Engine is bucking while cruising

[turbo conversion]

Well he is using the stge 3 cams and i have the stage 2 and i dont know the specs of the stage 3s but i heard it depends on the amount of overlaps on the cams. When i get off work today i was going to do some research and compare the cam profiles and see if they are much different

The stage 3 cams will be more radical than the stage 2 so stage 3 cams would be less smooth at low rpm and load.

David

[gruff511]

On the vehicles that have performance cams in them that are running with no bucking, what changes have been made to the vehicle, have the tires and rims been changed to shorter tires, etc. Just because they haven't changed the gearing in the trans, they may have changed gearing using tire height. If your cams are bucking under load and light throttle, another thing to check is mechanical causes of bucking, I have an old 4 speed el camino and when I was idling in gear or doing low speed cruising in high gears, the vehicle used to buck... I found a bad motor mount and a loose pinion. tightened the pinion and replaced the motor mount bucking gone. don't discount possible bad mounts or cv joints etc.

Their setups were pretty much the same as mine. my tires are probably a 0.5"-0.75" shorter then their stock sizes. And all of them had the same stock transmissions as I do. And i know nothing is loose or broken. everything is brand new and it ran great for 8,000miles until i installed these cams.

[turbo conversion]

On the vehicles that have performance cams in them that are running with no bucking, what changes have been made to the vehicle, have the tires and rims been changed to shorter tires, etc. Just because they haven't changed the gearing in the trans, they may have changed gearing using tire height. If your cams are bucking under load and light throttle, another thing to check is mechanical causes of bucking, I have an old 4 speed el camino and when I was idling in gear or doing low speed cruising in high gears, the vehicle used to buck... I found a bad motor mount and a loose pinion. tightened the pinion and replaced the motor mount bucking gone. don't discount possible bad mounts or cv joints etc.

Their setups were pretty much the same as mine. my tires are probably a 0.5"-0.75" shorter then their stock sizes. And all of them had the same stock transmissions as I do. And i know nothing is loose or broken. everything is brand new and it ran great for 8,000miles until i installed these cams.

Actually with the shorter tires the gear ratio will be lower than stock i.e. higher rpm per mph, this would actually help with larger than stock cams.

Have you double checked the cam timing since the engine ran great for 8000 miles before the cam swap?

You can miss the timing by one tooth either way and the engine will still run but not correctly.

David

[DaveEFI]

This sounds like an EFI version of the old Burns and Allen sketch; "Tuner, tuner! My car shakes badly when I drive below 2k and above second gear." "So don't drive like that!"

Downshift! You're not 'carbureting' properly, you're barely charging your battery, and the oil films on your bearing surfaces probably don't appreciate the impact loading ...

Hehe. My BMW cruises at well below 2000 rpm at the legal limit in the UK. But will rev to almost 7000 rpm.

[gruff511]

On the vehicles that have performance cams in them that are running with no bucking, what changes have been made to the vehicle, have the tires and rims been changed to shorter tires, etc. Just because they haven't changed the gearing in the trans, they may have changed gearing using tire height. If your cams are bucking under load and light throttle, another thing to check is mechanical causes of bucking, I have an old 4 speed el camino and when I was idling in gear or doing low speed cruising in high gears, the vehicle used to buck... I found a bad motor mount and a loose pinion. tightened the pinion and replaced the motor mount bucking gone. don't discount possible bad mounts or cv joints etc.

Their setups were pretty much the same as mine. my tires are probably a 0.5"-0.75" shorter then their stock sizes. And all of them had the same stock transmissions as I do. And i know nothing is loose or broken. everything is brand new and it ran great for 8,000miles until i installed these cams.

Actually with the shorter tires the gear ratio will be lower than stock i.e. higher rpm per mph, this would actually help with larger than stock cams.

Have you double checked the cam timing since the engine ran great for 8000 miles before the cam swap?

You can miss the timing by one tooth either way and the engine will still run but not correctly.

David

Yes actual timing is correct.i rechecked all that to be positive. Ive really just come down to i need cam gears and degree the cams.

[turbo conversion]

If the cars you rode in have the same cams as you with stock cam gears running MS run fine,
then I can't see why yours would need to be degreed.

David

[billr]

Actually, the OP has already stated that the "good running" cars have more aggressive cams, and stock cam gears. Yeah, makes no sense to alter cam timing from designed, we must be missing something here.

[turbo conversion]

Are you still using the same spark advance table as in the msq you posted?

If so then I think your timing below 3000 rpm is quite retarded compared to most tables I have seen.

Here is my msq if you would like to take a look for an example.

David

[gruff511]

Actually, the OP has already stated that the "good running" cars have more aggressive cams, and stock cam gears. Yeah, makes no sense to alter cam timing from designed, we must be missing something here.

I talked to someone at crower, they said the amount of overlap on the cams will effect the idle and cruising and the stage 3 and stage cams will drive differently.
so in theory if i could degree the cams it will help adjust the overlap.

[pbreaction]

Are you still using the same spark advance table as in the msq you posted?

If so then I think your timing below 3000 rpm is quite retarded compared to most tables I have seen.

Here is my msq if you would like to take a look for an example.

David

I agree its way too low... How did you decide to run the car at 7 degrees idle its quite a drastic change between 2500 and 3000 rpm

i would try something along these lines

[gruff511]

No im not running the same msq. as i originally posted. Im actually running more timing now in my current msq. And it drives great. Except for the cruising under 2k rpm. I will post my latest msq when i get home today.
the first msq i posted with less timing was what i had to do to get the bucking to go away but the motor didnt like that low of timing. Im running more timing now but the bucking is still there.