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Old 8 Feb 2010, 14:10 (Ref:2629295)   #1
buterworth
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Need Help.Poor Mid-range Toque of My Stock Engine

I was about to make some necessary modifications(suspension,brake pads,tires,fuel mapping,intake,etc)on my car for the track day of my first time.Before modding it I had found a big problem.
My car is powered by a replica Toyota 1zz 1.8L engline made buy a Chinese automaker named Geely.It has a variable valve timing system on the intake side.The ECU come from Bosch.This engine should produce 137hp@6100rpm and 172nm@4200rpm according to the official figures.

Last week I dynoed my car and it put down 109.7hp@5900rpm . This is really a satisfying number cause our dyno machine always shows huge friction loss even to a FWD car! But its mid-range torque is too low.The peak torque comes from 5500rpm.That's weird for a stock family-use car engine.
Usually a common stock NA 4-valve engine always outputs its peak torque around 4500rpm,and the torque will begin to decrease from about 5000rpm.I've driven another 2 cars of the same model at my dealer.I felt they are almost the same as mine. I've got 24MPG in city and 38 on highway.So I don't think my car has any mechanical problems.I doubt that there must be some issues that limit the mid-range torque output.The air-to-fuel ratio is OK for a stock car.May it be the ingition timing?
I dynoed my car in the 3rd gear,the topspeed was 135km/h.
I don't know where's my mid-range torque .
Here's my dyno chart.


My car(1.8L 16V manual gearbox) vs Jetta MK2 (1.6L 8V with 5-speed automatic gearbox)

Last edited by buterworth; 8 Feb 2010 at 14:17.
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Old 8 Feb 2010, 23:08 (Ref:2629575)   #2
Notso Swift
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It may be my connection but your graph is not showing however, I will say...
More power up high means more torque up high, simple as that, and (especially with VVT cars) it is now very common for manufactures to push the "head line" numbers up while still keeping fairly good in the lower ranges (on the first timing position), helping emmissions. as a result it is quite common to see an apparent hole in the curve BUT, that hole is reletive as the curve is usually better than any fixed cam.
If you are tracking your car you want the torque up high.
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Old 8 Feb 2010, 23:23 (Ref:2629584)   #3
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Sorry, just had a thought, these graphs, are you looking at a motive force instead of actual torque
Most rolling road type dynos mis-state torque because of the gearing that the power goes through, not just losses but you have tested in 3rd, plus a diff plus tyres.
Do the same test in 2nd and 4th and see what I mean. trying to reconcile with a proper engine dyno is pretty much futile, all you can do is take the original figure and say these are the changes, these are the benifits. That is why you need to use the same dyno with the same settings every time, it is a point of referance, nothing else
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Old 9 Feb 2010, 11:17 (Ref:2629801)   #4
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Could it be that the VVT isn't working - that the inlet cam is fixed in the fully retarded position?
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Old 12 Feb 2010, 17:21 (Ref:2632232)   #5
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Originally Posted by Notso Swift View Post
Sorry, just had a thought, these graphs, are you looking at a motive force instead of actual torque
Most rolling road type dynos mis-state torque because of the gearing that the power goes through, not just losses but you have tested in 3rd, plus a diff plus tyres.
Do the same test in 2nd and 4th and see what I mean. trying to reconcile with a proper engine dyno is pretty much futile, all you can do is take the original figure and say these are the changes, these are the benifits. That is why you need to use the same dyno with the same settings every time, it is a point of referance, nothing else
I did test it in 4th gear,and the torque curve was almost the same except for lower hi-end torque.All this results show that the car has pool mid-range torque.I don't care about torque blow 4000rpm,but torque from 4000-5000rpm is still lower than it should be.

I tested several stock cars.Although the results are a little bit far from official numbers due to drivetrain loss and the inaccuracy of the dyno,the torque curves can still show that all the tested cars can reach their peak torque around 4500rpm.But my car can't on this dyno.
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Old 14 Feb 2010, 22:30 (Ref:2633474)   #6
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OK I can see the graphs now (not sure why I couldn't before)
Straight away I can see it is motive force. First clue is that the Power and torque do not cross at 5252. Ignore your numbers and re-calcualtre the figures if it is that important to you. Look at the shape, a flat torqe curve that increases in the second half, that looks like the cam being advanced by the VVTi to me, exactly as it is it should. OK, so you have more torque up high... I bet this is how the motor was designed.
I have driven a Corolla sportivo (road car, which I think has the High performance version of the same motor) and the way I remember it was that you had to rev the tits of it you make it go, to me this graph is indicative of that. I will go back to what I said before, this will be the way the motor is designed!
Here are the realities of life, you don't get something for nothing with cams and NA motors (although VVTi and VTEC do the best they can through two completely different ways). More torque up high means more power, to the detriment of lower and mid range. To put it in to perspective you torque curve is better EVERYWHERE than the VW motor (which is known to have ports that are too large to the detriment of torque)… and the problem is…
Now if you do not like that and are going to modify you need to concentrate on increasing the efficiency at lower RPM, but that will cost at the top end (or more likely may not allow the maximum possible) this means increasing gas speed down low, maybe smaller headers that scavenge better, working on the valve seating so flow at lower lifts is better, that sort of thing
People who race want to keep as much high end torque as possible and we gear so that you do not fall off the curve
EDIT I just looked at our local spec for the Corolla Sortivo max torque is at 6800(!), and max power at 7800
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