Stroker 3500 possibilities...

[2.8-350TBI]

the squatiest Ls1 piston I could find was 1.050 compression distance. for a 6.125" rod with a .25" offset grind, you'd need a piston with a .913" compression distance def custom, and would need some kind of a ring support.

My math was wrong with my last calculation. .425 longer rod, and .125 higher pin at TDC from the extra stroke + .10 (radius of .20 if I decide to use SBC journals =.65" higher at the top of the piston pin compared to stock, which I think may be a no go

I took these pix from the store, so the credit goes to Ben.
Judging by the oil hole positions in the underside of the piston, there isnt much space to move the rings up that far, even with custom pistons. Maybe a 1/4 inch tops.





Triple edit:
Basing myself off wanting a 1.75 R/S ratio with a 6" rod, I would end up with a 3.43" stroke, .12" over stock.
This would net me 3624CC based on an otherwise stock 3500.

So that puts the piston pin at +.42" at TDC over stock, and at .52 using an SBC piston pin.
These little engines are a squeeze...

What do you guys think an acceptable R/S ratio is?

[Joseph Upson]

It saddens me that no one remembers my struggle.

3.555" stroke crank, 2.00 pins, did it.
3.43" stroke crank, 2.00 pins, did it by accident thanks in part to the grinder not paying close attention to my instructions. It's still for sale $175 + shipping.

I'm using 5.7" H-beams narrowed but I posted somewhere that you must use at least 6.0" rods or you'll end up clearancing pistons #3 & 4 if you use an internal 7x crank trigger wheel.

I used Forged LS1 pistons which I did an in block valve notch job on.

3900 to 4200 V6.

Things I would have done differently: 5.85 or 6.0" rods, low tension piston rings if available, deeper valve notch to take advantage of some basic VVT function for best fuel economy while cruising. It's getting better with tuning but so far is about 20c/28hwy with a best of 30 hwy on a 60 mile round trip. The previous motor with the cam fully advanced was getting great mileage considering how long it took the gauge needle to move.

The turbo has been removed temporarily for repair but that still doesn't stop the car from seemingly buckling the pavement on launch. It's still being tuned but getting better and better.

[2.8-350TBI]

It saddens me that no one remembers my struggle.

3.555" stroke crank, 2.00 pins, did it.
3.43" stroke crank, 2.00 pins, did it by accident thanks in part to the grinder not paying close attention to my instructions. It's still for sale $175 + shipping.

I'm using 5.7" H-beams narrowed but I posted somewhere that you must use at least 6.0" rods or you'll end up clearancing pistons #3 & 4 if you use an internal 7x crank trigger wheel.

I used Forged LS1 pistons which I did an in block valve notch job on.

3900 to 4200 V6.

Things I would have done differently: 5.85 or 6.0" rods, low tension piston rings if available, deeper valve notch to take advantage of some basic VVT function for best fuel economy while cruising. It's getting better with tuning but so far is about 20c/28hwy with a best of 30 hwy on a 60 mile round trip. The previous motor with the cam fully advanced was getting great mileage considering how long it took the gauge needle to move.

The turbo has been removed temporarily for repair but that still doesn't stop the car from seemingly buckling the pavement on launch. It's still being tuned but getting better and better.

I actually remembered your build yesterday before bed and found the thread, but I was referring to you.

And thats where im at right now, wanting longer rods, and seeing if there are pistons that can accomodate that.

[2.8-350TBI]

Well, ben just got back to me, and it looks like the min compression height for the 3500 pistons is 1", so that puts me at getting the full 1/4" extra stroke with 5.7" rods. 1.6 R/S ratio, which should be pretty good on torque. 3843cc with a .040 over bore

If I split that to use 5.85 rods, I would only be able to add .10 to the stroke for a 3.41 stroke, which would put me at a 1.72 rod stroke ratio, which is stock. This would net 3.6 liters and 3.7 with a .040 over bore

These are my two options

[geoffinbc]

Don't get too obsessed with rod/stroke ratio. It does not play nearly as larger a roll in power production and cubic inches, compression and airflow. On an engine operating below 6000RPM it had almost no effect when kept in a reasonable range. In 2008 or 2009 John Kasse built a Ford Clevland motor with a very tall piston compression height and a short rod considering the motor had a 4" stroke. He could have added more than an inch to the rod length but chose not to in favor of a tall piston that would be more stable in the bore and reduce friction and ring flutter.

If it were me I would buy a high quality piston with a well designed skirt and a full ledge below the oil ring. If that would work with a stock length rod then I would not even consider the rod/stroke ratio. If you can afford any rod you want then just make sure the piston is as good as you can get and buy the rod the exact length you need to connect the dots.

[2.8-350TBI]

Don't get too obsessed with rod/stroke ratio. It does not play nearly as larger a roll in power production and cubic inches, compression and airflow. On an engine operating below 6000RPM it had almost no effect when kept in a reasonable range. In 2008 or 2009 John Kasse built a Ford Clevland motor with a very tall piston compression height and a short rod considering the motor had a 4" stroke. He could have added more than an inch to the rod length but chose not to in favor of a tall piston that would be more stable in the bore and reduce friction and ring flutter.

If it were me I would buy a high quality piston with a well designed skirt and a full ledge below the oil ring. If that would work with a stock length rod then I would not even consider the rod/stroke ratio. If you can afford any rod you want then just make sure the piston is as good as you can get and buy the rod the exact length you need to connect the dots.

Makes good sense, and a very good point about the piston in the bore, but too short a rod also increases side load, and you know what that does.

Just look at the difference between the 2.8 and the 3.4 engine. The 2.8 is inherently revvy due to the r/s ratio it has, which is 1.9

The 3500 has a 1.72, which is still pretty good by performance standards, but anything below, I think will make a noticeable change.

I am trying to tailor my engines peak torque rpm to be in the 3500-4500 rpm range, and I think stock length rods will help with that
Even if I choose not to change the rod length. I have read that shorter rods help tailor the peak torque toward lower rpms

[geoffinbc]

It wont.

If all is equal between 2 engines except the stroke then the smaller engine will be more rev happy since the intake heads and cam have less cylinder to fill.

High rod/stroke ratio is beneficial because of the extra dwell time at TDC which gives the flame front more time to spread before the piston starts to speed up down the bore. This action puts more pressure on the piston. It is much more pronounced in a high compression high RPM motor. The higher the compression ratio the faster cylinder pressure drops as the piston travels down the bore so it is in your best interest to make maximum pressure when the piston is closest to the top of the bore. This also allows you to open the exhaust valve sooner with no penalty in power loss. This extra exhaust duration means you can run a smaller exhaust valve and in turn a larger intake valve. This all contributes to the big horsepower picture.

You can now begin to see that rod/stroke ratio on a low compression, low RPM engine is not such a big deal as it would be on a 500CI, 16.5:1 Compression, 8000RPM Pro Stock motor. Dwell time at low RPM is plenty long even with a "bad" rod/stroke ratio.

John Kaase ran that Ford Small block with a 1.56 Rod/Stroke ratio and cleaned house. He made more power than even the roller cam engines that were run in years before. The following year he kept it all the same but used a roller cam that was now allowed by the rules and a tunnel ram intake and made even more power and won again on the same rotating assembly. The operating range was 2500 to 6500 RPM. He had a 2" compression height on the piston so he had tons of room to better the rod/stroke ratio but chose not to. He also could have created a much lighter piston but instead kept with a design that was more like a diesel piston. The point I am trying to make is that everyone likes to make all these golden ground rules to build engines and if you don't follow them everyone thinks it will just fire the rods out of the side of the block. But if everyone followed the "rules" then a 350 small block would still make 350horsepower like it did in the 60's.

Your number one concern should good piston design. Stock is a good design. It has a proper skirt and good well spaced ring lands that keep compression loss, heat and oil control in check. Your driving a street motor that needs to last years. Not a race motor that needs to last 4 hours. So build smart.

[2.8-350TBI]

Thats some good reading, thanks for taking time to post it!

I am trying to build a durable engine that can take abuse for a good amount of time. Not saying its gonna last forever, but I do plan on putting good time and good parts into the motor.

What do you think of the diamond pistons available through the store?

[Joseph Upson]

The chevy small block 400 had a 3.75" stroke and a connecting rod in the 5.4" range if that helps. It's problem was with cooling due to block design from what I recall.

[geoffinbc]

Diamond is a good piston. In fact all of the brand name piston makers are really good.

[2.8-350TBI]

Diamond piston is what im planning to run, just with the pin moved up to accomodate the extra stroke

[ericjon262]

The chevy small block 400 had a 3.75" stroke and a connecting rod in the 5.4" range if that helps. It's problem was with cooling due to block design from what I recall.

mainly because coolant couldn't pass between the cylinders with the siamesed bore, easily corrected by drilling steam holes.

I've always heard a good r/s ratio is around 1.5-1.6, more is better, but not always nessecary.

[ericjon262]

Keep in mind while speaking on connecting rods, shorter rods will dwell longer @ BDC, and promote better cylinder filling which should equate to more lower end torque.

EDIT: I have no Idea where I was when I posted this, this is completely wrong, 110%

[geoffinbc]

Dwell time will be the same at the top and bottom for any given rod. Longer rod means longer dwell.

[ericjon262]

I have no idea where my mind was when I posted that... sorry.