rod strength?

[Davy]

How much can the stock rods handle?

 

[deth2u]

1g or 2g?

 

[Davy]

2g rods?

 

[Polk]

First of all RPM's are what kill rods faster than anything else. The stock 1G rods are pretty strong for a factory rod. The 2G's on the other hand are a joke. They look like a Honda d series rod if you ask me.

I think that 400 hp is not a prob for a 1G rod. I bet you could make closer to 500 without a worry if they were cryoed.

As I said before rpm's are what kill rods, but a ton of cylinder pressure can kill them too. If you are making 300@ the wheels then you put a 75 shot of N2O on top of that and have way too much timing in the motor with a 4G63 (decent rod ratio), this is what can kill the rods. Too much load on them.

Now lets say that you have the same setup and making the same hp but with a stroker motor. The rod ratio is much worse. But what happens here is that the break over point of the stroke has a greater ratio than before. This means that you can get away with more timing or more cylinder pressure before trying to kick the rod out of the motor. This also is the reason a short rod motor makes more torque than a long rod motor.

There is some trade offs with this. The side load on the motor goes way up with a short rod motor. This is bad if you are wanting to turn the motor out the roof with rpm's. But if you are running a turbo then a short rod, long stroke, and a lot of timing are going to get that turbo going quick. You should not have to turn the motor very hard (rpm's) with this set up to make a ton of power. The rods will live a little eaiser, but with more torque comes more driveline problems.

I know that everyone out there have their own ideas about long rod/short rod motors. To each there own, not here to argue(that is what DSM talk is for) just sharing some of my expirence I have tried over the years.

Polk

 

[GRNDSM]

>The 2G's on the other hand are a joke. They look like a Honda
>d series rod if you ask me.

Well, now, we all know what looks can be deceiving… I know that they look MUCH smaller than the big rods. As I recall, they have “I” values of as little as 70% of the big rods. But I have seen several small rod motors push out 400-450hp at the wheels (that is 500-550hp at the crank) with out any problems… So would not consider them a joke…

If I had a 7 bolt 2G motor, I would be more concerned about crankwalk and not the rods. The odds are that carnkwalk will take your engine before the rod failure.

Leon
RR

 

[insane147]

dont the rod bolts usually fail first? ive seens 2gs dynoed at 350 whp, then tear the rod bearing apart, could small bearing area cause enough loading to desroy this? when we ordered the eagle rods, they used 1g rodbearings, so i figured it must spread the load better.

 

[GRNDSM]

When you say "they used 1g rodbearings", do you meant 1g 7bolt? Because you can't fit 6 bolt bearings on a 7bolt crank.

Leon
RR

 

[insane147]

yes, they fit 1g big rod bearings on the stock 2g crankshaft. i called EAGLE directly on it and everything, they reassured me to use 1g, 1990-92, not any later. it works, the cars been running all year with about 500 hp@ the crank.

 

[GRNDSM]

Have you tried fitting it yet? I am 90% sure that "big" bearings are too wide for "small" crank and physically can not fit in there...

Leon
RR

 

[ShapeGSX]

6-bolt bearings will not fit into a 7-bolt engine. Not even close.

So, for anyone reading, don't try this.

 

[GRNDSM]

Thanks for confirming this Josh, I thought I was going nuts here .

Leon
RR

 

[ShapeGSX]

Leon, I thought you had 6-bolt rods in one of your own numerous 7-bolt engines that had to be cut down on the big end to fit the crank.