Difference tzr125 and dt125

[Irongamer727]

From what I've read they have different bhp output, different compression ratios and different gearing. I thought they were identical? (Apart from the gearing difference)
Same engine just different chassis basically.
Let's assume they are the same year model.

[Calum]

Only the Belgards used a similar engine (not the same). From mere observation, the belgarda engines are closer to the KTM LC2 engines.

The general TZR used 2RK 2RH Engines which are nothing like a DT engine. Competely different.

[Irongamer727]

@calum what? Also more powerful I would guess? I read on the technical document for the Athena 170 that the Dt produced 25,9 or similar and the Tzr 29,2 bhp. Are the engine mounts the same? Feels like you would benefit from changing to a Tzr engine?

[Calum]

@irongamer727 Nope.

Read through my build mate, it's all in there.

https://dt125r.co.uk/topic/15/the-leviathan-project/90

I ran a Belgarda engine. Cute engine, but the casting was flawed and the gearbox doesn't suit the DTR and the barrel isn't great (Still running the 4DL barrel).

It's all there though if you're interested. What you want is an SP. But then it's no better than a Rotax Engine yet the last time I saw an SP barrel (no valve) it went for just under £1000.

[Irongamer727]

@calum what's an SP?

[Calum]

@irongamer727

As said, good luck finding one. And it would be criminal to remove it from such a sweet chassis for a DT....

[Irongamer727]

@calum why not make these for the Dt125's as well? More expensive? 4DL, isn't that what you got ported and wasn't satisfied with?

[Calum]

@irongamer727 I want to make it clear, it's not the porting I wasn't satisfied with. The porting, the tuning etc etc fantastic work.

I was disappointed with how shit the 4DL is. It's the SP that is the dogs danglies and you cannot get them. I am told it is as smooth as a baby's bum, yet as powerful as an RS. But to my mind that doesn't justify the price. An RS is far superior due to its availability, cost and out the box performance. The SP may very well outperfrom an RS, but you can't even get a barrel for the cost of a complete running engine, loom cdi from an RS.

The 4DL was just a 3MB with a 1mm exhaust port increase.

https://www.youtube.com/watch?v=P8okvTxe-Bs&list=PL66C1264C7D6205BB&index=8&t=0s

Instead compare it to a 4FU which, on the face of it, is drastically different to the 4DL and fits onto a DTR bottom end. And I reckon is the better barrel of the two. But after years of tuning the DT I have moved on now. Never investing the time nor the money on the 4FU. But if I had my time again, I would be looking into the 4FU.

[Irongamer727]

@calum it must be accomplishable to port a 4DL to perform like the SP right?

[Calum]

@irongamer727 No mate, the port timings are completely different. The transfers, the fact it has auxiliary ports.

Just good TZR SP barrel and compare it to your stock DTR barrel, then you'll know what I mean.

[Irongamer727]

@calum sounds like one nice cylinder.

[Calum]

@irongamer727 Psst

£60 buys you

Again. simply doesn't warrant the price for an okay barrel.

[Irongamer727]

@calum going a bit off topic now but what would you say makes the enduro 125's cylinder's produce so much power?

[Calum]

@irongamer727 Higher compression, more aggressive port timings, bigger transfer ports, cleaner transfers, bigger boost ports. Auxilary boost ports. More spark advance. Increased squish clearance. Better designed crank journal spaced for increased fuel atomisation. Smoother inlet tracts. No emission laws to adhere to. Smaller piston to wall tolerances. Less blow by, single rings... The list goes on.

If you're really interested then I'd recommend reading a book on a the subject as it's not something I am going to describe in a sentence or two...

[Irongamer727]

@calum jeez.

[Calum]

@irongamer727 I'd recommend Tuning For Speed By Phil Irving PDF available online

http://tuningforspeed.com/files/Tuning_for_Speed.pdf

As a start

Then have a read of Graham Bell's Two Stroke Performance Tuning
Then Graham Bells Engine Performance Tuning

You always want to read in Chronological order. Phil's book was written several decades ago, Grahams during the late 80's.

Irvin was way ahead of the curve and received the highest engineering award they have in Australia. Named after him called the Irving award. The guy is a genius.

[Irongamer727]

@calum I have Graham 2 stroke at home. First time I read it I didn't understand much. Perhaps time to do it again.

[Calum]

@irongamer727 I refer you to my previous statement.

Start in chronological order. Ready Phil Irvins book first. As this will introduce to the concepts at the time, which are assumed or taken for granted in later books.

[declan]

@calum can you not just re sleeve a barrel like a blank slate and the copy what ever port you wish as long as the barrel it’s self allows

[Calum]

@declan The barrels are cast with only so much metal in them. It's not a case of inside liner. The walls are only so thick and can only be ported so much.

You could spend thousands and thousands porting the barrel, and the result is ultimately worse than a £60 RS barrel. It's cost vs Reward.

If I was going to spend X amount of money for maximum bang for buck, do an engine swap. It'll be cheaper and better.

So I'd rather swap the DTR engine out for a 2RK engine out of the UK spec TZR. Or better still Rotax 122 engine, or a YZ engine or anything else.

By all means, mildly port and tune the DTR engine, but accept that there are limitations. Ensure that what you spend, is less than what it would have to have simply swapped the engine.

That accounts for time as well as money. An engine may cost less than a decent port, but if it takes a year to fit then it's cost you time.