Timing chain or belt for 9500rpm?

[Cubic_Cleveland]

Cambelts have tensioners because otherwise they would get too tight as the engine warms up. The engine gets bigger.

Huh?
Cam belts use tensioners to hold TENSION on the belt so it doesn't slip! Not to stop them getting too tight as the engine warms up.

Also, not all cam belt systems use tensioners...

[vwchuck]

Belts most certainly expand and contract. Run an instrumented engine reading torsional vibrations on the crank and also the camshaft. If the cam is geared you will see the torsional transmitted to the cam with a belt you will see the torsional shrink significantly. The only way for this to happen is for the belt to stretch a little and absorb the torsional. Then is retracts back to its original length. We are talking thousandths of an inch but that is all that is needed.

[statsystems]

Belts most certainly expand and contract. Run an instrumented engine reading torsional vibrations on the crank and also the camshaft. If the cam is geared you will see the torsional transmitted to the cam with a belt you will see the torsional shrink significantly. The only way for this to happen is for the belt to stretch a little and absorb the torsional. Then is retracts back to its original length. We are talking thousandths of an inch but that is all that is needed.

I've been asking for this info for decades. If you have some info on vibration transfer I'd love to see it.

[statsystems]

Less mass in a belt.

You can run the belt dry.

Easier to change a belt.

True, but not by much.



So what?


Again, so what? If the gear drive is a quality, fixed idler gear drive you don't have to change anything. Unless you run it dry and kill a bearing. My GD has been going since 1984. I lost count of miles and passes on it.


Also, a quality fixed idler gear drive will not make noise. No one knows I run a gear drive.

[statsystems]

Easier to optimize the cam index.

This is true MB, but how many guys actually do anything but stick the cam in where the cam card says and let it go. I had a hard time getting guys to run a lash loop, let alone change cam timing on the dyno. In fact, I was doing an engine for a guy and he picked the dyno he wanted to run his stuff on. During assembly, I mocked P/V in every position from 6* advanced to 4 * retarded. It looked to me like the cam wanted to be retarded. I suggested doing it. The dyno operator piped in that you have no idea how much P/V you have after the change. I pulled the file out and showed him. My customer was happy where it was so we never changed it.


BTW, when we were load up the engine, the dyno guy asked if I checked P/V like that on every build. I said I check it on every build, and when going on a pump I check it like I did this one. He laughed and said I was a time burglar. He said he never did shit like that. Waste of time.

[SupStk]

Belt drive all the way! Take a look what is being used in any pro stock engine. Where HP is king you'll find belts.

[statsystems]

Belt drive all the way! Take a look what is being used in any pro class pushrod engine. Where HP is king you'll find belts.

Yes, those would be the people who actually test shit. The rest of us don't usually do it.

It's also makes see, monkey do stuff as well. I can't say I've ever seen a fuel engine with a belt drive. Can't think of a blown ally deal with a belt either. There may be some, but most run gear drives.

[SupStk]

Easier to optimize the cam index.

This is true MB, but how many guys actually do anything but stick the cam in where the cam card says and let it go. I had a hard time getting guys to run a lash loop, let alone change cam timing on the dyno.

I do it all the time. Not so much if the engine has to come apart to change cam timing. Belts make it a breeze.

[statsystems]

Easier to optimize the cam index.

This is true MB, but how many guys actually do anything but stick the cam in where the cam card says and let it go. I had a hard time getting guys to run a lash loop, let alone change cam timing on the dyno.

I do it all the time. Not so much if the engine has to come apart to change cam timing. Belts make it a breeze.

I'm agreeing with you.

I always test cam timing, lash loops etc. it's sometimes hard to get the customer to do it. And, you and I both know, if we are completely honest, there are builders out there who just line up the dots and say [DELETE THIS POST] it. I know a guy who refused to use a GD because he had no idea how to degree the cam!!!!!!! He had no starting point to line up to get him going. This guy has 2 dynos, a CNC machine and has been doing this for way longer than I have. I was stunned when he admitted it. In fact, I had my engine on his dyno and I pulled the front off to change the cam timing. With a GD. Took about 38 minutes to do it.


Like I said, it isn't that hard with a GD, burn my experience, not many guys actually test anything. Other than timing and jetting.

[SupStk]

Belt drive all the way! Take a look what is being used in any pro class pushrod engine. Where HP is king you'll find belts.

Yes, those would be the people who actually test shit. The rest of us don't usually do it.

It's also makes see, monkey do stuff as well. I can't say I've ever seen a fuel engine with a belt drive. Can't think of a blown ally deal with a belt either. There may be some, but most run gear drives.

You are right on the blown stuff. They aren't looking for the last 5 HP. Their concern is in the bellhousing. It's what gets those cars down the track.

[roc]

Cambelts have tensioners because otherwise they would get too tight as the engine warms up. The engine gets bigger.

I'll reboot my computer and read this once again. In the meantime, I might take a leak and sip a cup of coffee...

WTF... get real Joe!

[MadBill]

I'm with joe 90 on this. As it heats up a block expands in all directions, relevant to this discussion: between crank and cam. For an iron block, it's at about the same rate as a steel chain; if aluminum at about twice the rate, amounting to ~ 0.005" more on a typical V-8. However Kevlar® and likely other belt materials has a negative coefficient of thermal expansion and thus a timing belt will get shorter c-to-c while the block is growing.

[Donnie]

This is not complicated
Gear Drives have Harmonics
Harmonics...BAD
Belt Drives have shhh
shhh ...GOOD

[wyrmrider]

Gear drives from back before belt drives were available
Gear drives work better in some applications than chains IDK if belts available) like Chevy 4 and 6 and Iron Duke using the straight cut gears not the fiber crap

[statsystems]

This is not complicated
Gear Drives have Harmonics
Harmonics...BAD
Belt Drives have shhh
shhh ...GOOD

Still waiting for this to be proven.