crosswind air gap or stock 4bbl manifold

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lilredridinghoo

lilredridinghoo

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more benefit or more loss ??

thinking about changing from
1971 OEM spread-bore 4bbl cast intake to crosswind air-gap intake

guess i will loose some power at the low end ...

but maybe gain some at higher rpm




- 273 .040 over

- CR 8.8:1

- Cam specs: lob 112, duration 050 lift 204-214, ad dur int.270 exh.280 Valve lift .420 .443

- Heads #920 runners opened up to 340heads size, bowl blended, valve bosses grinded down, exhaust runners and combustion chamber polished

- Valve springs compcams 901-16 (353lbs seat load 101 closed load 242)

- Headers

- Rear end 3,91 with sure grip

- Tires 26.1 hight

- Holley spreadbore 650cfm (4011)
 
So for that cam i would like to say the stock 4bbl intake is the better choise!

BTW: is the Holley spreadbore a mechanical double pumper?
 
The 4011 is a vacuum secondary carb. I had one.
 
Stock intake should be fine for that setup..if you do buy an Air-gap buy the "real" one an Edelbrock not that crosswind chinese junk..
 
If you get the chinese one , be prepared for it not to fit, basically, they suck. I'd spend the money trying to raise your compression..
 
Yeah that cam will put the Dcr down around 6.77. With those 3.91s, and short tires, a good Dcr to target would be around 8.0 to 8.5. I'd go high.
So that would be 10.5Scr for a Dcr of 8.0 with a 69* ICA. And 11.0Scr will get you 8.4Dcr, at that same 69*ICA.
The extra compression will, really get you off the line, and make a nice fat midrange. Plus then you could put on almost any street intake that you like.
 
The 71 340 intake is the best of the 4bbl intakes only better SB intake would be the 6 pack. I would not go to a air gap for your application.
 
That cam seems to me to be a pretty small cam at 204-214 @ 0.50"
Can't see it effecting DCR that much.

The air gap is definitely gonna give more top end
Maybe with a little loss at bottom end. On 340/360 they don't seem to sacrifice much bottom end but who knows on a 273.

Your build right now is at the border what I'm mean by that is everything you pretty much do will trade bottom end for top end like if you go up in cam, carb size etc..

So you got to decide what you want.
 
A 273 needs to rev to get power. Mopar made the factory manifold to get a "best of both both worlds" approach. I like mine. :burnout:MT
 
If you switch to the air gap intake you will need a square bore carb or an adapter for one.Keep the stock intake.It isn't hurting you.
 
The .050 duration has nothing , absolutely nothing, to do with calculating Dcr. Only the ICA matters, along with several other specs,such as; the true Measured Static cr, rod length, and boreNstroke. In this case the 270 adv duration and the 114LDA translate to an ICA of about 69* depending on where you install it. In this example,I chose to install at 114*CL.
If the posted specs are correct, this cam has some very looong ramps.( 270 - 204)/2 = a 33* ramp.. I have a hughes fast rate cam that is published as a 232*@.050, and is only a 276 advertised IIRC. (276 - 232)/2 =a 22*ramp. So for nearly the same advertised duration, my cam is 232 - 204 = 28 * bigger. Thats about 4 cam sizes or better. My cam will idle like the OPs, but make peak power some 800 to 1000rpm higher. The extra rpm builds mathematical or theoretical horsepower.Let it breath, and it becomes real.
Those 050 cam specs sound very familiar.Isn't that just a tad bigger than a 360-2bbl cam?
 
I just looked on Ebay. The crosswind is $255 with free shipping and the real Eddy Air gap (new) is about $300. For only $45 more you can get a proven performer that will absolutely fit. And don't forget that all Edelbrock products are made in the USA.
 
If you're not going to stick with the stock 340 spread bore intake, then I would say the best one for a 273 is the old Edelbrock D4B for the 64-65 273, or the Edelbrock LD4B for the 66-69 ones.

They pull great off the line and will give it some top end also... And will match the stock ports better if you didn't already gasket match them to the 340 intake...
 
harrisonm said:
I just looked on Ebay. The crosswind is $255 with free shipping and the real Eddy Air gap (new) is about $300. For only $45 more you can get a proven performer that will absolutely fit. And don't forget that all Edelbrock products are made in the USA.
Click to expand...
Love your country and supports it's workers!!!
 
Thanks for your opinions and input. .. and sorry for my late reply

Time to give you an update / more info

Regarding the cam mentioned above... it's very very tame, as i found out in the meanwhile, it was supposed to be sold as a exchange cam for pick ups like W200 etc with 318 engines
So i will just swap that stick against a XE274H from compcams i have laying around

About the carb . Nope it's not a double bumper it has vac.secondaries. . It's a nice carb but it starts to get issues when it's really heated up

As i just purchased a 600cfm Holley squarebore unit, i will also switch the 4011 against that one.

The Chinese Crosswind is also allready laying around in my garage (bought that one to put it on a 318 magnum which is also stored in my garage, but couldn't manage to go on with this block at the moment, but maybe i should let the 273cui as it is, and work on the magnum instead. Even in stock trim with manifold and carb the magnum should make decent power)

Heads are gasket matched for 340 runnersize also ported etc

The question is now. .. just swapping intake cam and carb on the 273 and trying out whether it will work or not (guess iwill loose bottem end power with the XE274H )
Or going with the stock 318 magnum and simply bolt on intake and carb (and the stuff needed like water pump, oil pan etc)
 
You don't mention valve size which would indicate what the bowl and transition might look like but you may already have too much port valume. That makes it sluggish even with a smaller cam. I would keep the setup you have, or locate a 318/360 Performer to use on it and don't port match it to the 340/360 but maks ure the roof of the intake and roof of the head port opening are matched in height (you can leave the intake's port narrower). That smaller intake port will help the response a little. If you run the larger cam I'd expect it to be flat regardless of whatever you do.
 
I would not buy cross crap intake and I ran a real Eddy air gap on a mosty stock 340 1.88 valve it ran better then the stock ... My mosty stock 340 responded well to a Eddy air gap intake and its good intake if you end up grading your motor in the future
 
oldkimmer said:
............That xe 274 will kill the bottom end ..............kim..........
Click to expand...

A set of Rhoades lifters can bring that back without sacrificing the top end...

Some people like them, some don't. I've had great success with them.
 
ChinaGap aint worth the "savings". Bolt bosses milled at wrong angle. Get ready to experience oil weeping up the bolts and making a nice pond of oil sure to make a mess. My 2 cents worth
 
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