Honda Car Forum

The dashpot also did that. On the Holley's an additional
bypass valve was also installed that would also eliminate
backfiring. Its operation was also controlled by manifold
vacuum. This valve was routinely destroyed when Pinto
camshafts wore down (due to missing oil holes eliminated by
Henry Ford in his American versions of that engine).

But the dashpot was adjusted unique for manual transmission
cars. Other carburetors used a more sophisticated system based
upon engine manifold vacuum. Granted it was not as
sophisticated as done today. But then everything back then
was a crude mechanical solution. No it was not linked to road
speed and gearing. That is the more sophisticated version of
something done decades ago. Just like carburetors could never
accomplish what fuel injection does.

The new version goes by names such as electronic throttle
control. New and fancier ways of doing the same old thing. A
function even back then so subtle that most people don't even
knew it existed or could be adjusted.

George Macdonald wrote:
> I thought the dashpots were just a damping device, related to
> manifold vacuum, to prevent abrupt throttle shut-off and the
> resulting emissions burp. I've never heard of it being linked
> to road speed and gearing.

JXStern <JXSternChangeX2R@gte.net> wrote in message news:<rvjf905hd0to7dokdcpqes1iru2vgvgahv@4ax.com>. ..
> On Mon, 03 May 2004 12:08:34 -0400, w_tom <w_tom1@hotmail.com> wrote:
>
> 1970. I think my old Accord was at least advanced enough to keep the
> RPM up around 1200 if, well, I'm not sure what it knew about road
> speed or gearing, but I think the number was constant, and might often
> enough approximate where the next upshift should be.
>
> Say, OP, what about downshifts, does it approximate the RPM on those?
>
>
>
> J.

I didn't think it did. When I drove it home from work I tried, and
no, it doesn't. Then I realized....how would it know if you're
upshifting or downshifting? So no, it doesn't. Besides, I only
downshift if my road speed is decreasing. I never downshift for
engine braking. Why put wear on your clutch when your brakes are so
much easier and cheaper to fix.

On Wed, 05 May 2004 14:09:25 -0400, w_tom <w_tom1@hotmail.com> wrote:
> But the dashpot was adjusted unique for manual transmission
>cars. Other carburetors used a more sophisticated system based
>upon engine manifold vacuum. Granted it was not as
>sophisticated as done today.

We're still trying to determine if it *is* done today.

Basing it on vacuum might avoid quick engine speed changes for
pollution reasons, and that might have *roughly* the effect of keeping
engine speed closer to the sync range on upshifts, but that would be a
a side-effect -- as I pointed out, it wouldn't help a bit on
downshifts!

J.