Tuning a tunnel ram

[Sirshredalot]

Hey yall. Just wanted to post some tips about how to tune a tunnel ram.
I know everyone has heard somthing different, or tried somthing different, or saw someone do somthing different, but this is just what I have found to work for me by experimentation.

Tunnel rams are great because they offer superior mixture distribution, profound advantages in flow capabilities, and the ever so important "wow" factor.

The most important things that I think need to be tuned for a tunnel ram are the Pump shot and the mixture velocity (carb signal).

Most tunnel rams have a large plenum volume...but suprisingly theyre usually not much bigger than a Victor.

ONe of the biggest problems you have to tune out of a tunnel ram is that lean cough/backfire right when you stab the throttle with a load on the engine.
A holley accelerator pump tuning kit is a good idea for the price and they come with enough to service the T-ram.

Upping the squirter size alone can help, its just depends on how radical youre getting....and if youve got single or double pumper carbs...I dont have alot of experience with the Double pumpers because I run vac-sec carbs on both my setups.

I cant give any hard and fast info on jet sizes, squirter sizes, etc. because every engine is different.

But I cant say that youll want a pretty aggressive accelerator pump cam profile. I used the orange cam and turned it backwards after a little filing to give the desired ramp.
Squirter sizing, I would recommend at least a 31 as a starting point.

If by tuning the cams and squirters you still have a cough or a bog, than you may need to step up to a 50cc accelerator pump kit. These little guys are life savers...and they move ALOT of fuel...after upgrading to this, you may have to back off your accelerator pump cam profile...even though the 50cc kit comes with a few cams.

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Dont let anyone tell you youre over carbed, two 600 cfm carbs will run just fine one he street or the strip.
Id really like to get my hands on a pair of double pumpers to try tuning those and see how they perform.

About maximizing carburetor signal strength...obviously the less venturi surface area you have...the greater the signal strength will be...Ive got a pair of 600 cfm carbs on my tuned tunnel ram...and Im in the process of tuning a pair of 390 cfm carbs....but tunnel rams dont like this 17 degree weather...so theyll have to wait for spring.

Camshaft specs have alot to do with this. Dont let people tell you a tunnel ram is only for super high RPM and needs the BIGGEST cam and the HIGHEST compression ratio.
If you want to properly use the intake setup than a decent performance compression ratio of about 10:1 is ideal...but that also depends on your cam too.
The bigger the motor that you can stuff under a tunnel ram, the better. that will increase signal and response...but a big motor is not necessary.

As far as camshafts go...you can choose a cam that gives you a given power goal...but I like to stick to a cam that has a wide lobe separation angle...like a 110-114. This IMHO will help to maximize signal to the carbs.

Tuning the vacuum secondaries. The best thing you can do for the secondaries is to link them with a vacuum line.
You can drill/tap/epoxy a piece of 3/16 steel brake line into the top of the vacuum diaphragm cover. Then link them with a piece of vacuum tubing. This will greatly help out with secondary opening problems and makes the transition into the secondaries much smoother.

Idle tuning.

IF you cam is big...please dont expect it to idle under 1000 rpms.

Depending on how big your cam is and how much or how little vacuum you have in the manifold, you may need help with the idle transfer slots. Ideally you want only about 1/5 of this slot exposed at idle. Exposing more than that it idle is a surefire way to get a cough or stumble or flat spot.
If youre engine wont idle with only 1/5 of this slot exposed than get out you set of drill bits and drill a 1/16 hole in the butterflies directly in front of the idle transfer slot...the bigger you make this hole the more air it bleeds into the manifold.
Dont go too big though, start small...maybe even 1/32. Try each size after its drilled to see how you like it.

IDLE feed restrictors

Most four barrel carburetors are set up to supply enough fuel at idle for 8 cylinders, so by doubling the amount of carbs, weve boubled the amount of fuel at idle.
To help this there are idle feed circuits in the primary metering block that need to be restricted. The more you restrict them, the less fuel will flow at idle. I would recomend again starting small at first, like .015 wire.

Bend it in a "U" or a "V" so that it will hook into both passages and hold itself there when the gasket is on.
I have a picture I can post of this later, its on my other computer.

Spark control and timing.

Tunnel rams like alot of timing for some reason. Mine have like between 10 and 14 degrees initial, but you overall total advance depends on how it performs and I cant tell you that.

I can tell you that the best distributor to get for a Tunnel ram is the Mallory Unilite. Its smaller than anything out there, very accurate, and looks like a billet points distributor...cool.

Youll definitely want to run an ignition box, not only to help prevent plug fouling , but because theyre awesome. An ordinary plain jane MSD 6A will do.

DIFFERENT MANIFOLDS

I have both the edelbrock street tunnel ram and the Weiand street tunnel ram.
I have no experience with the large tunnel rams like the holley pro-ram or pro-ram II, or the dominator tunnel rams.

Runner length helps keep the rpms down, so a small diameter, long runner will have better street manners than a short runner with a large diameter/volume.

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Dont let anyone tel you youll lose torque with a tunnel ram, if you lost torque...you didnt tune it right.
But the standard rules for mismatching parts apply. If youve got a combo that needs a 4000 stall and you stuff it in front of a 2500 stall hoping for streetability, performance will suffer and youll never be able to tune out that bog..

Tunnel rams like good flowing heads and exhaust too...but dont think that you have to go huge.
I would recommend the hooker 2129's over a smaller tube header.

Make sure your fuel pump is up to snuff....youre supplying twice as much fuel to twice as many carburetors, ditch the holley red pumps, and go with a 130gph mechanical pump or a holley blue pump.
Also...do yourself a favor and get a bypass regulator also...itll make tuning fuel pressure so much easier.

Dont be afraid to defy convention...I have also tried working with 2 350cfm two barrels...I never put alot of time into them but I will go back and try to work them out...it pretty much makes a 700cfm double pumper split in half.

IM sure I forgot alot of stuff...so if I remember it, I will post it later.
plese ask all the questions you want and I'll try to answer them to the best of my knowledge.
I'll get that picture posted later too....but I gotta run...Its my birthday today....HOOHAW!!

God bless
-Shred

[spyder_xlch]

Happy birthday Wes.

[MIKESMONZA]

Shred;
Wow that is a lot of info, to digest ,,
but I am glad You Brought Your Knowledge to this Forum,

Where myself and other people can find out,,
where they went wrong with the install,,,
thinkng it was Plug N' Play,
and having bad performance and thinking They Needed Guidance.

Just like Looking for a Book Titled "Tunnel Ram for Dummie's"
In the Quick Study Section for up coming Tests and Term Paper's ,,,(in your local bookstore).

And Thank's for a Nice Job,

Also Have a Happy Birth Day ,,,,
Mike

[chevyart]

hey wes with all that gas coming in and a nice big cam with alot of duration, you could use probably anywhere from 15 to 18 degrees initial at idle(around 1000 rpms)without this early timing you can possibly have alot of gas not getting fired up on time. old school used less initial timingin their tuning. of course you have to check the other end of the timing curve and make sure you dont have too much total timing. a good distributor lets you custom tailor in your own preferred advance curve. I use the mallory comp 9000 diatributors in mt engines along with the hyfire ignition boxes, and mallory HP coils. with domed pistone you can always use more total advance 38-42, and with the more modern flat top pistons and smaller combustion chambers you can usually get away with anywhere from 32 to 36 degrees total advance to obtain max performance.. this is some of the tuning procedure i like to go by , and it is usually the method alot of the racers tune by. happy birthday(how many years have you been on the planet) chevy art

[BillPappy]

Text book tuning of a holly carb on any engine... Not just tunnel ram. Nice job Shred.. I was going to write this back sometime
ago but never got my A round toit...

I had gone back and reread your post..... I been tuning holleys for years.. Nice tip on the secs. I alway tuned Big DPumpers

[Sirshredalot]

Im 24 as of yesterday....Just waiting for those gray hairs to start showing up.

God bless
-Shred

[chevyart]

hey shred another point with these holleys. with stick shift cars the small accelerator pumps are enough, as you can control the rpms alot better at launch. the auto guys use them in the rear of carb, and check this out. alot of the foot brake guys put the big accelerator pump in the front and small one in the rear. these gust have their takeoff down to a science, so that is why they use the big shot up front instant gratification. also the power valves in these carbs are impoortant. if you want me to chime in with what i know about them, then give me a shout chevy art

[Sirshredalot]

One point about the stick-shift cars is that at launch rpm, their engine is not loaded in staging like an auto car with the converter pulling on the engine...but(unless they have a slipper clutch), theyre loaded so much more instantly and need to compensate for that when they drop the clutch. More like a ski boat engine where you just gotta mash the throttle from a dead stop and get your skiers out of the water.

I always wanted a stick-shift tunnel ram car....but a Jerico (...wood....drool...) is just a "tad" out of the budget.

I also dont know a whole lot about high speed air bleeds in the HP style carbs...Ive messed around with a few quick fuels and a demon...but never got that deep into it.

Obviously power valve tuning is very important...not only in relation to vacuum tuning but also to tuning to how rich an idle circuit you have or, in a drag race only scenario, launch rpm vacuum.
I like to tune the power valves an 1.5" off of idle...some like 1", some like 2".
The more load you have on an engine, the closer it will like the power valve to come in.

Please feel free to chime in with anything that you feel might be helpful or inspire creative thought...Im all ears.

Also....with tuning vacuum secondary carbs, its SO much easier if you have the flip top vacuum secondary housing for quick spring changes...its a pain in the butt to fiddle with aligning that diaphragm every time to take that cap off.

Also...Among the dozens of other side projects that I have going on, Im tuning a pair of edelbrocks for the tunnel ram to see how they compare to the holleys...I think I'll have trouble with the accelerator pump volume.

God bless
-Shred

[NixVegaGT]

Great article, Wes. That's what I like to see here. Good stuff. THanks man.

[greg72]

Nice write up Wes.

and Happy Birthday! 24 ??? holy crap , that's how long the tunnel ram has been on my Vega!!!

Years ago we set it up much like you outlined in your post. It was funny because so many people said we couldn't run a tunnel ram on the street. But it worked very well.

[Sirshredalot]

Well...I personally have alot more work in my intake than I outlined.

There are modifications that you can do to turn a tunnel ram into a tow truck intake....well...almost.

The ratio of port size/diameter in relation to intake track length is what gives you your mixture velocity...or lack thereof.
By keeping runner length the same and reducing the intake diameter...you effectively increase mixture velocity or manifold vacuum/carb signal because you now have less intake volume to draw the same amount of vacuum on.

LIke reducing brake line pressure by going from 3/16 to 1/4 line...or increasing it by the inverse.

If you want to try this ...be my guest...just be prepared to have to grind it all out if you dont like it.

How to make a tunnel ram a street beast torque monster.-----------------------------------------------------

What youll need...

Depends upon how you want to go about it....youll need:
- quite a bit of moroso A/B epoxy or similar fuel proof epoxy.
- a carbide cutter with long shank...preferably an 8" shank...but a dremel will do in a pinch.
- a section of sheet/plate aluminum roughly 22" x 6" x .200 or thicker.
- an intake gasket, matched to the size of the head port.
- A crap load of free time and patience.

If your case was like mine, I picked up a tunnel ram used that had been ported to roughly Huge x Large dimensions.
I needed to reduce the runner size to match my heads.

Grab your grinder tool and run along the CLEAN intake surfaces inside the runners in a zig-zag pattern...dont be afraid to push too hard and "gouge" it...the rougher the better.
The epoxy will need somthing to stick to. Make a sort of cross-hatch pattern inside the intake or large connecting "X's".
NOTE: in extreme cases Ive seen guys run sheet metal crews from the outside of the intake into the inside of the runners so that they protrude in the runner...giving them ALOT more retention strength...just grind the heads off for appearance purposes and port the tips off.

MIx up your epoxy and spread it on the CLEAN intake surface to roughly the desired size...NOTE:
JB weld is a great epoxy and holds very well....but is too thin/runny to use for this application so I would recommend a 2 part putty epoxy....we can go into alternative methods of doing this also.

Youll want to spread the epoxy in a manner so that as it goes from the head mating surface to the plunum...it tapers and thins...leaving it thicker will just leave you with more material to smooth out. Do only one surface at a time letting the intake sit in whatever direction to ensure the epoxy stays level to the ground and doesnt slip or run.

Welding is an option...that I would recommend...but I epoxied mine so well see how it lasts. If you want to divide the upper plenum, that is where the plate comes into play.
I experimented with thin (.030) sheets to get the right height and shape first.
Cut the piece to the size of the upper plenum and divide it from front to back..just like a "dual plane" intake.

Sounds simple but Ive got over 25-30 hours of work in mine and im still not happy with it...but Im gonna run it for now.
The finish work is all up to you...match the exit ports in the intake to match the gasket that was ported to match the heads and youll have a smooth transition from intake to head.
You can leave the intake fill a little taller/thicker than the head...but you dont want the air coming into the cylinder head to see a lip...thats bad.
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ALTERNATIVE METHOD

This method was explained to me by a fellow hotrodder, but I never ventured to try it.

-Go to lowes and get yourself some high density foam insulation...the blue kind.
-Cut the foam into strips to the desired shape of the intake runners that you want.
-Insert them into the itake runners and let them protrude from both ends...so out of the bottom and into the plenum.
-File down the foam at the head side of the intake flush with the mating surface.
-cut a piece of foam large enough to be bolted to the bottom of the intake and completely seal the ports...back it with wood for support.
-Use a liquid 2 part epoxy...I believe common to marinas, mix and fill the intake from the top of the plenum, letting the epoxy run into the runners and fill the voids. Tap the outside of the intake to prevent bubbles from being trapped.
-Once filled to the top of the runners...let the epoxy pool very shallowly in the bottom of the the plenum...just enough to seal the runners.
-ONce the epoxy has set up...heating it slightly will speed the cure time, Fill the upper plenum with acetone and let it completely eat all the foam fron the runners.
- From here you do all the same port work and matching.

PORT FINISH------------------------
- You DO NOT want your runners smooth...matter of fact you want the m fairly rough.....this helps keep the mixture suspended in the air so that it doesnt pool or run at low RPM.
Port is good.....POLISH is BAD.
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I couldnt find the liquid epoxy locally, but I know it exists....so I did the first method.

This effectively makes a GREAT flowing intake with a great line of sight to the intake valve, that also looks cool and has KILLER throttle response with good top end and great torque.

But dont blame me if you ruin you intake....lol...good luck if you want to try it.

God bless
-Shred

[cosvega76]

LIke reducing brake line pressure by going from 3/16 to 1/4 line...or increasing it by the inverse.

Sorry, Shred, I'll have to disagree with you on this point. There is little flow in a brake system to change pressure by altering line size. Brakes work on principles of hydraulics, and are engineered on the premise of equal pressure throughout the system. The only non-active device that will change line pressure (not counting ABS systems) is a proportioning valve, which will reduce pressure on the outlet compared to the inlet once it has attained a predetermined pressure threshold.

Chuck

[Sirshredalot]

I look at it like this though....you always have the same volume because you arent changing the master cylinder.

So if you always have the same amount of volume, but you reduce the amount of space in which that same volume must respond, that increases pressure...correct?..because as pressure increases volume decreases because a smaller line will hold less physical fluid.

Like pinching off a mcdonalds straw and blowing into it, then try pinching off a paper towel roll and try blowing into it. Youll create more pressure inside of the mcdonalds straw.

God bless
-Shred

[spyder_xlch]

Or like when you were a kid and drilled out the nozzle on a squirt gun so it would shoot more water but it didn't work so well, did it?

[cjbiagi]

24 years old??? My car is older than you As far as the brake pressure issue, trust me Chuck knows brakes.