Thread: c.h.i.e.f 's 110 Isuzu county

Originally Posted by c.h.i.e.f

I agree with these statements...we are not really stopping the vibration more along the lines of moving it in the rev range...from what I can gather the easiest way is as you mentioned dougal (weight for extra inertia) I do have concerns with what Rick said though (throttle response will not be as quick) but whilst under full load I can imagine it will be much smoother...

A heavier flywheel will *reduce* the vibration (you can never actually stop it, just make it really small). It won't shift the problem up or down the rev-range.

The throttle response Rick mentions will be most noticable on how long the engine takes to spin down between gear changes. I don't expect it to be a problem at all, but if you want to count the half seconds, you might be able to spot it.
Take a look at the size of the flywheel on the industrial 4BG1T for the extreme example. For an engine that just runs at one rpm, bigger is better. Drawing here, look at the section view: http://www.isuzu.co.jp/world/product...f/b_draw02.pdf

Originally Posted by rick130

Yep, the only downside (and it may not be, depends on the driver) is less throttle response with more flywheel inertia.

The reason the 4cyl engine hammers the gearbox, etc. is that the peak/instantaneous torque delivery of an engine is a greater % above the mean torque output the less cylinders you have, as well as the fact that there are less firing pulses/degree of crank rotation too.

Explanation here Torsional Characteristics of Piston Engine Output, by EPI Inc.

Indeed - when I was looking at buying an engine dyno for work a while back, the suppiers told me if I wanted to run 4cyl engines I would need a higher spec dyno than if I wanted to run 6 or 8 cyl engines ony.

Originally Posted by Dougal

A heavier flywheel will *reduce* the vibration (you can never actually stop it, just make it really small). It won't shift the problem up or down the rev-range.

The throttle response Rick mentions will be most noticable on how long the engine takes to spin down between gear changes. I don't expect it to be a problem at all, but if you want to count the half seconds, you might be able to spot it.
Take a look at the size of the flywheel on the industrial 4BG1T for the extreme example. For an engine that just runs at one rpm, bigger is better. Drawing here, look at the section view: http://www.isuzu.co.jp/world/product...f/b_draw02.pdf

Yeah when you explain it like that it does make sense...the only problem I can see with say Justin's situation is if the vibration is happening at his crusing rpm which is partly governed by gear ratios there will always be a vibration but can be lessened by increasing the inertia....the Isuzu being so robust internally is probably a part of our vibration issues...the inertia ring is about our only chance of helping our problem in my opinion...interesting to see what randy has done!

Originally Posted by c.h.i.e.f

...the inertia ring is about our only chance of helping our problem in my opinion..

You forgot a 6BD1...

Originally Posted by Dougal

A heavier flywheel will *reduce* the vibration (you can never actually stop it, just make it really small). It won't shift the problem up or down the rev-range.

The throttle response Rick mentions will be most noticable on how long the engine takes to spin down between gear changes. I don't expect it to be a problem at all, but if you want to count the half seconds, you might be able to spot it.
Take a look at the size of the flywheel on the industrial 4BG1T for the extreme example. For an engine that just runs at one rpm, bigger is better. Drawing here, look at the section view: http://www.isuzu.co.jp/world/product...f/b_draw02.pdf

You'll notice it on acceleration too, particularly if you blip the throttle on a downchange, it'll just take longer to spin up.

Originally Posted by c.h.i.e.f

Yeah when you explain it like that it does make sense...the only problem I can see with say Justin's situation is if the vibration is happening at his crusing rpm which is partly governed by gear ratios there will always be a vibration but can be lessened by increasing the inertia....the Isuzu being so robust internally is probably a part of our vibration issues...the inertia ring is about our only chance of helping our problem in my opinion...interesting to see what randy has done!

I'm good at 2000rpm cruise, but 1600rpm is pretty rough in 5th. I'm hoping doubling the inertia will drop that roughness to about 1200rpm and give me smooth pull from about 1500rpm up in every gear.
Pretty much all modern diesels (and some turbo petrols) have a dual-mass flywheel to get around this problem. If there is no dual-mass option then more mass is the next best thing.

Mine is a lot better now with my homebuilt T2560 turbo. The smaller T25 was encouraging me to run even lower rpm which meant I was driving in rougher spots more often.

Randy was running auto gearboxes. There is a lot of weight and damping in the torque converters. He's back on 4BTswaps.

A 6BD1T will always be a lot smoother.

Originally Posted by isuzurover

You forgot a 6BD1...

Haha yeah

Originally Posted by Dougal

I'm good at 2000rpm cruise, but 1600rpm is pretty rough in 5th. I'm hoping doubling the inertia will drop that roughness to about 1200rpm and give me smooth pull from about 1500rpm up in every gear.
Pretty much all modern diesels (and some turbo petrols) have a dual-mass flywheel to get around this problem. If there is no dual-mass option then more mass is the next best thing.

Mine is a lot better now with my homebuilt T2560 turbo. The smaller T25 was encouraging me to run even lower rpm which meant I was driving in rougher spots more often.

Randy was running auto gearboxes. There is a lot of weight and damping in the torque converters. He's back on 4BTswaps.

A 6BD1T will always be a lot smoother.

Mmmm interesting..... I had symptoms but unfortunately I cannot compare rpm's with yours as I do not have a tacho however the "terrible" way I drive the car it was rarely a concern for myself...I personally have not had good experiences with dual mass flywheels...I replaced a dual mass flywheel on a new bt50 with a solid mass flywheel and it now has vibrations if you load the motor up say in 3rd going around a corner until it pics up the revs and everything is fine... I have considered a 6bd1t but there is 2 things stoping me 1:the 4bd has nothing wrong with it and 2:I would probably prefer a 6bg1t however they seem rare...