Mr. Lamar,

whatever happened to the slide throttle fuel injection you
have on your website? Seems like a good answer to both efi
and carb in terms of cost, reliability, and simplicity.
Vlad


Thanks for reminding me. I just took it off the web site.
Too expensive to make.. Technically risky. If the fuel pressure is less
than about 5 psi vapor lock on auto gas is a real problem. I just took
it off the web site. I recently discovered the  Holley 500 CFM
two barrel carb with leaning capabilities that is far cheaper
with way less technical risk.

The slide throttle is still viable for fuel injection
both 555 type and computer type. Some people may prefer
one over the other. The computer type is probably mandatory
for turbo charged engines.

As I see it today you have five good choices in order of cost
and HP for 250 HP p-port engines taking into considerations idle quality.

Holley 2B or other carb. RX8 eng only. ~ $400
555 EFI ... butterfly up stream from the plenum. RX8 eng only. ~$500
555 EFI ... slide throttle. ~ $500
computer EFI ... butterfly up stream from the plenum. RX8 eng only. $1000
computer EFI ... slide throttle. $1000.

My guess is the difference in HP from top to bottom would be less
than 15 HP all with the same 2.8:1 gear ratio.

The cost can vary some what particularly if you are willing to find
cheap throttle bodies and fuel injectors in junk yards.

The 555 systems use a mass airflow sensor and the computer types
use a manifold pressure sensor which is fundamentally a cheaper device.
Also the computer systems can take up to an extra year to tune and install.
If you have a lot of electronic expertise this process can be shortened
but then you can also build a 555 system. The carb of course is the
easiest, quickest to install and requires zero electronic capabilities.

It is amazing how fast things can change.

Paul Lamar

Seems I stand corrected. So much for cheaper and more reliable. I may
be pissing into the wind by asking but why is the slide throttle fuel
injection system so risky other than the vapor lock problem? Also, when
you say 5psi, you do mean fuel pressure right? I may have misunderstood
what you wrote but why a 2bbl for a Renesis only?
Vlad

You need a leak free moving joint between the slide and the housing.
If you copy the Ellison type a whole bunch of tiny holes are required
which turned out to be real expensive. Ellison gets over $1000 for their
similar carbs.. The 5 psi referred to the fuel pressure. Car gas boils at a lower
temperature and pressure than 100LL aviation fuel. Get Steve Bennetts
book on the subject from Great Plains Aircraft. Dozens of low pressure
carbs (~ 1 psi) have been tried on VW aircraft engines so Steve knows what he is
talking about.

The p-port RX8 engine does not require a butterfly or slide throttle next to
or in the rotor housing to idle well. The p-port 13B on the other hand has
p-ports on the exhaust AND on the intake with lots of port over lap so they
idle like crap. The down draft carb must be mounted at the end of a 18 to 22 inch long
runner for organ pipe tuning reasons and still idle well on a p-port RX8 engine.

Paul Lamar

Wow, not only did you completely answer what I asked but also what
I was going to question thereafter. How do you think the home depot
bleed valve leaning system compares to Tom McNeilly's leaning block?
I understand bang-for-buck may go to the bleed valve, but the
leaning block is a time tested device.
Vlad

The McNeilly's can go to idle cutoff which is much better.
The bleed air device would have to have a rather large hole
to make that happen.

Paul Lamar