Re: Proper 500HP Carb
 

The newest cam will be fine and you should have no problems with reversion. You could even go bigger. I definately would.

My cam is a Crane 168731. Its .587/.610, 226/236, 112 lob sep and its in 454. Idles at 700rpms in gear and no problems with reversion. I would not go any smaller than this for 490ci.

Re: Proper 500HP Carb
 

when we went through my 500hps we used 850 cfm marine demons I am prsently at 565hp

Re: Proper 500HP Carb
 

I tried getting those numbers for the first cam and they didn't have them. I forgot to ask for the second cam. I'll ask when I talk to them again. Sorry

Re: Proper 500HP Carb
 

Here's a good comparison of 3 Mercruiser hydraulic roller cams. One is for low hp 454's, next is for Magnum 454/502 motors, and third is for the 502 HP500 (carb) . Take a good look at the .004" , .006" seat #'s , .050" #'s, lift, etc,etc

If we just went by .050" #'s we'd probably make incorrect assumptions about all the rest of each cams spec's.

Also, since most manufacturers don't come out and tell you what the seat °was taken at (.004", .006" or what have you) imagine if you where told cam #1 had 280°,299° advertised duration and cam #2 had 288°, 288° seat duration. We'd be screwed !!! This is why all of us, when comparing cams, we need to know where the seat ° durations are taken at. Impossible to compare two cams without EXACT info.

Merc Std BB Roller
.004” 280,299
.006” 266*/284*
.050” 204*/209*
.200” 113*/114*
Lift .480”/. 483”
ICL 115.5*
ECL 120.5
LSA 118*

………………
Merc Mag Roller
.004” 300*/ 300*
.006” 288*/288*
.050” 225*/225*
.200” 125*/125*
Lift .483”/. 483”
ICL 109*
LSA 115.5*

……………………..
Merc HP500 Carb
Crane Gen VI#169611 Grind#HR-284-2S-10IG
Adv 284, 292 at .004” Lift with 1.7 .576 / .598
At .050” 222, 230
ICL 105, ECL 115
LSA 110

Re: Proper 500HP Carb
 

Ok, so maybe I'm back to this (168731) or
Merc 500EFI
Gen VI #169621 Grind#HR-292-2S-14 IG
292,298 at .004” Lift with 1.7 rocker .598” , .610”
230, 236 at .050”
ICL 109 , ECL 119
LSA 114

It appears to be similar except for a little more intake and lobe separation. Since I wouldn't mind sacrificing a little top end for more assurance of a better idle and no reversion, maybe this is my best bet. Of course that's where I started in the first place. With the HP500EFI cam, just not the specs I thought that cam had.

thanks again everyone

Re: Proper 500HP Carb
 

Similar - Let's look closer.

Hp500.....731.....500EFI
#19611...#168731...#169621

Note: figures below include cams ground or installed 5°advanced

IVO...33BTDC....33BTDC.....33BTDC
IVC...71ABDC....75ABDC.....79ABDC
EVO...77BBDC....82 BBDC....84BBDC
EVC...35ATDC....36ATDC....34ATDC

68°......69°.....67° overlap measured from .004"

105°....107°....109° intake centerline
115°....117°....119° exhaust centerline

284°.....288°....292° intake seat duration at .004"
292°.....298°....298° exhaust seat duration at .004"

222°.....226° ...230° intake duration at .050"
230°.....236° ...236° exhaust duration at .050"

Re: Proper 500HP Carb
 

In case one hasn't logged in I edited info to include the 731 as was being compared. Sorry. So please log in to see the 3 cams side by side with each other. Kind of interesting anyway when looking at them this way.

Re: Proper 500HP Carb
 

Bc, Talk to Tyler about Quickfuel Carbs. They know how to build them. They engine test each one. They will be cheaper than a stock Holley or Demon. Mine on my previous boat felt like fuel injection. Tyler can order one set up perfect for your app.

Re: Proper 500HP Carb
 

Thanks for the direct comparison! My educated guess would still be that the 731 and 500EFI would be pretty similar. They're pretty close except for intake duration (+4 deg) and overlap (+2 deg)

Actual power output would probably depend on the In/Exh flow balance of the heads, but the 500EFI would probably also idle a tad better and make a little more torque down low. The 731 might pull it at the top end if the heads were intake dominant.

Then again that might just be mental M@$terbation given that who really knows what a cam will do in an engine.

Re: Proper 500HP Carb
 

Thanks, I'll do that. Up until know I had settled on a 850 Barry Grant, but I'm still open to suggestions, especially if Tyler feels more comfortable tuning them.