Progressive Carb Linkage

BCoupe · Post by **BCoupe** » Fri Dec 14, 2007 2:02 pm

I want to put a pair of Edelbrock 500's on top of a tunnel ram (350 Chevy stroked out to 383).

I have been reading up on fitting a progressive linkage rather than the standard rod connectors and as they are not too expensive have ordered one from Summit.

Any tips on fitting it? ... main carb at the back? ... second carb to open when?

The model B is very lightweight so the normal "problems" that you can get with a tunnel ram on the street are pretty much not evident (or rather weren't before the engine blew when it was last fitted LOL)

Cheers

Eliot · Post by **Eliot** » Sat Dec 15, 2007 8:40 am

I take it you are aware that the carb has a progressive linkages.

ian.stewart · Post by **ian.stewart** » Sat Dec 15, 2007 9:25 am

If I think what you have bought is right, I dont think the progressive linkages will work in the way you want, the progressive linkages are for letting a carb be slow and easy to control at low throttle openings and be progressivly quicker opening to WOT, not designed to be used to run a secondary carb progressivly from the first. Obviously TriPowers do work but are vacuum actuated, and the 2 secondary carbs are directly over 4 ports each, these are designed for the job and even trying to set them up for a standard engine is a total nightmare.
As for setting up a carbs and manifold that is designed for WOT and not really a street manifold, I would think the main problem would be the mixture dispersion from one carb around the engine with the 4 pistons below the carb running rich and the other 4 running lean.

JSF55 · Post by **JSF55** » Sat Dec 15, 2007 10:01 am

I think Ian has got it right, u need to balance the pair of carbs to open at the same time and floow sufficent fuel to kep it at idle then rework the rest of the carbs to give good WOT response, it might take a while but will make for a more practical drive

JC. · Post by **JC.** » Sat Dec 15, 2007 4:25 pm

Can you get manifolds off the shelf that let you run a Rover V8 on two edelbrock 500's ?

Post by **katanaman** » Sat Dec 15, 2007 4:52 pm

JC. wrote:Can you get manifolds off the shelf that let you run a Rover V8 on two edelbrock 500's ?

Dont think so, this thread is about a 350 chevy

JC. · Post by **JC.** » Sat Dec 15, 2007 5:12 pm

katanaman wrote:
JC. wrote:Can you get manifolds off the shelf that let you run a Rover V8 on two edelbrock 500's ?
Dont think so, this thread is about a 350 chevy

Thanks... don't quite follow you on the 2nd part???

JSF55 · Post by **JSF55** » Sat Dec 15, 2007 6:03 pm

This thread is about a 350 chevy engine running a tunnel ram, as for the rover, i think someone produced a manifold at one time to run 2x 2 barrles, i think 2x 4 barrels would over carb the motor, some people struggle to get the jetting down low enough with one !

ian.stewart · Post by **ian.stewart** » Sat Dec 15, 2007 6:37 pm

Both Edelbrock and Offenhauser have offered twin 2 barrel manifolds for the 215 Buick, I dont think they are available new anymore

kiwicar · Post by **kiwicar** » Sat Dec 15, 2007 7:24 pm

Hi
the stuff I've read on street running a tunnel ram on a small block chevy have said the best results are achieved with vacuum secondary carbs, using a progressive linkage that opens both primarys together but slowley at first then more rapidly as the pedal is pressed. This set up is meant to be work well giving similar drivability to a single plane manifold at light throttle. An all mechanical set up is meant to be very tricky to get to work as it is difficult to get the linkages set up so as to give small enough throttle openings at the start and still have enough range on the throttle peddle to get the secondarys open by full throttle, without it being like an on/off switch from half throttle not a problem on a drag car, in fact a posotive advantage as it gets the engine effectivly on full throttle quicker.

Keep in mind these manifolds are designed to let each pot see the equivilant of a 1000cuft carb at full throttle, until the revs get up above about 3500 just the primarys open on both sets of carbs will be enough to feed the engine without restriction.
Juts opening the primarys on one carb to start with, then trying to open the second carbs primarys while the secondarys on the first carb are opening would not work, mixture distribution would be all over the place and you would have very uneaven cylinder filling.
Mike

BCoupe · Post by **BCoupe** » Sun Dec 16, 2007 10:32 am

kiwicar wrote:Hi
the stuff I've read on street running a tunnel ram on a small block chevy have said the best results are achieved with vacuum secondary carbs, using a progressive linkage that opens both primarys together but slowley at first then more rapidly as the pedal is pressed. This set up is meant to be work well giving similar drivability to a single plane manifold at light throttle. An all mechanical set up is meant to be very tricky to get to work as it is difficult to get the linkages set up so as to give small enough throttle openings at the start and still have enough range on the throttle peddle to get the secondarys open by full throttle, without it being like an on/off switch from half throttle not a problem on a drag car, in fact a posotive advantage as it gets the engine effectivly on full throttle quicker.

Mike

Thanks for the replies,

Mike,that's pretty much as I had understood a progressive linkage to work so I'll give it a try. It was running very well on the straight linkage but was advised by a few guys in the States who are running dual quads to give a progressive a try.

The Chevy was around 450 HP before the rebuild and should be easily in excess of that now it is going out to 427 cu in (7008 cc) so on - off switch at 3500 rpm will be interesting as SBC's are know to be capable of revving to 6500 without problem.

Only hassle will be running it in which I'll probably do on a Performer manifold with a single four barrel.

It will have a session on a dyno at the end of the running in to give me a benchmark...

kiwicar · Post by **kiwicar** » Sun Dec 16, 2007 7:26 pm

That should be fun

427 with an on off switch for a throttle

, lets hope they take the average speed cameras off the M1 before you head up to the pod with it

.
What heads and cam are you using?
Mike

BCoupe · Post by **BCoupe** » Sun Dec 16, 2007 7:43 pm

kiwicar wrote:That should be fun 427 with an on off switch for a throttle , lets hope they take the average speed cameras off the M! befor you head up to the pod with it .
What heads and cam are you using?
Mike

Mike,

Edelbrock Performer Heads, Nitrous Comp Cam, 6" rods, forged pistons. 3000 stall convertor - TH350 auto.

The blocks away at Real Steel for prep, line bore / hone, fitting main cap, cam bearing, deck block and balance.

Hopefully, it will hold together LOL.....

I'm just looking for reasonable manners on the road and a hooligan on the 1/4 mile.....

... or have I got that the wrong way round

mgbv8 · Post by **mgbv8** » Sun Dec 16, 2007 8:24 pm

"I'm just looking for reasonable manners on the road and a hooligan on the 1/4 mile..... or have I got that the wrong way round"

Nope, that's exactly what I want from my car. I can put up with a little extra attention needed to use it while on the road. But when I hit the track I want an animal that needs to be grappled with for max fun.

kiwicar · Post by **kiwicar** » Sun Dec 16, 2007 8:42 pm

I think you may have an interesting time through town with that combination. 3000 stall converter and a tunnel ram may be tricky if you are trying to pootle along through heavy traffic, but if it is mainly to get you to and from the drag strip then it should be a fun ride. What do the heads flow? I would think the performer heads are a little on the small side for 427cui and at least 250 deg of timing at .05" on the cam would be in order with the engine size and the converter and tunnel ram. Is it a flat tappet cam? or a roller?
Sounds fun I chickened out at 383cui
Mike