The B20VTEC discussion thread

**Touge Tom** · 08-07-2010 11:20 PM

Originally Posted by tinkerbell

so 'piston throw weight' is just about 'rod stretch' is it?

piston throw weight would also affect torque /power figure's due to the fact that considering there is now more kinetic energy acting on the piston in the upwards motion, away from the crank rather then the force pushing down on the crank to make the torquing/ rotational motion to turn the wheel's.

so when looking at a dyno graph. and the point at which the torque begins to drop. i think this would be that particular motor's piston throw weight point. and using lighter weight pistons would shift this point higher up in the rev range.obviously holding the torque longer to make more power. considering the piston weight is now less.

**TODA AU** · 09-07-2010 08:08 AM

Originally Posted by ewendc2r

Ok so lets talk about the difference between using ported IM/68mmTB/BigTubeHeaders-70mm exhaust on the setup vs stock ITR IM/63?mmTB/

a little off topic ... But a restrictive header or intake would act as a restrictor i.e. limit hp but not torque?? so, theoretically (and maybe this is where i am going all wrong) by using my current bolt ons I would limit peak output to max flow capability of current boltons. so Torque may taper off instead of building at high rpm?

i.e. Can we discuss, what effect on torque curve will restrictive bolt ons create?

TB -- I've sent you a pm.

Your OEM intake manifold & throttle are good for 240hp at the engine (unmodified)

A restrictive header or intake will act as a restrictor - Yes
But the same effect is found using intakes & or exhaust components that are too big.

Eg: With a big ported B-series head to get the most out of it, you start needing some extraordinary lengths to pick up the air speed. (Intake & exhaust)
However when std valve sizes are used with clever porting the same or higher peak power & torque can be seen with more finness.

Regarding bolt-on on a big motor core...
If the intake or exhaust is wrong, the power will flat line...
If it's really wrong it'll loose power on a really late Vtec swap.
When it's right the Vtec swap is around 5~5500rpm near where your peak torque should be.

**TODA AU** · 09-07-2010 08:12 AM

Originally Posted by Touge Tom

piston throw weight would also affect torque /power figure's due to the fact that considering there is now more kinetic energy acting on the piston in the upwards motion, away from the crank rather then the force pushing down on the crank to make the torquing/ rotational motion to turn the wheel's.

so when looking at a dyno graph. and the point at which the torque begins to drop. i think this would be that particular motor's piston throw weight point. and using lighter weight pistons would shift this point higher up in the rev range.obviously holding the torque longer to make more power. considering the piston weight is now less.

& the crankshaft counter weight's role in life is?

Have you got another term to describe what you're talking about?
Also the point where an engine starts to drop torque can be shifted readily with changes in volumetric efficency.
Be that component selection or engine set up or tuning.
(2nd order Harmonics are generally the biggest issue with large inline 4cyl engines)

**Chr1s** · 09-07-2010 08:46 AM

I agree with Adrian. I can't see how it's
possible that the 'throw weight' of the piston governs the point of max tq/hp. That contradicts the idea of camshaft: manifolds, etc.

So nobody has heard of this term?

**ewendc2r** · 09-07-2010 01:53 PM

Thanks Adrian -- that clears things up for me nicely.

I've also noted that a lot of people (ok, some people) are using ITR Exhaust camshaft and a more aggressive intake cam ... As the majority of flow occurs as the valve opens (from my understanding) or at least the highest velocity, can you compensate for valve size with cam selection? i.e. a cam with slightly less duration / lift with an equally aggressive ramp rate?

**Samm928** · 09-07-2010 04:13 PM

KLR-16a. your pm box is full.

**Touge Tom** · 10-07-2010 12:52 AM

Originally Posted by Chr1s

I agree with Adrian. I can't see how it's
possible that the 'throw weight' of the piston governs the point of max tq/hp. That contradicts the idea of camshaft: manifolds, etc.

So nobody has heard of this term?

i know it doe's not govern the total out come. but is a factor. i believe toda au is correct. and i did say (a particular motor's) piston throw weight point. but what i don't get is that the piston will travel much further distance than a counter weight attach'd to the crank. so logically the piston would have more effect on the crank than the counter weight. right?

**ewendc2r** · 10-07-2010 01:06 AM

What are the other pistons / rods doing? As long as they are equal weight and equal compression / combustion force then they should counteract each other to some extent.. ?

**tinkerbell** · 12-07-2010 09:54 AM

Originally Posted by ewendc2r

What are the other pistons / rods doing? As long as they are equal weight and equal compression / combustion force then they should counteract each other to some extent.. ?

FWIW - the only stuff i found on the "piston throw weight" related to non-internally balanced engines. Honda B series are internally balanced.

**riruiz_88** · 14-08-2010 10:45 AM

so whats the go with choosing the right timing belt. i will be running B16A water pump, B16A oil pump, B18C cam gears. should i be using a B16 timing belt or B18C timing belt?