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#1
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Cam selection
Hey
I'm almost ready to assemble my 318 project -9.4:1 compression -edelbrock heads -rpm air gap -1-5/8 headers -3100lb car -3.91 gears -4 speed what I'm kind of stuck on is the cam and carb selection I am willing to sacrifice a bit of torque for higher horspower. rpm range of approx 2000 to 6500 the front runner cam wise at this point is the hughes HE3644AS solid lifter with .509 intake lift and .533 exhaust lift it is running 236 degrees of intake duration and 244 degrees of exhaust duration both at .050 lift. from what i've read hughes cams have better idle characteristics for a given size. So this should work on the street carb wise it's between a 750 cfm afb off a 440 or a new 650. lastly will 273 iron rockers hold up in this situation or should I drop the 3 bills on a set of aluminum pieces. Thanks a lot for the help and good luck with your projects |
#2
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IMO, I would use the 650 cfm carb. 700 cfm max. It's plenty for the 318. The stock 273 rockers will do fine. So save the $300 unless you really want them.
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#3
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As far as the cam, that is pretty big but with a 4speed and 3.91 gears in that light of a vehicle it should be quite a warrior! Just don't go with real tall tires, that will kill the gear ratio. And go with the 650 or even a 600 carb. The 750 will not ever want to idle with that big of a cam in that small of a motor. And 600-625 cfm is plenty for the top end also according to the Holley selection guide.
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#4
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Thanks for the advice I'll probably end up going with the 650.
Is there a major performance difference between the holley, and an AFB. |
#5
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Another point about that cam, its a solid cam, so its going to act smaller than a simmular hydraulic due to valve lash. Ive read in Car Craft that your suppost to subtract about 8 degrees duration when comparing a solid to hydraulic cam. So in theory it should be like running a 228 hydraulic. As for the carb, the 750 would be ok but the 650 holley would probably be the better choice. You can get away with running a bigger carb with a dule plane intake v/s a single plane. Im running a 750 holley on a 318 much milder than yours and it runs fine (doesent bog) even with out a secondary spring! (of coarse I have a 4 speed, i would not try it with an auto) Anyway, that thing should not have a problem hitting the 12's with proper traction. Another thing, stay away from the aluminum rockers for the street. They would last more than a few years if you drive the car on a regular basis. Anyway, enough babaling, good luck with your ride!
340 party |
#6
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My experience with Carter AFB's and Holleys is the Holleys flow better from midrange on up. They are also easier to get to idle with a large cam. The Carter's are great for all-weather drivability and off-idle punch but don't seem to let the engine pull as good up high. My 1/4 mile times were better with the Holleys. My daily driver experiences were better with the Carter's.
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#7
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would anyone mind throwing the combo into desktop dyno. I'm aiming for the 350 horsepower range and would like to see how close the combo actually is.
thanks a lot |
#8
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I put your combination in dyno 2000 and it says peak HP =415 @ 6,500 RPM and 376 ft/lbs torque @ 5,000 RPM. Below 3,000 RPM you will not have much torque/power. You would probbly realistically need almost a 4,000+ stall converter to get on the torque curve of the engine.
Here is the numbers: RPM HP TQ 2000 103 269 2500 136 285 3000 173 302 3500 220 329 4000 269 353 4500 317 370 5000 358 376 5500 389 371 6000 404 354 6500 415 335 7000 404 303 7500 388 272 8000 353 232 |
#9
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Cam Too Big?
I think the cam is too big if you plan on driving it a lot on the street. If the torque peak really is at 5000 rpm, then that seems like more of a strip car. I put a MP 284°/.528" solid lifter cam in my 340-S and the car was actually slower than the stock cam. It is a 4-speed car with 3.91 gears and 25" tall M/T Sportsman S/S. I didn't put headers on it as they are a big pain in the @$$ for a driver. I think I'd use a 225° to 230° @.050" duration cam if it was my c
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#10
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no question the hughes cams are the preferred cam,but for a 318 its too big Id look in the 220 @ .050 ,youll be happier and probably faster.The 650 is plenty if set up correctly,do not put a spacer on the Air Gap.
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#11
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Spacer?
Holeshot;
What have you found with a spacer on the RPM and which one/style did you use? |
#12
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When I ran the Desktop Dyno sim from home, I used the "single plane" intake manifold model because the big RPM intake on a 318 will probbly simulate HP more accuratly, but since the RPM intake mannifold is a dual plane, your torque may be slightly more, and it may peak a few hundred RPM sooner.
Since you have a 4-speed and 3.91:1 gears, and a light car you should be OK for a strip car, but for a street car the big cam will probbly become annoying, Examples: no engine vacuum, rough idle @ 1,200 RPM, having to slip the clutch at every stop sign/light (Torque? at Low RPM), poor gas mialage, probbly really bad emissions (if they are checked.) With the big heads, intake, and cam used on a smaller 318 with only 9.4:1 compression, you will probbly have very low velocity in the ports at LOW RPMS, and this will probbly result in poor air/fuel mixture getting to the cylinders, so you may have to run the carb rich, and a Multi-spark ignition like an MSD, Crane, Jacobs, etc would be a very good improvement. Running more compression will really help. With 236 duration @ 0.050" on the cam, 10:1 compression should not be a problem on pump gas. |
#13
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Thanks for the desktop dyno numbers. I called Hughes today and they said to go with HEV3945BS which is even bigger .546 intake lift and.560 exhaust it has 239 intake and 245 exhaust duration. I don't know if I trust them. They also gave me the hard sell on their aluminum rockers, saying that the iron rockers were basically shit. Any actual grind #'s that would work with this combo would be much appreciated. I don't have enough experience to do it on ny own
Thanks again DTACK |
#14
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If this it a track car, sure the HEV3945"AS" (The BS is for big blocks) cam would probbly work better with the heads, intake, etc. This cam is also on a 107 CL so it has even more overlap (will hurt low RPM even more.) Rember this cam has almost as much duration @ 0.050 at the Mopar 296/0.509" cam.
Since to use all the airflow you have from the combination you will really have to wind the 318 pretty hard (maybe 7,000+ rpm?), so any lightweight valvetrain part is a good Idea. IF this is going in a race car, why not use more rear gearing like 4.56:1? |
#15
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Cam recommendation
Dtack64,
You haven't stated whether this car is more for street or strip, but I'll asume it's more street due to the low compression ratio. Now that cam that Hughes recommended is way too huge for your combo on the street. I don't know what he was smokin but you were right not to trust him. Now if you haven't already ordered the rockers and you still have to have them, I say go with the 1.6 ratio rockers and a much smaller cam and you'll be way ahead of the game. Also, I keep trying to spread the word that Engle grinds cams for Hughes and I bought mine from them for $50 less than what Hughes was charging--same cam. As far as a cam recommendation would go, I would recommend something with around 224 duration @.050 with a 110 to 108 lobe separation angle and as much lift as you can get with that duration--usually around .500", and with the 1.6 rockers, you'll get a little extra. Otherwise, save the cash and run the iron rockers, there's nothing wrong with those. But don't take my word for it, Call some succesfull racers such as Dick Landy, Bob Mazzollini, or Ray Barton and see what they have to say. That's my $.02 |
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