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Originally posted by Cord The 731 would be a acceptable choice. Maybe a tad big. A little less cam would give you some more low end torque. I'm more concerned about your exhaust choice. You'd be better off with a long primary header. Cmi sport tubes, Stellings, Lightning, or Keith Eickert heads would work good. Your manifolds would be a good choice if you are going to add a blower later on. As a matter of fact, so would that cam. Thanks Rob |
Originally posted by formula31 I stayed away from a roller cam because of my Mark 4 block. I have heard of enough problems using the "adapted" roller lifters on these blocks that I chickened out. Im sure plenty of people have had success with them though. You can get 30 or so more hp out of them but Im not so sure about reliability. My machine shop guy said Mark 4 blocks should have the lifter bores bored true to the cam and sleeved. He said many are not perfectly perpendicular to the cam and thats where the problems come in. The later Gen blocks that are built for roller cams are fine. Mine has ran Solid Rollers for quite a while with no problems. I will check into this though. When you say 30 more hp is that at the same rpm or higher. If I can get 30 more hp at 5300 going roller, it would be worth the $400 to me. if I'm only gonna gain 10 there it probably wouldn't. Rob |
Originally posted by Leathl_WS6 Sledge what kind of speeds are you seeing on what boat how heavy? prop and at what rpm? Have you ever had it dynoed? Looks to me the benifit of roller seems to be higher lifts at the same duration. I wonder how much HP that extra lift is good for. So many people say lift doesnt matter. If I go roller I think this will be the 731 cam. Just wondering if I would gain much hp in roller vs the 134241 its just hyd almost the same duration as the 731 but way less lift. 134241 Int./Exh 226/236 534/553 LSA 112 139731 Int/Exh 226/234 587/610 LSA 112 Anybody know if the more lift would be good for more HP? If so how much? 5? 15? 30? Would it be worth the extra $400? |
Well, I'd be looking for less duration. This will usually corespond to a little less lift too. I'd be looking for a 721 cam, but I don't think they make one in that series. Besides, I believe those cams are not for the ol Mk4 anyways. You'd have to cross reference the part number. We're just talking about the profile. Either way, I'm sure there is 30hp in a roller cam.
Is the exhaust a Tri-Y? ie the the 4 ports merge to 2 in the manifold and then 2 into one at the end of the riser? If so, then it's ok. There are two cylinders on each bank though that need to be seperated because they fire adjacent to each other. If I recall correctly, the stainless manifolds don't separate these cylinders. I believe that all 4 ports just end at the riser. If so then the primary length won't be long enough. Your goal should be 30" of primary length with a N/A application. I believe those manifolds are less than 16". The lightnings are around 24". The CMI sports and the Eickerts are around 30". There is proably 30hp in the exhaust. |
Its not just the lift and @ .050 duration that you need to consider here. While both the flat and roller have nearly identical durations @.050 the roller will have significantly ( in inch/degrees) more duration than the flat increasingly from @.100 lifter thru @.300 lifter all the way to max lift. Your heads are just beginning to build flow @.050 (.085 valve). The important values are mid-lift (@.150- @.250) where your heads are really making some significant flow numbers, and thats where a roller has a considerable advantage over a flat tappet. You will see a significant performance increase using a well matched roller in your combination.
Bob |
I was thinking the cam with less lift was the hyd rollers for the street series...sorry for confusing the issue.
Another possible source for cams is Schneider. I had them grind a custom 224/230 .540" lift 114 lsa cam a couple of years ago and it was a sweetheart in a 502mpi...wish I was still running it...it didn't need alot of spring either. |
Thanks guys thats great information..
Cord how much smaller is the 721 cam I thought the 731 was kinda mild? So what are you thinking like a 220 230 or 210 220 at what lift? Looks like will be going roller. The exhaust has me worried now. I will look into that. I just bought it used and I'm not 100% sure how it is dsigned. I know the runners are no more than 20 inches for sure. Thanks Rob |
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Well, the 731 works great with a 502 but would be a bit large for a 454.
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Thanks again Cord who makes that cam? I noticed the firehawk in your avitar. Do you have one?
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Leathl_WS6
Spec cards for both cams. Bob http://dab7.cranecams.com/SpecCard/D...1=Display+Card http://dab7.cranecams.com/SpecCard/D...1=Display+Card |
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