The first few lines on their website got my attention, 1/3 power loss due to incorrect air horn length???? Ideal length, horn lip to valve, 17" for 7000 RPM??? 13.7" for 9000 RPM??? Wow.
Mike