Engine Stroking, Long Connecting Rods, Short Connecting Rods

GoreMaker

Member
Joined
May 7, 2021
I'm planning an engine rebuild over the winter. The '87 GN engine I'm working on has well over 200k miles on the OEM long block. This is for a mostly street-driven car. Goals are good low-end torque and solid mid-range horsepower, not so concerned with high revving. Fuel economy is also a minor consideration. Top consideration is a solid, resilient engine (another 200k miles sure would be nice! :LOL:) I'm seriously considering aluminum heads and roller cam with roller rockers. I kinda like the way the engine feels now (stock turbo, stock IC, alky, TurboTweak chip, 60# injectors, hotwired Walbro pump, headers, 3" cat-less exhaust), but it's clearly starting to eat oil, and the turbo lag on launch is a little annoying. It would be nice to improve that initial throttle response.

So I'm looking at rotating assembles, and I see options for stock stroke, stock-length rod stroker, and long rod stroker. I understand the implications of these things on n/a V8 engines (like Chevy and Pontiac), but I'm not sure what the consensus is when it comes to a Buick turbo V6.

First, would a stroker help with low-end grunt and reducing turbo lag? Seems like the extra exhaust volume and velocity might spin up that turbine faster, and even allow me to run a bigger turbo more efficiently. Or am I way off base and should just look at other means of improving low end torque?

Second, how big of a MPG hit am I looking at with a stroker? Assuming I'm not running in the boost all the time, are we talking a significant difference? I currently manage about 22 to 24mpg in a 4500+ pound car. It sure would be nice to stay above 20mpg.

And finally, if I go the stroker route, are the benefits of a stroker with longer rods worthwhile? I'm a big lover of boost and alky and all that jazz. It seems to me the stock rod length would result in more piston top material which is better at handling boost, and the increased peak piston speed would help spool the turbo faster. But I see these long-rod kits and I wonder if they offer any benefits I'm not familiar with other than piston stability.

Would love some advice from those more knowledgeable than I!
 
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~JM~

Wrinkled Member
Joined
Oct 31, 2007
I read up on the longer rod length & stroker benefits in naturally aspirated engines many years ago. I recall these to be an interesting write ups: Connecting Rod vs. Stroke Analysis: panic Tech Paper No. 1

The long rod sounds beneficial until it intrudes into the ring lands.
 

GoreMaker

Member
Joined
May 7, 2021
That's a fascinating read and a great resource, thank you.

I just realized that the long rod stroker kits are basically keeping the same rod/stroke ratio as the OEM spec. So rather than gaining or losing any side effects, those kits are just maintaining the status quo and avoiding the unintended changes imposed by most stroker kits. I guess since these kits are intended for use in a turbo V6, the pistons should be more than adequate for whatever boost they might be subjected to. So if I do decide to go with a stroker kit, the long rod variant would likely be the best way to go.
 

Mr.Spool

Well-Known Member
Joined
Nov 6, 2006
I'm planning an engine rebuild over the winter. The '87 GN engine I'm working on has well over 200k miles on the OEM long block. This is for a mostly street-driven car. Goals are good low-end torque and solid mid-range horsepower, not so concerned with high revving. Fuel economy is also a minor consideration. Top consideration is a solid, resilient engine (another 200k miles sure would be nice! :LOL:) I'm seriously considering aluminum heads and roller cam with roller rockers. I kinda like the way the engine feels now (stock turbo, stock IC, alky, TurboTweak chip, 60# injectors, hotwired Walbro pump, headers, 3" cat-less exhaust), but it's clearly starting to eat oil, and the turbo lag on launch is a little annoying. It would be nice to improve that initial throttle response.

So I'm looking at rotating assembles, and I see options for stock stroke, stock-length rod stroker, and long rod stroker. I understand the implications of these things on n/a V8 engines (like Chevy and Pontiac), but I'm not sure what the consensus is when it comes to a Buick turbo V6.

First, would a stroker help with low-end grunt and reducing turbo lag? Seems like the extra exhaust volume and velocity might spin up that turbine faster, and even allow me to run a bigger turbo more efficiently. Or am I way off base and should just look at other means of improving low end torque?

Second, how big of a MPG hit am I looking at with a stroker? Assuming I'm not running in the boost all the time, are we talking a significant difference? I currently manage about 22 to 24mpg in a 4500+ pound car. It sure would be nice to stay above 20mpg.

And finally, if I go the stroker route, are the benefits of a stroker with longer rods worthwhile? I'm a big lover of boost and alky and all that jazz. It seems to me the stock rod length would result in more piston top material which is better at handling boost, and the increased peak piston speed would help spool the turbo faster. But I see these long-rod kits and I wonder if they offer any benefits I'm not familiar with other than piston stability.

Would love some advice from those more knowledgeable than I!
On a 109 using a stock stroke or destroking the motor will make it stronger.
 

Reggie West

Well-Known Member
TurboBuick.Com Supporter!
Joined
May 28, 2001
For what your goals are you can a stock stroke crank and rod and be just fine. There are those out there who swear that a long rod stroker is OK but the dwell time at the bottom of a 3.625 stroke is not ideal. I think either way works but remember you have to clearance the block in a couple of spots to keep the crank from hitting the bottom of the piston bores. Availability of parts may be your deciding factor too. Good heads and cam will certainly help , no question.

Here is where you can gain some low end repsonse for free. Bump the CR to 9.5 to 1 that will help a bunch. Gas or E85 you wont hurt anything.
 

GoreMaker

Member
Joined
May 7, 2021
On a 109 using a stock stroke or destroking the motor will make it stronger.
Everything I know about engine building tells me that de-stroking results in less low-end torque, which is exactly the opposite of my goal. Especially with the heavy car this engine is moving around, this doesn't seem very beneficial.
 

GoreMaker

Member
Joined
May 7, 2021
Here is where you can gain some low end repsonse for free. Bump the CR to 9.5 to 1 that will help a bunch. Gas or E85 you wont hurt anything.
That's interesting... I haven't come across any reasonably priced rotating assembly kits with increased compression. Can you point me to some?
 

Mr.Spool

Well-Known Member
Joined
Nov 6, 2006
Everything I know about engine building tells me that de-stroking results in less low-end torque, which is exactly the opposite of my goal. Especially with the heavy car this engine is moving around, this doesn't seem very beneficial.
sounds like your looking at it na,the turbo makes the power!raise the compression with a good set of pistons with a bb turbo and a good converter and tune.
 

GoreMaker

Member
Joined
May 7, 2021
sounds like your looking at it na,the turbo makes the power!raise the compression with a good set of pistons with a bb turbo and a good converter and tune.
Yeah but until the turbo spools up, that low-end torque is lacking, and that's what I'm hoping to resolve. At least that's what's currently happening with the well-worn engine. Plus a shorter stroke seems like it would delay turbo spooling. Besides, with well over 200k miles on the current OEM long block (might even be closer to 300k) with lots of abuse, I'm not terribly concerned with longevity with the stock stroke.

I do like the idea of increasing compression ratio, though!
 

Reggie West

Well-Known Member
TurboBuick.Com Supporter!
Joined
May 28, 2001
That's interesting... I haven't come across any reasonably priced rotating assembly kits with increased compression. Can you point me to some?
All the vendors here will have a kit. They can spec one out for you. If you need help with it let me know. Earl Brown here on the board can recommend a combo as well. He has super secret pistons too.
 

Pronto

You can't knock them up with spit.
Joined
Dec 9, 2002
Stock ported heads, 206 roller cam, stroke kit and smaller turbo, matching converter and 3.42 gears. What rear gear are you running?
 
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