Cam for 470 inch pump gas motor

[wyrmrider]

start with your flow demands and determine if they can be met with valve lift curve with cam and 1.5 rockers
if not then use higher ratio rockers.
sometimes you need high ratio rockers to get higher lift quicker while keeping duration and overlap reasonable
rather than using them for more max lift

[andyf]

Thanks, I might do that if I was trying to win a championship of some sorts but I'm just building a street/strip type motor. I have a good set of 1.50 rocker arms so that is what I'll use. I'm thinking it shouldn't be too hard to find a set of lobes that works with the 1.50 rocker arms to make decent power. I called Bullet the other day and they recommended a cam which is a little bigger than I expected. Their recommendation was a 270/460 single pattern grind. The stock valve springs should be able to handle that but I'll have to double check the VP clearance. This engine has shelf pistons in it so it will run out of valve clearance at some point.

On the flip side I recently spent some time talking to a NHRA racer who runs a BB Mopar. His engine has about the same compression as this one but his heads aren't quite as good (rules limitiations). But he runs more cam and makes a ton more power and shifts at 8000 rpm. It is always interesting to talk to those guys just to see how extreme some stuff gets taken.

[wyrmrider]

what you have to watch out for is maintenance issues with heavy valves and an 8000 rpm motor with a radical cam
Don't try and run a fast action SBC/ SBF master in a BBM

[andyf]

You're going to need to make peak power at 6,800rpm
Here's what you'd need for a cam.
Cam# R78453-79431-108
264/266 @ .050"
.453"/.431" Lobe Lift
108 LSA

Hi Mike,

It turns out that the 260 cfm on the exhaust side was measured with a 2 inch pipe. I do not have the exhaust flow without a pipe but based on my experience with similiar heads it is probably in the 230 to 240 range. Does that change your recommendation or were you assuming that the exhaust flow was measured with a pipe?

[CamKing]

You're going to need to make peak power at 6,800rpm
Here's what you'd need for a cam.
Cam# R78453-79431-108
264/266 @ .050"
.453"/.431" Lobe Lift
108 LSA

Hi Mike,

It turns out that the 260 cfm on the exhaust side was measured with a 2 inch pipe.

I calculated the cam, based on the flow numbers, assuming it was flowed with a pipe.
I don't like to use exhaust flow numbers without a pipe. I don't find them to be accurate.

[andyf]

Hi Mike, I'm back with some dyno data. I ended up running the 271/271 cam with the .460 lobes and 1.50 rocker arm. Engine made approx 590 ft-lbs at 5200 rpm and 660 hp at 6400 rpm. So the bigger cam peaked a bit sooner than I thought. I was hoping the extra duration would carry it up to the 7000 rpm point but either that didn't work, or else something else in the engine is preventing it.

Cranking compression was 165 psi with the 271 duration cam so perhaps the 271 lobe was just a little too big for this combo. I do have a shorter 259 lobe cam that I can swap in to get another data point. Your 264/266 recommendation might have been the way to go. Who knows, I might even eventually work my way around to trying it!

DSC_9179 (Large).JPG

[Powertrip]

Andy,
That 271 cam would probably work with some port work on the manifold, and some more compression. You could probably go up to 11.5 to 1 and still burn pump gas.
Those sound like the new Trick Flow heads, what rocker arms are you using?

[andyf]

Yes, that could be. I don't have a ported low deck intake so I'm out of luck there. I wouldn't be surprised that the intake is the restriction on this motor.

I'm using an old set of RAS rocker arms. One of the best shaft rockers ever made for big block Mopar engines but they've been out of production now for a few years. Glad I held on to one last set.

DSC_9124 (Large).JPG

[Powertrip]

Those RAS rockers are sweet, I wouldn't give them up!
Like I said previously, a little more intake manifold and a little more compression would probably wake that combination up. Then again, Cam King's grind might work some magic also. Please keep us informed on your progress.

[andyf]

I can get the intake manifold ported but the compression is fixed. The engine is designed to be a pump gas engine that drives to the track. The design seems nice and safe where it is now so I'm not going to mess with it.

One interesting thing is that the BSFC is fairly low with these Trick Flow heads. The BSFC is down in the low .40 range for most of the dyno pull. We would have to run a step test to get an accurate read on BSFC but the normal ramp pulls are kicking out readings that are lower than normal for a Mopar big block.

[Powertrip]

I believe you could get away with more compression, but 10.5 to 1 is definitely safe.
Get the intake ported, or Cam King's grind, and see if that gets you where you want to be.
That is interesting about the BSFC, that usually is an indication of an efficient combination. How much ignition timing does it like?

[F-BIRD'88]

Nice build

[sjre]

Hi Mike, I'm back with some dyno data. I ended up running the 271/271 cam with the .460 lobes and 1.50 rocker arm. Engine made approx 590 ft-lbs at 5200 rpm and 660 hp at 6400 rpm. So the bigger cam peaked a bit sooner than I thought. I was hoping the extra duration would carry it up to the 7000 rpm point but either that didn't work, or else something else in the engine is preventing it.

Cranking compression was 165 psi with the 271 duration cam so perhaps the 271 lobe was just a little too big for this combo. I do have a shorter 259 lobe cam that I can swap in to get another data point. Your 264/266 recommendation might have been the way to go. Who knows, I might even eventually work my way around to trying it!

DSC_9179 (Large).JPG

Andy if im reading this correctly how can a smaller int duration carry the rpm higher? Or was it choking from not enough exh. duration or too narrow lsa.I have seen this but couldnt figure out why. 505 rb with 275-275 730 lift 106lsa peaked at 6300 w/edel. max wedge heads .????

[CamKing]

Hi Mike, I'm back with some dyno data. I ended up running the 271/271 cam with the .460 lobes and 1.50 rocker arm. Engine made approx 590 ft-lbs at 5200 rpm and 660 hp at 6400 rpm. So the bigger cam peaked a bit sooner than I thought. I was hoping the extra duration would carry it up to the 7000 rpm point but either that didn't work, or else something else in the engine is preventing it.

Cranking compression was 165 psi with the 271 duration cam so perhaps the 271 lobe was just a little too big for this combo. I do have a shorter 259 lobe cam that I can swap in to get another data point. Your 264/266 recommendation might have been the way to go. Who knows, I might even eventually work my way around to trying it!

Let me know when you're ready for the correct camshaft.

[andyf]

I ran my engine numbers thru Controlled Induction 2016 and it says I need a 270/275 cam with .470 lobes on 108 centers advanced 5 degrees. Very close to what I have right now except with a little more exhaust duration.

CI says my engine will make 590 ft-lbs and 660 hp which is exactly what it is making.