500, 472, 425, 368 Discussion, 1975 Caddy Needs More Power From 500 in Cadillac Engine Discussion; Okay...
I am the proud owner of a 1975 Cadillac Coupe Calais with 54,000mi. Gotta luv it. I know that ...
I am the proud owner of a 1975 Cadillac Coupe Calais with 54,000mi. Gotta luv it. I know that 500s are capable of some major power, but I don't know where to start. Thus far I have put on duel exhaust with Flowmasters and no cats (it sounds mean), an Edlebrock airfilter, replaced the cap and coil, and other tune up stuff. I need to know where to head next. I think the carb could be rebuilt. Would an Edlebrock intake add much horsepower? How about a new cam? A step in the right direction would be helpful. One other thing, how would I go about lowering the beast? Should I cut the springs, have some custom made or is there some company out there that makes lowering springs for this car...I don't want to sacrifice too much ride though, that's the best part of the car, but it does need a better stance. Any advice would be great...
Make sure your distributor advance is working properly. HEI's have a tendency to rust and bind.
You probably won't make any significant power unless you change the heads and cam. Learning to tune it can make a significant increase both in gas mileage and power. Carb tuning and dist adv tuning can make a big difference. I don't do it much anymore but on the 60-late 70's cars it could be a 25% increase in gas mileage. Can't ggive you a percentage on performance but "seat of the pants" said quite a bit.
I would have the Q-jet rebuilt. Also, on the site zonie listed, check out the manifold with the plenum cut out, and look at the numbers compared to the Edelbrock. I would advise you to do this as it's a very cheap way to gain power, and you get to retain the A/C without any custom brackets and different compressor, which would be required if you ran the Edelbrock. The cam is pretty weak, and a mroe agressive one will really wake it up. About the heads though, you don't need to change them. A good porting makes a difference, as does larger valves. All things to think about. Also, if you get a more agressive cam you will need new springs and retianers, and possibly new rockers depending on how much cam you get. It really all depends on what you want from the engine and how much you are willing to spend.
Automobile(s): 1995 ETC, 75 Deville, Cad500 powered 73 Apollo, 94 Mark VIII
Re: 1975 Caddy Needs More Power From 500
First thing, cut the center divider out of the intake manifold like the pics show on my site (pics courtesy Torque INC) and use a 1" carb spacer. The Edelbrock 2115 isn't a bad piece, it has minor fuel distribution problems that wouldn't be a big issue in your car IMO, and it saves a pretty good chunk of weight. But the center cut divider and 1" spacer flows within about 95% of the Edelbrock. According to Potter (and others for that matter) the Edelbrock will pull to about 5500rpm, so a center cut one should be perfectly fine for a >5000 application. I do not know if the 2115 will clear your hood, I've never checked if it would clear mine but it looks close.
Next I'd go with a cam. Nothing too radical, something along the lines of an MT10 from MTS, or an equivalent from the other vendors (check the "vendors" page on cadillacowners.com.)
Then go for some headers, if you don't have access to a good welder to stick Cad flanges on BBC headers then I'd suggest the Deville headers MTS sells. A good dual exhaust is key, hope you didn't go real HUGE, a nice 2.5" mandrel bent system would be great for this application.
As a beginner I wouldn't touch the heads, unless you have them off and disassembled in which case you might want to whack .020 or .030 off them for a bit more compression.