rmcomprandy wrote:Oddly enough, the tunnel-ram made more torque average while the upper range horsepower average remained about the same as a single plane and single 4 barrel.
How big is the engine?
I could see this happening with a big cube engine, but I wouldn't think that to be normal for an engine under 400ci.
Does the tunnel ram have real long runners?
Hmm... Vizard's formula would suggest a choke of ~46 mm and a throttle bore of 58 mm for this app. Not a cheap or easy to find size..
His flow tests show for example that going from a 34 to 36 mm choke on a 40 mm carb increased the flow by only a couple of percent but reduced the signal at the aux. venturi by 50%...
48's weren't adequate for some of the old-school engines running lass than 350cid. I used 58mm Webers on the 494 CanAm engine I ran in my street Boss, but I had to use a "pancake" plenum that was 1.25" deep to allow the engine to breathe,
In the mid-eighties, we converted two of the mini-Indy engines to carbureted configuration for an SCCA race. The rules only allowed Webers with extremely small throttle bores. Once again, a shallow plenum connecting all of them saved the day.
If you have the time to machine one (a plenum), you may find it'll work for you too.
Guess we'll find out in the morning how our stuff fares. Thanks to Mike Jones for help with some cam options. I think they will do well. I felt better about last year's entry than this year but who the heck knows how these things go. It might not make any power but it looks shiny.
I considered doing just that, but ran out of time.
Considering the dismal (thus far) air fuel curve, it might have been worthwhile to budget some time for experimenting with a plenum.
We have 1" carburetor spacers, and I was thinking of inserting thin wall tubing (maybe around .900") into them and running short hoses to a plenum. Or, possibly connecting cylinders in such a manner that an active cylinder could utilize the carburetor airflow of an inactive cylinder.
I've had the cure. From now on, I'm a fuel injection person. lol
We're up and running. 300+ pulls on the 'test' goodies, and the jewelry got installed over the weekend. Now it's back to the pump and we'll see what we find with the changes. Would love a little more bottom end, but I've got to say- the top end is pretty damn good.
Maybe everything in life just gets better at 7,000 rpm...
We'll be there, ready to play. We've been tuning on local MN gas (lots of alky in it) but we've got some of the spec gas here for the final tuneup before we roll out. With less alky, it should be measurably better. We'll see.
Parkhurst wrote:We're up and running. 300+ pulls on the 'test' goodies, and the jewelry got installed over the weekend. Now it's back to the pump and we'll see what we find with the changes. Would love a little more bottom end, but I've got to say- the top end is pretty damn good.
Maybe everything in life just gets better at 7,000 rpm...
We'll be there, ready to play. We've been tuning on local MN gas (lots of alky in it) but we've got some of the spec gas here for the final tuneup before we roll out. With less alky, it should be measurably better. We'll see.
~SP~
300 + pulls Will any of the details make it into your website/ magazine?
Last edited by nitro2 on Mon Sep 28, 2009 8:12 pm, edited 1 time in total.
We’re headed back to the pump one more time tomorrow. I’m starting to get a better idea of the function of Weber Carburetors, and hopefully we can make some sense of the lean spike.
I’ve been a little concerned that our merge choke point was a little tight @ 2.375" ID, so I opened it up to 2.750" ID. It’s a roll of the dice - hero or zero, as there’s no going back to the small choke.
I’ve spoken with everyone that I could find in the “World of Weber”, and have come away without much insight. In fact, almost every source is in total disagreement with every other source. Either the whole Weber deal is super top secret, or some of the folks don’t know as much as I’d expect for someone who makes their living in/around Weber carburetors.
Harry Brannan, who posts on this site, is very knowledgeable and articulate. He has taken the time to ‘splain things to us, and offered what I consider some very sage advice. Thank you very much, Harry.
Good, bad, ugly (or very ugly), I’ll post our results tomorrow night.
In honor of Joe Caroll we boke on the dyno tonight as well. Had our hail mary cam in and it killed a pushrod in less than a minute. Swapped cams, reajusted stand height for less lift and borrowed a rocker cup and got it going again with a less angry cam. Just made one little pull before closing up for the night and it looks ok but we are miles away. Lets hope the DTS picks up a hundred points or so...
revolutionary wrote:In honor of Joe Caroll we boke on the dyno tonight as well. Had our hail mary cam in and it killed a pushrod in less than a minute. Swapped cams, reajusted stand height for less lift and borrowed a rocker cup and got it going again with a less angry cam. Just made one little pull before closing up for the night and it looks ok but we are miles away. Lets hope the DTS picks up a hundred points or so...