Tunnel ram tuning anybody?

So i got this 37 chevy masteer coupe, 350 4sp 4:11s. the 350 supposed to be rebuilt & it looks like it with new freeze plugs, balancer etc. But the cylinder pressures are low, like 125lbs. The things got a tunnel ram tht had 2 600s on it when I got it, mind you this is a mild 350 with just a little bumstick in it. I took off the 600s, put on 390s, it runs a lot better but has the dreaded dead spot off idle. When i get it up to 180 degrees it's not near as bad but still there. I'd like to drive it a little before the new motor goes in like it is to continue debugging. Anybody got any suggestions on jet sizes,squirters,accelerator pumps? I can start swappin parts, but if I could do it once or twice it would save me some good time.

 

Do 390's have power valves?

 

I never usedem befor but I would think so, probably 6.5s

 

You just described how mine ran with those two sentences.
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It ran like shit until you got it up to 180F. And after you got it up to temp there was still a dead spot from idle to 2k rpm. But it was wicked from 2k rpm on up.

 

Are you running progressive or 1:1 linkage?
dave

 

Drjones, what did you do with it?

 

Runnin both carbs @ the same time, I guess 1to1.

 

Power valves won't make much difference w/ the stumble ,try going w/ a 31 or bigger shooter,tunnel rams do not run well until thoroughly warmed up , no fuel atomization , just dropping raw fuel. Some SLIGHT stumble is to be expected at low RPM [below 2000 +-]
dave

 

A mild somewhat low compression (125 PSI cylinders) you should probably be running progressive. Even with the smaller carbs that is still a lot of iar to be throwing at it.

Check your vacuum @ idle. You should start by making sure that you have power valves that are right for the engine.

By flat spot do you mean it stumbles or doesn't pull hard @ low RPM. If it is just not pulling hard at low RPm you have to realize that you are running a tunnel ram and they don't pull hard in the lower RPM range. if it is stumbling perhaps you can fiddle with the accelerator pumps to get a better squirt. Sometimes it is a pump adjustment and sometimes you have to go to the bigger pump. Start with playing with the cams that acruate the pumps and maybe even adjust the little bolt/spring setup that actuates the pump itself to get it to start squirting sooner.

 

A few questions. First, which tunnel ram do you have? Is it a "street" tunnel ram? What size cam does your 350 run? With low cranking pressure (125 lbs) it sounds like you have low compression heads on it, right? How much vacuum is it pulling at idle and at cruise? Stick or automatic?
Gotta know these things to help ya. Also if the "new" motor has more cubic inches or bigger heads or more cam or all three of the above then keep the 600s handy, you'll need them.

As usual, not enough info to make an accurate call. Waste of time until all the facts are known.

 

I think we just kind of accepted it's flaws in how it ran and just drove it as is. We fiddled with jets and crap but nothing we did really improved it and sometimes it even behaved worse. It seemed to run the best when we ran the out-of-the-box carb setup.

We didn't mess with progressive linkage. Somebody would have to draw a picture of how to do that on a 2X4 holley setup for me.

We had the single inlet vacuum secondary 600cfm holley's like this one except 1991 vintage.

 

Will be signin off in a minute or two, but let me answer you John with what I know. The tunnel ram is the same Weiand you get with the summit combo pack, Haven't seen the cam but was told about 480 lift, don't know the duration. The motere came out of a 72 el-camino. I did check the numbers on the heads & there the 76 cc chambers 1.94 intake valves. 4sp. muncie, 2:20 first gear, 4:11 gears. I'm keepin the 600s, the new motor is a 406 with brodix aluminum heads, hydraulic roller.

 

Seems like mine had float level adjustment on top of the bowls. Do the new ones not have that anymore?

 

Not to be an ass, but wouldn't a single four manifold run much better on a mild motor? Wait for the nasty new motor to run the dual quads?

 

Tom,
You will never get it really to be responsive with that big single plane top. Google "Real Street Ram" and you will find the cure. It costs, but it works like crazy, even on bone stock motors.
- Wayne

 

Do an advanced search using thread title only with the words cross ram, tunnel ram, crossram and tunnelram. You will find a TON of info on how to get this tuned and make it work as well as a bunch of guys saying it can't be done.

Go do the search and then spend more than a few hours reading up on the fine points from guys that have been there done that.

 

I have seen the "Real Street Ram" before and I have to say it is a well thought out set up. Very complete. Two separate plenums with a choke @ mid point in each plenum. Can the plenums be opened up to supply more HP? I also think that the vacuum secondarys are part of the key to drivability.

 

The plenums cannot be opened up without wrecking the fuel distribution. Working on another scheme that will trade away some of the bottom end performance to gain more top end. Stay tuned.

 

Tunnel rams have a higher power band just like air gap manifolds
Not designed to run well at low rpm

 

Hi all!! I think I just broke the rules by posting my first post here(finally have a topic I can help) I type with 1 finger so forgive my short responses,also in construction for 33 years so its a wonder I can walk upright)I have a 302 ford roller motor with a b cam(284 dur-498lift?)gt40p heads,limefire headers.pertronics dis.,5spd stick in a glass 32 3 window(2640 with me in it)old wiend tunnal ram 2 390 vac sec carbs in sink.stock squarter is a 25 went up to a 35,stock jets 51(.050 drill hole) went to a #67(.068 drill hole),6.5 power valve.purple sec spring. stock squarter is a none tube type,guy a drill set # 0-60,drill out the squarter and jets till u dial it in it will save u money from buying squarters and jets(when dialed in buy what u need in the sizes that work) at idle i have 20 on the vac guage at highway i have 12 so when i step on it the vac drops below 6.5 the power vale opens and then the secs open with no bog,same with the squarter to help with the transfer to primary circuit. I also had to adjust the secondary throttle plates to close them to bring the idle down to 800rpm(1/4 turn counterclockwise) hope this helps Pete

 

Yeah...this is the impression I got from experience.

Also it's probably not the best to have a tunnel ram with a 1500 rpm stall converter and 2.83 gears. You live and learn right?

 

Hey me again!! Forgot stock 30 cc pumps with a orange cam (466) make sure that the instant you move the throttle the squarter shoots fuel.(50 cc pumps were to big) timing is at 10 degrees btc at idle and 34 advance Pete

 

I don't know about Air Gaps being "high" end. Seems they are bout the same as Performer RPM manifolds. Again there are many factors to take into consideration.

 

Prpmmp, are you absolutely sure about that jet size? Going up 16 sizes on the jets should result in continous black smoke and changing plugs every 20 miles.

Generally folks go up 3-5 sizes to try to bandaid the crappy fuel distribution on a regular tunnel ram, but 16 is totally off the wall.

 

Hey!! Yes the jets sizes are correct. I could not believe it,The plugs are brown(maybe a hair rich Im still tinkering)I was told the higher the carbs go up the intake the richer the carbs have to be.I started out with the stock jets and went up 2 sizes at a time,The jetting got rid of all the driving lean bogs then i dialed in the squarter of idle bog,It has a 5 sp (m5r2 ford truck trans,1st gear is a little low) and a 355 rear.You can almost let the clutch out at idle to get the car moving,it does not take much to break the tires loose in the first three gears(light car + L78-15s not much of a tire)remember jets are the most important part of the carb( to big of a squarter and to high # powervalve will mask fuel distribution). this thing runs,I'm going to get many tickets or kill myself,I CANT KEEP MY FOOT OF THE FLOOR,This thing screams!! I,m to old for this I need a flatty!! Pete

 

I would change the power valves out to something very small, or you'll get sore eyes from the rich idle with a tunnel ram! Stock PV's in your engine are most likely around 8's, and I went down to #3.5 Quick Fuels to get mine cleared up.
I also went with the 50cc accelerator pumps to get a better squirt on my .040" over 327. The nozzles need to be bigger too, and on mine the #30 or #32 worked. (can't remember which I ended up with)
Can't go progressive on the Weiand tunnel ram as it will end up with cylinders at one end or the other being too lean from fuel starvation. Keep the setup for linkage you have.

 

Hey!! on the 390 carb the stock powervalve should be 6.5,you are right you don't want the powervalve cycling while you are driving.I ran a vacuum guage inside the car off the bottom of the carb and had my son ride with me to see when the power valve would go on when you get on it. it should make a smooth transfer from the primary circuit to the secondary circuit when the secondaries open(purple spring and 6.5 power valve for my set up) Pete

 

I seem to remember something about if you have to up the primary main jet size more than 10% then you need to go up to the next cfm carb. The carbs are calibrated to flow a certain amount of fuel x the throttle plate size x throttle opening x cfm. I would think a pair of 450s would be a better choice, considering how much you upped the primary main jets. I know that a large selection of different carbs to experiment with is not always practical, but it is something to think about. Also, on a street machine I feel vacuum secondarys are the only way to go.

Opinions?

 

Wouldn't 450's be the best? Isn't that what there made for?

 

Air Gaps are fantastic on a street motor!!!... Just gotta know how to tune a Holley to get that "snappy" performance out of the hole with that intake... It can be done...