SB

From : http://www.offshoreonly.com/forums/s...d.php?t=139026


Didn't want to hijack the other thread, so we'll discuss this here.

When you mention the '241' and '561' cams I'm assuming you are referencing the flat tappet Crane #134241 + #132561

Let's take a look side by side.

..........#134241.....#132561

I dur .004" 286°..... 296°
I dur .050" 226°..... 228°
E dur .004" 296°..... 306°
E dur .050" 236°..... 236°

Notes: similar enough ? No. #'561 has 10° more Int seat duration but only 2° more at .050" . Also has 10° more Ex dur on seat but same at .050" as #241 . Therefore, the #241 is lifting/closing valve faster.

Lift : .534", .553"......530", .551"
Notes: none really. Close enough to be counted as same.

Max lift ° (ie: centerlines)
ICL .................. 107°......109°
ECL ................. 117°......119°
Resultant LSA°...112°......114°

Notes: Wider seperations usually make a naturally aspirated motor 'lazier' than tighter LSA's when using same lobes .....within a reason, of course, and motor parts combo, etc,etc. Peak hp may be same but I'll tank the 'stronger more lively one' thank you. So, take this loosely, but it does apply to your engine. People forget that having the valve placed at 'highest flow' vs where piston is and how fast it's moving in a certain direction is BIG importance.

Actual valve events .004":
IVO ..........34°BTDC.....35°BTDC
IVC...........72°ABDC.....83°BTDC
EVO..........83°BBDC.....87°BBDC
EVC..........33°ATDC.....39°ATDC
Overlap......67°............74°

So, with a low compression motor big thing here is IVC. An engine can't start making compression until intake valve closes...remember, piston is coming up when int valve is closing.#'241 closes intake valve 11° sooner than #'651.

Next thing is overlap. #'241 actually has 7° less overlap than the #'651. Although we need overlap for making power, as we know too much is not good with wet marine exhausts. We have to keep this in check for this and the rpm we are going to turn these things.

Above/below are just my thoughts - I'm at about a 35-45% knowledge level, where your real good cam designer's are at about a 70-75% knowledge level. I don't believe anyone is at or over high 80's to 90%. If you know what I mean. Always room for improvement.

So, on a typical 8.5:1 to 9.5:1 454 with typical performance parts added, I would sway towards the #'241 (over the #'651 if this is all I have for choices)
with it's quicker lifting/lowering ramps, lower seat durations, almost identical at .050" durations, same lift, earlier closing intake valve, and slightly tihter (LSA) lobe seperation angle.

=============================
As a side note since you seem to be interested in how to make your engine powerful - not because I'm being mean, I personally do not like the Weiand X-Celerator intake manifolds. The runners do not transition into the cyl head runners well at all. This was the industries 1st attempt at high performance single plane intake manifolds. Take a good look at them vs the more modern Dart, Vic Jr, Brodix, etc,etc runners and how they have longer more sweeping turns to get a longer, straighter shot before going into the cyl head runner.

Again, my 02 only since you seem to be interested and I like to help and atleast make people think.

Disclaimer: as stated earlier, I'm only at a 35%-45% knowledge level.

Thunder Struck

SB - wow that is some serious information that I can take to my engine builder.... when one is chosen.

What is the compression ratio of the Merc '89 420? I have a pair that are untouched since '89, bone stock and it is time for a rebuild. They have 850+ hours on them. The timing was retarded a number of years ago to run on regular 89 oct. but they were run hard every time out and lasted this long. See my related link in Jeff 32's post.

Thanks again for the info.

Trevor

Payton

Thanks for the great comparison! Looks like I made the right choice in cam. Untill I make the mover to roller. It also looks like Wiand/Holley doesn't even make the X-celerator in a BBC version anymore. At least Summit doesn't have it on their website. Just put them on in the spring of 2005.

thsnks again

SB

Remember - my comparisons + choices where between two cams given. Not free reign on whatever I wanted.

Payton

and I apreciate it.

Thunder Struck

SB

I would appreciate your insight into what you feel would be the best roller cam / compression combination for my 420's given I am looking for 500hp to push my old tub around with. Running of preumium is not an issue, I am willing to pay the bucks for the time I get out of it. Can I hope to get this by keeping my exisiting heads and doing a mild valve job?
You seem to have put a fair amount of thought into this engine combination already.
Thanks in advance.

Trevor

Payton

Trevor, I would think you would be very close to that with jimV doing a little work on your heads. But then you might as well go full roller valve train.

http://hometown.aol.com/valakoracehe...raceheads.html

give him a call.