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bored-out throttle body?[S70/98] posted by Terry Gibson on
Thursday, 3 September 1998, at 11:50 a.m.
What are the trade-offs involved with the installation of a bored-out
throttle body? I note two vendors selling these things:
http://www.teleport.com/~mvprd/ (MVP Products)
http://www.group-6.com/B-1.htm (Group 6 Performance)
The MVP page is fairly restrained in its description of the modified
throttle body. The Group 6 page claims 28(!) additional HP with no loss
in gas mileage.
As with many of these performance-enhancing parts, I'm thinking, "Some
Volvo engineers made a decision about the diameter of the throttle body
opening. Are their design goals in disagreement with what I'd want
for my car?"
Any input will be appreciated.
Terry
98 S70 non-turbo
Re: bored-out throttle body?[S70/98] posted by davespeed at bigfoot dot com on
Thursday, 3 September 1998, at 3:20 p.m.
Well, nothing beats a trial like a failure. However:
Bigger is not always better. If your engine displacement was bigger,
and it gulped/pumped/flowed more air, a larger throttle body would make
(a hell of a lot) more sense to my way of thinking.
If you compare the restrictions inherent in all the lenghts and turns
in the intake and exhaust plumbing, you should see that the throttle
body's maximum flow capacity is hardly constraining, much less strangling,
your engine's performance...
The common problem with oversized throttle bodies is that, even on many
race tracks, fine control of the throttle is as important as maximum
output, and a too-large throttle makes fine control much more difficult.
Even in those cases where an enlarged throttle body does increase maximum
output, driveability typically suffers: as engine revs rise (as a car is
accelerating in gear) the engine's flow capacity/requirements increase.
The larger throttle body makes it more difficult to match the intake
system's flow with the engine's needs at lower revs. A too-large
throttle body/opening tends to result in "eddy currents" or otherwise
perturbs the flow of intake air, instead of keeping it rushing in a stream
towards the intake valves.
If you can lock your transmission in a gear such that you can
accelerate from low revs in that gear, you should find that it is
possible to achieve better acceleration by gradually opening the
throttle in concert with rising revs (opening it only as large as it
needs to be at a given rpm to keep it from holding back the engine)
than you can by immediately going to w.o.t. and waiting. In fact, as
cars get smarter and drive-by-wire throttles proliferate, drivers of
manual transmission cars will be able to immediately go to w.o.t. (to
indicate their desire for maximum acceleration) and let the engine
management system accomplish their goal for them by optimally varying
the throttle opening for them as revs rise.
In my experiences, on flat level pavement at sea level, a strong-running
Turbo automatic can break traction from rest, without using the brakes
or steering, but only by using the optimal amount of initial throttle
opening. (ie by NOT going to w.o.t. immediately!) More is NOT always
better. The implications of the effects of a larger throttle body on this
phenomenon are clear.
As always (since nothing beats a trial like a failure), I am keenly
interested in hearing results of such experiments. However, as most
people who've driven these cars have discovered, Volvo did an
exemplary job of matching engine displacement, intake system (incl
throttle body), exhaust system, and turbocharger sizes (turbine and
compressor) to one another, as a complete, balanced system, already
pretty well-tuned, and not far from the point of diminishing returns
and trade-offs.
I suspect the cylinder head will need to be relieved/ported/polished (or
the engine's displacement increased!) to increase the engine's flow
capacity enough to make a larger throttle body both useful and helpful
under a variety of conditions.
- Dave; '95 854T, 67K mi; K&N and a bit of extra boost...
Re: bored-out throttle body?[S70/98] posted by David Delgado-Rucci on
Thursday, 3 September 1998, at 5:46 p.m.
Since you have a non-turbo vehicle, you have the larger throttle body. I know becasue I used to have a 1996 850 GLT wagon, non-turbo. I called Group six. After several phone calls, the guy told me that a modified throttle body on a non0turbo was not going to do anything since the non-turbos have a larger throttle body. I also posted a notice on this on the aftermarket board on this subjce tand received a couple of responses.
As a little background, racers put on big bore throttle bodies as a way of getting more air into the engine and hence more power. Volvo engineered its throttle body with the consumer in mind. Keep in mind that with more air, you will use more gas. Also, too much air will cause you to make the mixture lean.
My advice is that since you have a non-turbo, you will waste your money on this piece. I would advise that you get yourself a K&N air filter and swap out your regular air filter. Also, look into a sports exhaust from the catalytic converotr back. This will give you a bit more powe (but also more noise.
Good luck
David Delgado-Rucci