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!!

https://cimg5.ibsrv.net/gimg/www.off...51a13798b5.jpg

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. 415@4,700? 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.

I like your current cam actually. What’s the overlap compared to the 731?

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.

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.

Okay, here is one of my quotes:

Originally Posted by sb http://forums.boatfreaks.org/images/...s/viewpost.gif
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

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

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!

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.

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.

I'll have to go pull the cam card, but by straight up I meant zero degrees advanced/retarded.

Essentially, yes, that is correct. They're a set of generic Bar BBC manifolds with a short riser. One of those, "this is what I had on hand" and don't want to throw a couple grand at an exhaust only to find out that it was wrong.

20 years ago it was running a cam quite a bit bigger than stock with that exhaust without any issues that I'm aware of. But, when you're in the boat business, everything is for sale if you know what I mean and I don't have that engine or the cam to reference. That engine had water issues one spring, so it came out, was fixed and sitting in the shop. Customer came in, "need an engine that will run with a 502, now!" and well.... buh bye. Dad sold it and the boat has sat shrink-wrapped for 20 years. After college 15 years ago I tried to beg, borrow, buy and steal it, but my father threatened to be buried in it. Took me six years to find a good hull that wasn't restored (wanted to build my own if you know what I mean), then an ex-wife and life got in the way. I started in earnest in Dec of last year and was then given my fathers boat in Jan, so now the one I bought is sitting shrink-wrapped waiting until... who knows.

I've been eyeballing the Seaward and EMI systems and I know Stainless Marine and IMCO also build good stuff, so I'm not sold on anything in particular. I'll measure hatch clearance, but suspect that +6 is do-able.

I would cancel the cam you ordered and put that $$$ toward good exhaust.

keep in mind that some of the after market heads ( AFR ) have raised exhaust ports, this will widen the gap you currently have.

Merlins I currently have already have raised exhaust ports, so I'm dealing with that already, but good point, thanks!

cam card tells you what it should be installed at. It doesn’t say what you actually installed it at. :thumbs

The last comp cam I degreed was off 3 degrees. I second questioned myself but after checking 3 times I was convinced. They were custom billet grinds. It’s partner was off 2 degrees.

my machine shop said advance cam 2 degrees.....
my cam card..
https://cimg1.ibsrv.net/gimg/www.off...6e74aed50a.jpg

I think I saw your card on one of my threads. Weren’t you propped for 5,500-5,600 if I recall. 548’s?? I’d think that cam would peak at like 6,300 or so (little less 2 deg adv).

i had a 731 in a 509, 5400 rpm fell flat, put a 741 in and 6000 no problem. cams were installed straight up. had a 420 mega-blower on it also with Bassett headers. 731 had a very mild idle, 741 had a nice choppy idle. And still idle at 800 rpm's just my 2 cents.

Would imagine you were getting 300 + more rpm with the blower.

don't know, i've pretty much always had a blower motor, every time going bigger. now i'm up to a 598 w/a 1071. this is the first engine i've bought that i didn't assemble. so far, so good.

That is because you had the 731 a 509ci. 731 is very close to 500efi cam so 5400rpms makes sense.
The 731 in his 467ci engine should pull hard to about 5800rpms.

We run the comp cam 284…..no issues with rev..