custom cam problem
 

Hey guys I recently had my engine completely rebuilt top to bottom. Which was fine when I got it back to break it in and was hitting 170% engine load in 1st and 2nd gear...awesome! Till we dynoed...i was at 360whp before the built motor and after was only able to hit 260whp at about 5500rpm then power would drop right off to about 200hp by 6000rpm them shoot up to 280hp by 6400rpm???? My question for you guys is would this seem to be a cam issue? Just my guess. There's a copy of the cam profile to go along with this, any help would be muchly appreciated cause im gonna dyno tuesday the 23.

After looking at it again, im not sure. The intake closing and exhaust closing 30* before/after bdc/tdc may be an issue with the VVT.

If you degree the cam to those exact specs and weld the VVT in that position it might fix it. The VVT can retard that intake cam another ~16* which makes it open ~18* btdc with the exhaust still open another 28*. From everything ive seen, this car does not like overlap at all in the lower rpm range.

You could also be getting some valve float if your running the stock springs.

After tuning and getting that weird dip in power the cams were changed to a stock set. I'm thinking this will fix the power loss but I'm new to tuning and what not. The shop that does my tuning and came up with this cam profile deals mainly with subarus, and I'm the first speed they have had come through their shop...yay!. But ya I don't have any of the logs which would probably help make more sense of all this but thanks for the info.

holy fuck is that a gook muscle camshaft profile looks like?....

yaowsers ...... tiny lift , tiny duration....what do profiles from 500hp + 4 bangers look like when they are turbocharged??

Ok I have no idea what your saying or asking. Lol. Im almost positive the cams the problem and I assume you are saying the same...?

nah just tripping on what i see.... i really have no comparison to base how large our cams should or shouldnt be.... even for a street motor those are low duration numbers....but new tech with vvt, 4 valves per etc etc ....i wouldnt presume to know.

can u find out what the specs of our stock camshaft are????

i dont how far the vvt extends the operating range of a camshaft but i can tell you that with that duration profile the rpm limits of the motor would be well below 6k RPM.....

very surprising to see this on an aftermarket performance cam


let me see what I can dig up on my own about the oem to get an idea of how this cam compares ......

im trolling cosworth for specs on their specs on mzr cams , and they have a more respectable duration..... i think the cams u got have a decent lift for these motors but the duration is shit.


not sure how much u understand about camshafts but ill run it down for u quickly....

camshaft is a shaft that has lobes (cams) that are oval shaped.... on about half (thats just a number for u to just visualize) of the lobe it is perfectly circular (this is where the valve is closed) and on the other half it ramps up into a peak or rounded top (this is where the valve is open at its highest point...aka the LIFT)

now the degrees of a 360 circle that the beginning of the ramp starts to the end of the ramp ends is its DURATION...... (basically how long the valve stays open (regardless of how far out)

problem with advertised duration (the complete number of degrees that the lobe isnt perfectly circular) doesnt really tell you the story about how "large" the camshaft is..... this is why every engine builder will look at the DURATION @ 0.050 LIFT.... this tells us how aggressive the ramp is and is a more accurate measurement of how large of a cam it is....

that cam seems to have enough lift from what I can see the comparable cams have,....(you dont want too much that will bind your valve springs or hit the top of the piston) but that duration is substantially lower than what I see from cosworth...which means valve isnt open for very long....and both power and RPM will be lower ......

i really would like to find the oem specs on a ms3 cam

Stock MS6 cam:
Ext: .321 lift with 191 degrees @ .050"
Int: .372 lift with 208 degrees @ .050"


Mine:
Ext: .348 lift with 204 degrees @ .050"
Int .398 lift with 216 degrees @ .050"

Lenny the reason our cams are low duration is that overlap isnt DI friendly since you are blowing fuel out of the cyl either through the intake or exhaust. The stock cams, for the most part, do not overlap the injector PW.

Basically we need a high lift, stock like duration cam if we are going to retain the VVT.

When you were tuning it with the aftermarket cams, did they set the cam timing to zero?

this may help

he gave you simulated vtec at 6400 rpms

so what you are telling me is that basically DI is pretty much good for only better fuel mileage wtf!! hahahahahha.... got it... i understand now.

Ya they set the timing to zero and ya all I could think of was I'm pretty sure I dropped off a mazdaspeed not a vtech when we were dyno tuning. Do you guys think that putting in a stock set would fix the problem? And ya I know logs would help as well as a corresponding dyno but I didn't grab them, I'm not pleased with the timeline on this build so I never grabbed any of it.

It might, how much boost were u running?

Only 17 ish lbs. We were just trying to get a good baseline before upping the boost, and that's where the problem of that weird dip came from and couldn't be tuned out. Ummmm ya, all the spark advance and increased timing was set back to 0 by the car when it hit its peak and came down to that 200hp iwas talking about, then all the timing and spark advance would come back, which is why I was thinking cam issue

What?

So the spark advance and cam timing were set to zero? You dynod 200hp, then at 5500rpm it started adding advance and cam timing and you added 60hp?

Sounds like your cam is fine and your tuner is a noob.

he didnt want him having traction problems......

Sorry i just read that and that didnt come out right. id have to show you guys the charts, ill get it for you guys tommorow im hoping...hopefully ill have a over 400whp dyno sheet to.

Bump... I'm very interested in this because I feel a MAJOR limiting factor on our cars are the stock cams...

I'm pretty sure you should take those cams out and give them to me. They are junk. I'll even pay shipping and give you my stock cams.

no, its the turbo

He has passed that limiting factor and is running a gt3076