CERV I Hobby Horse Prototype Fuel Injection Unit

[Jim L.]

Re: CERV I Hobby Horse Prototype Fuel Injection Unit

Bob, what nozzles are in your FI unit?

A typical 4800 unit would have been manufactured with Q12 nozzles. Since the venturi cone has been relocated, creating a weaker venturi signal, my hunch is that the nozzles have R or S flow codes to compensate

Jim.

[Bob B.]

Re: CERV I Hobby Horse Prototype Fuel Injection Unit

Jim,

You're good! The nozzles are S-14, which are supposed to be the biggest available when the Hobby Horse was put together.

Bob

[Jim L.]

Re: CERV I Hobby Horse Prototype Fuel Injection Unit

The nozzles are S-14, which are supposed to be the biggest available when the Hobby Horse was put together.

Bob,

S-14 nozzles are probably a good choice, as it turns out.

I've got flow data for a stock air meter and for an air meter with the cone on .125 spacers. This data is incorporated into a spreadsheet which lets me model various FI configurations. According to the spreadsheet, the amount by which the mixture would go lean as a result of spacing the venturi cone can be mitigated by switching to nozzles which flow 10% more fuel (at a given pressure) and by slightly tweaking the two ratio lever stop screws.

S nozzles satisfy this 10% requirement with respect to Q nozzles.

With S nozzles, a good starting point for the ratio lever screws would be to position the Economy Stop screw to protrude from the mount boss .412" and the Power Stop screw .170"

Eyeballing the spacers on your FI unit, they seem to be slightly thicker than .125. If so, then the actual venturi signal for your unit will be weaker than what my spreadsheet understands. When you mount the HH FI on an engine, you might need to bias the ratio lever screws more rearward (richer) than what I noted above to get an acceptable air/fuel mixture.

Jim

[Bob B.]

Re: CERV I Hobby Horse Prototype Fuel Injection Unit

Jim,

285 is a pic of the ratio lever screws as the HH ran. The right screw is a chrome screw with four flat washers. I installed the screws back like this, but will adjust as you say, as necessary. 290 shows the spacers for the cover over the fuel meter air vent. These are exactly the same size as the spacers for the diffuser cone. Pic 463 shows the regular diffuser cone spacer and the extra one, which looks to be nearly three-sixteenths of an inch. 397 is a pic of the nozzles at the bottom of the runners. If you take it off the intake manifold, you sure can't just set it down on a table with these sticking out! 592 is a pic of the fuel meter. With the FAB.W1 cast on it, this may be a prototype of some sort.

Bob

[Jim L.]

Re: CERV I Hobby Horse Prototype Fuel Injection Unit

Bob,

On a properly calibrated FI unit, the distance between the tips of the two stop screws will invariably be between .4" and .5". As found, that distance on your fuel meter looks to be greater than .5" so I wouldn't put much faith in those settings.

In fact, the settings my spreadsheet suggests will probably need tweaking in the rich (more rearward) direction since the actual spacer thickness on your unit is greater than that for which I have flow data.

That might present a problem.

At or near the limits of ratio lever travel, changes in screw settings have relatively less effect than they do near the center of their range of travel. You may find that you can't get the Power Stop adjusted rich enough. If that turns out to be the case, you will need to replace those S14 nozzles with some which are farther down the alphabet of flow codes.

The letters "FAB W1" appear on all production, sand cast fuel meters such as used on your 4800 and also on the 4360, 4520, and the later 7300 FI units.

You've done a nice job with the restoration, BTW. The finished unit looks great.

Jim

[Bob B.]

Re: CERV I Hobby Horse Prototype Fuel Injection Unit

Jim,

If you ever do a fuel injection book, I'll be first in line! You need to share all the data and knowledge you've amassed over the years.

Question: If the ratio lever adjustment may not be adequate and the S14 nozzles may need to go smaller, how would the unit have worked on the CERV? It got 350 HP from 283 CI. Or are you talking about these issues at a lower RPM?

Thanks,

Bob

[Jim L.]

Re: CERV I Hobby Horse Prototype Fuel Injection Unit

Bob,

I couldn't write a complete, ultimate FI book. There are too many things I just don't know. It's possible that a collaboration of several competent FI rebuilders could produce such a book. But by the time it would be finished, would there be anyone still around who cares?

On a serious note, though, none of us who work on fuel injection are spring chickens. In the next few years, I think you'll see a lot of FI knowledge simply disappear as rebuilders retire or pass on. So maybe there does need to be a book.

You might be surprised to discover that getting 350 HP out of a 283 isn't that uncommon or difficult. I know of several 283s used in vintage racing which dyno at or slightly above that level. The FI unit, as it turns out, is not the bottleneck on these engines. One bone stock FI '58 unit I prepared sits on a 283 which produces, as I recall, right at 360 HP. Of course that's at something just north of 7500 RPM.

327s are another matter entirely. A big, dumb Holley will pass more air and fuel and make more power than the most radically prepared, single air meter 7375 or 7380 FI unit.

With that said, I'm still eager to drop my mongrel FI on my friend's '57 airbox car. I want to know if his Seat-Of-The-Pants-O-Meter can tell any difference.

But back to the HH FI....

Just to clarify.... nozzle flow codes farther down the alphabet, "W", "X", etc... are larger and flow more fuel than those earlier in the alphabet, "Q", "R", "S"....

So how could the HH FI have worked "back in the day"?

One possibility is that the "S" nozzles have been enlarged by drilling. That wasn't uncommon back then, although I think the motivation to do that was often misguided. Another possibility is that the air meter has been treated to a modification which recovers some of the venturi signal which was lost when the venturi cone was spaced outboard. What kind of modification? I'd have to study it to find out.

When you are ready to get that FI unit dialed in, you will want to employ the services of a shop with an engine dyno, or a shop with a chassis dyno, or buy and use a wide band air/fuel gauge to calibrate it yourself. (Doing it yourself isn't that tough.)

I use a wide band air/fuel gauge connected to a laptop computer which records everything which happens during a test drive. My reasoning for taking this approach (as opposed to employing a shop with a dyno) was pragmatic: There are no dynos within any convenient driving distance and the ones I know about charge $100 - $200 per hour. At those rates, my equipment paid for itself within half a dozen test drives.

What are your plans for the HH FI? What car and engine will it eventually go on?

Jim

[John D.]

Re: CERV I Hobby Horse Prototype Fuel Injection Unit

Fuel Injection Book needed. One project I always wanted to do and just never pulled it off is this. The best fuel injection information is in the Corvette Servicing Guide ST 12 manual. It's the only manual that features the hi-pressure gear pump.l
The '63 shop manual was an attempt to cover the '63 unit in the old days but was lacking. When RP and GM recalled the early '63 wobble pump they never came out with a follow up manual with the later style pump and changes.
If you own a midyear FI the ST 12 manual should be in your library.
Now for the punch line.
Someone needs to take the fuel injection in from three manuals and combine them into one. Not that difficult to do.
Take the Corvette servicing guide that covers '58 to '62 FI (not '57 as advertised on Ebay), the '63 and the '65 supplement.
The '65 supplement just has 1/4" of a page on the starting system.
That would be a great manual. Go for it for the next generation.
Who is going to take over for us old guys you ask when you die. Well friends there aren't that many young people interested in the antique fuel injections. John D

P.S. As Lockwood mentioned the S14 nozzles were the biggest available in the C1 years. Not that great on a typical '283 though as they tend to run rich. Chevy sold them over the counter as a one that fit all part. Supposedly the nozzle fit '57 to ''62 which is the reason so many of those units come in for restoration with that nozzle.

[James G.]

Re: CERV I Hobby Horse Prototype Fuel Injection Unit

GREAT lessons here. You guys need to teach at the UNIVERSITY before everyone forgets.

[George J.]

Re: CERV I Hobby Horse Prototype Fuel Injection Unit

Yes, a seminar at a National would be great. Some of us aren't THAT old.

George