KAAMA

iTrader: (1)

BTW, we degreed in these new cams in at 108-108.5* intake lobe

WETTE VETTE

Do you think maybe your compression is to low for your original cam choice? It sounds like you may have been lacking some heat and that could be why you were getting incomplete combustion. Did you try leaning out the carb to see if it clears up? I am just curious because I run a solid roller 272/280 duration at .050 and have very efficient cylinder heads. My transom is always clean and there isn't any sign of excessive unburned fuel. I am running 13:1 compression which is probably providing enough heat for a complete burn despite the scavenging and valve overlap. What is your compression and cubic inch?

blackhawk

When we work on snowmobiles we NEVER dyno the motors directly. We dyno the power getting to the ground and make adjustments accordingly. You know how many "160 hp" sleds I've beat up on with my 110hp sled because they weren't running the correct rpm?

My point is if I was doing some motor mods I would use a propshaft dyno with my exhaust, ignition, etc.

KAAMA

iTrader: (1)

Wette Vette,

I'm running 540 cubic inches, Dart Pro-1 fully ported aluminum heads, about 9.7 comp ratio. Also, keep in mind I am running HYDRAULIC ROLLERS, not mechincal rollers. And the figures I gave on my cam specs are @ .050

BTW, I am running #79 size jets on all four corners and BSFC was averaging about 42 which is kinda low and EGT were about 1300* which seems okay, but the BSFC numbers and the EGT numbers just dont seem to jive together too well. It seems that if my BSFC numbers (as low as they are, 42) would make my EGT numbers to go higher than the 1300* temp mark! So It must be that I am throwing unburned gas out the pipes and making my EGT's cooler. It's just a guess, but it seems like that may be what's happening.

WETTE VETTE

Have you done any compression checks with either of those cams? My motor is around 180 PSI cranking. I ran a cam that was on a 114 + 4 installation and the cranking pressure was only 120 PSI. If you did a comparison between your two cams I would be interested in seeing how they compare. I would guess the 114 cen. and slightly shorter intake duration will make for 20 to 40 psi less than the longer 112 cen. Only guessing though.

formula31

Again correct, my 114 +5 advanced only reads 115 at cranking speeds. Oh and if anyone decides to try advancing their cam, be very careful of intake valve to piston clearance. Advancing the cam timing reduces this clearance.

KAAMA

iTrader: (1)

Wette Vette,

I haven't done a compression test....but you know, that sounds like it might be a good idea to know what it is and where I'm at with it. We'll test it tomorrow and I will post what we found then. Thanks

cobra marty

Kamma, With your good ported heads maybe you don't need to run a split duration cam. The greater duration on the exhaust is to make up for poor/fair heads or supercharging and it's greater air/burn. You might need a straight 236/236 cam. Look at desktop dyno- it's fun to play with and all this is easily changed.

WETTE VETTE

I built a 12:1 comp 496 and installed a solid roller Erson cam with 268/276 dur at .050 and it had .688" lift. It had fully ported GM 990 rect. heads. I was getting 5600 RPM and the cranking cyl pressures were 240 PSI. Erson suggested a re-grind on the cam and they turned it into a 278/284 dur at .050 and kept the .688 lift. The motor woke up. It was 6100 RPM on top and the low end and mid range didn't seem to suffer to much. According to Erson on that motor 240 PSI would have led to detonation and that is the biggest reason for the re-grind. The longer duration created 170 PSI cranking which Erson said is adequate for good low end torque and low enough to keep the motor out of detonation. Before I did the re-grind I retarded the cam in 2 degree increments a total of 6 degrees. Each time the cylinder pressures dropped slightly, but it was still at 215 at -6 degrees. This gave Erson the data they needed to pick numbers for the re-grind. Both of these cams were designed for 112+4 installation. On smaller motors the 114 lobe centers are for blower or turbos and they lower the cranking pressures. On larger engines 114 to 118 degree lobe centers are good in controling pressures on naturally aspirated motors. I am very interested in what KAAMAs pressures are cranking with that cam. The duration seems somewhat short which raises pressures, but the 114 cen will lower pressure. Let us know what you find KAAMA. I guess 236 dur at .050 on a hyd roller isn't that small. I am used to solids.

RumRunner

KAAMA

Your BSFC is showing your how much fuel it is taking your engine to convert it into HP. At .42 it shows being a little more efficient than some. If you were cooling your exhaust with raw fuel your brake numbers would be higher. A .42 Brake and 1300 exhaust temp is not that far off.