Performance improvement

[Big Blue]

 If I follow the instructions in Cliff's book about modifying my Rochester Quadra jet for my 500 in.³ Eldorado, how much of an improvement should I see in the performance and the gas mileage of the vehicle ? Also, is this far too difficult of a task for a newbie to attempt ?  Thanks, just looking for an answer or something before I get in over my head.

[Cliff Ruggles]

What has been done to the engine?

All of the later q-jets are emission calibrated, so pretty lean.  With this new fuel and ethanol it ALWAYS helps to custom tune them exactly for the application.  The later carbs have APT, so it's much easier than with the early units.....Cliff

[Marx3]

For your information: I once rebuild a 1780215 for a hot 383 stroker, but never got to using it on that engine. Later on I bought a 1975 Coupe De Ville. The car and engine was completely stock ( 500/th400 with 2.73 rear. )
I put the 17080215 on it and the engine couldn't have run much better.
With base timing bumped up to about 20 in idle ( giving a total about 30 ), it pinged a little on part load. My wide band read 17:1 at cruise. It had 73 jets/44 rods in it. I upped the jetting to 74/ 45 if I recall correctly. This put the afr at  about 15.5:1 and cured the pinging.

The rest of the set up was:
All air bleeds: .070
Idle tubes: .038
DCR: .054
Can't remember if it had idle bypass. Don't think it had.
Secondary rods were Cliff's DA's. Can't remember what hanger, but wot afr was dead on at 12.8:1

The car ran perfect. Startet even better. Even when it was half cold, it would jump to life just by looking at the ignition key and WITHOUT touching the gas pedal :-)
The stock untouched Cadillacs, from the late 70's,  I have had my afr on, all showed near optimal afr's with the original Qjet.
Feel free to copy my setup. After all it WILL make your caddy run perfectly and should also give the best mileage possible.
Just my 2 cents.

[Marx3]

Edit: just found out that the 17080215 did have idle bypass air at approximately .110

[Big Blue]

Marx3,
Thanks for all your information. As a newbie, it is going to take me some time to digest all the information you passed along.
I may just take you up on using your set up.
I don't think anything has been done to my '76 Eldorado. It has 32,000 miles on it and needs an exhaust, so I'll be taking off the catalytic converter off when the new exhaust goes on.
My carb is pretty clean, but the casting wholes have been filled with epoxy. At Cliff's suggestion I am going to pressure test them before I tear the carb completely apart.
My unit is a : 17056230, 1976, Quadrajet 4 barrel-Federal Standards, Cadillac, Automatic Transmission, if. My decoding is correct and it should be, because it matches the car then.
Thanks again.

[Big Blue]

Hi Cliff,
There has been nothing done to the engine that I'm aware of. The car has 32,000 miles on it, it's a 76 Eldorado convertible. It needs an exhaust and when we put that on, we're going to take the catalytic converter off.  The carburetor number is 17056230, and matches the car perfectly. The carburetor looks pretty clean I'm going to pressure test the casting plugs on the bottom this morning as I get started they are filled with epoxy but at your suggestion from an earlier conversation that we had on the phone you said that that shouldn't hurt anything in that normally they aren't leaking I bought a rebuild kit from you about two months ago and I'd have to look at it in order to determine what  parts were actually included. I'm going to say that it was for standard rebuild but we also included new choke pull offs. So I'll be getting back to you in the future about probably all doing some modification after I get the car up and running again and I'll pull the carb back off. By then after getting the rebuild on I'll have a little more experience and maybe I won't be as intimidated about doing the modification from your book still looking for any help and suggestions though thanks to everyone.

[Cliff Ruggles]

I would rebuild the carburetor and leave everything stock.  I would remove the plug over the APT screw, and thread the casting for a set screw, so you can remove it and fine tune the APT without taking the carb apart.  Nothing else should be needed anyplace....Cliff

[Big Blue]

Cliff,
I certainly appreciate your input and knowledge and will follow what you have to say. I had thought about doing the modification because it's there in the book and I thought that it would possibly help to increase the mileage and the performance of the vehicle a little bit but if stock is going to do the job then obviously it's that much  I had thought about doing the modification because it's there in the book and I thought that it would possibly help to increase the mileage and the performance of the vehicle a little bit but if stock is going to do the job then obviously it's that much easier for me and keeps me from getting into something maybe over my head.
 I'll let you know how it's running as soon as I have it back on the road thanks Cliff

[Marx3]

Funny thing, and I just took a look at a 17056230 yesterday. It's on my good friend's '76 Eldorado.
The jets are 70 and the rods are 41P.
Even with the APT turned up pretty high, the engine was still feeling a little tame at low rev's.
I installed 71 jets and had to back the APT out about 4 turns to get a good result on tip-in.
I bumped the timing up to 12 in idle ( this gives a total of low 30's at around 3200 rpm ) and installed an adjustable vacum can for the HEI.
The car went from slow, stock and tame to frying tires when launching too hard in 1st gear. Mid-range power has increased quite a bit. It takes a lot less throttle opening to keep the car at 50. My wideband read 14.3-14.5:1 at cruise.
I installed DA secondary rods because the car developed a loud clattering noise that sounds a bit like detonation. Don't think it is though.

[69dvc]

Hey Marx3 or anyone suggestions welcome..

I was intrigued by the Caddy 500 setup mentioned above. I've a 69 472, stock w/ Electronic ignition. My stock engine has a different cam, displacement and higher compression ratio than the 500.. 

I have sized up from 70 jets to 72 on my 7029231 OE quadrajet

It runs quite well with advanced timing BUT it knocks / pings badly at WOT at highway speeds. I feel it is running lean and was considering going up to the 74 jet / 45 rods which worked well in that 75 Caddy

Could this cure my pinging?

[Cliff Ruggles]

One you have the primary side working as it should, ALL full throttle tuning is done with the secondary metering rods.  Trying to fatten up full throttle with larger primary jets will just hurt fuel economy.......Cliff