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Old 01-05-2017, 04:08 AM   #1
AntParker
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M20 2.8 Stroker Build Proposal.

Hi Guys.

I’m new to the site, but have been doing some homework with regards to M20 stroker builds, I think this Forum looks very good and is full of knowledge.

I have an E30 Track car, pretty well sorted as far as handling is concerned, I built an M20 last year with a basic ish spec. (more of a fast road engine than a track engine) engine is good and strong Dyno’d to good numbers.

However the quest for more power continues. I am now going to build a 2.8 stroker. And plan on the following spec.

In an Ideal world we would be making somewhere between 230 and 240bhp, but appreciate that numbers aren’t everything and I’m encouraged by the torque of the 2.8.

Current Planned spec is the following:

• M25b25 block
• M50/M52 crank
• M20B20 Standard rods (balanced and with ARP bolts)
• M20 325i Stock pistons.
• 288 Kent Cam kit (will include valve springs, followers etc)
• Cam Vernier
• Aftermarket management (Currently running Canems ECU)
• Upgraded injectors (Currently running either 190 or 210cc, but was planning to go bigger if required)
• Individual throttle Bodies.
• Obviously engine will be thoroughly cleaned, De-Coked, new shells fitted, oil pump etc.

Yet to start stripping the new donor engine but already have a couple of questions:

Does the above setup sound sensible?

I believe the block will need decking with this setup.(probably look around 10.5:1 comp) And possible machining to piston skirt for clearance, the spacer is also needed for the front of the crank. Is there any other machining required?

What sort of power can we go to with standard m20b20 rods?

Is the head going to be a major restricting factor if maintaining standard size valves?

Look forward to hearing your responses.

Thanks Guys.

Last edited by AntParker; 01-05-2017 at 04:55 AM.
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Old 01-05-2017, 09:41 AM   #2
SkiFree
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Welcome Parker


Does the above setup sound sensible?


It looks like a pretty decent setup. Is this a bit of a budget build? If you are racing and looking for durability along with torque, I don't think reducing potential rod length from 135mm to 130mm and running re-purposed oem pistons is in line with your plans. Additionally, you will end up needing to cut some pretty deep valve pockets in those oem pistons if you plan on running a 288 cam while shooting for 10.5:1 comp.


I believe the block will need decking with this setup.(probably look around 10.5:1 comp) And possible machining to piston skirt for clearance, the spacer is also needed for the front of the crank. Is there any other machining required?

Again, if racing and durability are the guiding factors of your build then you will not need to do any block decking or piston machining if you utilize custom forged pistons. Regardless, you will need to chamfer the bottom of the bores a tad, along with some clearencing around the intermediate shaft.

If you manage to find one of those smaller-counterweight 84mm cranks that Digger references in the other recent stroker thread, I would love to get the identifying casting number and actual counter-weight dimensions.


Is the head going to be a major restricting factor if maintaining standard size valves?

Assuming you are running an 885 head, then it will not be the major restricting factor. Your restricting factors right now are rod length and piston choice.

As digger reminded me recently, I understand not every build is on an "unlimited budget". However, it appears like you are racing and opting for some pretty decent hardware. In the overall scheme, budgeting for proper pistons (and a set of reconditioned M52/S52 135mm rods) would return dividends when it comes to the torque and power band (not to mention engine life).


----------------------
Hope that helps, sounds like you have a pretty fun car there.

-Andrew
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Last edited by SkiFree; 01-05-2017 at 10:36 AM.
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Old 01-05-2017, 03:35 PM   #3
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if you choose to do the OEM slugs instead of the Mahle MS ones from IE for a 2.8L then choose the 9.7:1 pistons.

in either case of OEM cast or forged set piston to head clearance to 0.9-1.0mm for better compression and combustion dynamics. the OEM pistons require 0.5mm nominally off the block (for status quo) but to set clearance closer to optimal it might require more removal than this depending which gasket you choose and thickness of head and block deck height

despite 9.7:1 having deeper pockets than the 8.8:1 slugs the 288 still probably wont clear so you'll need to deepen them by about 1.0-1.5mm (there is alot of meat to do this). i would look for a schrick 288 as it looks to have more lift

Which ever pistons you choose you should easily make your 240bhp goal provided you get the RHD itb kit. Another member on here with similar build using the lower compression oem Pistons did it quite comfortably with a much smaller 272 cam and headwork. A properly fettled cylinder head is never a bad thing, the number 1 restriction is always the inlet valve.
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Old 01-05-2017, 03:49 PM   #4
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Injectors will be too small. We ran out of injector @5k RPM with 200cc, and were at 80-ish % duty with 250cc with the following engine we did for a client not long ago...

Made 217whp/202tq using a 272 cam and stock pistons, 130mm rods and OEM +.5mm over pistons. With a 288 cam and a bit more compression, you will do better with your setup - probably closer to 240whp/230tq to make a guess based on the dyno curve we got. We took .010" off the block (.4mm) and .004" (.1mm) off the head to give a final clearance of .045" head-to-pistons clearance. With the 272 it gave us a .057" intake and .075" exhaust valve-to-piston clearance. Of course your numbers may vary, but these can give you a guide to get you close.
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Old 01-05-2017, 11:55 PM   #5
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Yeah it will make a lot more power from 6000rpm onwards. Some 1d sims I've done show an extra 8-10ftlb and 30bhp with a almost 1point CR increase and added duration. The RHD intake as so much more potential that what stock engine can utilise, stroke, compression and cam make it shine
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Old 01-06-2017, 03:37 AM   #6
AntParker
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Thanks for the extensive replies guys, lots to take in there!

This is a budget build in that I donít want to spend tonnes of money, but then again who does!! Willing to spend money in the right places to get a good strong reliable engine.

With regards changing the rod length to 135mm from the m52 engine, would this not lead to me needing a different crank as well? I have already purchased an M52 Crank, not sure if itís a small or large counterweight crank, would need to reference some pictures and figure it out!

The head I have should be an 885, but again will need to double check this to be sure.

So essentially the main Census of opinion is that we should go for non stock pistons, and possibly 135mm rods from the later engine?

Looking online, the Shrick 288 is available, will check the specs of this vs the Kent, and make a decision. The shrick is a lot more expensive and does not mention upgraded followers etc. are std springs suitable for these cams I notice they sell a spring kit, I assume these are upgraded for the harsher cam. Havenít looked properly myself yet and this is a kind of hasty reply Iím afraid!

Is Ireland Engineering the only option for custom forged pistons? Do we think they will give us a huge advantage over the OEM Pistons, I notice you spec a compression, so I guess this would avoid the need to deck the block.
Is 10.5:1 too high compression for these engines, will we run into issues with headgaskets etc?

Many Thanks
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Old 01-06-2017, 11:34 AM   #7
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Quote:
Originally Posted by digger View Post
Yeah it will make a lot more power from 6000rpm onwards. Some 1d sims I've done show an extra 8-10ftlb and 30bhp with a almost 1point CR increase and added duration. The RHD intake as so much more potential that what stock engine can utilise, stroke, compression and cam make it shine
Yeah, should have over-cammed it in the beginning, but he was at first pretty intent on keeping it a 2.5l. I was actually surprised when he called to bring it back in.

Quote:
Originally Posted by AntParker View Post
Thanks for the extensive replies guys, lots to take in there!

This is a budget build in that I donít want to spend tonnes of money, but then again who does!! Willing to spend money in the right places to get a good strong reliable engine.

With regards changing the rod length to 135mm from the m52 engine, would this not lead to me needing a different crank as well? I have already purchased an M52 Crank, not sure if itís a small or large counterweight crank, would need to reference some pictures and figure it out!

The head I have should be an 885, but again will need to double check this to be sure.

So essentially the main Census of opinion is that we should go for non stock pistons, and possibly 135mm rods from the later engine?

Looking online, the Shrick 288 is available, will check the specs of this vs the Kent, and make a decision. The shrick is a lot more expensive and does not mention upgraded followers etc. are std springs suitable for these cams I notice they sell a spring kit, I assume these are upgraded for the harsher cam. Havenít looked properly myself yet and this is a kind of hasty reply Iím afraid!

Is Ireland Engineering the only option for custom forged pistons? Do we think they will give us a huge advantage over the OEM Pistons, I notice you spec a compression, so I guess this would avoid the need to deck the block.
Is 10.5:1 too high compression for these engines, will we run into issues with headgaskets etc?

Many Thanks
10.5 should be fine on premium gas and 288 cam. The longer rods tend to make an engine last a little longer due to piston side load. If you use longer rods, you just can't use stock pistons, the pin height would just need to be higher (ie you can still use that crank).

There are a lot of pistons available, just make sure you get them with the factory domes on top, or you will not have a squish band.
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Old 01-06-2017, 01:26 PM   #8
digger
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Quote:
Originally Posted by AntParker View Post
Thanks for the extensive replies guys, lots to take in there!

This is a budget build in that I donít want to spend tonnes of money, but then again who does!! Willing to spend money in the right places to get a good strong reliable engine.

With regards changing the rod length to 135mm from the m52 engine, would this not lead to me needing a different crank as well? I have already purchased an M52 Crank, not sure if itís a small or large counterweight crank, would need to reference some pictures and figure it out!

The head I have should be an 885, but again will need to double check this to be sure.

So essentially the main Census of opinion is that we should go for non stock pistons, and possibly 135mm rods from the later engine?

Looking online, the Shrick 288 is available, will check the specs of this vs the Kent, and make a decision. The shrick is a lot more expensive and does not mention upgraded followers etc. are std springs suitable for these cams I notice they sell a spring kit, I assume these are upgraded for the harsher cam. Havenít looked properly myself yet and this is a kind of hasty reply Iím afraid!

Is Ireland Engineering the only option for custom forged pistons? Do we think they will give us a huge advantage over the OEM Pistons, I notice you spec a compression, so I guess this would avoid the need to deck the block.
Is 10.5:1 too high compression for these engines, will we run into issues with headgaskets etc?

Many Thanks
I wouldn't sweat too much if you end up using oem pistons it's a reasonable enough compromise . As forcedfirebird said others can do Pistons to but for something equivalent it's not going to be any cheaper nor will they be any better. The mahle ms Pistons are a step in the right direction in many areas.

With the 288 I'd probably use the schrick springs or something from eibach it might be too much cam for stock valve springs. The schrick has higher lift (on paper) and they have very good reputation. In my experience you get what you pay for with them so that's why I recommend them.
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Old 01-11-2017, 01:49 AM   #9
AntParker
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Hi Guys,

sorry for the slow reply- been flat out busy around here for the last few days.

Thanks for the replies. Looks like i will be aiming for the 10.5:1 compression then, maybe a little higher.

I guess the important thing is if we want to use the 135mm rods, we need the forged pistons, if not we can use a 'factory piston' of these i guess the mhale are the best bet?

Decision time on pistons then i guess... i will probably wait until its time to purchase before making the decision. if we are replacing with new 'OEM' pistons anyway then the cost difference isn't too significant, but if i can use those already in my engine, there is a significant cost save.

Will also look for where i can purchase a shrick and springs here in the UK.

On the subject of top end, where are the limitations of standard valve sizes. should a well ported head with standard valves flow enough for the sort of power i am talking about here?

Many thanks

Ant
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Old 01-11-2017, 02:23 AM   #10
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For OEM Pistons Do KolbenSmidt also make early 9.7:1 Pistons? Idk but mahle certainly did. Either will be fine though. If you find good set of Pistons and block then you're good to go.
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Old 01-11-2017, 03:28 AM   #11
AntParker
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thanks digger.

another quick question, I may be able to get my hands on an e34 tds crank, would this be better than the m50/52 crank i already have??
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Old 01-11-2017, 12:26 PM   #12
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thanks digger.

another quick question, I may be able to get my hands on an e34 tds crank, would this be better than the m50/52 crank i already have??
from a clearance point of view i dont know, youd have to measure it.
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Old 02-15-2017, 02:10 AM   #13
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Hi guys,

Sorry to go digging up this thread again.
Have started to collect up some more parts now, have also got hold of a set of S50 con rods- so will be placing an order for some IE Forged pistons soon.

Am definitely planning to use the shrick 288 cam now. I plan to upgrade the springs to suit, additionally, is it worth upgrading the rocker arms at the same time, I notice there are some available on the market, are they really necessary, or is it a bit of a novelty?

Finally, do you guys have any recommendations on headgaskets please, seeming we will be going with custom pistons we will probably go oversize on the bore (86mm) at the same time to get maximum displacement.

At the same time, what is the general opinion of you guys with lots of experience on 85mm bore against 86mm bore, the total displacement difference is small, but does the change in bore/stroke ratio have a dramatic effect on the power delivery of the engine? Just interested to hear thoughts before I go ahead.

Many Thanks
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Old 02-15-2017, 12:49 PM   #14
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I’ve had good experiences with MM peened and inspected rockers with an aggressive camshaft and stiffer valve springs over the last decade.

Others prefer the HD rocker approach but while they have improved meat in areas, the quality seems to be slightly lower plus the ones ive seen seem to have different pad geometry and id want to make sure its truly compatible with an aggressive cam as ive seen cases where they arent. 288 is likely ok but ive not checked contact interfaces to confirm.

Difference between 85 and 86 bore is not much, a couple % or so, if you want to use an OEM gasket then 85mm is the better bore as most 86mm pistons won’t permit OEM gasket and those that do compromise. That’s the only real downside in a NA engine as there is plenty of meat in the block.
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Old 02-15-2017, 05:51 PM   #15
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I agree with digger. Don't sweat the bore/stroke ratio as rod/stroke ratio is more important and you have maximized that with the 135mm rods. You really can't go much longer on the rods without putting the wrist pins in interference with the rings (didn't read back, but think that was discussed here). If you are willing to deal with a custom gasket and want to squeeze every ounce of displacement, go for it, but it's honestly not necessary.
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