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[Cyncwby]

Howdy to all, Dave from So. Utah, retired street cop from So. Cal..... new to the Cadillac 500, last Cad I worked on was my Dad's old '47 flat motor......a long time ago (I'm 64 now GEEEEZ) anyway I'm in the process of building a '32 Victoria with a 331" sbc and 700R4, it was a very nice set up but as you guy's know...Everyone has a Chevy in their hot rods, wanted something different.

When a guy made me the proverbial "offer I couldn't refuse" for both eng and trans I sold it and started looking at the Cadillac. I found a complete rebuilt w/40K miles '75 500 w/ 400 T for $250 and snatched it up. I'm going to put some horse power in it so when I pulled the heads you could still see the cross hatch on the cylinders and the .030 Silvolite pistons look like new. I already have a set of forged rods w/ ARP cap screw bolts.

My question is what are the best type of rings to run on these engines...moly or cast? Parts list will be Edelbrock 2115, 770 or 870 Holley, #15 cam, Dave's small cap HEI, home ported heads (I've done about 20 sets over the years...don't go hog wild) MTS non- adjust shaft roller tip rockers. Shooting for 9:1 compression, hope to learn a lot on this forum....ok, I'll shut up now......

[Nashalac]

If going to do a machine hone on the cylinders the moly are best. If doing a "dingle ball" hone the iron rings are more forgiving

[Cyncwby]

It will be a machine hone, just going to "kiss" it a little to re-establish the cross hatch. There's no ridge or taper so I think it will work out ok. Also which carburetor would be best for this combo...and keep in mind this will be mainly a cruiser with an occasional WOT blast on a lonely stretch of road, 770 or 870 Street Avenger? I still have the 800 cfm Q-jet that came on the engine...but they are sooo butt ugly.

[Schurkey]

Originally Posted by Cyncwby

I still have the 800 cfm Q-jet that came on the engine...but they are sooo butt ugly.

But they are sooo superior in part-throttle metering; while giving up nothing at WFO if properly calibrated.

[Cyncwby]

Yes I agree 100%, I've had several...but they are ugly as hell compared to a Holley. So besides a Q-jet which cfm would suggest for this engine build, a 770 or 870?

[Schurkey]

Originally Posted by Cyncwby

Yes I agree 100%, I've had several...but they are ugly as hell compared to a Holley. So besides a Q-jet which cfm would suggest for this engine build, a 770 or 870?

CFM is primarily related to engine size and maximum RPM. Secondary factors are engine pumping efficiency and intake manifold type.

How high are you going to spin this thing?

Displacement X RPM / 3456 is the base equation.

EXAMPLE:

500 cid X 4500 RPM / 3456 = 651 cfm

651 X 75% volumetric (mass) efficency = 488 cfm

488 X 130% (Manifold correction factor) = 634 cfm

Where 75% volumetric efficiency and 130% manifold correction are wild-ass guesses at your engine combo. More efficient engines can use a larger carb; more efficient manifolds can use a smaller carb. The two often offset each other to a large degree.

Clearly, a Holley square-bore at either 770 or 870 is WAY larger than you'd need at 4,500 rpm. You'd have more flexibility with a 750--800 spread-bore because you'll still get good metering on the small primaries.

[Cyncwby]

Even with the upgrade to forged rods and the shaft rockers I will have a self imposed redline of 5,000 rpm (on rare occasions), just no reason to twist it any higher past it's power curve. I'm aware of the VE formula and it makes perfect sence but thanks for the reminder.

The decision to run the Holley is based on two factors...one, I know how to tune it and have never really "tuned" a Q-jet. Two, which I know is pretty vain on my part, but as said the Holley just looks a lot better. I'm not into all the polished alum. (except valve covers) and billet stuff but with a hot rod you want the engine to "look hot rod".

So assuming I stick with the Q-jet and the fact that I really know nothing about the high perf. tuning of one who's book or website should I look at. I am aware of a couple of the perf. Q-jet shops, called one several years ago and it was something like a 6 month wait and $600 to rebuild MY carb! No thanks. Schurkey...I do appreciate your knowledge and help.

[Schurkey]

http://www.amazon.com/Rebuild-Modify...=31ORN63IXRW6M

This is one of two "must have" books for Q-jets. This is the one for learning how to tune the carb, and it has beautiful in-focus color photos. The other is more for understanding how the carb is supposed to work. Of course, there's a lot of overlap--which is why I suggest buying both.


This is the other one. Older, still worthwhile. My edition is even older, and has no color photos. I expect this one is the same.



http://www.amazon.com/Rochester-Carb...=31ORN63IXRW6M

[Cyncwby]

Ok, very good, I learned the Holley, not too old to TRY and learn these...thanks, Dave
One more thing...is the '75 year Q-jet a good candidate for a perf. rebuild or should I look for another carb?

[Schurkey]

Originally Posted by Cyncwby

Ok, very good, I learned the Holley, not too old to TRY and learn these...thanks, Dave
One more thing...is the '75 year Q-jet a good candidate for a perf. rebuild or should I look for another carb?

75 was something of an interim year; first year of the new-style "modified" Q-jet (Mod-Quad) and some of them had difficult-to-work-with internal metering parts--aneroid bellows, goofy part-throttle metering. IF (big IF) the Caddy carb you have doesn't have the worst of the goofy internals...yeah, it'd be fine as a starting point. If not, find a '76 or newer unit. I expect the choke and throttle linkage would be similar if not the same, so it should cross back to your '75 engine nicely.

A bit of research; and some help from Ruggles' web site for Q-Jets (he's the author of the first book, above) should get you going.

http://www.cliffshighperformance.com...machinesforum/