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razor1115
11-29-2001, 12:32 PM
OK guys, I built a 540 cu in , fully ported, polished, oversize valves in the rec port heads and manifolds, EMI ss exhaust, 10.2:1 CR, CAM 108 center 112 lobe sep 244 int 252 ex @ .050" hydraulic roller. I dynoed engine - 585hp @ 5700 rpm, 595 ft lbs torque @ 3500.
The power never peaked and wanted to keep going even though comp said it peaks @ 5500.
The boat 24 baja is now a dog out of the hole and performs worse than the GM perf parts 502. I can't even pull a higher pitch prop - but there seems to be nothing wrong with the engine - runs fine. A buddy with 75 more hp is right on 90 mph same model boat. The cam acts likes it's huge (duration). I pulled the intake and checked the cam with a degree wheel - everything jives. I'm now beating my head against the wall hoping the unconsciousness will be more pleasant than racking my brain anymore. HELP

Havasu Hangin'
11-29-2001, 05:10 PM
My, what a big camshaft you have... http://www.goldenplasma.f2s.com/forum/smilies/happy06.gif
What RPMs are you pulling on the top end? Have you made any changes (carb, ignition) since it came off the dyno? What kind of exhaust was on with the dyno pulls? Same as on the boat? Any other diferences to the dyno pulls? What were the exhaust temps?
Just curious- what CC are the intake runners & chambers on the heads? Who built the motor?
http://www.goldenplasma.f2s.com/forum/smilies/happy25.gif

Infomaniac
11-29-2001, 10:31 PM
Razor:
The duration alone of your cam tells me it will peak around 7,000 RPM. You need a cam that has duration @ .050 of 215 - 220 range. Been there done that with boat cams.
Your peak torque RPM should tell you something. What RPM do you get on plane with? The cam you need should make good torque at that RPM . Also, the ideal stern drive cam should produce peak HP around 5,500 RPM for general lake/performance use.
Sorry to say it but without a blower big valves/ports do not help make low end power.
I can suggest a cam if you are interested.
My last sterndrive boat ( still have it but not the same engine) is a 21' Seebold stepped V. 400 small block with a B&M street blower. 635 ft lbs torque and 575 HP. I used a smooth idle hyd roller cam and it ran 93 MPH on GPS. Peak HP was 5,500 RPM on the dyno and I ran it 5,200 RPM. Worked out great.
ADDED THIS: I dynoed it with my stainless marine exhaust manifolds wet. I know it would have made bigger numbers with dyno headers. I wanted to make sure it made whatever power it was going to make at the RPM I was going to use it.
[This message has been edited by Infomaniac (edited November 29, 2001).]

razor1115
12-03-2001, 08:12 AM
The engine pulls 5250 RPM. Comp Cams said it would top out at 5500. Looks like the torque is dropping off before it has a chance to get the engine into the horse power numbers to build more speed. Carb is a 950HP DP, and the exhaust was 2 1/2" primary to 4" secondaries on the dyno header. As for exhaust temps, I'm not sure. If they were recorded, I need to scratch up the data from the dyno sheets. (Are you looking for a lean condition cyclinder to cylinder) As for the heads, cast iron GM 325cc runners, 118cc chambers fully ported, polished, gasket matched, oversize intakes (2.25")
Originally posted by Havasu Hangin':
My, what a big camshaft you have... http://www.goldenplasma.f2s.com/forum/smilies/happy06.gif
What RPMs are you pulling on the top end? Have you made any changes (carb, ignition) since it came off the dyno? What kind of exhaust was on with the dyno pulls? Same as on the boat? Any other diferences to the dyno pulls? What were the exhaust temps?
Just curious- what CC are the intake runners & chambers on the heads? Who built the motor?
http://www.goldenplasma.f2s.com/forum/smilies/happy25.gif

Infomaniac
12-03-2001, 08:25 AM
Razor:
At 5,252 RPM torque and horsepower are equal. HP will just begin to exceed torque at this point. Check your dyno sheet.
This is true with any engine. This is due to torque being the actual mechanical measurement taken by the dyno and HP being calculated mathmatically from that torque reading. The constant for this calculation is 5252.
Torque is always higher below 5,252 RPM and HP is always more above 5,252 RPM
If you plan to run your engine at this RPM it needs to have a flat torque curve and very low RPM peak HP
What is the cam part # ?

Havasu Hangin'
12-04-2001, 07:40 AM
Originally posted by razor1115:
...As for exhaust temps, I'm not sure. If they were recorded, I need to scratch up the data from the dyno sheets. (Are you looking for a lean condition cyclinder to cylinder)
Yeah, I had a lean condition one time that messed with the peak numbers on the dyno pulls. Just scratchin my head...
Like Infomaniac said, that is a big cam. For example, Merc's 500HP package only uses a hydraulic roller with 222/230 and .576/.598.
Keep in mind that I am no engine builder, but I would bet you $1 that your engine would pull hard in a car with a clutch or stall converter, but the boat seems to be another story. I think you may have hit the nail on the head with your torque observation.
Did you have the carb massaged?

razor1115
12-04-2001, 07:50 AM
the carb is stock out of the box. We staggered the jets to match the Merc 500HP due to the smae Dart single plane intake with unequal length runners. I"ve talked with Curtis at Billet Marine. He wanted to compare build notes with his 540's. He runs a little bigger cam yet and pulls 625-650 hp @ 5500 RPM with 650 lb ft torque. Just some observations and conversations with other engine builders...
Originally posted by Havasu Hangin':
Yeah, I had a lean condition one time that messed with the peak numbers on the dyno pulls. Just scratchin my head...
Like Infomaniac said, that is a big cam. For example, Merc's 500HP package only uses a hydraulic roller with 222/230 and .576/.598.
Keep in mind that I am no engine builder, but I would bet you $1 that your engine would pull hard in a car with a clutch or stall converter, but the boat seems to be another story. I think you may have hit the nail on the head with your torque observation.
Did you have the carb massaged?

Havasu Hangin'
12-04-2001, 11:46 AM
Originally posted by razor1115:
the carb is stock out of the box. We staggered the jets to match the Merc 500HP due to the smae Dart single plane intake with unequal length runners..
My motor is nowhere near yours, but my out of the box Holley was giving my builder problems. He just kept rejetting to get the temps down. I took it to a Holley guy who cross-drilled, venturi conversion, set the acc pump, and jets. It helped alot.
Single plane, huh? What ignition and curve? Still scratching...
http://www.goldenplasma.f2s.com/forum/smilies/happy25.gif

Tinkerboater
12-04-2001, 05:19 PM
I don't know why you guys need to mess with those 950's I'm running a pair of them on two 502's .060 over that are highly modified and all I had to do was rejet them. These engines run great. also those intake valves are too small for a 540. I'm running 2.30 intake valves with a sollid lifter .251 IN .259 EX at .50 with .601 and .625 lift at 110 deg. lobe sep. stock engine pulled a 23 mirage at 5200-after-5800. I'm now running 26 lab finnished bravo's at 5400. Yes I know that a roller cam will have better flow at part valve lift than a non roller cam. without being there to look at the motor it will be very hard to find out what is wrong-but something is definitly wrong. With that much cubes you should have more bottom end power than the stock engine even with a big cam.Hey razor if you ever decide to come up to holland / Grand haven area e-mail me
[This message has been edited by Tinkerboater (edited December 04, 2001).]

Boater Bill
12-04-2001, 06:48 PM
Did you state what exhaust you are running? I only see what was used on the dyno. Also did you go up or down on the jets after the dyno run and what is the current jetting? I'm not an outdrive guy (jet boy) but you may have to change gears to get the motor in its sweet spot.

razor1115
12-05-2001, 05:23 AM
I'm running the Merc Thunderbolt IV. It's the HP module with 20 deg. advance built in. The engine actually liked 38 deg and more timing but I set it at 36 in the boat. I always run 93 octane and have had no problems (I know with iron heads and 10.2 CR, it's the minimum) I dynoed the Thunderbolt ignition against an MSD 6A and there was only a 7 hp difference in favor of the MSD...
Originally posted by Havasu Hangin':
My motor is nowhere near yours, but my out of the box Holley was giving my builder problems. He just kept rejetting to get the temps down. I took it to a Holley guy who cross-drilled, venturi conversion, set the acc pump, and jets. It helped alot.
Single plane, huh? What ignition and curve? Still scratching...
http://www.goldenplasma.f2s.com/forum/smilies/happy25.gif

77charger
12-05-2001, 07:04 PM
I think its a matter of matching gears or prop to that motor.bigger cams will take away low end torque and hp to move to a higher point.So your motor will have to work at a higher rpm to take advantage.In my bbf(429) jet i went from a 214@50 550 lift that spun an a impeller at 4850 to a 248@.50 590 lift cam well the rpm dropped to 4700.I had the impeller cut to an ab and picked up 500 rpm as well as speed from matching my power curve to the impeller my motor is 475 hp @5500.

mcollinstn
12-09-2001, 07:03 AM
big cam - no low end.
single-plane intake - no low end
----------------------------------
using lots of good parts here. I assume you have no desire to run 6,200rpm? Then try the following: advance your cam 4 or 6 degrees (did you say whether you had actually checked and verified the installation position?). This will rock the power curve back 250-500 rpm.
Replace the expensive and beautiful Dart intake with an Edelbrock RPM Air Gap intake. It's a high-flow dual plane with temperature isolation. Should boost your lower end numbers noticeably and should not cause HiEnd restriction til 5800 or so.
Degreeing the cam (borrow a wheel, mag base, and dial indicator - buy some silicone permatex and be glad you arent pulling the cover off a dang smallblock). Intake: $230 at Summit. A set of gaskets. Some more permatex. (you may want to add a $20 valley splash pan to keep hot oil off the bottom of the intake, too).
$265.00 - much improved bottom end.
still good hp on top. Happy day.

MIKEHTMSR24
01-04-2002, 09:26 PM
Razor1115
check me out on hyd roller cam post
I am running 80's w/PV in the front and 90's w/no PV in the rear.