PROFILE

Do you think this cam could have water reversion problems with Gil exhaust,too much duration?
240 int, 253 ex dur @.050
113 lobe sep
575 int, 595 ex lift

I'm running this cam in my motor(502,b&m blower), it made the most usable power according to desk top dyno.
Getting slight water in #7 and 5 cylinder,worse in#7.Minor signs(rust specks) of moisture in 1,3,an#4.Seems to be a problem at idle,cause it will clear out once I speed it up.
Pulled exhaust and pressure tested it=OK.
Cometic head gaskets looked ok.
I question the internal flappers in my exhaust tips,maybe need to add flappers on end of tip.
I'm gonna upgrade to better heads and want to be sure the wateris not a duration issue.
Any thoughs,suggestions.
Thanks

PatriYacht

I would guess yes, reversion will be a problem with that cam. What you will need is tailpipes that go through transom and only dump a small amount amount of water to cool the tips and mufflers. ( You will need mufflers now.) Have an extra bung welded on the tailpipe to dump the majority of the water overboard. That's what I had to do with a cam that was 244/256 114 lsa.

KAAMA

iTrader: (1)

PROFILE,

I would do a little more research on the cam vs. the one you picked or have your eye on that you mentioned in your post. This is my .02----but to me, your the cam you have mentioned is way too large for your engine CID (cubic inches displacement). AND it is too large for a blower application as well. There may be some other guys who disagree or may want to beat me over the head for what I just said, however if I were you I would re-think your cam profile for the application for which you are using it for. There is a member on here with the screen name of "rmbuilder" (Bob) who has the wisdom, integrity, and background in selecting a camshaft that will work for your goals with the components, and application for which you are using the engine for. Of course you can do as you wish, but I think I would seek him out, and speak with him first.

PROFILE

KAAMA,I respect your advice.
I picked that cam after comparing it to many different cams using desk top dyno as the comparison tool.It peaked tq=634@3500 and hp=536 @5000.All of the other marine cams I tried fell short of those #'s.
I think the stock heads are holding back the hp because when I use flow #'s from better heads the hp really picks up.
I'm considering canfield 310cc, they seem to flow well.
I guess I should just go ahead and up it to hydraulic roller, crane 731?
I want to stop the water reversion problems.Maybe teeing off some of the tailpipe water is the answer?
Any cam recommendations?
thanks

cstraub

The cam is way to large for a blower engine. I would think something in the 220 on intake and 232 on exhaust would better fit the bill with a max of around 5500 rpm. More lift on the intake then the exhaust. Only real way to get the cam exact is to pull the heads and flow them.

Chris

Lmarth

I'm with Kaama on this one. I'd wait for Bob Madera (rmbuilder) to chime in or to PM him. I don't want to speak for Bob, but if you do a search on this site, I thought he said a few months ago that he wanted to know the specifics of any reversion problems involving a blown motor. I'll admit that I'm talking a bit in code here, so let's just see what Bob has to say.

jdnca1

For reference, I ran a 252/258 @.050 .680/.708 114 LSA solid roller on a NA 502" with wet Gils and absolutly no reversion probs, fully ported GM iron heads with 2.25" intake vavles. Not sure how that crosses with a flat tappet though. It seems huge if its a flat....

That was a Nickerson blower cam, but it worked great NA.

rmbuilder

Profile,
The cam is a Comp Cams Hyd-Flat
11-568-4
CB NX 284H-13
@ 0.006 Tappet Lift
284*/ 305*
IVO 34*
IVC 70*
EVO 90*
EVC 34*
@ .050" tappet
240*/253*
.338"/.350" Lobe
.575"/.595" Valve
68* Overlap
108* ICL
118* ECL
113* Lobe Sep
What is your target peak HP and WOT RPM?
Bob

PROFILE

Bob,
Thanks for replying.Yes thats the cam I have now,but I'm thinking its the cause of my reversion problem.
I would like to make some where around 650hp or better and 5500 wot. Do you think this is a realistic goal?

rmbuilder

Jdnca1,
I believe the .050” number and lobe lift on your cam would net you a rated duration of about 285*/290*. That said, your overlap in degrees of rotation with a 114* LSA and a 110* ICL would net you only 59.5* of overlap, less than the hyd-flat in question. The solid roller allows very aggressive ramp rates while still keeping the rotational overlap in check even though your overlap area may be greater. Also when you subtract the lash allowance @ the .050” solid vs. that of the hydraulic, the comparable numbers would be approx. 244*/250* for your roller. The hyd-flat will have a greater probability of reversion, all things being equal, to your solid roller. The solid will have greater lift at the crossover point, but there we get into low lift flow, reverse flow, and a multitude of other considerations.
Profile,
“I picked that cam after comparing it to many different cams using desk top dyno as the comparison tool. It peaked tq=634@3500 and hp=536 @5000.”
I would strongly suggest that the use of .050” duration figures in “trend tracking” with computer sym programs would yield no useful information. I have seen syms set up with seat-to-seat figures that arguably suggest trends, but .050” numbers skew data to the point it cannot be considered. I believe your target of 650 HP @ 5500 rpm with a 502 blower motor is realistic, but that cam is not your best choice.
Bob