360 coming back together

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340 Dart

340 Dart

I don't know ****.
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Tore apart the 360 in the 75 dart a couple of weeks ago to have some valve seats repaired. While they were there I had them do some mild porting.

The stock "J" heads flowed 180 before and 240 after. Stock size valves still.

I remember reading somewhere that for every ____ cfm's of flow you got ____HP. Anybody know anything about this?


I ordered Keith Black pistons tonight also, should get me about 9.8 to 1. :headbang:

By this time next week I hope to have some serious traction issues!
 
A lame mans rule of thumb is 2 hp per 1 cfm is a possible outcome. Though you could exceed this guesstimate math by really seeking the max power output by use of all race parts on a hitting the "Balls to the wall" build up.
BJRracing had something on this.
 
I just got off the phone with him. It was 180 before and 220 after at 600 lift.

If its 2 hp per 1 cfm and he increased the flow 40 cfm its 80 hp??? I hope that is true because that will be the best $400 I ever spent!

This has got to be too good to be true! Even if the numbers are backwards and it is 1 hp for every 2 cfm its still 40 hp.

Either way I am stoked :headbang:
 
340 Dart said:
I just got off the phone with him. It was 180 before and 220 after at 600 lift.

If its 2 hp per 1 cfm and he increased the flow 40 cfm its 80 hp??? I hope that is true because that will be the best $400 I ever spent!

This has got to be too good to be true! Even if the numbers are backwards and it is 1 hp for every 2 cfm its still 40 hp.

Either way I am stoked :headbang:
Click to expand...

I'm sure it will be better than before - but just remember, if your valve lift is only .500" the flow increase beyond the .500 number will not be much sure to you.
Compare what flow you had before to the valve lift vs what you have now. That will be the increase in hp to anticipate.
 
Always remember that once the peak is reached, a few cfm gain is not worth using a .600 over a .550 or over the .500 or whatever lift cam is in your head right now. The extra push on the valve springs is just asking for more maintenance and the small cfm gain isnt going to be a noticeable increase in power. 1 cfm = 2 horsepower, think about it, flow charts reflect that, 250 cfm generally pulls 500 or so horsepower, once your hitting the 280-290 (the ceiling on a decent pair of aftermarket heads) you should be around 550-580 horsepower.. Also, porting too much raises the powerband which destroys any low rpm breathing, and thus, any chance at driving smoothly on the street is destroyed. Not only that, its just harder on valvetrain. Dont forget about torque either, low end is important.. port velocity = torque, big ports arent always the best way to go.

Good luck, hope the build goes well :salute:
Ryan
 
If the porting job doesn't increase the low lift numbers, then the above equation is true.
Porting the head to flow big numbers above a cam lift of .500, the porting work is more likely wasted. I have been asked if porting a head for a cam of .600 lift and then getting a .500 lift cam would be a good move.

More likely, the answer is a big NO! Becaue of the added are in making the port larger, which is often the case, to get the bigger flow numbers kills the air and fuel speed that would be better to have with the smaller cam.

Now if you can port the head to flow a whooppping 300 cfm while maintaining a high port velocity of a milder port job and smaller window, your really in good shape.

Case in point is the magnum head. Smaller ports, high velocity in a small port. Win win win! This is why this head can work well on a 318 and a 360.
A X or J head with larger ports flowing less or equal will perform worse than the Magnum head for this reason. The X or J head will not pick up until that engine starts to spin fast. Not so great for the street daily driven rides.
(Though it may have a spot in a wild 318.)
 
Thanks for all of the input everyone.

The cam is only a mild 480 lift. I'm trying to get in the mid 12's with this build.
There are a couple of parts that don't fit perfectly but I will sort that out later.

Rumblefish: I'm glad you talked me into keeping the stock valves. Thanks.
 
Your welcome. You'll like it. The 2.02 is a few ponies up top. Not worth it down low. You have plenty of cfm for the task at hand.
The plus side is you saved alot of money.
 
Every body here is pretty much correct with 2 to1 ball park.
The actual formula is hp=cfm/1.67*3.44, so 220/1.67*3.44
equals 453 hp. But as stated you should be more concerned
with the number at .480 lift and lower.
cudaj380
 
I pick up the heads on Friday. I will get the whole printout from him and check out the 480 lift numbers.
 
The cfm/hp ratio is a VERY loose guide. Using the 220cfm at .600 rating, your max hp "should be 440hp. Except, a larger cam and rpms can push it beyond that. Like these guys are saying, it's the flow in teh lift range of your cam that matters. If they are close to 200cfm at .500, and (guestimate) 175 @ .400, then your hp "should" be around 350, assuming all else is working at an average level. Meaning you're not running a huge carb, or an oversize intake, or a 2bbl carb and intake, factory manifolds, etc. It's really a very loose guide. To get an average A body to 14-105mph you willneed about 340 crankshaft hp, so you're pretty close to your goal.
 
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