Datsun Roadster Forum-311s.org

nothing like a nice stiff rod!

Gents,

I'm having some more 1600 rods built by Carrillo and they've said that with an order of 10+ rods, the price will be $294.50 per rod. I'm in for 5, so I'd just need one guy to order 5 more (one set + a spare) and we'd both benefit. Carrillo's are 3/4 of the weight of a stock rod, meaning you save the weight of a rod in a set. They're one of the reasons I've been able to remain competitive in FP against the Miata's. They're virtually bullet-proof (unless you suffer a catastrophic cam break, like me). Even if you turn a bearing and smoke the big end, Carrillo will recondition them for $120 per rod. You can't buy a better rod for your 3 or 5 main 1600. I've used them for years!

Thanks,

Bill

Bill,
When I talked to them a while back they quoted each rod at 450 - 500 grams. That's like losing the weight of 1.5 of the 1600 rods (~800 gm) or 2 of the U20 rods (~1000 gm). They can be used in the U20 with different pistons.

I was considering this for a stroker with custom pistons coming in at about 325 grams each, losing almost 400 grams per cylinder of reciprocating weight (more than 3 1/2 pounds for all 4). This will make a big difference in acceleration, as well as a noticeable horsepower gain (unlike a lightweight flywheel which only affects acceleration).

Interesting calculator here: http://www.wallaceracing.com/Calculate- ... Piston.php" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;
With this calculator you can see where 50 to 75 grams can make a difference of hundreds of pounds of inertial force. Although this is a 'piston' calculation, there will be similar effects for the rod. Dropping the weight, and therefore the inertial force will also take some stress off the crank......

Do you have to stick with stock dimensions on the rod/piston in your class?

What pistons would a U20 build use with these rods?

There is a VG30 piston that is talked about on this board, or custom pistons.
Carrillo makes each order custom so you can also spec a length of rod/small end to work with what you have/want. Tho with Bill's order they may require 10 rods the same specs......

Beautiful rods that do help the engine rev faster etc. and are super strong. However, I don't think there is evidence that they will actually increase HP, just allows it to build faster like other efforts to lighten components. Typically one is trying to increase the safe max RPM, and in racing getting there faster is better, so your car ends up quicker. But on a dyno it won't produce MORE power by my understanding... But I'm open to different opinions!

The way I understand it (subject to correction, of course):

Rotating parts like the flywheel, crank, balancer: more weight takes more energy/time to accelerate, takes longer to decelerate. At steady state doesn't make a difference so no affect on steady state horsepower readings.

Reciprocating parts like the pistons and rods, because of the inertia involved in changing direction twice every rotation, takes energy away from the crank rotation every direction change. If you lower the weight of these components, you lower the inertia (parasitic loss?), therefore increasing horsepower and acceleration capabilities. Also the higher you rev the engine the bigger the horsepower gain will be (which is why they don't normally worry so much about big heavy components in an industrial engine). If you do calculations with the above calculator using the same components and change just the rpm (6000, 6500, 7000, 7500, 8000) you will see a huge increase in inertial forces over the 6000 to 8000 rpm range. Do the same calculations using a 400 gram piston and a 350 gram piston and see the difference...... Should also help in understanding how lighter pistons/rods take some stress off the rods and crank.

I haven't figured out how to calculate the weight loss into a horsepower gain (ie: -100gms = ? hp), but if I figure it out, OR find out I'm wrong, I'll post it here.

I think if this were in the tech discussion rather than/as well as roadster racing it would get more response also.

Wow, crickets for weeks and then (after I'd given up hope) some responses..

Yes, I'm bound by specs to stay stock dimensions in crank stroke, rod length and displacement (0.040 over bore). Pistons are free but Garm, I have no idea what piston to use with a 6.00" rod on a U20 crank, no experience with that.

I think Greg you are technically correct, but it's the time it takes to make that RPM change and that is where lighter reciprocating parts get you to the next corner quicker than the other guy!

See you at the track!

Bill

gpdatsun wrote:
I think Greg you are technically correct, but it's the time it takes to make that RPM change and that is where lighter reciprocating parts get you to the next corner quicker than the other guy!

See you at the track!

Bill

Yes, exactly!

Greg, Bill,
I have been searching specifically on the horsepower gains and getting answers of yes, no, and minimal.
A couple of sites talk about improved 'efficiency', which to me sounds like power and milage, but......
The improved acceleration seems to be universally accepted tho.... as well as less stress on the crank (at the same rpms).

Bill,
Would this require lightening of the crank throws to keep it all balanced? I've seen mention somewhere about 4 cyl cranks not requiring the piston/rod weights for balancing, but can't find the info now....

Daryl,

I keep it simple and balance just the crank on it's own, use the carillos and matched pistons. I've never balanced the assembled reciprocating assembly,though I think it's been done, just not with anyone I've worked with.

Bill

The machine shop, who worked with a partner speed shop, wanted all parts; crank, rods, pistons, flywheel and clutch to balance it all.
Was not expensive and I trusted then fully. Very happy with the results but don't race it or anything. Seems to be smooth and very rev happy.

You don't need to balance the entire rotating assembly on our 4 cylinder engines like you would a 6 or 8 cylinder. The 4 cylinders are paired 180 degrees out of phase so you can balance the crank separately and then the individual components to make sure they match.

Mike