Auto performance cam in Merc 260...problems?

[erikgreen]

Hi all;


I finally got ahold of the specs for the "300 hp" cam that Rapido built into the Chevy 350 long block that they built for me last year, and I wanted to run them by the engine experts here to see what you think.

Specs are as follows:

.050 Duration ADV Duration V lift Lobe ctr
224I 224E 291I 287E .450 .461 114 114

According to the info I have this is equivalent to a Melling 22210 camshaft, which is equal to a GM 3896962 camshaft, which was made for corvette engines.

So, my questions are:

1) How will this camshaft affect performance of my boat engine - what is the HP output and RPM range I should look for?
2) Does the valve timing present any danger of water ingestion?


Thanks,
Erik

 

[FreeBeeTony]

Re: Auto performance cam in Merc 260...problems?

Hi Erik..........how does it perform? I'm just curious.........is it a dog or does it have some get up and go?

 

[erikgreen]

Re: Auto performance cam in Merc 260...problems?

So far its performance is "ok"... I had it out last weekend and a 3500 lb. boat with a deep-V hull and a 19 pitch prop did 40 mph... not bad, but the general opinion in the prop forum is that it should go faster. Especially since I removed a lot of weight this last winter.

Anyway, I guess the answer is I dunno, so far. I'm testing the tach and I'll adjust the throttle next outing too to see if it helps.

Erik

 

[Maclin]

Re: Auto performance cam in Merc 260...problems?

Overlap and duration would be the key parameters that affects the propensity for inversion.

The lobe centers indicate the overlap, that cam is on 114 degree centers. As I recall that would be less overlap than say 110 degrees which is what I remember as being a hot high rpm cam. This is from memory and I will defer to anyone with more expertise in this area.

Having typed that, I do not know at what point inversion occurs at a high enough level to be suspect for water ingestion. My opinion would be that this cam is probably as "hot" as a small block can get before inversion is a problem.

 

[FreeBeeTony]

Re: Auto performance cam in Merc 260...problems?

Was the 40MPH at WOT?
What is the WOT?

 

[MikDee]

Re: Auto performance cam in Merc 260...problems?

Here you go, I thought it sounded familiar it's the L82 350/330hp cam! The 2nd one down on this page near the bottom:

http://www.sallee-chevrolet.com/Camshafts/index.cfm

P.S. This appears to be exactly the same as the old 350/350hp cam, the only difference in these engines I believe, is the 350/330 had 10:1 compression, & the 350/350 had 11:1 comp. But this cam raises the horsepower up the rpm scale!?

 

[erikgreen]

Re: Auto performance cam in Merc 260...problems?

Was the 40MPH at WOT?
What is the WOT?

40 mph at WOT, with tach reading 4800-4900, although as mentioned there's a need to verify the tach reading... I have a spare, new tach I can put in.

 

[erikgreen]

Re: Auto performance cam in Merc 260...problems?

Here you go, I thought it sounded familiar it's the L82 350/330hp cam! The 2nd one down on this page near the bottom:

http://www.sallee-chevrolet.com/Camshafts/index.cfm

P.S. This appears to be exactly the same as the old 350/350hp cam, the only difference in these engines I believe, is the 350/330 had 10:1 compression, & the 350/350 had 11:1 comp. But this cam raises the horsepower up the rpm scale!?

Seems like it, only I'd be willing to bet I have "normal" compression, which is something like 9.x:1... hence this thing being sold as a "300hp" cam???

 

[MikDee]

Re: Auto performance cam in Merc 260...problems?

I am familiar with, and have used a cam with specs very similar to this, but yours is the newer design. It was the 327/350hp cam factory #3863151, reproduced here by crane #1236450 (#13 on this list). Both of these cams are factory specs, and about as hot as you'd wanna go safely (for marine) I'd guess?

It had a groovy, lumpy idle, (yours should have a similar idle also) and less low end torque then a stock cam but more upper rpm, & power. I put it in a 75' Chevy Monza 2+2 Sport coupe with a 262V8, the only issue was I lost some vacuum for the power brakes at idle. With the stock worn out cam, it could not reach 4000rpm, after the cam swap, It sounded like a dragster at idle, & like a corvette when revving! It would do 7000rpm with stock hydraulic lifters, and a 2bbl carb! That's as high as the factory tach read anyway, but I lost some low end torque, at least the car was stick. In order to get, and maintain good power, It had to be run between 3K-6Krpm!

I would think you need to run at more then 4600rpm at WOT to get the benefits of the specs on this cam, but what figure I don't know?

 

[FreeBeeTony]

Re: Auto performance cam in Merc 260...problems?

Just for comparison info:

my boat weighs 4000lbs, ~30MPH @ 3800RPM turning a 15x16 4 blade prop

haven't hit WOT yet............still only 8 hrs on the engine

 

[John_S]

Re: Auto performance cam in Merc 260...problems?

It appears to be designed for a more free flowing exhaust than a boat would normally have. Are you running thru-hull exhaust? I thought you were running thru-prop and with the older slightly more restrictive log style exhaust manifolds. How are your on plane times? Does it seem to struggle, and then take off?

 

[bolo78910]

Re: Auto performance cam in Merc 260...problems?

i the same rapido in my 26 montego i started it up and breake in the cams man , this thing sound like an animal, i still dosent take it out for the break in as yet, hopefully this weekend the latest about tusday i will post my outcome.

 

[Mkos1980]

Re: Auto performance cam in Merc 260...problems?

Stock 350 Mag 270 HP. Stock Merc cam. 200/212 400/415 110LSA 4600 RPM WOT 53.6 GPS 21P Laser II

 

[erikgreen]

Re: Auto performance cam in Merc 260...problems?

It appears to be designed for a more free flowing exhaust than a boat would normally have. Are you running thru-hull exhaust? I thought you were running thru-prop and with the older slightly more restrictive log style exhaust manifolds. How are your on plane times? Does it seem to struggle, and then take off?

To me it seems to struggle a little, but a friend with more boating experience says it seems fine to him.

I'm running the through-prop exhaust and log manifolds as you say... gonna replace those as soon as I can get the cash together, they're old.

I'm really starting to think I need to verify my tach and check trim. Is it even safe to run this engine up past 5000 rpm?

It does sound good when in use, although the idle is less smooth than I would have thought, so I guess that's the cam.

One more thing: I had it out on idle for a bit last fall using no thrust washer... not long enough to even take paint off, fortunately. Right now I have it together with a thrust washer and there's about a 1/4" gap between the leading edge of the prop hub and the trailing edge of the lower unit. I would think this would let exhaust gases out "the easy way" instead of through the hub, causing ventilation??

 

[John_S]

Re: Auto performance cam in Merc 260...problems?

You are not going to hurt anything by going to 5200 rpms for short test runs.

Gap at front of prop sound like a problem. Wrong thrust washer? But, if it was ventilating, you would know it.

As far as the cam, sounds like its not that bad of a match that you need to change it. Keep an eye on the plugs to see if you are getting inversion. If the back plugs (7 & 8 w/log ex) are very clean compared to front (1&2), probably means its sucking in some water.

 

[MikDee]

Re: Auto performance cam in Merc 260...problems?

After going over the specs on your cam the 350/350hp I see it's a bit less duration, but a bit more lift, compared to the 327/350hp cam, so apparently being a later, better, design, it's a bit milder, with a bit more torque, this is a good thing. I would venture to say in a car, it would reach peak maximum horsepower somewhere around 6000rpm, but IMO in a boat they normally use less total spark advance, bringing the rpm down, but keeping torque up. I'd say this engine needs to run at least 5k rpm just to breathe in a boat.

I just realized cam #1, & #13 are basically the same on the chart I gave you, And cam #14 is the "plain vanilla" cam that is usually used in almost all the stock chevy small block V8's. It came out in the 1962'- 327/300hp engine (which I had in a 62' Impala SS), and has been used as the standard cam ever since. It is a good strong all around ordinary idle cam, that's has good usable power to about 5k rpm. This is probably the stock 350/260hp Mercruiser cam.

All of these cams will rev higher, but won't gain any more horsepower.

 

[MikDee]

Re: Auto performance cam in Merc 260...problems?

It does sound good when in use, although the idle is less smooth than I would have thought, so I guess that's the cam.

The idle will probably have a lope to it, but it should be a constant steady strong rythym. This is a decent hi performance cam, it is a factory designed clone, one step above the stock cam, and should provide good power, & smooth running, without going crazy with extra lift, & duration, that usually causes: a loss of low end power, valve clearance issues, rough idle, vacuum loss, or lifter float, problems.

 

[erikgreen]

Re: Auto performance cam in Merc 260...problems?

Great, thanks for the info.

I guess my next step is to verify the tach, and maybe try out a 21p prop if I can lay my hands on one.

Erik

 

[z284u2try]

Re: Auto performance cam in Merc 260...problems?

The cam specs I see are a good all around mild cam. I had a similar cam that was 224/224 583lift @114lsa with 4 degrees ground in this was in a car. made power to 6000 and held it to 6500 flat. tq started out large but fell off fast.

Anyone know if split durations work well with a boat.

 

[Coors]

Re: Auto performance cam in Merc 260...problems?

You are not going to hurt anything by going to 5200 rpms for short test runs.

Gap at front of prop sound like a problem. Wrong thrust washer? But, if it was ventilating, you would know it.

As far as the cam, sounds like its not that bad of a match that you need to change it. Keep an eye on the plugs to see if you are getting inversion. If the back plugs (7 & 8 w/log ex) are very clean compared to front (1&2), probably means its sucking in some water.

Thru hull Time!