tuning for a tunnel ram

[whale]

I am new here and have a question. Have any of you all had any experience with a tunnel ram ? Most intakes are IR. The problem is......that it is hard to tune for cruise. I can tune for idle and or WOT, but not all three. Let me say first that this is on a 426 HEMI. Yes I know that this is not a Hemi site but you guys seem to know what your talking about. I do own a ford, 64 Fairlane that I am building a Thunder Bolt clone. So I will appreciate any and all of the help. So does anyone want to tackle this......if so I will give you the specks, or what I have tried so far. I am closing in but not sure how to close the gap. Thanks , wayne

[CobraEd]

I have always wondered about tunnel ram manifolds. They are supposed to be for very high rpm power. But over many many years, I have heard all kinds of different stories about the power or the lack of power, and where in the rpm range the power exists. So many stories that all seem to conflict. I would love to see some actual torque curves comparing them to the Victor and RPM air gap manifold.


.

[Jerry Clayton]

If you were closer I'd give you a hand with it----

However----things I need to know to maybe point you in the right direction---
is the 426 stock bore /strke?
Compression
Cam specs and where it is degreed at
dist timing and curve
which tunnel ram and plemun
carbs?
power valves?
jets P & S
accelerator pumps and nozzles

[whale]

Thanks for the help. Engine is a 60 over with a stock stroke, cr is 11.8:1, Comp cam, solid roller;D264/268, L 673/653,LS 108. Cam was not picked for Webers. We changed our minds later so the cam is not the best for the job. It is set on a 106 CL. Timming is set at 36 Total coming in fast....cant remember exact number, but I will look and check. Carbs are 48 IDAs, we have reduced the venturis from 37 to not sure. Somewhere around 28, we also changed the auxiliary venturi. In other words we cut off the tube on the top. We put in 300 needle and seats. Carbs are set with F10 holders and 60 IJ, F4 E Tubes, 180 AC, 210 MJ. Tunnel ram is a stock Nascar Bathtub for a single 4 barrel. We made a plate and machined it for 4 Webers. This was very common back in the late 60s and early 70s in Boat Racing. We had a hard time in the begining getting enough fuel at WOT. but was very rich at cruise. I am using a Fast Wide Band to tune.....we made a plate to go down the middle, but latter added a box to isolate the middle and only leave the outer sections under the carbs . This is very hard to explane in words if you have never seen this intake. I test drove the car yesterday and at 2000rpm A/F is 9.8, at idle it is 11.8 to 12.5, WOT is in the 10s. I changed the ET to F4s, at idle it is 13.8 to 14 with the mixture set at 3/4 out. Was not able to test drive , hope to tomorro. Thanks, wayne

[Jerry Clayton]

Uhhhh on the webbers

Wasn't the top plate on that manifold depressed in the middle and had some deflector ribs on (under) it?
I did a jet drag boat with that manifold and a Fisk? carb limited to single carb class.

[mreid]

I ran a tunnel ram on my '41 Willys and on my GT40. Both topped off with dual 4 barrels. They were awesome, even at low rpm, but that was mainly due to low vehicle weight. If this is a specific weber questions, then I have no answer. Sorry, but here are some pictures:

[whale]

Yes that is it. We machined a 1/2 plate for webers instead of the orginal top. So now we have a flat plate with 4 webers. Looks like fuel injection.This intake is a cross ram instead of a tunnel, but I did not think anyone here would have had experiance with a cross ram. What I have ended up with is a cross ram intake that has a box under 2 webers on each side feeding the other side. The open plenum experience is what I am looking for. Most of you have IR manifolds, and tuning is different on a cross ram or on a open plenum.

[Jerry Clayton]

its a loser for cruzing---that manifold was tuned lengths for high rpm and will only hurt you at anything under 6ooo rpm

webbers have no place on a hemi

[whale]

Well you may be right....but there are several world reckords that have been set with the same set up in GN class. And yes it was WOT but they were and are on a hemi. Should be fun trying........thanks again, wayne

[Jerry Clayton]

and I'll bet that they weren't on the nascar tub and hadn't been reduced in size like yours!

And whats your GN class??

[zimmy]

Definitely contact Jim Inglese at http://www.jiminglese.com/index.html

If anyone can help he can - I am sure!

[Jac Mac]

If you have reduced the venturi size to around 28mm thats about the same size as a 1 3/32 bore venturi in a holley 465cfm carb, now obviously the holley & webers wont flow the same amount of air per bore, but it gives you a ball park figure to think of, Now you essentially have two inline holley 465's with 1 to 1 throttle linkage & all eight barrels opening at same time, a progressive throttle linkage is going to help. With each dumping into one long plenum for each bank, Im not sure that your 'mid plate' is the best way to go as it will favour the end cyls, also remember the impulses for each bank are uneven due to the firing order, it might work better if you were to establish a 180° sequence in linking up the individual runners & reduce the plenum volumes. An individual barrel extending down from each weber throat toward the port each throat will service might also help if thats feasible.

Interesting I'll let you nut it out though

[whale]

Thank you for your insite Jac Mac. We have made a lot of progress with this system since we started. It has always had excellent throttle responce.....just not good at cruise because of the large volume full of all that air and fuel. The box and smaller venturis has really helped. The addition of side dividers to make it as close to a IR is the next step. We have talked about tubes from carb to the runners and have not rulled that out. Using a wide band and fuel injection the A/F for power is around 12.8 to 13.2 depending on the engine. I am not sure what that is with webers. It seems to like more fuel ie, 11.5 to 12.0 with this system. Thanks again for all of your help and coments. wayne

[Jerry Clayton]

Again what is GN?

And what is your exhaust header specs???
You lobe separation angle is very close and the 28 venturi size makes the carb think they are running wide open, (an 80cc gokart uses a 28mm carb)
each carb needs to be bigger, not smaller and once again---that manifold is for very hi RPM ---meaning---runner length tune rpm---any thing lower than optimin suffers

[whale]

GN stands for Grand National. It is a class under APBA it means Endurance Racing. The boats are 20 to 21 feet long and run either NA engines or bolwn engines. Kind of like nascar on water. My set up is in a 65 Plymouth 2dr post. It is what the company raced as a factory A990 or SS. I am not sure what size the venturis are I guess them to be 28, and if they are that would give approimately 1000 cfm per side and 2000cfm for the engine. These engines came with 2 770 cfm carbs on a cross ram intake. The bathtub was for a single for nascar, but it is what the boat racers used in this class with this intake set up just like mine. I am just trying to use it on my car. Headers are made by TTI they are 2 1/8 equal length with a 3" collector. It was 80 today and the car ran well.....hot idle was at 800 rpm at 12.5 to 13.9 AFR , cruise was 11.3 to 13.2. WOT 10.5 to 11.8......needs a little more work. It seems the change to F-4 E tubes helped a lot. By changing to the smaller chokes I hoped it would speed up the air flow. I can change back to the 37 chokes and see what happens.

[MR. KILOWATT]

Jerry, this boat has won more Grand National championships and set more kilo records than any boat in the history of the sport. Notice the NASCAR bathtub intake. This was the intake of choice if you were from the Chrysler camp. Keith Black built the weber lid and sold them for years.

[Dumpling]

First it's a tunnelram, then it's a bathtub, then under a couple of pictures of normal tunnelrams, it's "yes, that's it".

What exactly is it? Does the Mopar bathtub have long runners running under the plenum, or short dumps straight from the huge plenum into the chambers?

[Jerry Clayton]

Mr. Kilowatt

Yes I know what the manifold is---I did a late model hemi and used that manifold with a Fisk? carb on a jet drive boat for boat drags back then. A boat keeps a load on the engine close to what a dyno does all the time---not like driving a car on the street. It is much easier to get the car to go fast than it is to get it to coast down from 60 to 40 or a stop or drive around a parking lot and park.
I have tried to make the point that the tunnel ram is set up for high rpm and that anything other than the tuned rpm it will hurt your numbers.I also asked aboout his exhaust. the exhaust and intake tuned lengths work together. Whale was completely too rich and as he got closer it has run a lot better.

[whale]

Jerry, I had a little time and warm weather today so I changed the chokes back to 37mm. Test drove the car and idle was a leaner and cruise was better as well. Still not enough...... but better. I am not sure but it seems to have lost some torque on the bottom end. I am not concerned with WOT right now but I have a question . I have the newer design webers and since I am having trouble with part throttle and 120 holders are as big as they make can I drill the holes bigger to help with the rpm range of 2000 to 3000 ? If so which ones ? Thanks wayne

[Jerry Clayton]

Sorry wayne, but I'm a Holley guy unless you want to run supercharged on Nitro--ch my gallery

Jerry