Blower cams
 

We are always talking about cams for NA builds, but what about with forced induction?

Take a look at this, and let me know your opinions.

Lunati has a 250/255 112 LSA .630 lift cam, that is labeled a "supercharger" cam. Lets take a look at this cam, compared to a Crane 244/256 114 LSA, "651" that many like for supercharged engines, and is labeled a supercharger cam.

First, lets look at the exhaust timing events.

Exhaust valve opens at 61.5, and closes at 13.5 on the Lunati.

Exhaust valve opens at 67, and closes at 9 on the Crane 651.

Both exhaust lobes, have nearly identical .050 duration. Lunati at 255, and crane at 256. But look how different the exhaust timing events are. Anyone have any thoughts on WHY, and how that would affect things?

Where do the intakes open on each as a comparison to the exhaust closing?

IO 15, IC at 55 on the lunati.

IO 13, IC at 51 on the crane.

Of course the crane is sporting 6* less duration on the intake side.

Is it maybe due to better flowing exhaust ports on aftermarket heads? Just a guess but 651 been around for years and possible was more toylored towards GMs chits exh port. Any thoughts? Just throwing this out there.

Did you compare it with the SR Crane I sent you last week.

From the research I've done on even split (single pattern) cams (my whipple 500efi's have them)... the increased intake duration, or lack of favored exhaust for that matter, the more efficient the exhaust port/exhaust in general, the less exhaust duration desired vs intake. My theory is you want to limit intake blow thru as much as possible to take advantage of the blowers efficiency but have enough to clean the cylinder.

Blower engines in general do not require near the exhaust scavenging due to positive pressure on the back side of the intake valve. In affect the blower induces the clean fill to a much larger extent and not need the overlap

Efficiency is everything but again I think when were looking at two blower shelf cams with a noticeable difference in exh valve timing events. Exhaust port flow and what exhaust is being used for the particular build would come into play. Just getting back to OP.

Why they look are nearly identical but are quite different ?

Lunati is ground with 2* Advance . So being on a 112LSA, this puts ICL at 110* and ECL 114*
Crane ground with a 5* Advance. So, being on a 114LSA, this puts ICL at 109* and ECL at 119*

Could very well be. I honestly don't know without researching it so will have to look up what most blower cams have for specs. If you get a chance MT post the specs of the sci one merc used.

Wazzup with the voices in your head??? Lol. Just noticed that but gotta admit I've had a lot of that going on lately but not snowmobiling. No snow up here...

Maybe the Crane 651 is also doing those specs for heat management ?

In regards to splits I did look up lunatis and did notice their blower cams do have less split than others. 4+- on blower cams and 8+- for non blower cams. Just a quick search I didn't go through all of them but..

With a hydraulic lifter, the exhaust opening can be fairly critical in a boosted application. In theory, and as seen in software modeling, opening the exhausts sooner to initiate blowdown pays off in hp. What I've seen in the real world is, opening too early against all that cylinder pressure can cause the lifter to bleed down, or beat your valve train up if you've got really stout lifters. Sometimes a slightly later exhaust opening will actually make more power due to better valvetrain control. It can also be boost dependent. A cam with an early exhaust opening might work great with 6 or 7 lbs boost, but start to have issues at 10-12.

And to clarify. That's not a knock against simulation software, which is an incredibly valuable tool. But some one who has never built a supercharged marine engine before could sell a hobbyist cams designed by that software and run in to trouble. Just because it says you make more power with a bunch of lift and an early exhaust opening doesn't mean it will live in the real world.. But I digress.. ;) Does the 651 cam have a boost psi recommendation?

Good post... never really thought about the lifter bleed in that regard but then again my personnel experience with hyd lifters suck. But certainly can see the extra pressure if events aren't right on Q especially in SC builds.

Crane says max boost is 20psi with 8.0:1 max static.

That part I get. My question was more or less related to actual valve timing events. People tend to get so wrapped up in LSA's, ICL's, .050 numbers, and rarely look at what the valves are doing relative to all that, and that imo, is what matters. The engine doesnt know or see, LSA's, ICL's, etc. It just sees what the valves are doing.

I think Haxby nailed a topic, mentioning opening the exhaust valve too soon, can be hard on parts. The cylinder pressure can be very high at exhaust valve opening.

Performance wise, I am guessing , that opening the valve earlier, with a poor flowing exhaust port, might get the cylinder evacuated better, but with a good flowing port, might be a waste? I don't really know. Or, maybe its relative to the level of boost..

Maybe I'll have to run 2 dyno sims, one with stock GM heads, and one with a dart or afr head, using both cam designs, and see what happens.

Good stuff.

Joe, you have the wheels turning on this topic for sure. Reminds me of what Bob Teague told me when degreeing my cams, he said to forget about all those @ whatever #'s and use the valve events from the grinders cam card. It makes sense, most people get hung up on the advertising of a cam and forget about the true #'s. Smokey Yunick says anything over 5 degrees advance or retard and you have the wrong cam, but we all know the 651 makes good power. You for sure have made me pay a lot more attention to the actual lobe on some of these cams vs what is advertised.

isn't it just easier to google a supercharger build to fit your needs and copy it.:Dwill save you a trash barrel full of cams that were suppose to work on paper and in an computer syms.:D

I prefer to try a little more technical attempt at things. Have I seen the 651 cam work well in supercharged builds? Yes.

Ive also seen stock 049 heads make what some would think, good power with an 871 on top. Does that mean a set of afrs or darts wont make more power and be a better setup?

Some of the top engine builders use modern software during engine development, as well as oem manufactures. By no means is it better than real world results, it might narrow down that trash barrel full of cams, to a picnic basket full of them.

Kind of hard to move forward, if we just keep copying someone else. The idea is to get a better understanding of why, something does what it does. Otherwise , your just a parts changer.

:rolleyes:

"Some suggestions for a blower Cam.
A wide lobe separation (112*-115*) to reduce overlap and blow through.
Blower engines need less (2*-4*) advance. An early IVO is unnecessary. The intake column is pressurized and early openings increasing overlap. A 110*/112* ICL on a 114* Lobe sep would work well.
Increased exhaust volume requires blower cams to have additional ex duration to rid the cylinder of spent gasses. This is dependant upon the efficiency of your exhaust port. 8*-10* spread is a baseline reference.
Stock exhaust ports need an earlier EVO to blow down the cylinder. The negative of and early exhaust valve opening is the loss of some of the increased cylinder pressure. The negative of a late EVO is increased pumping losses. Optimizing your exhaust port will help, allowing you to delay the EVO, negating the pumping losses.

The shelf cams (marine) available today were designed around flow numbers from cylinder heads designed 25 years ago. This is particularly true of marine catalog grinds that haven’t been updated in years due to the relatively small market share they bring to the larger companies. Simply put they will not come close to optimizing the flow capabilities of today’s AFR/Canfield type cylinder heads. The durations are to long and the splits to wide given the near 80% I/E ratios that are commonplace today. Much of the potential HP/torque increases available are underutilized by improper camming of these engines. It doesn’t make sense to bolt on a set of CNC AFR’s and cam it with a piece that was designed around flow #’s that aren’t even close and send those increases “out the pipe”. Due to advanced modeling and software, custom cams (designed around your particular parameters) are now affordable and readily available option to the marine market. There is extensive development going on today in marine camshaft design especially in the 502/540+ displacement area that is making high, flat torque numbers on the dyno, easier on the valve train, with much better VE and BSFC #’s. This is all done while keeping peak torque/HP numbers right where you need them."

I recall that post from Bob about 10 years ago. Mentioning the cams designed around heads from 25 years ago.

Interestingly though, the 651 cam, and the cam he designed for a buddys blown engine with cnc afr heads, were very similar. Duration and timing event wise. Just a 680 lift, instead of 632. Made good power. Not sure how its holding up, as he sold boat with around 10 hours on the engines.

It be interesting to see how a blown 540 does, with a cam like the lunati supercharger cams, that only have 5 deg of split, with a 112 LSA, vs the tried and true 651 , with some cnc heads .

I believe my Lunati cam for my 575sci is 240/[email protected] .642/.642 114ls 110icl, I havnt even fired the motor yet but I wish I would have went a little bigger and did the 4/7 swap. Also not sure about the 5* split. At this point I dont think it would be worth the investment as I dont have anything to put it in. So, with AFR325 cnc chambered, stripped 871 with whipple chiller, stock 502 bore, 8.25:1 CMI ETops...what is my safe estimated HP on 93? The problem I see is supplying enough fuel with the dump truck injection system.

I think it will make some good power. The fuel injection will prob be the limiter on that combo. Those things dont flow alot if cfm if i recall?

You sure your cam isnt a 112 LSA lunati?

http://www.rootzefi.com/theinjectionplate.htm maybe

Custom grind specd out by Ron Sporl, 114 on the cam card, I believe he keeps them on the shelf.

Pretty sure you have had your hands on my Throttle bodies, they should flow better now. Eddie young has the kit I would most likely use if I was going to keep it.

Gee Joe.. how about my cams that defy all logic lol :rolleyes:

Nice build. What are you thinking around 8-9 pds? Gonna make some good power.

I find this article kinda interesting,,may won't to note the split on the winning cam.:D

http://www.superchevy.com/how-to/eng...ower-cam-test/

Cool article. Pretty clear the big cam simply won. Bigly.

Not surprising that much cam split did well, when you look at the flow numbers from a stock LS3 head.

im currently doing the same thing to my 575sci, going with the Eddie young injection tho, what would the 4/7 swap bring to the table? i remember reading about it awhile back but thought it was on a small block. is yours still a 502 JRider?

4/7 swap makes the firing order the same as the LS and 8.1, it makes a few more horsepower, about 15? cant exactly remember, but I was told it has to do with crank shaft flex. All that needs to be done is swap the wires on the cap. NASCAR uses that firing order as well.

Yes, mine is standard bore 502, I would have went to a 540 if I knew my injection could supply it.

single swap, 4/7......C swap......4/7 3/2 ( double ) minimal gain maybe less than 10hp @ over 6000 revs from what I've read, I ran C-swap in my 540's, you can really hear a difference through the headers. I think the Pro stock guys started this way back in the day, it is suppose to be easier on the crank and bearing's tho.

with that cam how high are you planning on spinning it? im in the same boat on my build currently

Stock ls3 flow numbers
 

0.617/0.595-inch lift split, a 231/248-


if the numbers inked below are confimed correct then it does make sense with what I would consider to be a funky cam. The exhaust flows like 2/3 the intake vs more common heads 3/4 especially aftermarket. Ratio varies lift depending but in a nutshell I can see how they came up with that grind after looking at the flow numbers.

I run the 2/3, 4/7 swap and you can definitely tell the difference. Kinda takes the bark away from the big block. It sounds tame, but smooth.

i didn't know you did that. Gotta be easier on inners but not as big of a grin on your face heading out grand haven channel. Lol... I knew the 4/7 swap tamed down and definately have a sound of their own so I can only imagine 2/3-4/7.

6000 but I am not sure where peak power is at. I actually spun it to 5800 with stock cam, not sure how much HP dropped off but the boat was fun to drive.