Flow Benches and head porting

[Notso Swift]

Corrections are nothing to do witht he maths involved with torque /HP they are purely designed so that people are comparing the same size apples with the same size apples.

I hope this image works it is an otherwise standard Suzuki Swift GTi with an aftermarket computer

This is logged at every 500 rpm, you may find the Yamaha thing is done at each 1000, which will give a resolution problem. Figures are actuals at the wheels, no coat down losses or any of that rubbish, just the actual reading from this particualr dyno.
Remember this is a standard road car, and the torque is highest a 6600 rpm

[AU N EGL]

Good Graph. There is a dip at 4000 and 5500 on the tq curve. Is there some valve float at those two rpms ranges?

My gues if those two rpms dips were corrected for a nice smooth curve it would give you more under the curve TQ. The peak many not be as high, but your overall power would be better.

[greenamex2]

I have yet to see a small capacity multi-valver NOT have a dip in the torque curve somewhere around 5000RPM.

No idea why.

[AU N EGL]

I think Flow bench testing is very important to start your build. Porting heads helps increase air flow into the engine and those new ported heads need to be checked. Then checking the Cold Air Intake ( CIA) for air flow and the exhuast headers and exhaust pipe for the best air flow.

Then an engine dyno to start your tuning. Finnally a chassy dyno to determan your useable power and the drive line loss.

Most drivelines tend to loss 10-15% from the engine, flywheel or BHP to the usable drive wheel power. Front or rear.

[graham bahr]

Originally Posted by Denis Bassom

I have yet to see a small capacity multi-valver NOT have a dip in the torque curve somewhere around 5000RPM.

No idea why.

i guess thats most likely cam related, almost every engine i've seen with a pretty radical sort of cam in it has a dip somewhere,

i had one engine which dropped 20bhp between 5000 and 5500 but between 5500 and 6000 power lept 40bhp, in practise on circuit the engine pulled through the dip so hard you never noticed it

[AU N EGL]

Originally Posted by graham bahr

in practice on circuit the engine pulled through the dip so hard you never noticed it

As long as there was no problems in those RPM ranges.

Noramly with engines of these sizes one wants to keep the rpms up in the power band which looks to be above 5000 rpms anyway.

[phoenix]

My first suspect for the dip in torque would be the exhaust manifold. It is impossible to tune an exhaust manifold that works positively at all engine speeds over such a wide engine speed range. At some engine speed the reflected pulses will arrive at the wrong time, causing not just a dip in scavenging efficiency but often a slight reversal of flow of exhaust gasses into the cylinder causing a reduction in cylinder filling (VE).

[greenamex2]

Makes sense.

Certainly the 4age is VERY particular about manifold configurations.

It is two completely different engines when you switch between 4-1 and 4-2-1.

[Notso Swift]

Originally Posted by graham bahr

i guess thats most likely cam related, almost every engine i've seen with a pretty radical sort of cam in it has a dip somewhere,

i had one engine which dropped 20bhp between 5000 and 5500 but between 5500 and 6000 power lept 40bhp, in practise on circuit the engine pulled through the dip so hard you never noticed it

No that was standard factory, off the top of my head they are about 7.4 mm and 236 deg, so very mild, It was the only graph to hand which would demonstrate the point to AU N EGL about torque in often peaking above 5252. I think it was most likely tune related, actually, because that was how we got it
The first thing we did to the car was put a set of cams in, 272 and 9mm, which was the max on the hydraulic tappets, the power was better every where, though there was still a dip. Max torque was a little higher, though it carried on longer so power was up to 105 from memory (it was a while back), rev’d cleanly to 8000+, sorry no graph though. In ultimate form the car got even bigger cams, a nice big valve head, new pistons, throttle bodies and good exhaust, rev'e to 9200 and made 130 at the wheels. It did 1 and a half laps and I put it into the wall hard enough that it trashed the block, leave alone the chassis

[phoenix]

Originally Posted by Notso Swift

It did 1 and a half laps and I put it into the wall hard enough that it trashed the block, leave alone the chassis

Ooops!

[AU N EGL]

Originally Posted by Notso Swift

It did 1 and a half laps and I put it into the wall hard enough that it trashed the block, leave alone the chassis

Ouch. Sorry to hear that.

[GORDON STREETER]

Notso
Looks like you don't need more power !!!!!

[Notso Swift]

Phillip Island is a cruel mistress. Trying to pass a guy around the outside of Lukey Heights, which is the blind left hander that runs into the right hand hairpin at the bottom of the hill (for those of you who don't watch the Bikes, both Superbikes and MotoGP have rounds at PI, it is one of the worlds great circiuts), anyway genuine 100 mph corner, I was starting at the back because I missed qualifing (still on the dyno!) and I had one to many brave pills. Too wide for that speed got on to the wet grass and hit the wall at 60 mph and couldn't laugh for about 2 months (fractured my splien). Worst part is they put in a bunch of new sand traps at the request of the FIM... you miss them in a car!