Thanks

Mine is for lighter parts, guess it won't work. It is 100 g with a .005 g accuracy.

 

..... I used the LS7 rods because they were available , affordable , and made of titanium ... about as close to unobtainium as I will ever get ! ... the original build used off the shelf Mahle pistons #SBC000155D08 that I bought for about $550 (currently near $800) ... I need custom pistons now because I melted one of the Mahles ... the block cleaned up at 4.157" and no one has that bore size available as a normal stocking item ... the new slugs are JE's and will cost me about $1400 for TEN pistons and rings ... The heads have SS valves and Isky Tool Room springs with titanium retainers and a T&D shaft rocker system to fluctuate them ... these rods have been north of 8000 rpm on more than a couple of occasions but that wasn't my goal ... the solid roller cam is mild by some standards and only makes power to 7400 rpm ... no flywheel , instead I have a flexplate and 9.5" torque converter ... You seem to know your way around the guts of a performance engine ... tell us about your mill ? .....

 

This has already addressed twice by me, and maybe also by others. So for at least the third time, crankshaft and flywheel masses have zero impact on reciprocating mass! They don't reciprocate - they only rotate. I don't know how to state that any more simply. Reducing connecting rod mass is mostly important because it saves on reciprocating mass. It does very little to reduce total rotating mass, and nobody would spend big money for exotic rods just to reduce rotating mass. Stop equating reciprocating mass with rotating mass. You're trying to solve an apple shortage by planting orange tress.

 

Don't know where you get your .16/.28 numbers but the atomic weight of Ti = 48 and Fe = 56 while Al = 27.. Of course alloys change those weights but that's all I have to work with and those are the major constituents.

 

Well a large advantage of the lighter rods and pistons is the it greatly reduces the tesile stress on the rod as it changes directions. I'm not going to do the math here but tensile stress increases exponentially with piston/engine speed. Lighter rods and pistons significantly increase a racing engines life.

As far as flywheel and crankshaft weight the lighter parts do help the motor accelerate/rev faster. That's important to some but others prefer a smother feel from a heavier flywheel on a daily driver/cruiser. Trade offs are made for performance.

 

Exactly.

Definitely, and rod mass would be the least effective way to change rotating mass that I can think of. And that is definitely not the reason the OP is using his Ti rods.

I forgot to address this earlier. I haven't researched the rules for NASCAR engines in a very long time. But my bet is that the rules require them to only use steel. They also had to use flat-tappet cams (no roller lifters) last I checked. No race engine builder in his right mind would use steel rods and flat tappets in an all-out build if the rules didn't require it. NASCAR engines are incredibly bizarre engines because the rules mandate them to be and their running environment is so specialized - they have little to no applicability to any other engine build.

Almost any top-level racing category is like this. F1 had some teams using beryllium/aluminum alloys for pistons and brake parts (maybe other parts?) for a few years before it was banned due to weight and the health hazards of machining it. If cost and rules were no object, steel wouldn't be used in very many automotive parts at all.

 

I just spent about an hour typing in a nice long reply - and something happened as I hit submit - and I had to log in to CF again - post was lost....


Bottom line - I get that reciprocating mass is different than rotating mass. Weight of recip assembly causes loads that increase with the square of engine RPM - so light weight rods lower those loads. I get it. The point I was trying to go to - was that typically the increased loads impact crank journals - piston pins, pistons and most importantly connecting rod bolts. I tend to think GM went to the Ti rods on their LS7 not because they were worried about rod bolt failures - but because the were worried about oil film strength with the 5W-30 oil they like to specify for fuel savings. 4340 steel rods have been proven to work in many pro racing applications where very high sustained RPM is the norm.

So - lighter weight cranks and flywheels will take less energy to spin up - so more energy will be available to accelerate the vehicle, and the results of losing 20 Lb of recip mass will be measurable. No way that results of lighter weight rods / pistons will ever be measurable on vehicle acceleration.....

 

LS rods are .945 wide and Gen 1 rods are .940 and length is 6.064 plus LS rods have no offset like a Gen 1 rod

 

I hate when stuff like that happens!


I can't disagree with any of that. We're on the same page now. Thanks for clarifying.

I know it's an absent-minded mistake, and I know you know the difference (I do this kind of thing all the time), but I want to point out an edit that needs to be made so that nobody else gets confused: see bolded word in quote above.

 

Yes, it's almost as if its sabotage sometimes. So I began to type in word, or word pad or note pad then cut and paste into the post box but most of my reply's are to short to bother. Problem is many times a short reply turns into a long one and its overlooked when its to late to save it. My tablet is worst culprit at killing my reply's.

 

I wonder how many of those^ engines have a 4" stroke?

 

Mass per cubic inch of material (or density). That is where the numbers came from.

The mass of an object does not increase linear with its increase in atomic number, as shown below, it depends on the material.

 

 

I'm just glad to hear it happens to other people as well !!! (And YES !!!!!!!! I get how an expected reply suddenly gets a lot longer than originally intended - happens to me regularly !)

I was wondering if I went too long typing, and the server didn't see "activity" per se and just logged me off...

 

OKAY ... When you say you are using a shaft rocker system - you just told me a LOT about your engine. I'm running a Jessel shaft rocker system in one motor that is used for 99.9% track stuff. I had tried to use some Comp Cams SS rocker arms - and they just didn't like sustained use in the upper half of the tach range... And Yes - having bought one - I know what one of those shaft rocker set-ups costs - so normally they are only used by people who have had experience with the limitations of individual rocker arms - or by people who pay engine builders to avoid having to learn the hard way... I have also had some experience with the Isky Tool Room springs - and again - they are not cheap - YES - they're VERY VERY GOOD springs - but they aren't going to be used by too many people who are worrying about keeping build costs down...

I have a couple of street legal Vettes and all but one has a stock engine. I also have a couple of dedicated track cars - one is a 1992 C4 with a LT1 based motor. It's a 383 with a forged 4340 crank and rods, and I believe Mahle pistons that run around 11.0:1. The motor was built by Golen Engine Service. The heads are heavily ported sock LT1 heads (done by Lloyd Eliott) and I have his middle of the road cam in that motor. The motor is PCM limited to 6250 RPM, and was dynoed right at 500 HP.

The other track vehicle started as a pile of steel tubing. It has a 415 SBC Chevy (3.875 stroke crank). World Block, forged 4340 crank, rods and I believe Wiesco pistons - it's running 10.5:1 compression. I am running Brodix Track 1 heads on that one, and it's fed by a good old fashioned Holley 750 DP (that was tweaked a good bit on the dyno). It makes 510 flywheel HP and the chip in the MSD Box is set to 6,100 RPM (so it starts pulling spark at 5,950). This is the motor with the Jessel shaft rocker system, and it's running a mellow solid roller cam. (I tend to think that even though the cam is one of the most mellow roller lifter cams available - it's acceleration rates were what killed the individual rocker arms I tried to use initially). But in a 3,000 Lb vehicle (wet - with driver) - it does a pretty good job - and it makes torque from about 3,500 RPM - and when you're playing on a road course - torque is a truly WONDERFUL thing !!! I've managed to run a sub 2:10 lap at Watkins Glen with that vehicle.

 

Well that's true as steel is much more dense than Ti but rods are not built by weight or volume/bulk. They designed and tested for strength so what you see is what you get. And I don't see a large difference between steel or Ti rods. Meaning if the Ti rod was 40% lighter it would look as if has nearly half the bulk/material as steel. . But I don't see that - maybe someone else does.

But the advantage of Ti that I do see is with its lighter weight it doesn't need to be as strong.

 

So I did a google for Ti LS7 rods and on top of the links was Crower Ti rods for sbc. 6" Ti rods for the sbc from Jeg's at $750.. Can this be true?

Today's technology moves ahead a fast pace. Whew! Think of a good idea and it's there like now.

 

..... That price is per EACH ..... Back a few years ago , the Chevy Parts retail price for new LS7 Ti rods was $778.00 each .....

 

..... Soooo , I think we can all agree that the substitution of lightweight internal components in an engine will NOT increase the horsepower output of that engine ? But will affect the acceleration in RPM/second ? ... the same for lightening external (behind the crankshaft) components ? ... BUT , Consider this : if 2 cars line up at a drag strip and we just imagine that scientifically all is equal between the two including the scale weights and horsepower/torque ... and the difference between the 2 cars is that one has extensive lightweight components vs the other with none ... will there actually BE a difference in acceleration as measured by the ET slip ? .....

 

I can't say for sure - but I believe the answer is YES ! As far as the lightweight components go - think about how much power it takes to spin up something like a flywheel - alternatively think about how much faster an engine revs with a lightweight flywheel vs. a standard flywheel. The power the engine makes is the same - the lightweight flywheel just lets the engine rev up/down faster. Now think about the loads imposed by the alternator or A/C compressor. We don't notice any significant difference in how fast an engine revs when the alternator is supplying say 50 Amps (think headlights - fan, stereo, and say rear window defroster) - which is equivalent to about 1 HP. We also really don't notice a difference in how fast the engine revs when we are running the A/C compressor (typically a several HP load). So - for there to be a noticeable difference - the energy required to spin up that flywheel must be equivalent to significantly more than couple of HP that the A/C compressor or alternator use. Even if it's effectively 10 HP - you should see that kind of a delta on the time slip (probably in the MPH - if not in the ET)