M20 B3x Naturally Aspirated Stroker build past, present and future

[digger]

An important piece to the puzzle finished. I needed a custom intermediate shaft to clear the big 93.8mm crank as even with a nice aftermarket slim rod it fouls alot.

Most people know the intermediate shaft drives the oil pump, but it is also an idler shaft and as such carries the timing belt tension and loads to drive the valve train which are cantilevered off the end. This is the reason it is so large in comparison to the oil pump shaft. if you do some load calculations and stress analysis and estimate fatigue life you cant just hack into it and expect it to be trouble free

If you machine the stock ones down too much you can cut through the heat treat and end up with flimsy shitty cast iron of sorts so didn't want to risk it. Fortunately with the 89.6 mm shaft it needs minimal material removal so most don't encounter this. i did however get told by someone who lightened one to reduce rotating weight that it failed and that it is indeed hollow to get oil to the inner bearing.

Those with engineering back ground will know what a bending moment diagram is and be aware that bending stress is proportional to (D^3-d^3) and stiffness is (D^4-d^4). So if you have say an 18 mm shaft and neck it to say 14 mm the stress goes up x 2.12 and fatigue life reduces x 10.

Knowing this i also tried to minimize the amount of material removed so that I didn't make it too flexible which might cause the intermediate shaft bearings to crap out too soon. The reason they can crap out is as the shaft bends the edge of the bearing gets very high local pressures and improper lubrication and I’ve seen some blocks where the front bearing has deteriorated.

To address all this I got the shaft made from high tensile steel bar and had it heat treated, plus i designed it with very low stress concentrations in the areas I modified so i didn't introduce any issues.

Since i had no drawings to start with i had to do my own so onto designing one I destroyed a couple of old shafts to get the gear off to use on mine (press fit) and the oil gallery plug as well as measure some important parts like the oil gallery hole size etc

I measured every dimension in fine detail and then 3D modeled in CAD with full detailed drawings including dimensions, tolerances, surface finishing requirements and heat treat. Its heat treated because the journals , the oil seal surface and the press fit.

I got one 3D printed to check clearance before going to production.







did a test fit into the block i will be using and it glides nice and smooth

it may seem like a simple part but even being an Engineer i realised there is a lot more that goes into it than at first glance and i learnt a lot through the research i did in designing and understanding what specs to use etc.

[ForcedFirebird]

Personally, I prefer boosted assist.

Drove a car today, just around the parking lot with a Chase Bay booster delete kit. Lee's is far better IMO. Both have fairly hard pedals, and specially on high demand stops, it's for the birds. Lee's has instructions to re-drill the pedal for the brake clevis pin, which helps a lot. Need to tell this client to do that same.

To the defense of both situations, the car had a stock master. With a smaller master, there would be more pedal modulation, but perhaps I'm just a wuss and prefer assist. :/

[digger]

x3 of these in client cars...

http://www.massivebrakes.com/brake-systems.php?p=brake-booster-delete

If you purchased from Lee, he is a super stand up for support. Shoot him an email. He recently helped me set up an e30 with 300mm/298mm rotor weird brake system an owner brought in. Front are 6 pot and rear 4 pot and he was able to tell me within seconds my bias situation for the hydraulics to function predictably.

its one of those things that id like to try before i buy

[ForcedFirebird]

what sort of numbers did that make?

Hasn't been on the rollers yet. Showed up a couple times during tuning sessions, left both times before it was his turn to make pulls.

[digger]

Yes, I know where the build is going, and TQ is best for a street going car. :)

Your new engine will be a torque monster!

I had the pleasure of driving and tuning a 3.1l m20 built at e30 motorworks with ITB, 11:1, 282/284 dual patter cam (85mm/89.6mm). With 4:10 gears it can actually accelerate from a stop in 4th gear! Pulls like a diesel truck, but not exactly a revver.

what sort of numbers did that make?

[ForcedFirebird]

x3 of these in client cars...

http://www.massivebrakes.com/brake-systems.php?p=brake-booster-delete

If you purchased from Lee, he is a super stand up for support. Shoot him an email. He recently helped me set up an e30 with 300mm/298mm rotor weird brake system an owner brought in. Front are 6 pot and rear 4 pot and he was able to tell me within seconds my bias situation for the hydraulics to function predictably.

[digger]

which boosterless kit did you use? like below?

https://www.r3vlimited.com/board/showthread.php?t=368382

i have the wilwood calipers 1.5" pistons and 280mm discs on the front, standard rear so not standard setup but not exactly huge either.

im not after something touchy like a modern jap car but something that responds linearly with no oh shit moments

[ForcedFirebird]

Oh, and have done a couple massive booster delete's. Definitely change the pedal ratio, you will need the leverage. The pedal will be rock hard, and with standard pads is an unhappy experience. Going to use the smaller master as Lee suggested to bring pedal modulation back, but in all honesty, any brake assist is better than none. The 2002tii booster is tiny and has almost as much vacuum surface area as the stock e30 booster, but is expensive for what it is. There are so many hot-rod aftermarket variations that are cheap and reliable (domestic US), but the master bolt pattern is way off of anything German.

[ForcedFirebird]

Yes, I know where the build is going, and TQ is best for a street going car. :)

Your new engine will be a torque monster!

I had the pleasure of driving and tuning a 3.1l m20 built at e30 motorworks with ITB, 11:1, 282/284 dual patter cam (85mm/89.6mm). With 4:10 gears it can actually accelerate from a stop in 4th gear! Pulls like a diesel truck, but not exactly a revver.

[digger]

Not volume I was targeting with the TDC comment as much as it was about piston speed at/near dwell and it's effects on event timing.

Sometimes I wonder if the chase for displacement isn't being misdirected in an m20. 84mm stroke and 145mm rods put it in a sweet spot. Add 85mm bore and you still have a ~2.9l with softer skirt loads, piston pin stays in the bottom, no worries about the dummy shaft, and a side benefit of 1.7:1 R/S ratio.

Granted, it gives up initial TQ lower in RPM, but everything is a give and take.

Can't wait to see how it all works out. Carry on mate.

its the same its not about the short rod ratio its the longer stroke driving the those negative things, even with a really long rod youd still get all the same issues they might be a percent of two better but they dont go away.

i can understand people not wanting to do a stroker, if you are chasing power you are limited by the head so it makes little sense maximizing the stroke which would just make it peak at lower rpm and less use able rpm. With a good head though you will end up turning alot of rpm with 84mm stoke which is harder on parts.

i actually think on a standard head the higher piston speed of the stroker and the relatively small choke size is an issue and it makes it go "turbulent" too soon so much so that you end with something that isn't as effective as it should be. A stock to mild head matches a 2.8L engine size better i agree

this build is about maximizing the torque 2500-6500 rpm so with the head i have the more stroke the better

i'd actually like to a booster delete with the massive kit and run a airbox with 3-4" longer runners to maximize the mid range but im a bit too scared to go booster less on the street

[ForcedFirebird]

Not volume I was targeting with the TDC comment as much as it was about piston speed at/near dwell and it's effects on event timing.

Sometimes I wonder if the chase for displacement isn't being misdirected in an m20. 84mm stroke and 145mm rods put it in a sweet spot. Add 85mm bore and you still have a ~2.9l with softer skirt loads, piston pin stays in the bottom, no worries about the dummy shaft, and a side benefit of 1.7:1 R/S ratio.

Granted, it gives up initial TQ lower in RPM, but everything is a give and take.

Can't wait to see how it all works out. Carry on mate.

[digger]

You mean wide as in the cap bolt area has less intermediate shaft interference?

The bigger problem I see in the m20 and huge strokes is the deck/compression height. Once you start getting over 84mm stroke, the rod/stroke ratio goes to crap. Your piston TDC dwell gets very short and you have to add a lot of advance, and the error margin goes way up for tuning. Then because of the short deck height, you start running into piston pin/ring interference (why BMW decreased pins on the s54).

Yes, the width at the part line or just a bit closer to the shoulder is the critical width. Typically it’s about 76 mm +/- on most rods.

The differences between dwell at TDC are actually miniscule as a function of rod ratio.

For example the difference in piston position is a follows 89.6 mm stroke 135 mm vs 145 mm rod (1.506 RR vs 1.618 RR)

Crank Angle/135rod/145rod/delta position/delta volume (cc)
5* -0.227 mm / -0.225 mm / 0.002 mm / 0.0 1cc
10* -0.905 mm / -0.889 mm / 0.016 mm / 0.09 cc
15* -2.025 mm / -1.991 mm / 0.034 mm / 0.20 cc
20* -3.574 mm / -3.514 mm / 0.060 mm / 0.35 cc
25* -5.532 mm / -5.439 mm / 0.093 mm / 0.54 cc

Now consider how much the engine expands with temperature cold vs hot and part lengthen with load (rpm) 2000 rpm vs 7000 rpm this is much more important as it will have 10x the effect on the volume at or around TDC than the rod ratio.

the stroke changes volume much more, people confuse the effect of RR and the stroke. a stroker has different characteristics and they almost always inherently have much worse rod ratios. the rod ratio is a second order effect. you never need to worry about on a street engine

If you crunch numbers on the MM 3200 rally engine with 138 mm rod, the compression height they use is under 24 mm. With a 135 mm rod 20 mm pin modern 1.0/1.2 mm top and 2nd ring this gives more freedom with stroke.

You could use a thicker MLS (or deck plate i guess) and have the piston come out even more to either use longer rod or more compression height.

You do start to pull the piston down the bore so at BDC the gudgeon pin gets ever closer to the being pulled out of the cylinder but it’s similar to the 84 mm stroke 130 mm rod which has the pin centre 17.1mm from the bottom of the bore.

you also start to put more side loads on the skirt, so it wont last as long as a stock engine but will still last many 1000's of miles. there are stoker kits running 98 stroke 139 mm rod on the S54. there are also production engines running under 1.5 RR

With the short compression height and skirt you’ll want to use a tight piston to bore clearance to reduce piston rock when cold/warmup. these days there are even abrade-able piston coatings e.g. line to line slick CC

there are mitigating strategies that could be used to go over 93.8mm stroke from a compression height /limited deck height point of view, but the part that would concern me the most is the shaft, a premature bearing failure because the shaft loaded one edge of the bearing excessively would be a potentially catastrophic failure the others wouldn't. its not a bearing material capable of high load

[digger]

i know someone who lightened the actual shaft and it broke in half but that was on the stock cast iron one that when you machine it way down you lose all the case hardening.

[ForcedFirebird]

the only solution i see for something bigger stroke than 93.8mm is a smaller crankpin and rod. as it stands many aftermarket rods are too wide even for the 93.8mm

You mean wide as in the cap bolt area has less intermediate shaft interference?

The bigger problem I see in the m20 and huge strokes is the deck/compression height. Once you start getting over 84mm stroke, the rod/stroke ratio goes to crap. Your piston TDC dwell gets very short, so you have to add a lot of advance, and the error margin goes small window for ignition tuning. Also because of the short deck height, you start running into piston pin/ring interference (why BMW decreased pin diameter on the s54).

[ForcedFirebird]

There's no reciprocating load on the intermediate shaft, so stiffness is a FAR less important concern than it is for a crankshaft.

I have seen multiple intermediate gears shatter, even on stock engines (one turbo). This is why the gears were upgraded to sintered vs stamped steel.

The timing belt setup on an m20 takes more back lashing that people think. There's no live spring tension on the belt. Tension from the tensioner spring only sets initial tension, once the belt starts stretching, the spring is invalid.