CR for M52 crank, 130mm rods, and SETA pistons????

[Overlord475]

Hey guys,

I'd like to know how to calculate different CR's.

Looking to do a mild budget stroker with the intentions of going FI someday.

Looking at

M52 crank
130mm ETA rods
84.5mm MaxSil SETA replica pistons

Should give a displacement of 2827.56cc and should put out about 189HP at the crank if I'm calculating things right.

Maxsil states that their pistons would maintain the 8.5:1 CR that a SETA normally has, but with the added 3mm stroke of the M52 crank I know the CR will be higher because of the larger displacement.

Thanks for the help guys.

[whodwho]

Won't work, you need to use b25i pistons and should be short skirt ones and there maybe some triming of the crank throws to clear the skirts.

and this is a good place to play with CR

http://www.zealautowerks.com/index.html?setup=6,m84.00,m206.0,m84.00,40.00,-22.00,m26.6,m140.00,m1.75,m0.000,7000,0,0

[digger]

Hey guys,

I'd like to know how to calculate different CR's.

Looking to do a mild budget stroker with the intentions of going FI someday.

Looking at

M52 crank
130mm ETA rods
84.5mm MaxSil SETA replica pistons

Should give a displacement of 2827.56cc and should put out about 189HP at the crank if I'm calculating things right.

Maxsil states that their pistons would maintain the 8.5:1 CR that a SETA normally has, but with the added 3mm stroke of the M52 crank I know the CR will be higher because of the larger displacement.

Thanks for the help guys.

i got theoretical value of 10.2:1


CR goes up because the combustion chamber volume reduces because piston sits 1.5mm higher and engine swept capacity is now 2.826L.

This is only theoretical getting it to work may not be physically possible.

[whodwho]

In the interest of gaining as much compression as possible or maintaining the best quench space you could trim the pistons or adjust with a thicker head gasket to make it work but with your FI statement it doesn't look like that is the goal.

If you are willing to go with new pistons for not much more you should consider going with some forged ones(obviously better for FI) and able to run longer rods for a more optimal rod ratio.

[Overlord475]

In the interest of gaining as much compression as possible or maintaining the best quench space you could trim the pistons or adjust with a thicker head gasket to make it work but with your FI statement it doesn't look like that is the goal.

If you are willing to go with new pistons for not much more you should consider going with some forged ones(obviously better for FI) and able to run longer rods for a more optimal rod ratio.

I am back and forth on whither to put all of my money and effort into a stroker or to do a ETA cranks, rods, SETA piston budget stroker and go FI.

I have the option of buying an S50 crank and matching 135mm Rods locally for a good price. If I go this route I would leave my FI ideas behind and go for a higher CR.

Were I live the highest octane pump gas is only 91. So I will be unable to too high.

If I go with this S50 crank and rod combo and bore out to 86mm what specs would I be looking for on the custom forged pistons you referred to above?

Top design (Flat, Dome, Concave)
Diameter (85.98mm???)
Skirt Length
Pin Position
**** Stoke stroke is 75mm with 135mm rods, new stroke of 85.6mm
**** with 135mm S50 rods. This seems to put the new pin position
**** 10.6mm higher than a stock "is" piston???? Seems crazy

I am using the M20B25 block so my deck height is 206.7mm

I've never bought custom pistons before so just looking for experienced advice.

Thanks again!

[whodwho]

I think you need to decide if you want to go FI or not, it really plays a big role on building a engine.

I like the idea of keeping the stock piston crown shape for either but would probably be less critical in a FI application. There should be some piston spec cards floating about, I have a few saved off and will take a look if any look close. You can/should work with the piston supplier to work out the specs as well.

The decision on cam specs will also matter if going FI or not.

[Overlord475]

I think you need to decide if you want to go FI or not, it really plays a big role on building a engine.....

I think I'm going all stroker. I won't have enough money for both.

That being said.... advice on crank, rods, and pistons combos would be appreciated.

At this point I'm so early into this that I can go what ever crank, rod, piston combo I'd like. I already have my rebuild engine ready to go (just needs to be broken down)

I was thinking of talking to IE for pistons design advice? Any other good M20 custom piston providers out there? Ones that are familiar with the M20 stroker family?

[whodwho]

The next decision is budget, you can with a M52 crank e rods and stock b25 pistons for a budget stroker or go with custom pistons (~ $900-1200) and that leaves you lots of options for crank and rod combos. I think JE might be the only one making one with the stock crown shape.

I think speaking with MM would be more productive then IE. ;)

[Overlord475]

The next decision is budget, you can with a M52 crank e rods and stock b25 pistons for a budget stroker or go with custom pistons (~ $900-1200) and that leaves you lots of options for crank and rod combos. I think JE might be the only one making one with the stock crown shape.

I think speaking with MM would be more productive then IE. ;)

So.... if I used the MaxSil 84.5mm b25 pistons with the M52 cranks and ETA rods what kind of CR would I be looking at? I know that with the stock 84mm b25 pistons compression is in the 9.7:1 range. how much would the extra 0.5 bore add????

Also, wont this (crank / rod / piston) combo place the pistons 4mm higher than stock???

Stock: 75mm stroke w/ 135mm rods = 210mm

M52 Combo: 84mm stroke w/ 130mm rods = 214mm

Will this cause (piston / valve) interference??? Will the pistons be above the block deck height?

Thanks!


O... and my budget is in the $3000 range

[digger]

So.... if I used the MaxSil 84.5mm b25 pistons with the M52 cranks and ETA rods what kind of CR would I be looking at? I know that with the stock 84mm b25 pistons compression is in the 9.7:1 range. how much would the extra 0.5 bore add????

Also, wont this (crank / rod / piston) combo place the pistons 4mm higher than stock???

Stock: 75mm stroke w/ 135mm rods = 210mm

M52 Combo: 84mm stroke w/ 130mm rods = 214mm

Will this cause (piston / valve) interference??? Will the pistons be above the block deck height?

Thanks!


O... and my budget is in the $3000 range

The throw (half stroke) on the M52 crank is only 4.5mm more (half of the stroke differences) while the rod is 5mm shorter so it sits 0.5mm lower not 4mm higher. You can easily skim that off and use an adjustable cam gear. This gives 9.7:1 (9.3:1 if not skimmed) assuming stock B25 pistons.

If you used 84.5mm pistons in stock shape it raise CR only by 0.1 not worth extra expense if you have stock pistons already.

Getting a set of euro B25 slugs yields 10.7:1 which would go nicely with schrick 284/272

For 3k M52 crank is best option I doubt you could get custom pistons and all the rest of the bits and pieces that are needed.

[Overlord475]

Thanks for the info! I’m definitely learning as I go along.

Are you referring to skimming the extra 0.5mm from the top of the block? With this extra 0.5mm removed from the block what degree offset would the adjustable cam gear need to be set to for correct timing?

The reason I am going with 84.5mm pistons is because I am thinking about buying a new set of MaxSil pistons from Bavauto. They only come in 0.5mm overbore, and are $500 shipped. Plus with the 84.5mm MaxSil pistons it gets me to a true 2.8L at 2827.57cc as apposed to 2794.2cc with the stock 84mm pistons. That, and I’m not sure that a set of Euro b25 pistons are easily found here in the States.

So far I’ve found really good deals on all my parts. I picked up my M20 locally for $150 and just bought a VERY clean M52 crank for $180 shipped. This will be a slow going build and I’ll only buy parts as I find good deals. I’m going to build the block first.

Thanks again!

[digger]

if you are going to spend $500 on pistons i would qet a quote from JE and see how much more they are. Then you could get a bigger crank

yes, takeing 0.5mm from top of block lets the piston sit at the original position at TDC in theory. I am not sure how much cam gear needs to be adjusted, if it is small then you might not need a cam gear at all which would save some money and you could put towards the JE pistons. If you get a hot cam it is a good idea to use an adjustable cam gear but not essential.

[MonkeyMadness]

The throw (half stroke) on the M52 crank is only 4.5mm more (half of the stroke differences) while the rod is 5mm shorter so it sits 0.5mm lower not 4mm higher. You can easily skim that off and use an adjustable cam gear. This gives 9.7:1 (9.3:1 if not skimmed) assuming stock B25 pistons.

wooo....
wait what? Ok i get the math of the m52 crank + eta 130 rods, and stock
"I" pistons leave the pistons at .5mm lower at tdc. yelds a 9.3:1cr????
is this true?
This would be great for a FI setup.... ;)
2.8 on boost.... :nice: