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Isky vs. 731 Cam?

Old 11-22-2021, 01:35 PM
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Default Isky vs. 731 Cam?

I know, yet another cam thread, yay!!

Everyone loves the Crane 731 and "never has reversion problems", so I considered those specs when making my selection.

I've installed an Isky 396265/275 roller in my Mk IV 454 +.060 and was told by one of the larger performance retailers that it's way too much and I'm going to have reversion issues. Basically wouldn't even talk to me about exhaust manifolds that weren't dry tip b/c of the cam. At his suggestion I ordered another cam a month ago (still waiting), but went back to look at the numbers I put together when selecting this cam and have this question.

The cam I installed isn't that far off of the 731; two degrees more exhaust @ .050, but 12 degrees less advertised (steeper ramp) and less lift. Am I out to lunch on this? Is the one degree extra duration at the end of the exhaust stroke going to go from 731, "never seen reversion" to "holy sh*t, its going to blow!!"? ;-) (I know I'm being dramatic, lol)

Currently running stock Merc exhaust, going to upgrade, just trying to decide which route to go b/c of the cam thing. Other engine specs at end of post for reference.

Should be self explanatory, top row is current, second row is ordered, etc.

As always, thank you!!


Mk IV 454 + .060
SRP forged pistons 11 cc dome
Forged GM crank and rods
World Merlin 320 cc runner, 119 cc chamber, rec port heads
Johnson short travel roller lifters
Comp Magnum XD rockers
Ferrea stainless intake 2.20, Inconel exhaust 1.90
Edelbrock RPM2 Air Gap dual plane
Holley 770 Avenger
Davis distributor, wires and rev limiter

Last edited by wlrottge; 11-22-2021 at 01:39 PM.
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Old 11-22-2021, 02:48 PM
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Originally Posted by wlrottge View Post
I know, yet another cam thread, yay!!

Everyone loves the Crane 731 and "never has reversion problems", so I considered those specs when making my selection.

I've installed an Isky 396265/275 roller in my Mk IV 454 +.060 and was told by one of the larger performance retailers that it's way too much and I'm going to have reversion issues. Basically wouldn't even talk to me about exhaust manifolds that weren't dry tip b/c of the cam. At his suggestion I ordered another cam a month ago (still waiting), but went back to look at the numbers I put together when selecting this cam and have this question.

The cam I installed isn't that far off of the 731; two degrees more exhaust @ .050, but 12 degrees less advertised (steeper ramp) and less lift. Am I out to lunch on this? Is the one degree extra duration at the end of the exhaust stroke going to go from 731, "never seen reversion" to "holy sh*t, its going to blow!!"? ;-) (I know I'm being dramatic, lol)

Currently running stock Merc exhaust, going to upgrade, just trying to decide which route to go b/c of the cam thing. Other engine specs at end of post for reference.

Should be self explanatory, top row is current, second row is ordered, etc.

As always, thank you!!


Mk IV 454 + .060
SRP forged pistons 11 cc dome
Forged GM crank and rods
World Merlin 320 cc runner, 119 cc chamber, rec port heads
Johnson short travel roller lifters
Comp Magnum XD rockers
Ferrea stainless intake 2.20, Inconel exhaust 1.90
Edelbrock RPM2 Air Gap dual plane
Holley 770 Avenger
Davis distributor, wires and rev limiter

Your cam on order is smaller than a 454/420 cam (10 deg less duration +-. I wouldn’t expect any noticeable gains with either choice with your build. What are your hp and rpm goals. [email protected],700? Just curious. I’d be in the search of some good 275 cc aftermarket heads and exhaust. The 731 does make a nice upgrade cam for a 454-468.
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Old 11-22-2021, 03:20 PM
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I like your current cam actually. What’s the overlap compared to the 731?
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Old 11-22-2021, 05:00 PM
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Crane uses .004” for seat duration.
Everyone else .006” for seat duration.

Crane’s seat #’s will look a bunch longer.

You can’t compare seat #’s without knowing what crane’s .006” ‘s are. Do a search under my name, i think i had listed the 721, 731, 741, 500efi, 525efi, and etc crane cams .006# ‘s.
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Old 11-22-2021, 05:09 PM
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Also, just so you know, merc put the Crane cams in 5* advanced from neutral. A little more ‘low and midrange power’ plus less overlap after tdc then neutral or etc position.

example :
A 112 lsa cam installed nuetral would be in at 112intace center line and 112 exhaust centerline

+5 degrees would be installed 107 icl and 117ecl.

114lsa cam installed neutral would be 114icl and 114ecl.
+5 would be 109icl and 119ecl.
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Old 11-22-2021, 10:53 PM
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Okay, here is one of my quotes:

Originally Posted by sb
Crane 741
Intake Exhaust
296° at .004” 304° at .004”
288° at .006" 296° at .006"
234° at .050" 242° at .050"
204° at .100” 212° at .100”
154° at .200" 163° at .200"
.359” lobe lift .372” lobe lift
.610" valve lift with 1.7 .632" valve lift with 1.7 + .022”
ICL 107° ECL 117°
112° LSA

===================================
Merc 500EFI
Gen VI #169621 Grind#HR-292-2S-14 IG
292º, 298º at .004”
284º, 290º at .006”
230º, 236º at .050”
150º, 156º at .200”
Lift with 1.7 rocker .598” , .610”
ICL 109 , ECL 119
LSA 114


525 EFI
Crane #16HR00004 ?

298º/306º @ .004"
236º/244º @.050"
.610"/.632" Lift Valve
114º LSA

=====================================

APBA Cam for 8.1L Vortec
Crane #268761
292, 298 @ .004”
284º, 290º at .006”
230, 236 @ .050”
.598”, .610” Lift with 1.7
114 LSA 109ICL/119ECL
Note: Same as 500EFI but 8.1L’s Firing Order
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Old 11-23-2021, 12:32 AM
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Define stock Merc exhaust???
If you're talking the cast iron manifolds and short 90* risers, any cam much over stock will revert water at idle, including the 731.

The first cam you listed will be fine with nearly any exhaust with long risers
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Old 11-23-2021, 11:50 AM
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Originally Posted by SB View Post
Also, just so you know, merc put the Crane cams in 5* advanced from neutral. A little more ‘low and midrange power’ plus less overlap after tdc then neutral or etc position.
Should I take that as a vote for advancing the cam? It's installed straight up now.

Going to take your data and add it to the spreadsheet, thank you!
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Old 11-23-2021, 11:55 AM
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Where is ‘straight up’ ? It’s a generic term, thus why i’m asking.

Exact answer would be telling us where the installed icl/ecl is and what LSA of the cam is.
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Old 11-23-2021, 12:08 PM
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Originally Posted by getrdunn View Post
Your cam on order is smaller than a 454/420 cam (10 deg less duration +-. I wouldn’t expect any noticeable gains with either choice with your build. What are your hp and rpm goals. [email protected],700? Just curious. I’d be in the search of some good 275 cc aftermarket heads and exhaust. The 731 does make a nice upgrade cam for a 454-468.
If the consensus is that first cam isn't an issue, I'll cancel the one I have ordered.

The Merlin's are pretty good for what they are, but I was planning to pick up a set of aluminum AFR's, Brodix, or ??? simply just to save weight. I'm not looking for ultimate performance, but cutting one to two hundred pounds out of the stern would be a good thing, so exhaust is also on the menu. The biggest "problem" I have is that the through hulls are in the SBC locations, so I'm having to monkey with getting the plumbing correct. I bought some hump hose fittings and 4" SS exhaust tubing to give me more flexibility to fit the hardwall and have some 45's on the way as well. Trying to decide which way to go with exhaust; clearance isn't an issue, so I could use a +3 or +6 riser.

Right now I'm just trying to get the engine and drive mechanically sound and running so I can get paint and upholstery done for the spring. Well, maybe not paint this year.... I would like to have it in the water, lol.

Goals.... I'd say that your 415 at 4,700 is pretty good and would be happy there, but would spin it to 5k +/-. Boat is essentially a higher freeboard Donzi 22; 1973 Chris Craft XK-22. 24 degree hull, no pad, just converted to Bravo 1 with hydraulic external steering. 4,400 lbs stock, so figure 4,800-4,900 now? I've not weighed it. This isn't an Outerlimits or Apache and I don't expect to run 110 mph, lol. The boat ran like a scalded dog for its size with a less powerful 454 and Volvo DP 20 years ago, just trying to get back to that, but with a safer, more reliable drive package.
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