Another "Different Cam?" Question about my 418 build.

[donraye]

Well here's the short block I have now ended up with and is being assembled as I write this, so it can no longer be changed. But the CAM still could be if really need be.
I may have to change the cam as the valve intake and exhaust timing seems very odd to me but I'm an idiot about stroker cams and that's why I will probably have to call Comp Cams tomorrow and get them to give me some expert advice, unless I can get what I need here.
The JE 17cc dish pistons I bought will give me 10.125:1 with my 67cc (actual) heads and an .039 gasket. The quench height will be either the 039 used to figure that compression (or could also be .040-.045 depending on which gasket I end up choosing if there's a good reason to change)
Now: The Cam I already have:
The valve timing on this cam @ .050 is:
Intake: open: 14 BTDC close: 42 ABDC
Exhaust: open: 53 BBDC close: 9 ATDC
Gross lift .555 and .576
Advertised duration @ .060 tappet: 287 and 293
With cam installed at 104 intake centerline:
Duration @ .050: 236 and 242
Lobe seperation 108
Lift @ .050 .347 and .360
The BIG question is can I use the above cam with it's valve timing and the 10.125:1 static comprassion ratio the short block with my heads have?

When I try to use some of the calculators like the one at KB Pistons it tell me the dynamic compression will be a little above the 8.5:1(which is not a good thing for pump fuel I've heard?).
But I have also been told by several people that that calculator is all wet and they ended up with considerably lower real world dynamic compressions than that calculator told them they would have, So...
I know it is nat the best calculator because my builder has a much more sophistocated desktop dyno the he uses and it calculated the static compression to be different from the KB calculator and I know his is correct as it had a lot more info used to do the calculation and his agreed with my other machinist's calculations as well..
Does anyone out there FOR SURE know if the above (cam,static compression,(rod length,stroke,etc.) combination will be OK or not? I know it will be far from "ideal" to many of you who would like to see a much larger cam for more high end power, but this is a 100% street motor and I am just wanting this set-up to work with pump gas and make good (not maximum) power.
The cam was chosen by Keith Craft for me BUT, it was back when I was originally building a 408 (not the 418 it has now become).
It became a 418 because the 408 internal balance cranks were backordered and my short block builder HAD the 418 crank in stock so I had him switch to it rather than hold up the build for a couple of weeks or more.
Will this cam (above)work for me or should I order a new one to get it right?
Don

[jdean]

I think that is a good cam choice for a street driven 418. Similar to the one I am using in my 418. I dont think the difference between a 408 and 418 is enough to worry about a change. Plus I dont think you can get much better advice than what KC can give.

[vector1]

hello don

good to see you making progress. i had the above cam made by mike jones for a 406ci sb with 9.8 compression, he spec'd out more lift but was reduced for valve spring longevity.

your cam seems a bit mild, especially for the compression. a cam will make or break the deal, if what you have doesn't seem right, go with something else.

with a custom cam made by "someone good" you get ramp rates that let you turn the motor higher rpm from what i understand. i've heard over and over again, it's how the lobes are ground that makes a difference.

also the above was for efi, your carb may require different stuff.

good luck

mark

[donraye]

Originally Posted by jdean

I think that is a good cam choice for a street driven 418. Similar to the one I am using in my 418. I dont think the difference between a 408 and 418 is enough to worry about a change. Plus I dont think you can get much better advice than what KC can give.

What static compression ratio are you running with your 'similar" cam?
the reason I'm a bit worried is that when we went to the 418 we also increased the compression a little bit. worried I don't have the duration needed for 10.125:1.
Not concerned about any poor advice from Keith as I agree he is tops, but he did not have all the information I have know when he rocommended this one.
D.

[767Jockey]

Why not ask Keith Craft what he thinks. He spec'd the cam originally, ask him if it is still the correct cam for your now changed engine and if it still fits your needs. It's fairly easy to change the cam now before it gets slid into the block, and it's not to expensive either.

[olddog]

The cam I am running is the same lift and duration. I think that is the same lobe seperation angle, too, but I would have to go dig out the cam card to be certain.

It is in a 347 stroker (5.0 block), with Mass Flow EFI. It idles good at 900 rpm. It will idle down to 600, but it sounds like crap. Engine doesn't smooth completely out until about 2000 rpm. It still pulls decent down to 1500 rpm, but not strong until over 2000. It pulls strong all the way to 6500 rpm (rev limit). By the seat of my pants I cannot feal any loss of torque, which is how I have hit the rev limit a couple times, as I do not want to turn it that high.

Previous owner (who had the engine built) told me he origonally had a carb on it. He said the EFI calmed the idle down a bunch.

With that said the extra cid in your engine should tame the cam a little more. If you have good flowing heads, I wouldn't think you would need any more cam for the street. I would not go any higher on the duration unless I wanted to turn higher rpms, which I wouldn't do.

I am not an expert. Many people around here know more than I. Just thought my engine would be of interest to you.

PS
I was told the static compression is 10.4:1. It runs fine on 91 octane pump gas.

[donraye]

Originally Posted by 767Jockey

Why not ask Keith Craft what he thinks. He spec'd the cam originally, ask him if it is still the correct cam for your now changed engine and if it still fits your needs. It's fairly easy to change the cam now before it gets slid into the block, and it's not to expensive either.

I did ask Keith and got an answer yesterday that the cam is fine for my application. Good news!
Thanks

[donraye]

Originally Posted by vector1

hello don

good to see you making progress. i had the above cam made by mike jones for a 406ci sb with 9.8 compression, he spec'd out more lift but was reduced for valve spring longevity.

your cam seems a bit mild, especially for the compression. a cam will make or break the deal, if what you have doesn't seem right, go with something else.

with a custom cam made by "someone good" you get ramp rates that let you turn the motor higher rpm from what i understand. i've heard over and over again, it's how the lobes are ground that makes a difference.

also the above was for efi, your carb may require different stuff.

good luck

mark

Almost the same cam. The difference in net lift is due to your specs. using 1.7 instead 1.6 rocker ratio. If I wanted to go to 1.7 rockers they would be almost identical.
Thanks, Don