Engine stroaking

MMamdouh · Post by **MMamdouh** » Thu Jun 23, 2005 4:34 pm

i came accross this subject twice in this forum on different posts and i wanted to make sure i fully understand the concep... i thought i tell you what i understood and you can corret me if i am wrong.

engine stroaking is a way to increase engine's capacity by replacing the crank shaft and connecting rods without messing with the stock cyl. bore.

the new crank shaft got bigger travel (would make the piston go to a higher TDC and lower BDC) and accordingly the lower TDC will increase the engie's capacity while the higher TDC will increase compression.

in this case the compression increase is too much so you change the connecting rods to shorter ones, this will make the BDC even more lower and increase the capacity more but it will lower the TDC too and lower the compression.

the typical case is boring the 1.3 engine by using the 1.5 crank shaft and rods so practically you are making your engine bigger by replacing few little parts.

this is what i understood about stroaking... so am i right or waht? did i miss anything?

also can you just swap the connecting rods to increase capacity?? i guess you can but you will sacrifice compression ratio... right? it is just like swapping just the crank shaft... the copression will be too big that the performance will suffer due to detonation and all.

maybe the shorter rods are good idea for turboed cars rather than using thick gaskets to lower compression... i mean shorter rods got less tendancy to break... right??

fell free to correct me if i am wrong and explain more if i missed out something here.

MMamdouh

Post by **PrecisionBoost** » Thu Jun 23, 2005 6:59 pm

Your on the right track.... but there are a few things that I should elaborate on.

First off.... yes.... using a crankshaft with a longer stroke will increase capacity.

In order to do this you need to shorten the connecting rods by 1/2 of the increased stroke length.

So if your stroke goes from 86mm to 94.5mm the crankshaft will push the stock rod/piston higher by 4.244mm ( half the difference in stroke)

In order to compensate you need to reduce the length of the connecting rod/piston by 4.244mm

There are two ways to do this....

1) Find a connecting rod that meets the new specifications or have a set custom made for your engine
2) Find a piston with a smaller compression height..... which is the height from the center of the pin to the top of the piston.

If you however wish to decrease the compression a little you might want to get a piston or rod that is a little shorter.

I would not suggest increasing the rod or piston length.... you have to take into consideration the fact that adding length will make the piston hit the cylinder head.

In most cases the top of the piston comes very close to the cylinder head so even a couple of mm might be enough to create interference.

Even if you did manage to move it up slightly without hitting the cylinder head you would have the problem of clearance with the valvetrain.

With the amount of extra material you would need to remove from the piston to clear the valves you probably would not gain all that much compression.

There are a number of other technical details involved with a stroker kit.... you could end up with a bad rod angle/rod ratio or you might see interference on the lower part of the cylinder.

Each stroker kit needs to be planned out carefully if your trying to put a larger crankshaft into a block that does not normally have a larger stroke version.

For example.... it would be very easy to stroke the 1.8L to 2.0L because they use the same block.... so you would simply purchase the 2.0L crankshaft, connecting rods and possibly the pistons.

The 2.0L to 2.2L conversion is tricky because they don't share the same block.... the 2.2L might fit into the 2.0L block but there might be problems with clearance on the bottom end.

So the biggest factor in how easy it is to stroke an engine is whether there are interchangeable crankshafts for the block you are looking to stroke.

tango · Post by **tango** » Thu Jun 23, 2005 10:18 pm

^^^^^ What he said ^^^^^

daewooluvr · Post by **daewooluvr** » Thu Jun 23, 2005 11:12 pm

Stroke It!

Stroke it to the east, stroke it to the west, stroke it to the gurl that I like best...

STROKE IT!!

MMamdouh · Post by **MMamdouh** » Thu Jun 23, 2005 11:47 pm

very very informative stuff Erfinder... thank you very much, normally i would rais my hat for you but i won't 'cause if i did you will know that i am bald.

one more thing... what is meant by clearance on the bottom end??

again thanks very much for the info.

MMamdouh

Audacity Racing · Post by **Audacity Racing** » Fri Jun 24, 2005 2:21 am

if the stroke is increased, the potential occurs for the con rod to strike the cylinder wall (when travelling to bdc). when the crank is in a position so that the piston is exactly between tdc and bdc, the connecting rod is at it's furthest lateral point (at 9 o'clock or 3 o'clock). this can cause the con rod to strike the block (if the distance that the con rod travels from the center is greater than the distance from the center of the crank to the lowest point on the piston sleeve). see the drawings for a better idea...

Post by **PrecisionBoost** » Fri Jun 24, 2005 4:14 am

Cool picture.... that's a perfect description.

Some people will actually get in there and modify the bottom of the cylinders to create clearance but you have to be very carefull that you don't cut into the waterjacket (where the coolant is located)

I also forgot to mention the method of stroking that I was planning to use.

Basicly I'm going to make a plate that will extend the cylinder length to accomidate for the larger stroke.

To go to a 2.4L I really don't have to add much but I want to make the connecting rods longer to get a particular ratio of rod length vs bore ( rod angle)

In an iron block engine this isn't all that easy because you have to ensure that the cylinders are absolutely flawless.

In an aluminum engine where there are sleeves it's not a big deal..... you just get longer sleeves and add an aluminum or steel deck on top of the old one.

I am planning on extending the deck ( top of the block ) by a significant amount ( about 1" ) but I'm going to be boring out my cylinders and installing some specially designed sleeves that are for drag racing engines.

So my engine will end up being similar to an aluminum engine with sleeves except my iron block will be significantly stiffer and give more support to the Centrifugal cast sleeves I'm putting in.

Audacity Racing · Post by **Audacity Racing** » Fri Jun 24, 2005 4:17 am

i'm willing to make the 3d solid models for your engine for analysis for 50 bucks

. i'll even run the fea on it (analysis) to tell you what all ya need

those drawings are a 3d solid model of my rc subaru motor that i just sliced and pulled all the exhaust off of for visual effect