Reversion

[RickR]

I would like to upgrade my exhaust to a Gil Magnum Choice system w/Turbulators. Rex Marine said I could not run a Crane 139631 Roller Hyd (226/234, 112 lobe separation,.587/.610) because the cam has more than .534 lift.

What does lift have to do with reversion?

The stock flat tappet cam in the 1995 454 Mag is 224/224,.483/.483,115 lobe separation.

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RICKR
mailto:riggerb@aol.comriggerb@aol.com</A>

[GEOO]

RickR,
I had this same conversation with my mechanic. Most boat's are larger and heavier then are Classic's and need the low end torque to get them going, this is usually why they stay away from big cams.
I have run Stainless Marine Exhaust on my small block for four seasons in salt water; I love them and I think they cost less and have a better warranty then the Gils.
My tail pipes dump the water as they pass through the transom. I Run a solid roller cam with about .635 lift. (9 hours on engine no signs of reversion) GEOO

[BigGrizzly]

Rick, I beleive thr primary length of the gil system is too short for what you are trying. the big cam that i used on the Corscian wouldn't run on the old log type manifolds. i even extended the secondary (collector) pipe with a tube within a tube waterjacket. yet with the C.M.I. headders it ran great. i don't use this cam anymore because cruise was too high. all you guys will tell me my lobe separation is too small, but here goes dur @.050 240/252 lift at valve .557/.583 with 108 lobe centers. i now use a 226/232 lift 538/550 again with 108 lobe centers. no reversion no problems. Tom on Lanier has ridden in it. I don't use captains choice. this is what in in my motor now and has been there for over 200 hours. you see reversion is a term used like too much compression and too much boost, when they should say , My components are not matched. Example my CR750 roadracing motor cycle has measured 13.5 compression, runs well and has 8 championships under its belt on 106-108 octane pump gas-no alcohol. my son's mustang has 9.5 comp is a 5.0 and has vortex blower and runs 14 psi. boost. he drives it on the street. has 15,000mi since he put it together. point is there system is too short and not matched to that cam.

[rayjay]

Hey BigGrizzly, did you race CB750's in AMA Superbike during the mid to late 70's? (There I am showing my age) Do you have one of the original CR750 conversions?

Duration, lift, separation, cam timing or position, static compression, piston dwell time, etc. all have to do with the overall package and where the engine developes its greatest BMEP. We ran an FZ750 (motorcycle) that had had 15.5:1 compression and by rules ran on pump gas (but define "pump gas"). Because of the engine design, and our cam knowledge at the time, it ran very big cams with late intake closing. It therefore only had 145 psi of cranking pressure, which is somewhat low by current standards.

I do not understand what the lift would have to do with reversion? I always though reversion was more effected by overlap, which is effected by duration, lobe separation, and how quickly the lobe gets the valve off the seat. rayjay

[BigGrizzly]

Yes i am that guy that has the big yellow Honda with the same name. I raced it from the early 70's (1971) until 1982. Then we retired and I went to work for American Honda. During that time AMA rules said specific gravity was to be no less than 0.7. when I said pump gas I was refering to gas you buy at a gas station. I raced against the TZ750's. You're right, to a point. I only added lift info. for comparison. But it does have a great effect on reversion, as does the length of the intake trac to the valve seat, then from the exhaust seat to the end of the megaphone, or in your case the end of the collector. But you should know that. After all, your Yamaha has one of the fastest piston speeds of any motor cycle next to FZR 600 of the Bob Muzzy famed Super Sport Series bikes. You don't have the problem on motorcycles that boats do, because your bikes have an extractor system on them. Even the stock mufflers on all sport bikes are extractor types.

My bikes - there are two, Big Grizzly the AMA GP bike and Son of Grizzly (named by Richard Chambers at its Datona debut)the AMA super bike which was originally a 1977 CB 750F. If you are from that era you also know it was the only succesfull sohc Honda in AMA racing.