when porting out a throttle body u want it to have a smooth finish or kinda rough like the intake runners inside? the TB should be smooth right? what about the opening inside the mani where the TB meets it , should that be smooth or rough?

 

Smooth is always better for high RPM operation.

 

ok . what would a good finishing grit be then for TB

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 97grnrs &raquo;</TD></TR><TR><TD CLASS="quote">ok . what would a good finishing grit be then for TB </TD></TR></TABLE>

I think 400 grit is sufficient. You can go finer but the gain is minimal at best.

 

Are you burning gasoline or alcohol? Back in the "old" days, A slightly rough finish was desired for gas motors and a polished surface for alcohol. But I'm talking about a carberated engine. The rough surface in a gas motor helped to keep the gas vapor suspended in the air. Not sure why a polished surface works for alcohol. With a fuel injected engine I’m not sure which way to go. My gut feeling is the smother the better. The gas is injected at the backside of the intake valve; so, all we need to do is get pure air to that point. Make sure the ports are matched. Use a new intake gasket and scribe on the intake manifold and the head. Grind away everything inside the scribe marks. I always port matched my MX bike and it was always good for 2 hp on a 125 and 3 or 4 on a 250. I may be totally full of @#$%^, so any thoughts from anybody else will be welcome.

Ken

 

i beleive u need roughness . for better fuel atomization . or else the fuel will fall out of suspension . if you know what i mean its better to port certain places to get a better low pressure in the runners

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Smoke_em &raquo;</TD></TR><TR><TD CLASS="quote">i beleive u need roughness . for better fuel atomization . or else the fuel will fall out of suspension . if you know what i mean its better to port certain places to get a better low pressure in the runners</TD></TR></TABLE>

Not for port fuel injection. The injectors are immediately before the intake valves. The intake valves open different amounts to induce swirling (turbulence) and mix the atomized fuel with the air. The fuel injectors do most of the atomization.

 

I still like to roughen up intake ports(about 60 grit), but the whole idea is to do it after the injector sprays...
before that there is no fuel to try to keep atomized.

 

true i miss read that part .. but you can still effect the atomisation in the ports . even though its fuel injected