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-   -   Retarding cam - help reversion? (https://www.offshoreonly.com/forums/general-q/350717-retarding-cam-help-reversion.html)

SB 11-07-2017 07:34 PM


Originally Posted by SB (Post 4592414)
They (Crane) say 6* overlap when measured at .050" .

Most measure overlap at .004" or ,006" . So, you'll need to run the #'s at .050" to compare..if you so desire.

Edit in: His overlap is 26* at .050" .

His ,050" cam timing says Intake Opens at 11*BTDC and Exhaust Closes at 15*ATDC

payuppsucker 11-08-2017 08:33 AM

Dry tailpipes/problem solved

Tahoe540 11-08-2017 08:50 AM


Originally Posted by payuppsucker (Post 4592480)
Dry tailpipes/problem solved

I wish, Lake Tahoe has very specific sound levels and they enforce it. Even with mufflers you should see the looks I get at the dock when I start it up.

Warship2k15 11-08-2017 08:57 AM


Originally Posted by payuppsucker (Post 4592480)
Dry tailpipes/problem solved

With dry pipes he might get 5700 without a big torque drop with a cam that won't stall at the dock etc.
It will be close.

With wet ones he needs to cut back on the overlap and keep in mind they won't flow enough to see 5700 with his cubic inches without a large torque drop off.

He needs to either go dry or change the cam to one with way less overlap and duration and prop it to match a 5000-5400 limit.

How do I know this I've talked to several cam companys and ran many dyno programs to get some ideas for my 550 inch build.

Now I know they are not perfect but give you a good idea of where the torque drops.

Tahoe540 11-08-2017 09:18 AM


Originally Posted by Warship2k15 (Post 4592487)
With dry pipes he might get 5700 without a big torque drop with a cam that won't stall at the dock etc.
It will be close.

With wet ones he needs to cut back on the overlap and keep in mind they won't flow enough to see 5700 with his cubic inches without a large torque drop off.

He needs to either go dry or change the cam to one with way less overlap and duration and prop it to match a 5000-5400 limit.

How do I know this I've talked to several cam companys and ran many dyno programs to get some ideas for my 550 inch build.

Now I know they are not perfect but give you a good idea of where the torque drops.

Thanks for that information. That is really good to know before jumping into having a new cam ground and not gaining much if anything but no reversion. My last trip out I feel I finally had the tune at its best all season and I was able to push the boat to 57 mph at 5200 rpm with a 20 pitch 3 blade. I could really be fine with just boating as is but I have set a goal to hit at least 60 on Tahoe with the N/A motor I have. The problem is I set this goal before I ever took the boat out or even knew how fast it would go and having no prior boating experience. I know speed is relative to people but what is fast for a single motor 30ft boat? I had it out this season on a lower elevation lake and I hit 62 mph and the boat felt stable and was a hoot to drive so I know I want to go faster. I am finding this to be a challenge but one that has been fun. I have certainly learned a lot about boating performance but I have an appetite for more. You have to pay to play, so maybe some good exhaust is in order to accommodate a decent cam change.

Warship2k15 11-08-2017 09:22 AM

Sent you a pm

adk61 11-08-2017 12:07 PM


Originally Posted by SB (Post 4592384)
In my opnion with no experience on this (shifting cam around trying to fend off reversion), I would think advancing that cam would be less like to revert.

Reason is overlap after TDC (when piston going down and exhaust valve still open) is when reversion happens...right ? So, retarding cam would put more overlap ATDC.

Again, my thoughts....speaking of which, I would think that cam, no matter where you have it installed, will revert with those exhausts.

thank you... I was thinking that too

getrdunn 11-08-2017 01:58 PM

Maybe put a call into SLR Cams. You made good power especially with stock heads. You could always exceed your goals by installing crane 651 cam and a 871 blower. There was a great deal on some a while back in the swap shop. Should put you in the mid 70's. Now that sounds like fun. Btw for a single I'd say your pushing that boat pretty well for a 30 footer.

Tahoe540 11-08-2017 02:41 PM


Originally Posted by getrdunn (Post 4592548)
Maybe put a call into SLR Cams. You made good power especially with stock heads. You could always exceed your goals by installing crane 651 cam and a 871 blower. There was a great deal on some a while back in the swap shop. Should put you in the mid 70's. Now that sounds like fun. Btw for a single I'd say your pushing that boat pretty well for a 30 footer.

I discussed this on another thread but unfortunately I have no space for any blower pulleys. I only have a few inches of space with the stock crank 3 rib v-pulley. Again me not even paying attention to this when I bought the boat because I have no experience.

getrdunn 11-08-2017 03:02 PM

2 Attachment(s)
Been around for many years but stil a great cam and I bet would work well with your current build / heads. I'm not sure what your plan is to do but thought I'd post the cam card anyway.


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