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Chryco's Tech Shop => Engine & Go Fast Goodies => Topic started by: Racer57 on May 05, 2017 - 02:47:33 pm

Title: Stroking... Is it good idea ?
Post by: Racer57 on May 05, 2017 - 02:47:33 pm
I have a serious question for those that have done it and truly understand whats being done, so please don't take this like a slam.

Throughout my entire life of being around performance engines either through racing or just street, everyone that I have personally known that either built or bought a stroked engine had wear issues long before stock configs would have. Of course all of them were pushing them, so it kinda confused what was really going on.

Here's my question.... If the stroked configs are so great, whay didn't the factories engineers ever use them ?
Title: Re: Stroking... Is it good idea ?
Post by: 7212Mopar on May 05, 2017 - 02:56:51 pm
I think packaging is a consideration for a given displacement. The height of the block governs how much stroke. Not many as fortunate as a Mopar SB. Factory also have to provide warranty so there is always reservation in the design. I looked into this before deciding to stroke my 340. I know wear will be higher due to higher piston speed but I will be driving mine in the weekends only.
Title: Re: Stroking... Is it good idea ?
Post by: blown motor on May 05, 2017 - 03:59:39 pm
I don't mean to hijack the thread but why a higher piston speed? To my thinking, if a stroked engine produces more power then you should be able to maintain a given speed at a lower RPM. I'm just trying to learn.
Title: Re: Stroking... Is it good idea ?
Post by: 73_Cuda_4_Me on May 05, 2017 - 04:15:19 pm
Higher velocity due to traveling farther distance in same revolution...

Most of that would be experienced by rings.. I think the biggest detriment (although small) is the fact there is more side force on the skirts of piston, as it is forced more sideways (right angle to crank) due to higher throws as crank rotates...
Title: Re: Stroking... Is it good idea ?
Post by: sprecks on May 05, 2017 - 04:26:44 pm
I don't mean to hijack the thread but why a higher piston speed? To my thinking, if a stroked engine produces more power then you should be able to maintain a given speed at a lower RPM. I'm just trying to learn.
I'm not an expert and may be wrong but here is my way of reasoning. The piston has to move a longer distance for every revolution of the crankshaft.  For example if a engine has a 3.75 inch stroke, the piston will move 7.5 inches for every revolution (3.75 up and 3.75 down).  On the other hand, if the engine is stroked to 4.5 inches the piston will have to move 9 inches for every revolution.  7.5 inches at 5000 RPM is 37,500 inches per minute (about 36 MPH) and 9 inches at 5000 RPM will be 45,000 inches per minute (about 43 MPH).
Title: Re: Stroking... Is it good idea ?
Post by: 7212Mopar on May 05, 2017 - 04:39:25 pm
I don't mean to hijack the thread but why a higher piston speed? To my thinking, if a stroked engine produces more power then you should be able to maintain a given speed at a lower RPM. I'm just trying to learn.

Same engine RPM, longer stroke has higher piston speed due to longer travel distance.
Title: Re: Stroking... Is it good idea ?
Post by: Cudaragtop on May 06, 2017 - 03:16:04 am
225 /6 = 4.125" stroke with 3.40" bore... 225 /6 are known to be very durable even with that long stroke.
Maybe apples and oranges but that is a long stroke.
An 1/8 of an inch longer stroke than my 4" stroked 340 that displaces 418 cubic inches. Now that's a big small block.
Every inch of displacement is another lbf·ft of torque
Good idea? IDK but I like it a lot.  :cooldancing: :aarg:

It's not a daily driver so not worried if it will go 100,000 miles...


Title: Re: Stroking... Is it good idea ?
Post by: 1 Wild R/T on May 06, 2017 - 12:18:43 pm
Stroking shouldn't be discussed on an open forum.....  :roflsmiley:
Title: Re: Stroking... Is it good idea ?
Post by: Beekeeper on May 06, 2017 - 02:03:19 pm
Stroking shouldn't be discussed on an open forum.....  :roflsmiley:

 :roflsmiley:

I agree with the earlier posts though that there is more stress on piston skirts as they go farther down in their bores and also that the piston speed is increased since it travels more distance with every revolution. Seems to me that the trade off with a longer stroke is less RPM potential.

As far as the six cylinders, not sure if their cylinders are a touch longer to provide additional piston skirt support but even if they are not, the stress placed on a six cylinder piston is dramatically less than a 450 HP stroked engine.

I can imagine that back when the 340 was designed, they may have considered things like:

1) keeping displacement at 340 versus 400 plus for some racing regulation or internal company policy on displacement limits.
2) maybe materials back then didn't hold up as well to the increased stressses of a high performance engine with a longer stroke. Materials are vastly better in strength and lightness today.
3) maybe they didn't want to outperform big blocks. They had big money tied up in the research and production of big blocks at the time. Who would pay extra for the heavier weaker big block motor?
4) maybe they were concerned about durability and longevity of the motors. Hurts business to sell motors that don't hold up as well as the competition
5) maybe they saw insurance issues on the horizon and wanted to find a balance between customer demand for performance and insurance crackdowns which hurt sales
6) probably more work and expense in producing a stroked version with beefed up components and they may have wanted to keep costs down so they could sell more. As awesome as the hemi was, almost no one could afford it so in a sense, it was over engeneered from a production/sales point of view.

Okay, now I can say I officially over analyzed the matter!
Title: Re: Stroking... Is it good idea ?
Post by: Chryco Psycho on May 07, 2017 - 01:15:28 pm
Unlike other makes Mopars has an advantage by using a much taller block & a very tall & heavy piston so you can build a stroker & still have more piston height & rod ratio than other engine do in stock configuration  still without a lot of the detriment of overly short pistons & side loading , the piston speed does increase though.
There is always a trade off with shorter life & increased wear but a Mopar stroker should out live a production engine with better ratios
 this is why I build 400 / 451 or 440 /512 combos even though you can do over 500 " in a 400 block & close to 600 " in a 440 block , when you go that big it takes the engine into a shorter life race motor rather than a strong long life street build
Title: Re: Stroking... Is it good idea ?
Post by: CUDA8U on May 12, 2017 - 12:00:32 am
 Correct if I'm wrong.If you were to have a goal of 600hp/tq and had 2 440 blocks,one stroked and the other not.The stroked engine can reach the goal much easier with less compression and a smaller cam.The non stroked engine would be very unstreetable with higher compression needing 93 or greater octane,low vacuum,higher spring pressures,large cam and more internal heat etc? The non stroked engine would need really low gearing,high stall and need to rev much higher ?
Title: Re: Stroking... Is it good idea ?
Post by: Chryco Psycho on May 13, 2017 - 03:56:17 pm
Basically true
More CI will make more power more easily & generally be more drivable at the same power level , the powerband on a stroker is generally lower as well depending on the parts used
Title: Re: Stroking... Is it good idea ?
Post by: jimynick on May 14, 2017 - 11:22:17 pm
Don't let us forget that the factory did, "stroke" their engines as well as boring them, towit the 273,318,340 and 360- all in the same exterior sized cylinder case. The wear factor is exacerbated with smaller rod/stroke ratios as CP mentioned and that's why the Chev 400 wasn't as successful as the 350s since it ran a 5.56" rod versus a 5.7 and that caused side loading of the piston and reduced engine length. A Chrysler runs a 6.123" rod so you're better right out of the gate. Higher piston speeds are an issue, but with todays honing methods and coated pistons, it can be reduced quite a bit. Proper fuel ratios are also a big part of longer engine life. Just my  :2cents:
Title: Re: Stroking... Is it good idea ?
Post by: 73cudabr on May 15, 2017 - 11:00:25 am
We also have the benefit of lighter parts today. Cranks rods and pistons are lighter and more durable. Keep the RPM/piston speed in check and it should live a long life. My stroker just came to life for the first time last night. So I'll report back in time as to the longevity.
Title: Re: Stroking... Is it good idea ?
Post by: CUDA8U on May 15, 2017 - 12:48:02 pm
 I just talked with a guy recently,he has had his 470/400 stroker for 12-15 yrs now and drives it a lot and many many runs down the 1/4 mile.He is selling it to build a 512 stroker.This 470 was obviously built with old components,todays parts are much better. 440source kits are pretty good from all the feed back but everything should be checked again anyway.

http://www.440source.com/strokerkits.htm (http://www.440source.com/strokerkits.htm)
Title: Re: Stroking... Is it good idea ?
Post by: Aussie Challenger on May 17, 2017 - 07:47:19 am
Don't let us forget that the factory did, "stroke" their engines as well as boring them, towit the 273,318,340 and 360- all in the same exterior sized cylinder case. The wear factor is exacerbated with smaller rod/stroke ratios as CP mentioned and that's why the Chev 400 wasn't as successful as the 350s since it ran a 5.56" rod versus a 5.7 and that caused side loading of the piston and reduced engine length. A Chrysler runs a 6.123" rod so you're better right out of the gate. Higher piston speeds are an issue, but with todays honing methods and coated pistons, it can be reduced quite a bit. Proper fuel ratios are also a big part of longer engine life. Just my  :2cents:
Don't forget that the SB Chev was a very weak casting compared to the MOPAR SB and the 400 SB Chev had heat issues when pushed.
MOPAR spent a lot of time developing their SB and as usual got it right.
Most manufacturers didn't want anything much bigger than the BB's they had already, it was really only the HOT ROD guy's wanting more displacement from a lighter and more compact package that saw stroking become more popular. Component manufacturers soon got on the band wagon producing what was needed.   :burnout:
Title: Re: Stroking... Is it good idea ?
Post by: V02Barracuda on May 22, 2017 - 09:12:05 pm
The original question was, Stroking - is it a good idea?  Here's the short answer.  If you're drag racing the car, then yes, it's a great idea.  If you're driving the car daily to work or for pleasure or to a show, then I would recommend not stroking it.  The piston speed isn't the thing that bothers me so much.  It's the fact that the piston isn't staying square in it's bore half way down.  Too much side loading was enough to turn me off.  That's my 2 cents.  Good luck.
Title: Re: Stroking... Is it good idea ?
Post by: 1 Wild R/T on May 23, 2017 - 01:19:23 am
The original question was, Stroking - is it a good idea?  Here's the short answer.  If you're drag racing the car, then yes, it's a great idea.  If you're driving the car daily to work or for pleasure or to a show, then I would recommend not stroking it.  The piston speed isn't the thing that bothers me so much.  It's the fact that the piston isn't staying square in it's bore half way down.  Too much side loading was enough to turn me off.  That's my 2 cents.  Good luck.


With the rod ratios in Mopar Strokers being better than the rod ratio Stock Stock motors from other manufacturers I'd say the side loading isn't much of an issue...  If you are really concerned perhaps a little reading will calm your fears..

http://www.enginebuildermag.com/2016/08/understanding-rod-ratios/ (http://www.enginebuildermag.com/2016/08/understanding-rod-ratios/)
Title: Re: Stroking... Is it good idea ?
Post by: xtopfuel on May 23, 2017 - 04:52:31 am
 :iagree:
engine builders magazine is an excellent magazine for real knowledge