Stroker / Bore thoughts?

[tdstuart]

Having to rebuild my engine and saw a stroker kit from mmr with bore sizing options. https://www.modularmotorsportsracing.com/cart/index.php?main_page=product_info&products_id=1056

Although as I understand to get to a 3.7 bore you need their sleeve kit (https://www.modularmotorsportsracing.com/cart/index.php?main_page=product_info&products_id=1045)

Has anyone installed this or something similar? I know there was another thread where people said they wouldn’t do it, but I’m wondering if the census has changed or if someone has actually had issues.

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[engineermike]

Depending on power level, the 5.2 block is a great and affordable alternative to achieve the 3.701 bore. I’ve been thinking more and more about this lately. If you want to retain a decent compression height and ring pack thickness, you’d have to go with 5.85” rods as opposed to stock 5.933”. This hurts the rod/stroke ratio but doesn’t put it in the terrible range; slightly better than the LS7 I believe. When I called MMR a few years ago they didn’t recommend it with forced induction but didn’t give any details.

5.4 liters can be achieved while retaining an acceptable rod/stroke ratio and ring pack thickness, using stock piston geometry even.

The mmr kit is $3000 and the 5.2 block is $2000. So if you assemble yourself then the cost is the same as an aluminator but presumably with better parts. This assumes mmr balances the kit.

 

[tdstuart]

Depending on power level, the 5.2 block is a great and affordable alternative to achieve the 3.701 bore. I’ve been thinking more and more about this lately. If you want to retain a decent compression height and ring pack thickness, you’d have to go with 5.85” rods as opposed to stock 5.933”. This hurts the rod/stroke ratio but doesn’t put it in the terrible range; slightly better than the LS7 I believe. When I called MMR a few years ago they didn’t recommend it with forced induction but didn’t give any details.

5.4 liters can be achieved while retaining an acceptable rod/stroke ratio and ring pack thickness, using stock piston geometry even.

The mmr kit is $3000 and the 5.2 block is $2000. So if you assemble yourself then the cost is the same as an aluminator but presumably with better parts. This assumes mmr balances the kit.

Was hoping to keep my stock block as I don’t have a ton of money to spend. And lethal sells the kit for 2,200 so I thought it was a nice detail. And then I think you can just buy their sleeves and sleeve your stock block.

Could you explain more about the rod/stroke ration and why it is important or point me in a direction to learn? Haven’t really dived into all the intricacies of engines and what matters for power and longevity.

 

[K4fxd]

Longer rods/better ratio, mostly reduces side loading of the piston to the cylinder.

This is something Smokey found a long time ago. He also thought longer rods made more power but that is debatable. With longer rods the piston dwells longer at TDC than BDC so some cam timing tweaks can maximize power for either.

Still most engine builders will use the longest rod possible.

 

[tdstuart]

Longer rods/better ratio, mostly reduces side loading of the piston to the cylinder.

This is something Smokey found a long time ago. He also thought longer rods made more power but that is debatable. With longer rods the piston dwells longer at TDC than BDC so some cam timing tweaks can maximize power for either.

Still most engine builders will use the longest rod possible.

Interesting. This is complex haha. So many things to building engines. Just wish I could find someone who has done something similar before.

 

[K4fxd]

Just wish I could find someone who has done something similar before.

There has got to be some good engine builders in your area. Maybe head to the strip and ask around. I'm sure someone will want to help.

 

[engineermike]

@tdstuart can you post a link to the $2200 stroker kit?

On the sleeves, that’s usually an expensive job. I think the 5.2 block might be a cheaper option in the end.

On the rod ratio, longer rods are usually considered better and the oems have gravitated towards longer rods. The 5.0 rod is 5.933 vs the sbf at only 5.1”. Sbc is 5.7” and LS went to 6”. The 400 sbc was generally considered a failure partly because of a poor rod/stroke ratio and it was 1.48. The 3.84 stroke mmr crank must be used with the shorter 5.85 rods, worsening the rod ratio from both directions, from 1.63 to 1.52. The LS7 rod ratio is 1.52 so it’s not in terrible company. Lower rod ratio actually improves leverage so low/mid-range is actually improved, but the piston tends to outrun the flame moving away from TDC so top end can suffer a little.

 

[Jackson1320]

I wouldn’t mess up the stroke but you can bore it. To install sleeves is more than the price of a new block. If you want a little more bore but not a lot of money use a gen3 block 3.661 bore $900

 

[tdstuart]

@tdstuart can you post a link to the $2200 stroker kit?

On the sleeves, that’s usually an expensive job. I think the 5.2 block might be a cheaper option in the end.

On the rod ratio, longer rods are usually considered better and the oems have gravitated towards longer rods. The 5.0 rod is 5.933 vs the sbf at only 5.1”. Sbc is 5.7” and LS went to 6”. The 400 sbc was generally considered a failure partly because of a poor rod/stroke ratio and it was 1.48. The 3.84 stroke mmr crank must be used with the shorter 5.85 rods, worsening the rod ratio from both directions, from 1.63 to 1.52. The LS7 rod ratio is 1.52 so it’s not in terrible company. Lower rod ratio actually improves leverage so low/mid-range is actually improved, but the piston tends to outrun the flame moving away from TDC so top end can suffer a little.

Really sucks to hear that sleeves are that expensive. Is it the amount of machining that costs a lot? Because it looks like you just put the sleeves in nitrogen and slide them in.

Lethal: (edit: actually I think lethal doesn’t have the stroker kit just a kit for bored blocks)

So stroking it would make the rod/stroke ratio worse. Would I still make decent power from it or would it not be beneficial to stroke it.

 

[Jackson1320]

If you’re block and bore are good then just hone it and build it. Boring it even to 3.700 is not going to give you much. Stroking it will probably hurt you more than help

 

[K4fxd]

So stroking it would make the rod/stroke ratio worse. Would I still make decent power from it or would it not be beneficial to stroke it.

Displacement is king. I wouldn't worry about rod ratio. Pro mod engines have terrible rod ratios and make lots of reliable power.

If your block is not able to clean up with an overbore I'd go with a 5.2 block.

 

[Jackson1320]

A normal machine shop will charge $1000-$1200 to install the sleeves and unless they have done it many times I would not let them. I had a local machine shop crack a block of mine trying to install a stock sleeve so a lot bigger sleeve would be harder

 

[Jackson1320]

Displacement is king. I wouldn't worry about rod ratio. Pro mod engines have terrible rod ratios and make lots of reliable power.

If your block is not able to clean up with an overbore I'd go with a 5.2 block.

Pro mod engines don’t have to last 100,000 miles

 

[engineermike]

Really sucks to hear that sleeves are that expensive. Is it the amount of machining that costs a lot? Because it looks like you just put the sleeves in nitrogen and slide them in.

Lethal: (edit: actually I think lethal doesn’t have the stroker kit just a kit for bored blocks)

So stroking it would make the rod/stroke ratio worse. Would I still make decent power from it or would it not be beneficial to stroke it.

The machine work is the expensive part of sleeving.

Stroking it would hurt the rod stroke ratio, but as I said…it’s no worse than the LS7 and will actually pump up the torque curve.

 

[K4fxd]

I have been involved in some engine testing using long and short rods. After tuning there was no difference in power.

Side loading and engine longevity are the main reason for long rods in production engines. The 1.52 or so you would get from stroking a coyote will not reduce the life by any measurable amount.

I'll use the 400 SB Chev as an example since it was brought up. They last just as long as any other SB. The guys making big power with them have cam designs that take advantage of the fast pull away from TDC.

Now should we talk about offset piston pins?

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