Dual plane porting results........

[70imp355]

Well I was having a good sized leak out the rear of the intake manny so decided to remove it today and while it was off i thought id put the ole porting skills to work and see how it went.

First thing I did was use the a piece of transfer paper and did a rubbing of the 195 AFRs so that I had the exact dimensions of the ports and then i transfered them to the intake. I scribed it to the intake, and was a bit shocked at how much they needed to be opened up. The ports of the rpm air gap are pretty rough n irregular shaped lol. So i spent about 30 to 45 mins on ea port matching it n opening up the runner as far as i could reach. Paid more attention to bad casting, smoothing out the radius, and improving the floor to give it a better entry to the head. All an all was very happy with how they turned out, started with my bits to get it cut to where i wanted n then final shaped with 80 grit sandpaper rolls.

Second thing i wanted to do was lower the divider bout 1/2 inch more, open it up n gasket match the entry. i scribed the top n opened it accordingly n out came the die grinder to make quick wk of the divider. i then spent 3 hours shaping, smoothing n cleaning up the entry, improving the ports for improved airflow. All n all i think it turned out nice n hoping the car enjoys the better breathing if nothing else the oil leak should be good now lol.

Things I have noticed was that it has even better response than before and this includes off idle and midrange. But the top end seems to hold on longer as well so I decided to see what my 1 inch HVH spacer felt like over the 1 inch open spacer I had on. I would have thought that the hvh tapered would have even better response and midrange but much to my surprise the 4 hole HVH was a dog off line, and didnt pull near as hard as the 1 inch open spacer. This was pretty strange to me since I made sure the jetting was optimum for both spacers. But over all the HVH feels A LOT slower over entire rev range than the 1 inch open spacer and that includes response and midrange.

Im starting to think that my car is simply begging for a single plane, because if both response, midrange, and top end are improving with the open spacer, with the divider all but gone an slows down with the 4 hole just seems like its wanting to breath. I may be wrong in my thinking so let me know what the pros think and on another note no more leaking seal lol.

[lada ok]

Well done, this is the part that wins races, not just bolting it on,
This is usually the first thing I do on a budget hop up. matching ports / flanges / carb bases, remove any choke spindles butterflies. and smooth out the carb top with polyester putty to then form a bell mouth . you can catch 8 - 15 % HP for almost zero cost

I would have radiused the upper port curve on the deeper lower runner if poss
having the open spacer tells me that all the ports can draw off all the carb, witch means less pulsing and the flow through the carb is greater
having a four hole spacer causes the opposite flow characteristics. Now one barrel is sort of supplying 2 cyl, with pulse interference from the other cyl's
I think you would find that if the mani had 1 hole / 2 cyl that matched the carb base, it would be miles better, although you may have to step up to a larger carb, and the botton end would never be up to the open spacer

[wyrmrider]

so how does this mod fit with the keep completely separate theory of dual plane performance
how would the rest of the mods work or be different if the divider had not been cut down

[70imp355]

as for how it changes things I have no clue it still flies off the line like nobodies business and will kill the tires if i let it. But like I said I thought with the tapered 4 hole that goes from 4 hole to open it would still be considered open but the results say differently. I have the one in the pic below and have it mounted properly with the taper pointed down ...... yes I have seen a guy do it upside down ..... lol maybe on to something lol. An for some odd reason it loses everywhere in the rpm range.

Hey lada ok would love to hear some suggestions I love to learn and tinker so i could make a fun weekend playing with it some more and like u said free horsepower is always the best lol. I tried to follow Chad Spiers awesome looking work i saw pictured below but couldnt see a lot of it so i know it can be better and wish i had a flow bench to even out the flow on ea runner and see if I can get them flowing more as well.

[lada ok]

Well, someone may be able to suggest a better mani /carb set up ?
So why didn't you remove that divider plate completely ? looks to me that it does more damage to air flow than good. Try it
Is there a mani available that mounts the carb at 45* to the crank C / L ? That would move the carb barrels further toward the front and rear cyl's
I think your getting close to the best that this combo may give
I've heard of a thing called a spread bore carb, whats that ? ( are the barrels further apart ? ) if so that would be a goer, and you would need a mani that was at least 3" higher with all the runners meeting in the center

The next step is also very easy and well within your capabilities by the look of it, means you have to pull the heads off, no biggie

[BOOT]

What size is your carb?

[70imp355]

Carb is a quickfuel SS-830 Dp, and is not a spreadbore like the qjet it has slightly smaller primary venturi than the secondary but the baseplate is square same size throttle blades.

I think I may remove it and take out the divider like Spiers did in the above pics and then open up the roof radius some more and then square up the mounting flange as well.

[Tuner]

A dual plane with the divider cut down like that will inevitably require stagger jetting. As an example The L-88/ZL-1 BBC carbs were 78-82 P and 82-80 S. Probably benefit from a spivy on a booster or two to steer the fuel to the lean cylinders. The L-88/ZL-1 carbs have the spivy on the boosters with the larger jets.

If the divider is cut down to the upper plenum floor the puddle of fuel will run into the lower plenum so the cylinders fed by the upper plenum will run lean and the lower will be rich.

The 3418 is used on the factory intake with the section of divider only cut out between the throttle shafts and down to about 1/4” above the upper plenum floor. The spivies point fuel to cylinders 4 and 5. You can find a picture in the “How To Hot Rod Big Block Chevrolets” HP Book. Jetting is 78-82 primary, 82-80 secondary, 82 jets go with the spivies.

On a SBC with a regular RPM Performer (not air gap) it required a spivy pointing at #8 on the booster feeding 5 and 8 to move fuel from 5 into 8 so the exhaust temps were 15-20 degrees apart instead of 300.

[lada ok]

make sure the bottom of the 1" plate matches the carb at that mating place but has big sweeping radius on the bottom face if it doesn't match the mani

[mag2555]

I have never seen a 4 hole spacer of any kind when bolted right up to the Carb mounting flange on a duel plan manifold do anything but knock power off of the motor and this is due to the spacer making for a tighter turning radius into the short plenum when it's the exact dam opposite that you want / need!
You can clearly see it screwing things up on a simple flow test!

[pamotorman]

if you completely remove the divider on a dual plane used in circle track racing you will have the passenger side rich and the drivers side lean because of the "G" force in the turns. the BBC L-88 intake left a small lip to prevent this in the turns.

[70imp355]

well i still hve a decent sized lip on it ill probably leave it as is so that i dont make the prob worse but i have already upped the jet size on the 2 that tuner showed above thats funny cus I had already read this in another article and so I did this to make sure i didnt have a prob. I have been reading the plugs and monitoring the afrs with my buddies afr gauge everything is pretty close according to those 2 things.

[PackardV8]

I didn't notice any mention of displacement and cam specifications, toleration of high/rougher idle and that's the determinant of what can/should be done with the manifold.

In general, if one wants street driveablility and fuel economy with a bit too much cam duration, preserving as much of the dual plane separation as possible will facilitate that. The more open the dual plane, or going to a single plane, the more of the overlap each cylinder sees during the intake opening.

So yes, opening the dual plane git's 'er going as the RPMs move up. Just know there can be bottom end and idle tradeoffs.

As an extreme example of that, a richie racer bought an old Can-Am with an aluminum BBC and IR injection. Maintaining and tuning the injection was a bit beyond his abilities, so he had it swapped for a single plane 4-bbl intake. With the IR, it idled nicely and could pull the close ratio gears around the pits and on parade laps. With the single plane, the idle had to be higher and even then was rougher and very difficult to get out of the pits and to keep running in position on the parade laps. He had to change the final drive way lower to be able to drive it. As previously mentioned, custom carb building/tuning with ears on the boosters might have helped, but personally, I'd have gone with a shorter duration cam with less overlap, since it made more power than he could handle anyway.

[70imp355]

Sorry Packard the engine is a 11.3 to 1 cr 39 quench 397 stroker sbc, 4.04 bore and 3.875 stroke scat light weight forged internal balanced crank, scat forged i beam stroker rods with 7/16 arp bolts, cp bullet 2618 forged pistons. It has 195 AFR street eliminators, SS-830 qf dp, 1 5/8 headers ( but having a set of 1 3/4 being made right now) cam is a hyd roller from clay smith designed by straub 292/294 adv 233/235 at .050 584/544 lift 108 lobe sep 104 icl (but having someone spec me a better cam) this is a daily driven car that will see the track during track season but is driven everyday. Has 3000 stall, jakes stage 2 th350 and 3.55 gears.

[Strange Magic]

Single plane manifold, 1 7/8th header, 3.5 inch can and it will be an entirely different engine. The power gains will be tremendous. Don't waste anymore time on that dual plan. It has enough arm and compression in that engine that you don't have to worry about air speed at low rpm.