Re: Throttle body..

From: BKBridges (bbridges@flometrics.com)
Date: Wed Jan 07 2004 - 19:20:43 EST


Tony,
Yes! The Speed/Density system used on Mopars relies on the manifold
pressure and throttle posistion (and air temp) to estimate mass air flow.
If the manifold pressure sensor and TPS are not "synched" (dont match or
come close to the original look up tables) all kinds of poor performance
issues can occur (the PCM "cant do the math")! If other sensors (O2, AIT
etc) are also on one side or the other, additional situations can crop up
that will hurt performance. Instead of one big vacuum based control system
(carburetor) we've got multiple sensors and a computer to meter fuel. I
wish it were as simple as it seems sometimes, but there is a "trick" to
throttlebody sizing that will optimize your performance if handled properly!
Also: My camera was "out on loan" but its back now. Ill send you those pics
we talked about
Bruce

----- Original Message -----
From: "Tony Cellana" <acellan1@tampabay.rr.com>
To: <dakota-truck@dakota-truck.net>
Sent: Wednesday, January 07, 2004 1:48 PM
Subject: Re: DML: Throttle body..

>
> On your second point, I beg to differ. Put too large a TB on, and whack
it
> wide open, and there will be a bit of a hesitation. Too much air too
quick
> from an idle. The computer has trouble compensating THAT quickly.
>
> I agree that in theory, it shouldn't happen, but real world results differ
> some.
>
> TonyC
>
> -----Original Message-----
> From: david.clement@verizon.net <david.clement@verizon.net>
> To: dakota-truck-moderator@bent.twistedbits.net
> <dakota-truck-moderator@bent.twistedbits.net>
> Date: Wednesday, January 07, 2004 4:46 PM
> Subject: Re: DML: Throttle body..
>
>
> >
> >In article <016801c3d3a7$8c4a8900$d75f2241@a.tampabay.rr.com>,
> >acellan1@tampabay.rr.com ("Tony Cellana") writes:
> >>
> >>
> >> Some miscellaneous ramblings on the topic:
> >>
> >> Not knocking anyone's product or thoughts, just tossing mine into the
> mix.
> >>
> >> TBs are a controlled hole in the intake manifold that will allow a
> certain
> >> amount of air into the motor. Some motors need more air than others.
> The
> >> amount depends on CID, RPM, and the tuning characteristics of the
intake
> >> manifold, cam and valvetrain.
> >
> >It is fairly easy to determine if you need a bigger TB. If you have (more
> than
> >approximately 1/2" H2O) vacuum in the intake manifold at WOT then you
have
> a
> >restriction and a bigger TB is warranted.
> >
> >> Some motors want more air than others. TOO much air isn't always a
good
> >> thing though. It can cause bogging, off idle hesitation and/or
stumble.
> >> This is often seen when abruptly opening the throttle from idle or near
> idle
> >> (think jumping off alight or drag racing).
> >
> >The bog, hesitation and/or stumble is a carb characteristic. This does
not
> >happen with a port injected engine with a dry TB. When a carb is too big
> you
> >loose too much air velocity as you open the throttle if it's too big
> resulting
> >in a loss of vacuum that is needed to pull fuel from the bowls. This is a
> non
> >issue with port injection. If you were so inclined you could take the TB
> off
> >the engine and use your hand to control rpm.
> >
> >Dave Clement
> >99 SLT+ CC 4x4
> >
>
>
>



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