Stage 2 engine balancing

[oldtimer]

What's the ideal bob weight per-centages for a stage 2 used for drag racing 95% of the time ?

Is 50% reciprocating the norm for Poly mounts and spinning 7500 RPM

Anyone try overbalancing ? Is it necessary ?

What about internal VS external balancing ?

Thanks for your help.

George

[DonWG]

Internal balancing makes for easier external component replacement. Flywheel, damper. For high performance, 50 percent is the recommended factor. It will require the installation of heavy metal to the crank. I'm using poly mounts with a stock style rubber trans mount and the vibration is very manageable. Hardly noticeable unless you really concentrate on picking it up.

[oldtimer]

Thanks Donnie,

much appreciated ! What piston to cylinder wall clearance would you recommend .... 4.005" bore

George

[DonWG]

I can only relay what I've used. With JE pistons (relatively high growth) I've used .0065" with no piston noise (Alky ver.2.0). I've used .0072" with a previous engine (Alky ver.1.0), again JE, and could hear slight piston slap until after the first run (heated up). Both cases were with alcohol fuel which runs a bit cooler than gasoline. HP levels around 1,000. Ring seal (gapless top Total Seals) stayed good throughout the life of the engine (2% leakdown and less).

[oldtimer]

Thanks Donnie

I should have mentioned that I'm going with JE's

George

[V6gofast]

Originally Posted by oldtimer

Thanks Donnie

I should have mentioned that I'm going with JE's

George

George,
The pistons you received has a spec sheet with a suggested clearance, I
have always used their recommended clearances without an problems. As we
talked earlier balancing the crank would depend on how it was originally done.

[oldtimer]

Originally Posted by V6gofast

George,
The pistons you received has a spec sheet with a suggested clearance, I
have always used their recommended clearances without an problems. As we
talked earlier balancing the crank would depend on how it was originally done.

Thanks Dan,

The sheet says for bores from 4.000 up to 4.200 the minimum clearance is
.0035 to .0045 (Quote ... Some applications such as supercharged, turbo, nitrous and endurance applications may require .001 to .003 to be added to the minimum clearances, unquote) so I was just wondering what the extra clearance might be for our stage 2 applications, if any.

Comments ...

George

[DonWG]

The suggested clearance that comes with the pistons is very general and usually does not take into account the exact anticipated application.
The more HP you're planning on, the more clearance you will need. More HP means more heat that will be transferred to the piston, which means more growth. This is a decision where experience comes in handy. If it is a street application keep it on the tight side. If it is a track only engine, go for the loose side. A little bit of piston slap noise when cold does not hurt a thing. It does give you some insurance in case an overheat condition comes up.

Just what HP level are you shooting for?

Dan's right on the balancing. Some setups might make it undesireable to try and change the balance configuration.