340 iron or Airgap-(knock-off) intake on 273 ?

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lilredridinghoo

lilredridinghoo

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hi there,

it´s been a long time that i posted something here...

as the magnum engine in my 1965 Barracuda suffers from a spun rodbearing and my wife allways complained that she was affraid to drive the light car with that engine. Also it was a bit tricky with short gears and aggressive bumpstick.
So i decided to put the orig. 273 back into it just to make it a nice street drivable car.

Using what is being around me in my garage im thinking of using a 340 HP camshaft with matching springs - Heads will be 318 with standard valves, bowl blended and a bit of port work.
Headers, stock converter and 3,91 gears (26" tall wheels in the back)

question is now: using the heavy 340 iron intake or the light AirGap-knock-off-thing which i used on the 5.2 magnum

for the carb i´m thinking of using a Holley with VacSec and 600 cfm, which i also used on the magnum

i´m a bit worry to loose too much on the lower end due to the bigger plenum the AirGap has, but on the other hand it provides good flow and has longer runners, which is also good for torque

thanks a lot in advance for your thoughts
 
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Just my thoughts is a good 650 double pumper on a dual plane manifold would work great on the street.
 
The LA intakes have a slight issue with bolting down on a Magnum head.... unless that problems taken care of...

Use the iron intake. 600 cfm's.
 
You didn't mention which 273 you had, the low compression or the high compression piston engine. The original 273 heads are closed chambered heads. The 318 heads are open chambered heads that will reduce your static compression into the 8's and your dynamic compression with that cam into the 7's. Teem that with your Air Gap intake (which won't even bolt to your 318 heads) and you have a disaster waiting to happen.
 
if he has the magnum/air gap knock off. it will bolt to both magnum & LA style heads.
both are dual plane, both are probably more intake than a mild 273 needs.
 
If you're using Magnum 5.2 heads on it (I would if it's just the lower end) run the aluminum deal you have. If it's a set of LA 318 heads, sell the knock off or trade for the 318 Performer and run that. I wouldn't run either intake you have with the LA 318 port head. It will run. Just not how I'd want it to.
 
@toolmanmike it´s the low comp 273 with flat top pistons 040 overbored

CR will be 8,8:1 (measured and calculated) with the given 318 heads ( #920 with opened up runners to 340heads size, bowl blended, valve bosses grinded down, exhaust runners and combustion chamber polished)

the guy which gave me the 340 cam - told me that duration should be somewhat about 210 Int and 220 Exh @.050" and lift should be .428" and .436" about as far as i know lift was about .429" and .444" maybe i should measure this

@moper i just had the same thought "what about running the Magum Heads on the 273" but it just leads to problems with valve size vs bore and also rocker oiling thru the pushrods will be the next issue...
 
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CR will be 8,8:1 (measured and calculated) with the given 318 heads ( #920 with opened up runners to 340heads size, bowl blended, valve bosses grinded down, exhaust runners and combustion chamber polished)
OK, You're good. The #920 heads are closed chambered heads. Us guys out here in internet land don't know what you have going and what you know unless we ask. There have been many unsuspecting Moparites that have bolted on some unknown small block heads teemed with a "too big' cam only to be disappointed with the results.
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Sorry to hear about your Magnum. With the ported heads the air-gap should be fine. Is the camshaft used or new?
 
Timo,

Chris has got the Offy 360° LA-Intake lying around from your old 318....send him a message, i think it´s for sale. Otherwise i´d use the crosswind intake.

Why not put a stock 5.2 Magnum (converted to carb) in the Car? They are cheap, and run pretty good. I put one together for Chris Valiant after he killed the 318....it´s running nice and smooth....would be a nice daily driver and can still do 14´s at the strip.

Michael
 
360duster said:
Timo,

Chris has got the Offy 360° LA-Intake lying around from your old 318....send him a message, i think it´s for sale. Otherwise i´d use the crosswind intake.

Why not put a stock 5.2 Magnum (converted to carb) in the Car? They are cheap, and run pretty good. I put one together for Chris Valiant after he killed the 318....it´s running nice and smooth....would be a nice daily driver and can still do 14´s at the strip.

Michael
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And the old LD4B's work very well on 318 heads.
 
lilredridinghoo said:
@moper i just had the same thought "what about running the Magum Heads on the 273" but it just leads to problems with valve size vs bore and also rocker oiling thru the pushrods will be the next issue...
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No issue on the oiling part. I'd think bore notches would be fine too although I never tried. The Magnum is a much better head than the LA 318, and you're already talking about redoing and porting those. Up to you but that would be my path unless and until there was no notch that would work.
 
lilredridinghoo said:
@toolmanmike it´s the low comp 273 with flat top pistons 040 overbored

CR will be 8,8:1 (measured and calculated) with the given 318 heads ( #920 with opened up runners to 340heads size, bowl blended, valve bosses grinded down, exhaust runners and combustion chamber polished)

the guy which gave me the 340 cam - told me that duration should be somewhat about 210 Int and 220 Exh @.050" and lift should be .428" and .436" about as far as i know lift was about .429" and .444" maybe i should measure this

@moper i just had the same thought "what about running the Magum Heads on the 273" but it just leads to problems with valve size vs bore and also rocker oiling thru the pushrods will be the next issue...
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What year is the 273? Does it have the stock solid lifter cam? Magnum heads will require a hydraulic cam (your 340 cam), oil through lifters, and hollow pushrods of a specific lengeth because Magnum's were roller cam engines and have different valve train. It can be done but you have to do your homework.
 
@360duster - Silvia was complaining that the 5.2 was way to aggressiv (it rev´d up pretty fast to 7000 RPM with the regrinded cam and the 3,91 gears), and i´m just thinking to get back to a simple streetable car. i also thought about replacing the rod and the crank and going on with the 5.2 - but there will be still an issue about having it "street legal" in Germany, you know (H-Kennzeichen etc :(...) maybe i will re-do the 5.2 magnum and stick it sometime in my D100-Truck ...
but thanks for the hint that Chris has still my old offy-intake. the offy was on the 273 when i bought it :) it was not that bad on the 273 these times.


@toolmanmike - the block is the original from 1965 which came with the car. But someone changed the heads in the history, so everything is converted to hydro cam and lifters.
Btw.. the 920 Heads are not closed chamber heads, but they do have smaller combustion chambers compared to most 318 LA-Heads i have seen - about 63-64 cc is what i measured

@moper - as toolmanmike wrote i would need oil through lifers and pushrods to get the magnum-heads work on a LA block. But your right they have plenty of flow compared to LA-Heads.

Both heads are allready done and usable as they are - no work needed on the Magnums or on the LAs.

at the end i´m also a bit on budget.... that´s why i tried to figure out the best way with the things i have laying around
 
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