100 grams per bore = 30 hp

[drag-n-cuda]

Has anyone heard this statement before and can confirm it is true? I've been thinking about getting rid of my trw forged "heavy" slugs and replacing with ones that are 100+ grams lighter and then having the whole assembly rebalanced. I know this will help the rods out, but will it make more power? Inquiring minds want to know.

Thanks,
drag-n

[345Dart]

I second your enquiring mind. I used the Speed Pro slugs in mine 4 years ago. Hopefully we get some good feedback from these more experienced Engine builders

[dwc43]

From what I've always read,been told and otherwise lighter weight pices for the rotating assembly will not increase hp. But it will allow the engine to accelerate faster to a given rpm over a heavier mass rotating part. This will not shop up on a dyno either, but it can be seen in lap times or e.t.'s and mph at the strip.

I try to use light weight everything. Even the steel wheels we have to run are from Basset. They weigh only 18lbs. each. Gun drilled axles, aluminum drive shafts and gun drilled shafts in the trannies. It all adds up to quicker accerleration.

A good person to ask is Sanborn over in the circle track forum. He writes much better and detailed stories than I do. Hope that helps out some.

[gsmopar]

Total amateur here so take it for what it's worth:

I took 100 grams out of my wrist pins (had them machined)... don't know if it made much of a difference. at least I can't feel it.

I've herd both sides of this argument from many people. One friend swears that lightening the reciprocating assembly is only to reduce stress on the moving parts. He ran heavier rods and pistons in his 351 C because he says that it's better for drag racing (same theory as using a heavy fly wheel). BTW, the car ran 12.2 in Albuquerque NM (5500ft elevation) with full interior in a 71 Mach I with NO power adders!!!

If you have the money, buy the light parts. If you're a shade tree mechanic like me.... bottle the crap out of it!

[panic]

Heavier rods and pistons for stored inertia?
I don't think your friend has a clear concept of how a motor works.
There is no stored inertia in reciprocating parts - they come to a complete stop TWICE every revolution. The power used to accelerate these parts is completely wasted as heat every single time the piston changes direction.

[b-1ken]

The lightest piston is better always. It, of course, decreases the tensile load on the connecting rods, but it also makes for a better crankshaft balance. When the piston is at TDC, the counterweight would have to be much heavier than what it should be at say 90 degrees below TDC to be correctly balanced. That's why engines are usually balanced at 50% of the reciprocating mass (piston & upper end of rod) and 100% of the rotating mass (lower end of the rod). This is a compromise which will only approximate a perfectly balanced engine and changes with rpm. A perfectly balanced engine could be achieved only if the reciprocating weight were zero. This means the the lighter the better with regards to piston weight. For drag racing, light counterweights also means less mass to accelerate up through the rpm range. I know of one very bright & famous engine builder who uses 42% for his balance jobs. I'm told that the engine shakes a bit at idle but runs much smoother at high rpm.

[panic]

An internal combustion engine can only be perfectly balanced only if it is a display, and does not actually run.
Read my article:
http://victorylibrary.com/mopar/crank-bal.htm

[dkn1997]

I have srp's (made by JE) in my 440. Revs real fast, relly gets up there quick. plus might last longer because of less weight. If your motor is in the car running already, probably not worth it...

[gsmopar]

Originally posted by panic
Heavier rods and pistons for stored inertia?
I don't think your friend has a clear concept of how a motor works.
There is no stored inertia in reciprocating parts - they come to a complete stop TWICE every revolution. The power used to accelerate these parts is completely wasted as heat every single time the piston changes direction.

Totally agree with you! However, the 12.2 was quite impressive from a 4-speed full bodied street car at that altitude. Probably would have gone 11's with a set of nice rods and Probe pistons???

[drag-n-cuda]

gsmopar,
When I say 100 grams, I mean per piston or 800 + grams per engine. I've got poor throttle response, I'm thinking partly to do with heavy pistons and a large plenum single plane intake. My mph says I should be going quicker than I am. Does anyone have a mph vs. et chart (ex. 108 = 12.4)

drag-n

[b-1ken]

For cars down to about 10 sec. the product of the 1/4 speed and the E.T. should be about equal to 1320 (is that a coincidence or what!?). Therefore the E.T. for a 108 run should be:
ET = 1320 / MPH = 1320 / 108 = 12.22. Since you only went 12.4, it means you could go a bit quicker with the HP you have. The factor gets higher for faster cars. For instance, Greg Anderson (hmm .. am I allowed to print his name on this kneejerk website?) went 6.67 @ 207. That equals 1380. A 9.0 car typically goes 149. That equals 1341. Clutch type cars generally run better mph because there is no converter loss.
Ken B.

[gsmopar]

Originally posted by b-1ken
For cars down to about 10 sec. the product of the 1/4 speed and the E.T. should be about equal to 1320 (is that a coincidence or what!?). Therefore the E.T. for a 108 run should be:
ET = 1320 / MPH = 1320 / 108 = 12.22. Since you only went 12.4, it means you could go a bit quicker with the HP you have. The factor gets higher for faster cars. For instance, Greg Anderson (hmm .. am I allowed to print his name on this kneejerk website?) went 6.67 @ 207. That equals 1380. A 9.0 car typically goes 149. That equals 1341. Clutch type cars generally run better mph because there is no converter loss.
Ken B.

You guys never cease to amaze me! That is the coolest rule since don posted the 5250 rule.

Oh, and yes it was 100 grams per wrist pin or 800 total for the engine. I'm running Speed Pro/TRW pistons, and have run them with a Wiend Hi Ram and M1 Single plane.

Later,

Greg