Lightening a crank

[The S is Silent]

Does anybody have measurements on wrist pin to piston top for both CB 2.2 and 2.5 pistons?

I am also considering milling the head, and using new cam keys to fix the timing.

Anybody know what the limit is for compression on a n/a motor running 93 octane pump gas?

[Putter]

I always figure the rule of thumb for premium fuel is about 12:1....at least thats what my effection compression ratio figures try to shoot for.....although with the t1 i ran up to 13.5:1 effective, and suffered from detonation....

12:1 is pushing it though for a motor with a good VE......
Nascar guys on restrictor plate races run higher C/R's because they intake less air.....so there is a balance.

sqrt(PR) * C/R = E C/R These numbers are rough and should be used for comparasion to what you have already tried, if you know that 12psi works at 9.5:1, then in theory 23psi should work at 7.9:1 all else equal......in theory

You should probably get a better opinion for max c/r for n/a motors from someone who's tried it. i.e. Not me...

[The S is Silent]

ha ha...maybe I'll just build it to a nice round 10:1 and see what that gets me.

[89acclaim]

Heck Una ran 10: 1 Megasquirted Shelby Charger
About throes pin to piston top measurements I did a little math with the deck height, stroke, and the rod length and came up with. That the from the pin to the deck the 2.2 pistons are 40.8 mm down and the 2.5 are 34.8 mm down. If you use the block from the HO 2.2 you have the deck clearance will be +.018". If you are dealing with a normal block the deck clearance is -.003 for the 83-85 flat top pistons. For the 2.5 common block -.008" deck clearance. I would double check with actual parts though. Hope this helps.

Daniel

[Putter]

10:1 n/a isn't out of ordinary, many factory cars today are 9.8

I ran 9.5:1 with no intercooler and 13psi. 10-11psi Was the SAFE limit at 9.5:1 for no intercooler.

[Shelby VNT]

Quote:

Originally Posted by Ron Here is a picture (not great one) of my crank after I got it back from South Florida Crank. It is forged crank out of my TIII. After knife-edging it weighs 36 pounds...equal to a cast crank and 8lbs lighter than what I started with. Works great!

Wow, now that's a cool looking crankshaft!

[fishbatman]

hey, how did the crank work out when you put it in?

[DirectConnection]

Quote:

Originally Posted by The S is Silent Drill out material from the rod jounals, and take the same amount of material off the counter weights.

It doesn't work that way. Being an inline 4 you are kinda thinking correctly, but it won't work without acces to a balancer. Your best bet is to remove material in the proper places and then have the crank re-balanced. Material removal from a crack is usually not at the very end of the counterweight, it's more towards the center of the crankshaft. Drilling out the rod journals...be careful not to go into the angled rod/main oil holes.

I balance cranks at work(along with other engine related stuff) but I don't do any lightening, but have seen lightened cranks.

[DirectConnection]

Quote:

Originally Posted by igotaneed4speed knife edging a crank on one of our motors is good for at least 20-15 h.p if used with a good pan and screen. Throw a dry sump and ull pick up 40 or more with the combo... no windage is more power

Those #s are extremelly exaggerated. Not say it's you...but whomever told you that. I discussed this at work about race SBC engines and the improvements found were not even noticed.

I wouldn't say it's a waste of time and $, but 20hp? More like only a couple hp on these motors.

Remember the ed peters claim of the HP loss with the stock oil port mis-match in the block? What was that...5 hp loss? If that was 5hp, then the pump must be using 20hp. Today at work, my boss had some new Moroso oil pump that only like 3 have been made so far. They ran some tests on it and we hooked it up to the brigdeport to turn the pump. The spring was waaay too much, but at 500rpms, we had 60psi oil pressre which would be 60psi at 1,000rpm engine idle minus about 10psi from oil pressure losses via the engine clearances. Pegged the gauge at 110 at 1,600 (3,200engine rpms). The motor on the milling machine that drove the pump is only a 2 or 3hp unit.

[DirectConnection]

Quote:

Originally Posted by mr_v8horsepower Good side of it was the weight was added closer to the centerline of the crank which keeps the flywheel effect down and the crank spins quicker, just like an ice skater when they pull their arms in while spinning.

The closer to the centerline of the crank, then the less of an effect the weight has, which means they need to install more mallory than say at the outer radius of the counterweight. The effect ends up being the same except for a heavier overall weight