TU8 or TU9?

[Arthur 14]

hi guys. All talks about 1.5, 1.4 short stroke alu tu engines and such now got me thinking. The EC8 engines from China seems to be the same iron block as TU5 but with 92.5 stroke and 79 bore. 

 

Now I'm wondering how big one could go with the iron tu. With 84mm cylinder spacing, what would be the max bore for non turbo? Would one dare to go 81mm? 81 x 92.5 would make a TU9JP4 of 1906,5 cc 

 

New crankshaft with 92.5 stroke are available dead cheap.

Edited October 22, 2024 by Arthur

[welshpug 1,678]

Why not start with a readily available XU ?

[Arthur 14]

  On 10/22/2024 at 11:24 AM, welshpug said:

Why not start with a readily available XU ?

Sure that would be possible. but I'm just wondering. And I just happen to like the TU setup. Maybe not logical, but oké. 

 

[SRDT 199]

The crank may be cheap but importing the whole engine could save you a lot of time and effort.

Maybe the crank can fit inside a TU5 block, maybe you need special rods and a bit of work on the block or maybe you will grind your way to the outside of the block before it fits.

[Arthur 14]

Yeah. Looking at pics of stoker builds there’s room left with 89 stoke. Whole EC8 was quite expensive but block and head looks the same.  So either they use shorter rods or lower ch pistons. Well, took the gamble and ordered the crankshaft. Guess I’m going to find out.

[SRDT 199]

Piston pin is very close to the rings, the head has "EC8" on it :

https://club.autohome.com.cn/bbs/thread/83a86e267aa9bb0f/80933612-1.html

https://kknews.cc/car/9oy242j.html

Edited October 24, 2024 by SRDT

[Arthur 14]

Hi all. I found a piston that is quite low CH and 80 mm from standard design. (and available forged).  I do not dare to go 81mm. Should fit with 137,75 conrods so the rod/stoke ratio will not decrease a lot. It would result in 1860 cc 

[Arthur 14]

Well, we have the crankshafts. To our surprise they have 43 x 20 mm crankpin while TU5 has 45 x 24. That will be 400 quid down the drain, EC8 Chinese conrods or custom rods. The Chinese conrods look kinda shabby and the pistons even worse.

I don't think any other car engine has 43mm crankpins. 

 

Rover 18K is a stroked version of the 16K and has relative short rods at 133.1 with 22,7 (very) low pistons. We intended to use those pistons at 80mm bore. But the 137.75 TU conrod doesn't fit both crank and piston. 

 

We have searched for some options and in that search we found out that Honda D series took stroking, to increase displacement, to an extreme. From D12 to D17, all have 75 mm bore yet stroke goes from 67.5 to 94.4.

 

So the Honda D17 is 75 x 94.4. Even more extreme than what I'm trying to do here and that redlines at 7200 standard. And Honda also decreased the big end width from 22 to 20 between D16 and D17. So also here less crankpin size on a bigger displacement. Standard honda conrods look far more descend though. At 137 long and 19.81 mm wide small-end would be perfect if not for the 19mm pin and 48 big-end (unless 2.5 thick bearings can be applied to get to 43mm) 

 

Why on earth would one decreased crankpin diameter on a stoked engine??? 

 

To make more room in the block?

Because the arm (stoke) is longer so the force is not that much?

Because they need more material in the crank webs?

 

Anyone got forged conrods with EC8 big-end and Rover 18K small end at 137mm long for sale 

[welshpug 1,678]

Offset grinding to an undersize and making a rod with a smaller bearing bore is probably cheaper for psa than a new crank

[Arthur 14]

Haven't thought of that. You mean they took the same casting and needed to go 43 x 20 to get the 92,25 stoke out of the same casting. That makes sense.  Also explains why it's common. Same casting for a stroker....

Edited December 17, 2024 by Arthur

[SRDT 199]

How much HP do you want? Standard EC8 rods should be fine for standard EC8 power : 137 hp and 172 N.m.

[Arthur 14]

Well, that's just the question. I could only buy 2 crankshaft, so I teamed up with someone. He was however hoping JP4 rods he had lying around would fit to not break the bank completely. 

 

But he builds racers. Even with this long stoke he's after at least 8000 rpm. His 1587cc engines go as far as 270 bhp....

 

Mines a road car, yet currently I do 7500 with 42mm itb's, good exhaust, no cat and JP4s cams. Currently 150 -160 ish I recon.

 

But for this build I was planning to go with not to extreme cams like cat 743's and stay at 7500. I recon an 1860 cc TU with itb's mild cams and 7500 will be around 200 bhp. I could risk the standard rods perhaps, but my friend can't.  Sadly most custom rods go by minimum 20 pc. 

[welshpug 1,678]

Robson Engineering will do you 4.

[Arthur 14]

Thanks. 

 

I got an good offer out of China. I've send one EC8 conrod locally from a trader to kingtec wuxi and for that, and some markup, they are willing to reduce the minimum order from 20 pc to 8pc. 

 

If this all goes according plan this TU9JP4 (shortblock only) will cost me about 2000 - 2500 EUR with forged kingtec rods and wossner forged Rover 18K4 pistons. Less that a single 89mm stroker crankshaft on it's own. 

Edited December 20, 2024 by Arthur

[welshpug 1,678]

Robson was about £600 a set.

[Arthur 14]

Yeah. He did answers my mail so cheers for that!

[Arthur 14]

Standard EC8 rod dimensions. 

 

Can't go back now. 

 

Edited January 3 by Arthur

[Arthur 14]

Finally

[Arthur 14]

Still progressing. 

 

I was told (and read) Strokers need quite a bit more air. Not only the increased capacity, but also the fact the piston is slower around top dead center with relative long rod ratio. My inlet was already quite good with 4 x 42 gsxr bodies, but we decided to increase outlet valve size as well. 

 

Specs

Bore x stoke 80 x 92,5

1860cc

135.6 mm rods (kingtec rods, ARP bolts)

23.8 mm compression height pistons. (rover K18)

EC8 crankshaft

43 x 15 big end bearings (ec8)

TU5 main bearings

Probably 0.8 mm steel head gasket and 1.5 mm of head and/or block to get to around 12 ; 1 (moderate) 

Increased exhaust valve size (dunno exactly how much but around 2 mm bigger) 

4 x 42 mm ITB, with total inlet track of 30 to 35 cm. (same as my TU5JP4)

Vems ecu (same as my TU5JP4)

Moderate (concerning strokers need more duration to get to the same powerband) cams at 262 deg, 9.8mm lift, 1.1 -1.25mm at overlap. 

7500 rpm limit, keeping hydro lifters and standard springs. More then enough for 92.5mm stoke imo. 

 

Hoping the rod will not hit the bore. 

 

My partner in crime for this project will go much crazier with cams buckets, springs and compression because he races them, but this is my predicted best setup for my preference. 

 

Think this will still be ~ 200 bhp @ 7500 / 200Nm at 5000, though. 

 

 

Edited May 16 by Arthur