pistons rods with a stroke of 3.625 5.85 rod and 350 engine???

[oldgold]

will that work

[dynoman14]

You will need to find a set of pistons with a CHT of 1.3625, and that is assuming your Block Deck Height is stock at 9.025". If you want you can use a common available piston with 1.250" CHT and mill the block .1125" to get to Zero Deck.

Best thing to do is mock up the short block with the parts you have and machine the block to fit. Any good machinist should be able to get you there.

[oldgold]

my block is now machined .005 in the hole with a flattop

[go2fast]

You would be better of to go with a 6.000 rod with a 1.188 ch or a 6.125 rod and a 1.062 ch and a 9.005 deck block with the 1.338 ch makes to much weight on piston

[dynoman14]

Oldgold,
You probably need to refine your question, what are you trying to make work? And what do you already have? You say you have .005" in the hole with a flat top, why not just run that as it sounds like it is already fit to go.

People have been running 5.850 rods for 50 years in sprint cars so they are not a problem, pistons are available in that CHT that are as light as ones for ony other rod length.

What question are you looking to get answered?

[parrot69777]

The only way the longer rod will work with that short of a stroke is if your going to turn 8000 rpm in a late model....open mod with an open carb. Everyone's argument is you can change all that with the cam...which isn't true.

The bad part of the deal is.....if you go to a 6" or 6.125" rod with that short of stroke....it's going to kill torque and you'll never get out of the corner. I would give up the piston weight and go with a shorter rod.

[dynoman14]

I am not doubting that if everything else is equal the shorter piston has the capability to be lighter, my point is how much difference can there possibly be between an 650hp piston with a 1.18"CHT and 1.36" CHT?

Diamond racing pistons sells a flat top and a dome for 5.850" Rod / 3.625" Stroke that is in the 450G. range depending on bore size. If you are capable of saving 100G over that more power to you, although I have not seen many 350G. pistons.

The super-light pistons are not capable of withstanding the cylinder pressures as well as pistons that have a little more mass in the right places. In most cases they are only recommended for 2-Barrel Flat top applications.

In a comparison of mass savings in relation to MOI, moment of inertia. Everything in this comparison is based off the center of crankshaft. 100g is roughly 3oz, x 8 throws x ( 6" rod + 3.5" stroke ) = 228 "/oz. For comparison if you save 3 oz of weight on your rear wheels 3oz x 2 wheels x 7.5" dia x 6.50:1 gear = 293 "/oz. If you then compare the 2 on a percent basis the 3oz at the rear wheels makes a 28.5% greater difference. That is almost 30% and unless you compare things on a direct basis you would never think 3oz at the rear wheels would be 30% greater MOI than 3oz on a piston.

For those of you thinking about the engine rpm-v-wheel rpm that would be an inertia equation that would entail way more calculations but in relation to the race car acceleration the results would be approximately the same because the engine still works harder to drag 3oz of wheel weight than 3oz of piston weight.

As far as everything else goes, I prefer to use as short a rod as possible in any of the engines I build as I prefer greater piston speed and instantaneous acceleration in the other direction of TDC. In my opinion this far outweighs the small differences in cylinder wall friction you pick up with a shorter rod. In a 350 chevy 3.48" stroke if you go from a short 400 rod 5.565" to a Cup rod 6.200" there is only 2deg difference in the angle of the rod 18.23deg v 16.6deg.

Fifty years ago when Smokey came up with the "friction on the skirt" and "bore side load" deal the piston skirts were a honking 3-4" almost as big as the bore size. Now skirts are about 1/2 that and with coatings, narrow barrel face rings, low drag oil rings and tight ring packs to the top of the piston, the friction is so minimalized that other things are more important.

In my opinion the pull that the piston actuates on the port is way more important to getting the flow charge to jump out of the head, after all negative pressure in the cylinder ia just like a blower on the top of the manifold.

But thats just me and I've only been chasing the deal for 35 years, I bought a Superflow flow bench when I was 20, saved up the money from porting heads to buy one of the first SuperflowChassisDynos when I was 25 and have been running it for 25 years to try and figure out what goes on in and around race engines and race cars.

I am sure there are other folks out there with other opinions and I would love to hear them...

[hpontap]

All else being the same, there is no reason to go over 6.00 on rod length in a sbc engine as no power is gained from less side-loading ,piston weight etc.
The shorter the track and tighter the turns, the shorter the rod I would use down to a 5.7.
If done right, a 5.7- 5.85 rodded engine will more than hold its own against a long rod engine on a 1/4 mile track.