I'm building a couple of 600 vacuum sec carbs for a guy with a tunnel ram. I told him that the 600's will work but are not ideal t-ram carbs. Since I'm not going to be present when he installs and tunes, I'm trying to get the initial dry settings close. What I'm not sure about is the power valve size. Since tunnel rams don't produce very much if any vacuum, I'm trying to guesstimate what size valve to get him started with. Any of you running a tunnel ram with 600's?? What size valves ya got? I was thinking around 4.5 hg. any suggestions?

Also wondering if there might be a benefit to step up the jetting and plug the power valve ports.

On the intake are they side by side or front to back . If they are side to side with no p/v part throttle the extra jet makes one bank very rich from what i have seen.

These will be end to end......but you bring up a point I would like to debate. If you think about the VERY small difference in throttle blade positions from being end to end or side to side.....first of all, one blade will be in the same spot (the passenger side front). If you think of that 1"-2" diff with the other throttle blade and the massive amount of plenum volume these rams have, You think that's enough to make on side of the motor richer? Not to meantion that the primary blades open towards the center of the carb and not the front. I don't have the equipment to prove you wrong. It just seems that there is not enough difference that a street motor with a 4 speed and low gears would see.

Does anyone know this to be true? I'll be setting up my own ram real soon with 450's and don't want to create an unnecessary rich or lean condition!!!

This is what Iv'e seen on the dyno . these were dominators on sheetmetal on a big block trying to get all there was . Just trying to help with what Iv'e seen .

......and it's appreciated Doug. I think those sheet metal tunnel rams are more of a straight shot anyway. Seems that you would have more of an issue on the street if anything since doms run idle to WOT. I don't know. Thanks!

Primary power valves are a must on the street regardless of the induction type.Blocked off primary pv,s are strip only imo.
Valve timing events/cid/initial timing/idle rpm are major factors dictating manifold vac #,s more so than the type or design of the manifold.
Stab a t-ram on a stock 350 and see higher idle vacuum than a single plane atop a 327 with a nasty a$$ solid roller ground on a 104 lsa at the same idle rpm.
As for the p/v opening point..it should be selected based off of real world cruising with a vacuum gauge.
Thats just a start with a street deal..the main jet should remain on the lean side..the pv opening point should be based on when enrichment is reqd on accel under load and the pvcr,s opened accordingly to compensate for the restriction in the smaller primary jet.
I most likely will get slammed by those that say an open p/v at idle vac will cause a rich condition.A blown/ruptured diaphram will leak raw fuel into the pv chamber and flood at idle..an open at idle pv will add to main well head pressure but the ifr still dictates and the volume of emulsified mix can still be regulated with the idle mixture screws.
Without knowing the total combo...err on the side of safety and go with a 6.5 pv .Testing with a vac gauge later will help you dial in the combo.Hope this helps you.

You and I think alike George. Already put them together and installed stock jets (66) with the stock 6.5 power valves. I told him to have extra valves and jets on hand. I would rather ship him some fat carbs than lean ones. runnin' fat won't hurt his motor but we all know what lean will do. It would be my luck that he would be real lean and love the power until she let go!!!

I've got dual 450s sideways on a weiand ram 406 sbc. I converted them to 4 corner idle to get the plugs to even out their idle color. When the carbs were inline they still had uneven plug colors (sec side was rich), the pattern was just 3478 rich instead of 2468. The motor ran the same either way. I've also converted them to vac sec to slow down the initial opening and get a crisper launch. I probably should have got the 600s (Summit combo) but when I ordered it I thought the 450s were vac sec. They work good now but it took a lot. Lucky I enjoy tinkering!

I've got dual 450s sideways on a weiand ram 406 sbc. I converted them to 4 corner idle to get the plugs to even out their idle color.

What? The only way you can correctly do that is to somehow plug the center of the idle transfer channel in the base plate that links the secondary bowl to the primary so the secondary gas doesn't go stale from someone not getting into the secondaries (light foot). You also have to drill idle discharge holes below the secondary butterflies so you can truly make it a "functional" 4 corner carb (plus base plate mods). Did you do all that??? That's a lot of work man.

I followed the Holley modification books for 4 corner idle and did just what you said. I had a pair of 3310s that I robbed the primary blocks to put on the sec side. I tapped the ifrs and the air bleeds for brass set screws drilled with smaller holes. I also converted them to vacuum secondaries using the sec throttle rod and diaphragms from the 3310, the main body has all the bosses and you just have to finish drilling the passages and tap the holes. It slows down the secondaries to get rid of any bogging, even with .025 pump shooters. I wonder if I should have gotten the 1850s instead of these 9776s.

Can you tell me who is the author of that Holley mod book? I have one that is pretty detailed but I don't think it goes quite that far. Most guys put on a sec block and think they have a 4 corner. I'm wondering if they have that book on Amazon.

As to your "wonder if I should have just gone the 600 route". You would end up with a total of 1200 vs 900 cfms. I'm wondering if, even though it was a lot of work, the modified 450's might be a better fit. They should create a better signal at the lower end giving you more streetable torque at lower rpm's which is why Holley developed them in the first place (that was almost a run-on sentence):D. The Holley tech guys told me I'd like the 450's over the 600's on my 460. I asked them that very question you are wondering about. Thanks for the good info Mark.

The book I have is an old S-A Design series by Dave Emanuel from 1980. It covers the 4 corner idle and basic theory pretty good. I haven't looked at a newer one, maybe I should. For the vac sec conversion I just compared the bodies and figured out what needed to be done. I get a lot of ideas from http://www.innovatemotorsports.com/forums/index.php in their general tuning section. They talk about restricting the transfer slots and air bleed tuning in great detail. Even without the Innovate meter you get an idea for things to try. One statement that keeps popping up is "give the motor what it wants regardless of the a/f/ ratio." Full throttle = tune for mph, street use = lean it till it gets stupid, then richen back to get driveability. I'm sure the meter would speed up the process some, and for a blown or nitrous car it's probably mandatory. Since the main circuits are flow activated a tunnel ram tuneup keeps mostly stock jetting. The idle circuit is vacuum activated so that needs to be cut down a lot with 2 carbs.(12 inches of vac under 2 carbs = double mixture, 900 cfm thru 2 carbs = 450 thru 1 carb so mains are normal.)

Yes but just remember that Holley made the 450's to be ran in pairs so they come with really small idle feed restrictors to compensate for just what you are talking about.