Stock, stroker or ghetto capacity increase? ( supra 7m gte pistons bmw rods )

[Error404]

OK I've had a read now
If you are starting from scratch, it seems like a good option, IF you can get the bits as cheap as you can in Eastern Europe.
My gut feel is that it will cost a lot more in the UK, everything is Quality machining is not cheap either, so definitely needs some reasearch. If you consider that your bench mark is £850 - £900 for a set of H-beam rods and a set of oversize Wossners

[Rusty]

True but it's good fun investigating

Stock Supra pistons don't seem to be that brilliant and forged ones are hardly bargaining but it's fun making a spreadsheet!

[Rusty]

144mm rods with 22mm little ends make a lot of sense to save machining costs.

[Rusty]

Can you get OE rod little ends reamed to 22mm? Or is it new little end bearing time?

[Rusty]

I've undated the sheet and fixed a calculation error that occured when changing the stroke. I've added in calcs for the 144mm FCP rods, 145mm BMW rods and then 140mm BMW rods when used with an eccentrically ground crank.

[ADP]

what about if i use 95,5mm diesel krank with 155 mm conrods and stock pistons!?

[VilkkuS]

I have/had "supra/bmw/AUDI" setup with:
NG block bored 82,5 -> 83mm
NPR pistons (Supra 7MGTE) STD 83mm
BMW rods 140mm / 22mm
The srtoke was 95,5mm
Crankshaft was machined for those 48mm (Big end diameter) rods, orig rods = 50,9mm

Engine was builded in Estonia last year. (if the stories were right, and i believe it, after seeing the pistons etc.)
I did drive with this car only this summer, and it was breathing heavily all the time.

Just opened the block and realised the problem...
Those BMW rods are 21,9mm wide and stock rods are 24,9mm
So, theres 3mm space to rods move sideways

Pistons might last, but not with those specs rods (not a long time at least)
Power was quite good and i was driving just 1.5-1.6bar KKK K27/K26
Example: TOP SPEED ON MILE, WAS 270KM/H

But I do not recommend this setup to anyone, because of those rods vs crackshaft wide diferencies. IF there's BMW rods with 23,9mm wide, i would be happy to build this again with those!

[rst]

What will happen if the rods are 3mm narrower from main bearing than stock rods?

[Thuppu]

I would guess the oil film/pressure between the bearing and crank doesn't hold as well as with wider rods. But I have no experience with this. Seems that these kind of setups have been used in baltian countries. Don't know about the power levels though..?

[VilkkuS]

Something like this would happen

Power was around 450hp... I think, not dynod
It also had vems with flatshift, that's why "Mile top speed" was littlebit better than I thought it would be.

Revlimit might be also little bit too high, for that setup, because shorter rods than stock ( 7500rpm )

I didn't broke this on that airfield....just afterwards when taking log, and driving to revlimit. But it was all the time breathing oil, so the damage was allready happend.
It was still driven to the "motor autopsy".
(ofcourse with the smoke and heavy breathing)

[Thuppu]

But the bearings are fine? Looks more like poor quality pistons or too tight piston ring gap.

[rst]

I have driven ghetto strokker for the past 5000km. It has had quite a rough life. 3 seasons on drag strips and weekend abusements.
I am using the same NPR pistons. I made some modification to pistons skirt because of oil squirters.
I modified diesel cranks so that stroke is 94mm. This way you dont have to mill down pistons from the top.
I dont get a lot of oil to oil catch tank. After five 400m runs there is about 50ml of oil in OCT. I previously used to run with 2bar boost then there was nothing in OCT. At the moment i am running 2.7bar boost.
I think i have quite maxed out HX40 Super with ethanol.
Dyno plot. Power is marked from wheels.

I have seen this sort of pistons failure before with NPR pistons. They were all milled down from the top(1.2-1.5mm). Maybe these cast pistons dont like that.

[VilkkuS]

Little correction: Piston rings was still in 1 pieces, when i open it,
(and those peaces of pistons were still on they plaze, but loosed and cracked on many ways)
So the picture was not framed totaly

[VilkkuS]

There was also other mistake, on this setup. The casked was not on 83mm bore (it was 82mm, when i measored it)
I have to check/measure the pistons, if they are machined on top....

[VilkkuS]

I looked specs about those NPR piston (11-639) STD 83mm, on NRP web site.
My pistons hasbeen modified atleast from skirt (a lot) The head side i'm not sure yet. (have to check this on weekend, cause i dont have those pistons near by)

Whole piston skirt hasbeen taken off. You can see the specs & picture of that original NPR piston here. VS picture, piston of mine.

Here's also 1 picture about the block, you can see that there hasbeen taken littlebit "iron" off, on the downstairs, because off those rods.
(not so pro drilled, but i guess it will do the job)
Also bottom off rods look "littlebit" awful

I would like to build this again, (with this cheap recipe) and try it with HX40super also.
But I dont know what is the main reason that killed those pistons.
It didn't "knock" when I listened engine on airfiled (e-phones with amp)
1 and 5cyl pistons were the main problems.(1cyl piston was that on pictures)
2,3,4 were quite OK (when I did compression test, I have not taken those pistons off yet -> Will do offcourse)