Engine difference – 3TB vs 4PT (missing 5 HP)
 

The 3TB model is supposed to be 33KW, but the newer 4PT is 29,4KW. Has it really 3,6KW less or is Yamaha just using different numbers for some reason? Anyone know??

FYI:
I have the 4PT model. For testing purposes I did take out the airbox snorkel and the muffler tip (I would not run the bike like that though, too noisy) .

Now the bike was more noisy but to my surprise I could not feel any power difference. The bike did not feel lean. Most bikes with heavily restricted intake/exhaust respond quite a lot to even modest “decorking”.

Yes its correct the new model has less bhp.

Ok, thanks. Do you know why?

I'm wondering if the 4PT can be upgraded to 3TB specs by swapping out parts.. The basic engine is more or less the same except for the clutch I am told.

Carb, exhaust making the difference? just my guess.

Check the intake boot inside diameter, the one that bolts to the motor. It is supposed to be smaller dia, so an old version will help.

Thanks guys.

I did compare part numbers (intake boots) and they seem to be the same. Maybe I will take it apart anyway, and take a look.

My last XT has a 4PT engine and a ´95 TT600S carb and everybody said that XT runs so well

I may be on to something. Apparently the XT lost the 5 hp in 1996, went from 45 hp down to 40 hp. That year they changed the camshaft.
1996 on camshaft: 1jk-12170-00
1986-2005 camshaft: 1JK-12171-00-00


I already have tried opening up the intake/exhaust with no noticeable change in power. Jens Eskilden has done lots of modifications to his bike without any big change in power.

A bike that is heavily restricted on the intake and exhaust should respond more to uncorking, so the bottleneck must be somewhere else.


1. First the basic question, has anyone compared the pre- and post 1995 XT600E? Is the power difference real?
2. Does anyone have access to pre and post XT600E/XT600 camshafts? Is there a difference in lift or grind?

Thanks Mezo great info. The numbers are not the same though, if you take a closer look. Unless I am misunderstanding something:confused1:

1996 on camshaft: 1jk-12170-00
1986-2005 camshaft: 1JK-12171-00-00

(You're not misunderstanding anything).

Sounds like you -are- onto something, G600 - it could well be a differently-profiled cam.

It may be that Yamaha tried to flatten the torque curve a bit, to make the torque even more usable, in which case the slightly-softened BHP would actually be a good thing (unless you have a racing XT!)... But then again, the cynic in me wonders whether it was more to do with reducing noise and keeping emissions in check :rain:. Maybe it was to address both angles.

Thanks Mezo. So this is not it.

Back to basics. Has anyone ridden the older and newer (pre-and post 1996) XT600E back to back? Are the older bikes more powerful?

Did anyone find out whats the difference on these engines, where did the 5hp go?

I would also like to know where the power went!!

Has anyone actually tested the 2 models to compare, on ie a dyno?
How does the stated Hp compare to what's written in yamahas own factory workshop manual (with all the specs)

Just so we know we arent chasing ghosts. I've seen HP-figures go up and down on many bikes, with the same engine. Some 2-stroke ktm bikes is even listed at under 50% of actual Hp

The 3tb I had was no faster than the 4pt :)

Due to more stringent emissions requirements, the power of the XT 600 E, which had become the only available model, was reduced by 4 kW to 29 kW (39 hp), and a tachometer was reintegrated in the cockpit. The clutch actuation on the engine body was moved from the left to the right side, and the muffler was no longer part of the rear frame.
MY 99-03 DJ02 XT 600 E 25 to 29 kW (34–39 hp)
XT 600 E 1999,00,01,02 DJ021 EUR

I dont know, all the other info is correct so why would they lie about the hp? I will try to compare them in a couple of weeks. But then with mine that have kn, new exhaust all the way and dynojet kit, the other only have changed muffler.

I found different combustion chamber sizes on the older bikes when the hp ratings changed , could very well be they opend them up a bit more or made the ports a little different size , doesn't take a whole lot if done to the right places. A person would need to have one of each head side by side and measure all aspects.

My 2003 model dynoed 34,6hp on the rear wheel with the snorkel removed, and a new exhausttip, and i think a pipercross airfilter. At that point it had over 50.000km on it, so perhaps the powermods just about made it up for the wear in the engine...

My friends ktm640 dynoed with a 10hp loss from the stated HP at the crank, to the actual meassured rearwheel-hp. If it's the same for the xt600, you would be very close to 45 hp on the crank :D

True Rear Wheel Horsepower

The SRX is the same engine. Who knows, maybe its all in the exhaust, maybe you got the 44hp when open up with more air and new exhaust.

Valve shrouding
 

On my 2001 E , the valves were badly masked by the sides of the combustion chamber even at full lift. I marked around the head gasket and opened the head away from the valves. It made a real difference.

Ok, so what you mean by badly masked? BTW i tested a 4pt with leo vince against 3tb and it seems similar, in my head it should have been a much bigger difference so i bet the exhaust makes less hp or it never was any less output on the 4pt.

He means the combustion chamber is closed over somewhat around the outside in a portion of the valves , valves can't "breath" fully. Think roof. The XT's aren't that bad , similar to most . The head gasket need to be shaped so they don't stick into the combustion chamber. My klx650's are horrible and 6-8hp gains can easily be had by going 2mm overbore and grinding the chamber open around the outside of the valves to match the 2mm bigger bore.

I haven't seen any of the newer heads to know if they changed the shape , that could easily loose several hp.

danimalu if you remove head again you can take a picture.

Has the 3tb a big valve head ?

Cheers
Min