FI nozzle size / unit series relationship

[G B.]

I've tried for decades to find a GM chart that cross-references FI nozzle orifice sizes to the different unit model series. I'm looking for a Chevrolet chart or text that says something along the lines of: "the 7017375 series used W nozzles except for the Z06 models which had X nozzles".

I've had no luck so far. The best info I've been able to assemble is a chart based on the nozzle sizes the other FI rebuilders have observed in supposedly original units. I've also collected and checked the Helm manuals for the different model years, but they only mention available replacement nozzle sizes.

I'd like to list the "correct" nozzle sizes on my website to spread the right info before it is lost to time. However, it may already be too late. Can anyone give me a hand with this?

[Alan Drake]

Re: FI nozzle size / unit series relationship

Jerry,
Not right on point, however I just looked at a 72 Parts Cat, Gr 3.332 and believe its a good start. Know others on board have earlier Parts Cat that can fill in the blanks. If you want me to scan in the page, email me at akdselectman@hotmail.com

[G B.]

I appreciate your offer

Alan, I've got a relatively well spread collection of P&A catalogs that cover this period. Unfortunately they only show the limited range of replacement nozzle sizes that GM offered over-the-counter. I don't think they accurately reflect the original nozzle sizes installed in units by Rochester for the assembly line.

[John D.]

Re: FI nozzle size / unit series relationship

Jerry, I don't believe such a chart exists. All my info I have is from hands on experience over the last 40 plus years. You mentioned the 63's. Most all of the 63 Z06's that are the real deal had "X" nozzles. Most all of the other 63's had "W" nozzles. Most of the 64's had "Y" nozzles and most of the '65's I have seen had "X" nozzles. Notice I say most. I have learned not to say all. Safer to use the word typical instead of most.
Meanwhile I have only seen bits and pieces of nozzle info. I would say that the Chev. parts manuals would not be the place to find this info. They tend to list just the replacment nozzles for a series of units. That's why we see so many S14 nozzles. They are the generic replacement for '57 to 62. But as you know they sure are a tad large for typical 283s. Also the midyear replacement nozzle was the "Y"'s. Like you said the rebuilders have their own made up chart. Brian Futo may have had a chart many years ago in the "Restorer". I once asked Frank Sciabica of Rochester Products about a chart for the nozzles. His answer was that none was ever printed to his knowledge.. I also asked Frank why you see some '62's with Q12's, some with R13,'s and some with S14's. His answer was they were just using inventory on hand. He said the bean counters were dissatisfied with the sales and the inventory was high and the profits were low so the assembly line was given instructions to use up parts on hand. Not a good answer I thought but a truthful one. If you ever find a Rochester Products chart it will be a miracle. If you want I can sometime send you my personal opinions. One last thing. The low HP units really used some weird tiny nozzles. '59 to 61 low HP used L's,M's, N's. Those were used on the 7200's and the 7300's. You don't see many of those around. Some day I may write a little undocumented article on nozzles. Maybe I will do it for our chapter newsletter. We need technical articles although the subject will be quite boring for our members but it is at least an article. Merry Christmas, Your friend, John

[John D.]

Re: FI nozzle size / unit series relationship

Correction to my last post. I meant to say that the L, M, N, nozzles were used in the 7017200 and 7017310 units. The 7017300 units did NOT use such a tiny nozzle. That particular unit used Q12's, R12's and R13's. Sorry about the typo. John

[G B.]

Re: FI nozzle size / unit series relationship

John, I've still got my notes from our conversation about this subject three years ago. Gail and Frank have also told me what nozzles they've seen, but I don't believe anyone has inspected the variety of units that you have.

I'm making this public appeal for documentation with little hope for success. If Rochester ever made a nozzle use chart, I think they stored the only copy in the file with the St. Louis Corvette build sheet records.

I'll circulate a draft of my nozzle use chart for comments before I put it on my website. That way everybody can help make it as accurate as possible. I want to end up with a calibration chart to go along with it. Many of the set pressures shown on the GM calibration chart are ridiculously high, and we need to get the correct info out there before we pass our manometers on to the next generation of wrenches. Well, actually Margaret says my FI tools are going to the landfill, but maybe some of the other tools will be passed on...

[Mike McKown]

A few questions:

When an assembly line worker picked up the FI unit and set it on the engine, how would he know the engine was going in a ZO6 and how would he know it contained larger nozzles or nozzles of any size for that matter. Just curious. The engine stamp pad wouldn't tell you. No ID on the FI to tell you either that I know of.

Is there any possibility Rochester determined nozzle size to match fuel pump output?

What good would it do to change nozzle size as long as you're running gasoline and not something like alcohol? You're still looking for the same air/fuel ratio. A Z06 engine requirement wouldn't be any different than any other SHP engine.

Just some things I've wondered about.

[John D.]

Re: FI nozzle size / unit series relationship

Jerry, The FI nozzles have always been a confusing issue. Most think that Rochester Products made the bulk of the nozzles. But actually Detroit Diesel made a lot of them. The sets in the small brown boxes not individually wrapped are from them. But we are not talking about who made them.
Sooo many confusing issues that took me years to unravel.
Let me site an example of two confusing nozzles to the novice and others.
Q nozzles: They came stamped, Q, Q11, Q12. Q11 was low HP. Q12 was hiHP. So then what is a Q nozzle? Until I learned the proper way to measure and test nozzles I though that an over the counter replacement Q nozzle was a hiHP. But in fact it is not. It has the same orifice as the Q11. Go figure. Orifice size alone is not the total picture. The screen has a lot to do with the flow also.
Now the S nozzle: S13 is hiHP for the 57-58 '4960's. S14 was typically used in 62's. I don't know if a 283 unit ever came from the factory with an S14 though.
I see the S14's in so many units that come in the door for restoration. I moan everytime I see those things because off the bat I know the customer is in for an expensive set of new nozzles. Failure to replace them means the unit will be coming back to haunt you.
Then there is the "S" nozzle. Another typicaly replacement nozzle which I have determined is a tad smaller flow than say the S14. Probably it is about the same as an S13. I have used S13's and plain S's in one unit with no difficulty.

Those two classifications of nozzles have made it difficult for the FI owner over the years.
One I forgot to mention is the "R" nozzles. You occasionally see a set of R12 nozzles. Those are rare babies. Typically you see the "R13" nozzles. I don't think RP had an R nozzle just stamped with an "R". If so I never saw one.
It would be rather simple to make up a chart of the various applications.
I am sure it would be a topic of discusion for many years but at least it would be a nice guide to follow for a start. Now is the time to do it as most of the guys involved with FI's are getting old like me.
Common mistake made on our antique fuel injections is uning too big of a nozzle. The units typically need more air flow and not more gas. Sorta like most of us on the DB. John

[John D.]

Re: A few questions:

Mike, I have wondered the same question forever. Don't know the answer. I have restored more Z06's than I care to remember. All but one had the X nozzles. I mean ALL. Course ALL means just the ones I have seen. But I have seen more of them than most of us. Whew! Hate to think how many Z06's I have restored and the real ones had X's. I don't know how the assembly line worker did it. Maybe there was a separate pallet to select from. Other restorer's in the business agree with my observation though. But it's not scientific. No documentation. Just plain old on hands experience. Wouldn't hold up in a court of law. But if I see a Z06 unit come in without "X" nozzles I tend to think that it is a little suspicious. Hopefully there is an old assembly line worker still alive that can shed some light on this mystery. I would be thrilled to know the answer.
Typical '63 FI cars use the "W" nozzles in case others are wondering.
"W"'s are the next size smaller. John

[Robert Jorjorian]

Re: A few questions:

JD maybe the airmeters had the nozzle size written on them.Ask Michael Hanson for a pic of one,Robert

[G B.]

Impact of FI nozzle size

In theory, you should be able to calibrate any unit with almost any nozzle size that Rochester ever offered. However, in the real world it just doesn't work that way.

The larger nozzle sizes work poorly at idle in an engine with a low fuel volume requirement, such as a 283 with a very mild cam. Such engines run quite efficiently at low rpm. They just don't need much fuel volume below 1,000 rpm. But, when you lower the nozzle pressure for a proper air fuel ratio at idle, the pressure gets so low that the nozzle doesn't actually "spray" the fuel. Gas will also drip or dribble from the tip. Dripped gas doesn't vaporize as quickly as it does in a spray, and the idle quality goes to hell.

The above only applies to those engines that are driven at normal speeds in traffic. I've noticed that many FI owners are not concerned about idle characteristics. They set their distributor advance timing with a dial-back light at 4,000 prm, and they idle their engines at 1,000 to avoid percolation and stumbling. They don't need no stinkin' 800 rpm idle. To them I say: Suit yourself.

[John D.]

Re: A few questions:

RMJ, Here's one for you about Z06's and FI's. I bet Zora had a lot to do with the Z06's and the FI's. In fact we know he did. I bet he was the one that said to put the bigger nozzles in them. Remember when the 63's were first racing they used to break down a lot. Why? Cause the 63 had a new axle link from the 62 down that had a cheep thin piano wire that was breaking. So the FI's came to a halt and the cars coasted off to the side of the track. Remember those days well with the Grady car that Dr. Blatchley from Greensburg, PA owned and drove. The axle link broke and Timmy and I put in a new one with the thick wire like the 64 and 65's. Zora was handing those new heavy duty links out for free to the race teams. He knew the 63 link was a POC and was breaking easily. You never see a 7380 link broken. See them wore out but not broke. So to recap I bet the old ZD saw to it that pallets of specially marked FI's were installed in the Z06's. Except for yours that is. Jr.Meanwhile what kind of wax you using for your tanker??? And what kind of shipper are you using. I mean come on guys., Lets talk technical. Make it a NY's resolution and quit talking about sissy stuff.

[Michael H.]

Re: A few questions:

John,

I seriously doubt there's any truth to the rumor about all Z06 cars having FI units with X coded nozzles.

First of all, the engines were shipped from Flint with the FI unit installed. It wasn't installed at the St Louis plant. This would have required the "special engines" to have some highly visible code or marking so plant workers in both Flint and St Louis would be able to pick out these special engines without having to look closly at an FI nozzle. In addition to that, there wouldn't have been time, or the space, to pull several FI engines off the rack, especially the upper levels, to inspect nozzles until an X nozzle engine was found. I don't know how much extra storage space the Flint plant had but I know no such event ever took place at the St Louis plant. Engines were ******ed off the rack and loaded on the conveyor. The letter code "RF" was all that was used for selection.

Also, I seriously doubt there is any actual performance benefit to a particular nozzle code, at least in the C2 cars. (not the case for C1 cars) Supposedly, all of the nozzle orifices were the same size, .0115", for all three of the available "375" and "380" nozzles. The difference was in actual flow numbers.

Several different variables in other components of the system called for different flow rate nozzles. The pump, fuel meter and nozzles were supposed to be a matched set in production. The middle flow rate nozzle, the X nozzle, was supposed to be the target. However, slight variations in other components would require a higher or lower flow rate.

One of those variable components, the pump, was responsible for much of the difference in low RPM line pressure. As I'm sure you know, every time you disassemble and reassemble a pump, the output pressure and volume changes slightly at low RPM. That's because it's nearly impossible to position the floater plate in the exact same position that it was in originally. One or two thou difference makes a difference in low RPM output pressure/volume.

This is one of the reasons why GM/Chevrolet serviced ONLY fuel meter assemblies that included the nozzles and lines in the very early days of FI. (1957) No "field service" specifications or manometers were available to dealers at that time so the entire package had to be replaced. If you ordered a new fuel meter, it automatically came with the other items mentioned.

Just another reason why most people should not attempt to overhaul their FI pump unless they REALLY know what their doing. I would recommend sending it to you or Jerry.

[John D.]

Re: A few questions:

Michael, Wonderful theory you have on the X nozzles. But why is it then that 99% of the Z06 units I have seen have the larger nozzles? Must be some explanation other than yours or mine. I have been asking Z06 owners for many years to let me know what there nozzles are stamped. W, X, Y. Most all came back with X. I realize that your nice letter sounds more realistic from a manufacturers standpoint though. But neither one of us have proof.
As far as the high pressure pump goes you are correct about the spacer clearance effecting pump pressure. That's why interchanging pumps can produce a difference in operation. One last thing is that there is a definite difference in flow between the W and X nozzles. I know you used to rebuild a lot of units. Too bad you still don't do so Michael. Keep up your excellent posts on this DB. Your posts are one of my favorites. The technical info you have supplied is an asset to our hobby. The photos you have supplied are educational to say the least. Now how about a close up of a Z06 with X nozzles. RJ's tanker has X's you know. RJ's '63 has "X"s. Do you know any other differences in the units besides the nozzles. ssshhhhh. John

[John D.]

Re: Impact of FI nozzle size

Jerry, My 63 with it's freshly rebuilt engine idles at 875 real nice. 875-900. At first it idled at 1100 for about the first two hours. After it got broke in a tad and I changed the BLUE spring it dropped down to the 875. I didn't try and go any lower although I thought of you and the 800 thing. Meanwhile in the hills of SW PA it is difficult to start our going up the steep trailer ramps with only 800 RPM. John