Ok, I got bored at school today and I got to thinking... Is it possible to modify a Cross Fire Injection manifold to take two 4bbl carbs? I think the basic design under the throttle bodies is pretty much the same as it would be on a 4bbl manifold, no?

And, even if it can be done, is it really worth the effort? I don't know much about the CFI and TBI systems on 3rdgens because i've never worked with one, but I kinda get the basic idea of how they work, and it seems like it could work.

Does any of this make sence/seem possible?

 

go on google.com and look up the crossram intake


tell me what ya think



btw, if you're doing a google search and just want pics, click the image tab....

 

Wow... that was quick, lol

I'm way ahead of you... i already did that. Its just that I've never heard of this being done before, and I can't find any diagrams or anything to see if the 'guts' of the manifold (the CFI manifold)would work properly with a couple carbs.

 

offenhauser makes a manifold thats similar to the cfi manifold and it probably flows a whole lot better too.

 

I saw that Offy one... nice peice. Just that it looks way too tall to fit under a stock hood, but I'm sure that a CFI manifold could.

I've been looking at a few websites about people modifying them, and it really does look like it would accept a carb pretty easily with some modification (read: butchering) of the top plate. None of these sites had people actually putting carbs on them, but had good shots of almost all angles of the manifold.

 

#1

 

#2

 

i think one of the complaints i heard was that they didnt flow all that well. I dont think those long runners in the intake base complement high revving engines that demand alot of air. Not to say that you cant make power with it, of coarse. Cant remember his SN right now but someone stuck one on a 400 and ran low 13's with it, but that was with a set of bored out one barrel tbis.

 

oh, i also remember someone on this site sticking a 4 bbl carb on one. He used a plate that he fabricated to mount up the carb.

 

So it can be made to work with a carb? Good to hear... I planned on using two small 4bbls though. One were each TB originally was.

And it doesn't have to feed a huge engine to absurdly high rpms... it will only have to feed a warmed up 305 (i'm guessing 270-300hp) which is being rebuilt right now.

As for RPM range, I don't plan to use the engine at anything over 5500 or so rpms.

Will that manifold, with two small 4bbls, flow well enough to feed this engine? I planned on doing quite a bit of reworking to the manifold, like smoothing out the ports (cast very rough from what I hear) and opening them up as much as is practical to do. The top plate would be either a whole new custom peice, or I would modify the original to work with the two carbs, like opening up the intake holes, probably to the same dimentions as another 4bbl manifold, and of course drilling new bolt holes to mount the carbs.

I like the idea of using one of these because it would be the only dual quad setup that I know of that won't stick up through the hood, as well as being able to keep an HEI ditributor instead of the old points type.

And plus, it would be very unique IMO

 

it should be enough to feed that motor. People run 13's though it so it shoudl be able to feed 275 HP or so.

 

Cool

So this custom top plate you mentioned a few posts up... how was it done? I mean, was it just sheet metal, or was it the original top plate that mounted two TBs modified to mount two carbs?

A pic would be great if you have one

I'm REALLY interested in doing this now...

 

if i was doing it.....

i would make a custom top plate out of some plate and mount 2 500cfm carter style carbs on there....


if i was doing it.....

 

lol, i jsut thought of somthing

if you modded the ends of the runners to have multiport EFI, you could hide the fuel rail and injectors inside the manifold.

 

i'm surprised no one has mentioned that this design evolved from the 1969 Z28 302 cross ram manifold

 

Just a few things thoughts..

Why a dualcarb setup on a mild 305 (or 350 for that matter)? Other than looks, it'll be a PIA to tune. If you do it, I'd suggest going down to the Holley 390CFM carbs

I recall on the DIY_EFI there was a link to someone who was tuning a CFI, they had the intake off and the ports were very small...something like 1.25in, maybe even less, also, IIRC, the way the intake was designed, there wasn't much room to open them up either.

Plus the layout of the CFI intake, probably doesn't yeild an off the shelf linkage setup for carbs, so you'll be fabbing your own...probably easier to go with an aftermarket setup that can be pieced together with off the shelf parts that work.

 

Thats what got me interested in this in the first place

That was the plan
I just want to go with dual 4s on this engine because I've just always liked multi-carb'd engines. I don't really expect it to make so much more power than a single carb set up, because i know a single 650 would be just fine. I've just always loved multi carb engines. AND, I have the patiece for them too, lol.

Plus, from what I hear about the old Crossfire '82 Corvettes, they were very torquey at the bottom end and, despite the small runner ends (I know, they are really small), they could feed the Corvette's 350 up to 5500 rpm without much trouble. Since 5500 is the highest I plan to wind up the 305, I think it will breathe fine, even though I do plan on a little port work on it.

Oh, and making a linkage isn't a big deal. I've done stuff like that before. Just takes a little creativity

 

Creativity is the essence of HotRodding ...I've fabbed several linkages on inline 6's for dual carbs (one for a triple setup), never did for V8's, it's neat to say "I did that", and have look and work good too.

Speaking of the crossram setup, back in the late '70's I raced a '68 or '69 Camaro w/a SBC and the crossram, he had a 4spd..I seem to recall he either had clutch problems or a high geared rearend...but anyway, he couldn't get off the line very well, I raced him 3 or 4 times and took him by 6-8 carlengths, then at about a 1000ft he'd come screaming up on me and pass me before the end of the 1/4 like I was standing still...definitely can make some HP with the crossram

 

Great minds think alike!

And, IIRC, the "problem" the 302 had with the original '69 Crossram, was that the runners were just way too big, and the carbs what were mounted on it were two 650 Holley DPs... definitely overkill. But isn't overkill also the essence of HotRodding?

As far as runner size and carb size goes, I think the smaller-runner Crossfire and two 390 or 450 Holleys is much better suited to low end grunt than the large runners and two 650 Holleys of the '69 Crossram was.

I know what you mean about those '69 Z/28s though... once they get going, they really haul ***!

 

Anyone else have any input on this little project before I do it?

 

I have already done this. It's on a 283 that is going to be in my 28 Model A. I can't take pictures of the setup because the engine is 12 hours drive away from me right now.

I got a 1/4" sheet of steel cut up and set up for 4bbl carbs at a local machine shop. See how long the runners are? I shortened the two middle ones about halfway by opening the top part of the plenums, and the other two I opened up all the way. Threw 2 390cfm 4150 Holley's on it. Once I bring it back to here to re-unite with the body, then I'll find out how hard it is to tune.

 

Port the runners! It's easy, because they are relatively straight, and it'll make the single biggest difference. In stock (as cast) form, the runners are too small for a 305 at 5500 RPM. But porting will make a HUGE difference, and it's easy and cheap.

 

My number 1 spark plug always looks like it has been burning leaner than the rest. I wonder if that set up would help get the fuel to the front cylinders better.

 

DETAILS DETAILS DETAILS!!!

When you get it back, you gotta let me know how it worked out!!!

Oh... and if possible, could you take a pic (or a few ) of it? I'd be very interested in seeing how you set up the carb linkage, and maybe how the openings in the top plate for the carbs were done if you get a chance.

 

I thought anything over 600cfm of carbbage (making up words now) was overkill for a 350, let alone a 305. I wouldn't port the intake, the restriction might help...

 

The restriction WON'T help. Even on a 305, porting the intake realizes a huge gain, for nothing more than some labor. AirAdam, Please port the intake, don't listen to aaron7.

 

The openings in the top plate are like how the TBI's had the top plates; they are just 4 holes to match the carb.

The linkage that's on there now is pretty ghetto IMO, its like a single plane linkage attached on both carbs with a crossbar synchronizing the two. Like this:

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I know its a bad pic haha. I've fired it up, but I didn't spend any time tuning the setup. I know it runs but how well.........well I'll have to wait.