Internal balance cranks

[MikeP]

We are looking at building up an internally balanced 347 which will rev well. Does anyone know which steel stroker cranks would be most suitable for this purpose. A price and supplier would also be very helpful. What would the rev limit be for a well set up internal balance bottom end with a mains girdle, forged pistons,H-beam rods etc.? Also any suggestions for a streetable cam to match a zippy 347.
Thanks
MikeP

[Paul Thompson 'Hooligan']

Nice plan Mike - but any particular reason you really desire the internal balance? Other than possible reduced stress on the crank.

A well built motor, even externally balanced will rev well providing it is correctly balanced. Roy's A4 302 would regularly rev to 8K without too many issues... Valvetrain was generally the weakest link we encountered.

Please keep us posted on how you go...

[Bill Musarra]

Mike,
Paul is right. Unless you plan to build a screamer, the internal balance is over the top. Not to mention the added cost. The lead alone is as expensive as a rebuild itself. To bore, stroke, and internally balance will run just the short block cost to around $6K or more(working from old numbers of about 3-4 years ago. For that you can just about purchase a complete crate engine of considerable size.

Bill

[Chas]

Mike,
We meet again in another thread! I promise I'm not trying to market you to death but I do have a possible suggestion to your question.
If you have a block and some components already, disregard my message.
If not, our short block assemblies may be advantageous for you to consider.

First, as stated in the 460 thread, all our stuff is internally balanced. Makes it easier to buy flywheels and dampers which are neutrally balanced.

Next is displacement. We offer 8.2 decks as 302's, (4.00x3.00) 349's (4.00x 3.47) and 371's. (4.125x3.47). Yes our 8.2 accepts a 4.125 bore and max bore is 4.155. All contain Eagle 4340 cranks, Eagle 5.300 H-beams and Mahle pistons. Now we run these assemblies in our Drag versions to 73-7500 RPM during dyno testing to no ill effect. I don't know why they won't go to 8000 if that's your intention. They can handle power in the 900 range if you can make it. The assembly is $5000 US and all the work is done for you unless, again, you are building your own project. Of course, the 108 Lb aluminum block is available as a short but either comes with nodular or billet splayed 4-bolt mains on all positions. (fronts and rears are upright, not splayed) No girdles needed. We have 9.5 deck versions in use in 6 second, 1700HP applications.

A word about compression. On the site they're listed as LC (low) or HC (high) compression. What that really means is approximately 10:1 or 13:1 with a 64cc chamber. If you need I can supply the dish/dome sizes when I get to the shop tomorrow. If memory serves the LC uses a 20cc dish.

Paul makes a good point about valvetrain and be sure to source a 16 or 18 pound flywheel and an SFI approved damper. (We use ATI)
See the Short Assembly product page on BILL MITCHELL HARDCORE RACING PRODUCTS HOME

Best luck and cheers.

[Rick]

My son is in the final stages of building an extremely nice 91 Mustang GT Drag/Show/Street car with an internally balanced 347. He is using a Dart 4 bolt Iron block with Steel crank, Eagle Rods, Diamond pistons, AFR heads, Jessel Valve Train topped with a Pro charger belt driven super charger. He is expecting over 600 HP and shouldn't have to RPM the engine too hard. It should have quite a bit of torque.

[MikeP]

Thanks for your input guys. Plenty more to think about there then! The motor is for Martin Gough's new Southern GT. He has a seventies seasoned block which is being line honed, decked etc. This will help in the dreaded SVA test as it will only need to not produce visible smoke to pass. He has an Eagle stroker kit for this block. The idea behind going for the internal balance is that we were told that the external balance over 6,500 rpm causes crank flex which will knock out the centre main and taper the end mains. The internal balance is "sweeter" running and much more reliable at high rpm and we all love motors which rev. The info came from two reputable race engine builders of long experience who say that all their vrace motors are internal balance. The cost of the internal balance could be about £600 plus depending on the number of heavy metal slugs (tungsten or Mallory metal?) which would be needed. The info we were given is that certain aftermarket steel cranks are more suitable for internal balancing as they have more material in the counterbalance weights and therefore need less slugs put in and that the crank we have may not be suitable.
Thanks for your info Chas as I am interested in exactly the kind of motor you describe for my car. Please continue to market away as much as you like - your ali motors look spot on.
I am uncertain about the mains girdle as the advice seems to be conflicting about the value. I do know however that a similar device on a racing Imp one litre engine raised the rev limit from 8,500rpm to 10,000rpm on a tuftrided standard crank with 125 bhp per litre. So I guess the jury is still out on that one. I take note of Chas's point that swapping dampers and flywheels is easier on a neutral balance set up.
Keep the input coming as my brain is now only doing 6,000rpm!
Thanks again
Mike

[Colin Artus]

Unless Eagle do a specific internal balance crank for your stroker combination I think you may have to settle for external balance. I made the mistake of balancing an Eagle crank internally and there simply wasn't enough counterweight material to do it economically ( ended up using a huge amount of heavy metal and costing £1500!). The stroker spec makes this more demanding. If it is a two bolt block then a mains girdle will help if you want to see 7k rpm. Or you could get billet caps for nos 2, 3 and 4 and line bore the block ( in some ways a better idea than honing).

[Big-Foot]

Eagle does make an internally balanced crank for SBF applications.
There's one going into my 331. No Mallory metal required - just clean-up balancing for the Bob-Weights that should be in the +/- 5 gram area..

Yes the internally balanced engines do seem to run out better and as most know the Small Block Ford (302 in particular) has had a checkered history with block/main failures. Obviously there are some good alternative aftermarket blocks that will help in this regard.

The only caveat I would have is that there are fewer flywheel / balancer combinations available for the Internally Balanced configurations. Virtually NO balancer available for the short serpentine balancer made for the later Ford Explorer and Mustangs..

[MikeP]

Thanks for the input once again. That cost figure for heavy metal does indeed seem to be a bit much. The idea of better mains caps might be a very good one for bottom end strength and long life.
The info from Big Foot about the correct crank for internal balance sounds like just the thing we need especially as it doesn't need a fortune in heavy metal. Do you have any info about maker/supplier and part numbers etc.? This info will be very useful for anyone wanting a more revvy type of SBF. We can't let these Ferrari guys get away with 8,000rpm on the road while we plod along at 6,500rpm!
Keep the info coming - it is very much appreciated.
Cheers
Mike

PS Job Vacancy -- Telepath wanted - you know where to apply.

[Russ Noble]

Mike,

Brian from AD Performance Cylinder Heads : ADPerformance, Your Source for Longblock Performance Parts has both Eagle and Scat cranks and some others. also pistons, rods, heads etc. Very helpful and pleasant to deal with. No problems and was happy to ship my stuff to NZ. Full details of options and prices on his website. May be cheaper and better than buying in the UK. Tell him what you want to do and your budget and he will advise your best options.

Don't forget the advertisers on this site. I have dealt with Keith Craft also and he is very good.

If you want to rev it, it is my understanding that you need a non-crossdrillled crank i.e. straight shot oiling, but I'll leave the technical stuff the engine gurus to comment on. I would definitely go internal balance. External may work OK but it's an abomination of an idea having out of balance forces flying around on the outside of a motor. IMHO

Cheers

[MikeP]

Thanks Russ. I'll check that out. Like you I don't like the idea of out of balance lumps of metal flailing around - particularly the later 50 ounce ones!