Bolt on Throttlebody suggestions

[Alan Barrow]

Ron writes:

> Fancy meeting you here ;)

Small world! Should have figured you were playing in this area as well!

> For my first EFI on the Pinz, I just used the
> Zenith carbs with the idle cut-off solenoids unenergized and the accel.
> pumps disabled as throttle bodies.

Interesting! If I went port injection, I would probably do a plenum, but
using the original bodies certainly is handy.

>  I mounted the injectors (Bosch, about
> 19lb/hr) to bosses that I welded to the runners on the stock manifolds.

You are braver than I am. If I could get $15-25 manifolds I'd be welding
now. But at $200 for a used pair I am not ready to take that step. Besides,
they are angled. I'm curious, I have not even looked. Are our manifolds
Aluminum or Cast Iron?

I'm thinking fabricate some flanges, and use DOM tubing for the runners. I
have found some weld on bosses for EFI I could use, and the CIS injectors
could be even easier with the injector inserts mentioned by others.

One of the Saab's has a nice plenum/TB that has 4 stub outlets which connect
to the runners with rubber couples.

> I am using a home brew ECU that at least works better than carbs but I
want
> to go with a re-maped 727.

Is this the best ECU to work with? I need cheap, well understood, and
capable of being FI only. (No ignition yet)

> I didn't want to use 2 TBI's due to the sequential pair firing order
> (1-2-4-3) of the engine.

one small CIS advantage.  Actually, I had not thought of the sequence issue.
The TBI's I would like to get (TWM, Jenven) are 2bbls with separate
injectors, but they are out of price range for now.

> Why do you want to use a mechanical injection on the Pinz?

Good question. Simplicity and availability of cheap donors is the biggest
reason. Also the fact that they can be dialed in better than a carb, but not
have to run at 14.7. (see text below)

As an EE with lot's of single chip embedded programing & design EFI really
appeals to me, and long term I'll end up there. But I also want to drive the
pinz, not play programming! The CIS requires far less sensor wiring, and
usually works or it does not. It will take some dialing in for sure.

> If it is the
> same one that I had on one of my old SAABs, you will have a tough time
> tuning it through the whole load range on the Pinz and it is sensitive to
> bumps.

Regarding the tuning range range of CIS, there are enough different airflow
sensor/distributor curves available on the cheap that I'm hoping it's not
going to be that complicated. It also helps that the pinz has a 4500
redline. A VW van setup might be a reasonable match for the curve of the
flow rate. (Hard to explain, the curve of the air sensor plenum controls the
air/fuel curve shape. Pressure controlls the steepness of the curve, and
rising rate regulators can influence that even more. The mixture setting
sets the baseline. OK, so it's not a map, but you can do a certain amount of
"programming" of the mixture. Just without the use of electrons!

Also, later K-jet distributors had modifications to reduce the inertia
effect with bumps.

Initially, I'm thinking two  simple plenums about 2" tall on the factory
manifolds with the CIS injectors mounted on top shooting down into the
manifold mouths. Sort of a CIS TBI approach! Since the injector nozzle will
almost be in the runner, I should be able to avoid differences in mixture
due to venturi effects from the airflow into the plenum being off center. A
single two stage throttle body between the two plenums and I should be in
business.

The only downside is that I will probably need to keep the heated air HW to
avoid icing, as the injectors are too far from the head. But, unlike the
traditional CIS setups, the injectors should stay far cleaner. ( I suspect
EGR valves are the main culprits)

Since complete CIS setups can be had for as cheap as $50, it should  be a
fun and reversable experiment. Lot's of 1.5-2.5l donor engines. Injectors
are cheap, and can be cleaned up.

> Do you really think that it needs to be richer than 14.7 of just make sure
> it never goes lean?

Well, the pinz manual sez to tune the carbs for 2-5% CO. The bug guys have
had lot's of problems with 14.7 EFI's offroad, and believe strongly to run
richer. Peak power appears to be richer at 12.6 according to Probst. The
14.7 setpoint is used primarily due to emissions. (Thus the wideband O2
sensors and the injector pulse stretchers on the market for performance
folks)

I'm thinking you have head temp sensors? If I get serious on this I want to
set up individual sensors due to the cooling airflow on the pinz. The
rearmost cylinder supposedly runs hotter anyway, so I don't want to make it
worse by being lean.

After taking another look at the DIY Wideband, I may rethink the EFI issue.
(Sure wish I had caught the kit order!)  I would need to see if there is a
cheap wideband O2 sensor available as well.

Well, good to chat. We'll have to stay in touch on this!

Thanks,

Alan


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