It is cam first. But the cam has to fit the application. And then the engine has to more or less be built around the cam.
You have already chosen all the components so now we have to fit the cam to the components.And the biggest reason is to not end up with a soggy bottom end that demands a 3500TC and 4.30 gears, and burns gas at an alarming rate; so much so that your 15,000 or 20,000 dollar or more machine, spends most of it's life parked.Phew, that was a mouthful.
See; at just 10.15 Scr it will be easy to overcam it now for street use in a 6000 pound truck, and run into detonation at WOT. But it will be almost as easy under-cam it and run into detonation at PT;part throttle.
I'm so glad you decided to put the 440 in the heavy machine.
>Have you stated your goals with this truck yet? Is it to have a first gear blast-off, and then sit back and mellow out? Is this the truck with 3.55s and 33" tires and the NP435? Have you figured out the gear ratios in that badboy tranny yet? Is it the 4.56-2.28-3.31-1.00 unit?
If this is right, then the Final-Drive TM(torque multiplication)ratio,in first gear , corrected to a 24 inch tire, is 4.56 x 3.55 x 12/(.5x33)=11.77. This is a huge amount of TM for a 440. Your bottom end would have to be pretty soggy for you to notice it.
On the other hand, this ratio will be revved out by 33mph at 5500. The rpm drop into second will be 2.28/4.56 = 50%, so 5500x .5=2750. This is pretty far down in the rpm band so your cam selection is gonna have to take that into account. Your typical 240@050,badboy idle,440cam is gonna be drowning at 2750, so it's kindof game over for the combo.
So, with that 240* cam you will have to rev it some more in first, to have something to work with in second gear. The problem I see is that the peak-torque may not come around until 4200, and your engine is not gonna want to spin to 8400, to get it. So the big cam idea you are gonna have to put to rest. Or put to rest any notions of rapid transit in any other gear until the revs get up there. Or slip the crap outta the clutch until the clutch dies.
So what is the answer?
The answer is to build an engine that can work with those tranny ratios. That means to build for torque, and forget about the fast way home. YTou have got to satisfy that tranny.
Ok so what to do? Well it starts with figuring out how to build a super wide torque band to satisfy that 50% 1-2 split. Typically the torque peak rpm comes in at about 75% of the power peak .So if peak power is at 6000, the torque peak might be at 4500. A better way to think of this is that the power peak rpm will be 1.33 times the torque peak. So if we want a torque peak at say 3600, then the power peak might be at 3600x1.33=4800.
>So now, if we rev the engine to 4800 plus say 10%(so5300) in first, then the Rs will drop to 2650 going into second. But if we somehow flatten the power peak so that we can rev it to say 5800, then the Rs will drop to 2900. That's getting close to 3600/the torque peak, and I'm betting, that a combo like this will be pulling pretty hard at 2900 already.
>So, for you, to continue accelerating in second gear, the answer is to build a torque monster, that has a long flat hp curve from 4800 to 5800 say; we don't really care about the specific number. But it has to make monster torque from say 1500/2000 (where you drop the clutch),and up. This to continue accelerating in second gear, with those 3.55s.
If you don't care about second gear, then you are free to choose any cam your engine can be set up to handle. So if you want a raunchy idle, then the 240* or more cam is your baby, if you got the compression to handle it.But I don't think you do.
The 240*cam is about 284/292/108. With a 66* ICA this sets your Dcr to 7.98@160psi, with that 10.15Scr. But you don't want this 108 cam It makes peaky power and steals the torque away from the bottom. What you need is a 114* LSA or more cam. This,at 10.15Scr and its 72* ICA, sets the Dcr to 7.56@149psi, not nearly enough pressure for what you want to do.
If you want to run that cam, 284/292/114+4, and have a stronk blast-off, with aluminum heads, then your cylinder pressure will need to be in excess of 165psi and pushing 180psi will be better. 11.3Scr will get you [email protected], kindof middle of the road; this to run that 284/292/114+4 cam.
So; how do we go from 10.15 to 11.3? The difference is 11cc.There is only one way; pistons.
Now go back to the opening statement."It is cam first. But the cam has to fit the application. And then the engine has to more or less be built around the cam."
Now, I'm not suggesting that the 240 cam is the best cam for you, cuz I don't read in this thread what you are up to. I kindof guessed. But the point is; the cam has to fit the application, and that tranny is severely restricting your options. Unless you are happy with a zero to 33mph blast-off and D-o-n-e.
Now, all you BB fellas and builders please chime in and school me, cuz I have no BB experience.please Be gentle .....lol
