13s and 15mpg Magnum head 360

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racingsnake440

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I've collected most of the parts i need for the new engine for my Dart and wanted advice on a few things.

I have:
fresh .030" over short block
magnum heads milled .030" and redrilled for LA style manifold
mopar performance thin head gaskets
Edelbrock LD 340 manifold
Weiand Action Plus manifold
Holley 600 and 750 cfm vac sec carbs
Thermoquad carb

Undecided on the cam, probably one of the following:
Comp Cams XE268H, Comp Cams 270H Magnum or Comp Cams 280H Magnum
Unsure on valvesprings/ retainers etc

I'm guessing my compression to be about 9:1 but haven't got anything to cc the heads and combustion chambers with. It's going in my 63 Dart which can't weigh more than #3,200? with 3.23 gears and a 4 speed with manual everything so I don't have to worry too much about idle vacuum.

Steve Dulcich used the 280H in a 318 buildup and i figure that what my motor lacks in compression will be made up for by the extra cubes to make it work ok. However I'm concerned at how well the stock rocker gear will stand up to aggressive cam profiles. I do about 15000 miles a year and want to get at least a couple of years out of this motor. The 318 article state that the magnum head has a good flow balance and favors a single pattern cam but I'll be running Durango manifolds as I can't afford headers and wonder if it might be beneficial to have some extra lift and duration on the exhaust side?
Finally valvesprings - I know there's not much selection for the magnums. Do Mopar Performance P4876062 or P5249464 use the stock retainers or do I have to use 2.2 retainers?

Sorry about the length of the post but basically I'd like opinions on the best cam/valvesprings/retainers to use (bearing in mind this is on a very low budget) to get as close as possible to running 13s and getting 15mpg.

Thanks
 
I would use the Weiand manifold and the 268 cam, and the 750 vac. Carb from holley. then the valve springs can be stock, but if not Comp cams has a good selection of them. This way you will have driveablity for your fuel mileage and have enough power to get into the 13's.
 
I am running the XE268H cam in my magnum headed 360 in my 68 Barracuda and it's run a best of 13.7 @ 102 and I get between 14 and 15 mpg around town. I have used a 600 Holley, 725 Demon and a 750 Holley, all vacuum secondary carbs. The 1/4 times and mileage numbers are with the 600 Holley. The engine runns better above 5500 rpm with the 725 or 750 but the throttle response below 2000 is so much better with the 600 that I usually use the 600. The Holley 750 is very close to the 600 and the 725 Demon is just not happy below 1500 rpm. I am using a Crosswind manifold and headers.

My heads cc'd at 64 and it's easy to measure. A graduated syringe from the pharmacy for a couple of bucks and a piece of plexi glass is all that's needed.

The two mopar performance springs require 2.2 retainers. I am using the RT spring which is good for .525 lift and was recommended by Comp when I selected the XE268H cam. Comp now has a beehive spring for the magnum heads but don't know if it works with the stock retainer. The stock rockers work fine with the aggressive XE268H cam.

I have KB107 pistons with the block machined for zero deck with these pistons. With an 0.039 head gasket I have 10.6:1 compression.
 
racingsnake440 said:
fresh .030" over short block
magnum heads milled .030" and redrilled for LA style manifold
mopar performance thin head gaskets
Edelbrock LD 340 manifold
Weiand Action Plus manifold
Holley 600 and 750 cfm vac sec carbs
Thermoquad carb

Undecided on the cam, probably one of the following:
Comp Cams XE268H, Comp Cams 270H Magnum or Comp Cams 280H Magnum
Thanks
Click to expand...

Here is what I would do:
OK fresh .030" over short block

OK magnum heads no need to mill if you can get the CR above 9.0:1

OK mopar performance thin head gaskets I would probably go with a good MLS metal gasket

CHANGE Edelbrock Magnum Performer RPM Much better manifold, same TQ, better HP, there is a also a cheaper "Crosswind" copy of the RPM with dual Bolt pattern

CHANGE Edelbrock 600 Elec/choke Carb (4106) good street carb if not drag racing, more than enough for a 318

CHANGE Hughes HEH1523AL Camshaft. Enough cam to make about 350 HP with a 9:1 comp 360ci motor, expect to get avbout an extra 1/2 point bump in compression with the magnum heads. Mild enough to have good idle and vacuum

VALVETRAIN:
Use the stock Rockers and shafts, stock pushrods should be good as long as they are straight still. Use a new set of 5001 Lifters and 1110 springs

I ran a similar 9.1:1 360 in my old Dakota with a slightly hotter 218/228 cam and mopar M1 single plane intake. It made a dyno proven 300 RWHP with the Hughes cam, It made good power and had 335 RWTQ from 1700 to 4800 rpm, flat as a table, not varying more than 10 lbft all the way accross. In a heavy Dakota with poor gearing and no weight over the rear tires it ran 13.79 @ 103 mph when the engine had over 115,000 miles on it.
360 dyno graph 301hp/335tq

You have a light car, which will work pretty well for this combo, here is what hughes recommends on this combo.
Light car, mild street: medium to heavy towing or RV. Dual exhaust or headers, 4 bbl carb. Street gearing 3.00 to 3.55:1. 150psi suggested cylinder pressure. Good idle, resto/cruiser. Hot daily driver, mileage OK.
 
I agree with BJR* if your not going to purchase new parts. In what I would consider a better combo posted by Flyboy01 with the exception of the carb. The AVS style carb is really the same as the AFB in much of it's design, save the air door on the rear.
The new parts I think would do better. But you do have a shelf full of stuff.

* If you could tune the T-Q well, I myself would go there.

DGC's combo is really cool IMO. And works well. Though he has headers, not exhaust manifolds.
Tune the carb well, get that ignition timeing in well.
 
Not without redrilling the heads. Cheaper than a new intake. Twice the hassle. (?)
 
Thanks, think I'll go with the 268 cam and Edelbrock intake and then see which carb works out best.
 
racingsnake440 said:
Thanks, think I'll go with the 268 cam and Edelbrock intake and then see which carb works out best.
Click to expand...
The 268 XE cam is probably the best for that combo. I'm not sure how much it costs to redrill, but you can get the Crosswind for about $160 and it has dual bolt pattern.
 
This is a combo I drove for 3 years. even passed emissions in CT at the time. E body, 3.23 grip and 4sp.
shortblock first was a 340, then a 318, both used stock.
heads were X heads, Magnums would be a much better choice.
Intake was factory '71 Thermoquad. LD340 is a good intake, but I agree either drill the heads for LA intakes, or replace it with a Crosswind dual plane Air Gap style.
Comp Magnum 268H cam. (no XE then, but I dont think you need it with a 360 stroke anyway)
Matching Comp springs..I wouldnt ever run anything over .450 lift with factory springs. Why build in a rev limiter?
I ran a Thermoquad, and would use the one you have if it's in good shape and you know how to tune them. If not, I'd run the smaller vaccum secondary Holleys but again, carefully tune them...
You have a much lighter car, and I touched 13s even using the 318 shortblock with close to 1000lbs more.
 
theres nothing that puts fear in muskrats and chebbies like hearing the sound of a thermaquad. when it opens up people always look, you can hear them over the motor trying to suck the hood thru.maybe loose a little performance maybe not, just have to test and tune .for daily drivers and weekend thrillers therms are cool. GReat start to a great street combo. :toothy7:
 
Yeah, I would like to run the Thermoquad but haven't been able to find much information on tuning them. Anybody got any good sources?
 
racingsnake440 said:
Yeah, I would like to run the Thermoquad but haven't been able to find much information on tuning them. Anybody got any good sources?
Click to expand...
Between the factory service manuals, the MoPar engines book, you can click here for parts, rebuild and racing services from a MoPar man.

http://www.thermoquads.com/

The Carter carbs, I have noted to a small degree, seem to favor a tad more torque and the Holleys a few more HP.

I've seen people post that re-drilling the heads cost approx. $60.
(Grain of salt here. Area dependent???)
 
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