some questions about speed pro

[fastrucken]

im fairly new to the whole speed pro system ( its actually on my friend's car). He reciently had to replace the cam due to a flattining lobe. now the motor doesnt run right. I started adj the speed pro and started to work out some of the hiccups but we decided to call it a night when we quit. we started to think about it a while and we didnt see a reason that it should run that different. It was running way lean during a cruise around the block and pop thourgh the intake... thats when i fattened it up. what we were wondering that since we were having to add more fuel that would be a good thing ?? any info would be really be a great help to get this 720hp motor running smothly again

 

[64duece]

Couple questions

Same cam? Popping up the intake, yeah if its real lean. If valve(s) are too tight would give same problem and also cause a lean condition. Something to check. If all things are same I'd give it a solid mechanical check. Does it idle @ same kPa? That's a good indication if something is different or if a vacuum leak may exist. Specially since it was just put back together. Good Luck

 

[fastrucken]

Here is the story with the car. I discovered the lifters (hydraulic roller) digging into the side of both the intake and exhaust lobe on cylinder #5 on my supercharged 408 (stroked 351W). So I replaced the cam with one exactly like it since the car ran so well (617rwhp). I also intsalled it exactly in the same position ( 2 degrees retarded). I verified the rockers are not set tight by checking each rocker arm at TDC for each cylinder with the wiggle check. Each rocker moved so they are not set tight.

The car ran great before hand but after swapping the cam out, I am experiencing lean pops in both the inake and exhaust. The car idles fine but once it is reved at idle or a load is placed on it, it stumbles and lacks power. (I haven't stepped on the gas more than 1/4 yet in fear of hurting something.) A data log on the Speed Pro has shown the car running lean at 1100 rpm of steady driving. So we forced the car into closed loop above idle and the car seemed to run a little better.

I guess my question is how could the program I had for essentialy the same setup not work now? I spoke to my engine builder (Keith Kraft Racing) and they don't think the programming is at fault. They are under the impression its an ignition problem. I'm going to try an MSD to see if this helps.

Does anyone have any other suggestions? We have noticed in the Unofficial Speed Pro Manual people have been setting the VE fuel table at 70 to get the idle richer. I have mine set at 40. Could this be a problem with off idle acceleration? (Remeber though, this program did work before the cam swap). We are running out of ideas. Why would it run lean with an ignition problem? Could someone with a bit of experience take a look at my programming and the data logs to see if there is something I'm missing? I would really appreciate any info, I'm at my witts end with this!!!

Paul

 

[64duece]

Same vacuum?

I see you said it idles fine. Does it idle @ the same vacuum/kPa? I'm trying to clarify the if base maniflod vacuum has changed. You mentoned "lean pops", when you added fuel, did they go away? It's popping form both intake and exhaust? Same time? Of course you can understand how tough "over the computer" diagnosis is.

 

[TurboTR]

Paul the speed/density system seems to be very sensitive to changes in engine breathing. One scenario is, you replaced a bad cam, which improved the engine breathing on at least one cyl and now the program that was ok for the bad cam is no longer enough VE for the good cam. Always hard to diagnose over the net, but it seems possible to me

FWIW I advanced my cam ~ 5 deg once, and then the car would no longer start the same as before. It made enough of a difference in breathing down low to have to update the VE table.

HTH. JMO. YMMV.

TurboTR

 

[Craig Smith]

Rather than focus on what the VE numbers are at any particular point, what target air/fuel ratio are you trying to run at? This doesn't sound like a motor that's going to be happy at the usual 14.5 and up a/f ratio. You'll probably need to idle richer than that to keep it happy. As far as the VE numbers are concerned, set them so that the target a/f ratio matches the actual a/f ratio as closely as possible, and then use the target a/f table to fatten or lean the motor out.

I'm not sure why it worked before and now it doesn't, but if you changed the cam and nothing else, it seems to me it must be either the cam or some possibly unknown difference as a result of changing the cam... a vacuum leak before or after the change or something like that. Have you verified that the ignition timing is correct since you bolted everything back together? That would obviously have a huge impact on how it runs.

If you check everything mechanically and it all seems OK, then I would simply continue tuning until it runs well and assume that something besides the cam was wrong beforehand.