I got a good price on a new set of 6.2 Oliver rods. My question is: What are some good combos with this size rod. It's obviously not a common size. Any advantages--disadvantages?? I've got a tall deck Dart block that they can go in.

Thanks,

B9radz

86' IROC ( future race car )

 

Without knowing the deck height of the Dart block (9.25?),I can't help much on the combinations available but you can play with your own choices by using the following:

Stroke divided by two. Plus the rod length. Subtracted by the deck height gives you the piston compression height (the distance from the wrist pin centerline to the top of the piston.)

Example: We know the standard factory block has a deck height of approximately 9 inches. I say "approximately" because the actual factory deck height is, I think, 9.025 but a used block may have already been decked and who knows how much. You'll have to measure for complete accuracy. With that said, here is the combo I am currently building. We'll plug in the numbers.

I am using a 3.25" stroke (large journal 327)crank in a 400 block with 6.25" rods. To determine what pistons I could use I did this.
3.25 divided by 2= 1.625. Plus the rod length. 1.625 + 6.25 = 7.875. Now subtract this by the deck height. 9.00 - 7.875= 1.125 or a piston compression height of 1.125. Oh look! What a miracle! Off the shelf pistons for a 400 using 6" rods have a compression height of 1.125"! What luck! Seriously, I'm making light of the fact that if you want to maintain some kind of budget on your build your going to have to consider what pistons are available over the counter with the compression height you want for what ever combo your after. Otherwise you will have to have a custom built piston and the cost will be quite large. Hope this helps.

 

I measured it and its not a tall deck. Its 9.005

 

The 4" bore or the 4.125" bore?

 

4.125

 

Read the article that made me interested in building my motor. It is in the AFR Magazine Achives entitled "The 350 Chevy Should Have Built". Here is the link : http://www.airflowresearch.com/artic...le03/A3-P1.htm
They used custom pistons. I went to the 6.25" rods to get around that.

Use can use 400 pistons for a 6" rod application (1.125" comp. height) and a 3.335" stroke crank with your 6.2" rods. The cranks are popular with NASCAR so look for them in websites that deal in NASCAR parts like http://www.racersauction.com
I know Sonny Bryant is one manufacturer of that crank but there are others.

A 1.3" compression height piston is common. This can be used with a 3.00 crank and your 6.2" rods to make a little screamer with about 330" of displacement.

I'll tell you now that your going to be told that you are wasting a great foundation in the your Dart block if you don't go a stroker motor. So get ready to hear it.

 

What advantages do the longer rod give you?

 

A longer rod puts gives you less side loading on the cylinder walls. I have heard other advantages, but I wonder how much if any advantage the other things provide. I am not going to mention them for fear of starting a flame war.

 

yes, alot of the "advantages are up in the air as a motor setup for street-strip will never come close to seeing most if any of the advantages they only advantage that would be noticed is the longer stroke does have less side loding on the cyl walls and will wear more evenly and last a little longer (street motor-daily driver) the rest just gets people fighting even the mags will say one thing and a few issues latter say another and have charts proof for both??? (dwell time/HP ect.)

 

Even the great engine builders can't agree on the advantages, if any. Lingenfelter and Smokey are absolutely sure of the advantages while Joe Sherman thinks it's a crock. I can tell you this, the Sherman tests were done on a 6" rod 350 versus a 5.7" rod 350. That difference in rod length is not going to do much. It has to be much more dramatic a rod/stroke ratio. The problem with the SBC is the relatively short deck height of 9.00 - 9.025 inches. If you want to make a big difference in the rod/stroke ratio, your going to have to give up some stroke. Consequently, you lose the advantages of a longer stroke, which means some torque. A longer rod motor is unquestionably more efficient in its use of fuel. That can be proved by the great brake specific fuel numbers it creates. Your gamble as a builder becomes will this great efficiency over come the loss of torque by using a smaller stroke.

I personally am looking for a different idea of the "perfect motor" than most people. A majority of guys and gals see the "perfect motor" as the one that produces the most power. I like power too! Don't get me wrong but my ideal motor must get great gas mileage too. I believe there is a lot of free horsepower to be gained by creating the most efficient motor possible. High rod/stroke ratios are one part of the equation but other efficient techniques and parts like blue print type assembly, efficient heads with newer generation chambers, true roller timing sets, and free flowing exhaust systems will complete the package. This motor I'm screwing together I hope will give me 300 hp at the rear wheels, 320 ft/lbs of rear wheel torque, break into the 13's and 20 + miles per gallon on 87 octane. Oh yeah, all this must be had at 5000 ft of altitude. The power figures may not seem like much to someone building a 406 or someone at sea level but it's a tall order for someone up in the clouds.