News:

Due to a technical issue, some recently uploaded pictures have been lost. We are investigating why this happened but the issue has been resolved so that future uploads should be safe.  You can also Modify your post (MORE...) and re-upload the pictures in your post.

Main Menu

1972 500 engine conversion to high compression

Started by hirvine, June 17, 2021, 12:27:05 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

hirvine

Hello:

I have the engine from my '72 Eldorado disassembled at a Valley Head Service in Los Angeles.  I don't want to make the car a hot-rod, but am considering moving it to the 1970-era compression ratio (10-1?) and a slightly more aggressive cam.  My understanding is that when GM lowered the compression, they did so by adding volume to the heads.

What would be the best way to get back that compression?  I have to get new .020 pistons.  Should I look for higher compression pistons, or should I try to do something with the heads?

Thanks in advance.

H

"Cadillac Kid" Greg Surfas 15364

Harlan
The difference in compression is in the pistons. That said for the 10.5:1. Impression ratio to be knock free you need at least 93 octane gas, something you don't have in LA.  That said there are high compression pistons available and I would suggest you talk to Courtney at CadCo. They seem to be the last of the Cadillac high performance parts suppliers left. Again that said I think you will be disappointed by just the change in compression ratio. You will pick up something like 20 HP which will be unnoticeable in that Eldo. Talk to CadCo about a cam. They have one that will improve your low end torque without sacrificing idle quality. There is a whole lot to learn about Cadillac high performance. They  be are mot small block Chevrolets. They are low speed torque motors. That's not to say they can't be built to perform. I am currently running a 575 hp/750 lb-ft torque motor in my 73 Coupe Deville and turning 12 second quarter miles, but it's taken a bit to get there.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

hornetball

Echoing what Greg said, big Caddies need torque.  Personally, I would keep the engine CR as-is.  It is setup perfectly for today's fuels.  A camshaft is a good idea.  Look for one that optimizes torque and smoothness.  I installed a Comp Cams High Energy 252H grind in mine.  The car moves out smartly and idles like butter.

fishnjim

www.cad500parts.com
This is who you want to talk to.   They build 'em, too.   Or post on the modified side.
Be careful what you ask for, you'll have an air polluting gas guzzler in no time.   Check your local air regs if emission compliance/tail pipe sniffing is req'd where U reside.

Can the front transaxle take the HP?   That's an early year.   Took a while to get them figured out.

Compression lowering was all about HC emissions and cleaner burning in pre-catalytic era.   They increase inches to provide the torq and partly cube envy-o-day.   

76eldo

I would try to get as much info from Greg as you can.
If he's running 12's then he knows how to make these Caddies boogie!
Brian Rachlin
Huntingdon Valley, Pa
I prefer email's not PM's rachlin@comcast.net

1960 62 Series Conv with Factory Tri Power
1970 DeVille Conv
1970 Eldo
1970 Caribu (?) "The Cadmino"
1973 Eldorado Conv Pace Car
1976 Eldorado Conv
1980 Eldorado H & E Conv
1993 Allante with Hardtop (X2)
2008 DTS
2012 CTS Coupe
2017 XT
1956 Thunderbird
1966 Olds Toronado

The Tassie Devil(le)

When I rebuilt my '72 Eldo engine, I went for the '70 pistons, and then planed the heads, decked the block, and ran a MTS No. 5 Cam, and fitted bigger valves.   Now run Water Injection to control the pre-ignition problems with high compression. (Used to run Octane Booster) and larger exhausts and a Predator Carby.

Bruce. >:D

PS,   The '70 pistons (1st picture) have a shallower dish than the '72 (second picture).   Head with bigger valves in the third picture, and blocked off Exhaust Crossover (Last picture)
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

"Cadillac Kid" Greg Surfas 15364

The number 5 cam is a good one but it's essentially designed for a low compression motor. First decide exactly what you want, what you will sacrifice in the way of smooth operation and what you want to spend. The answer to the appropriate mods will then be simple.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

The Tassie Devil(le)

Thanks to information from Greg Surfas, it turns out that the cam in my car, which I took to be an MTS No. 5, is actually the same cam Specs that went into the  actual 1973 Indianapolis Pace Cars.   Mine is a Lunati Brand.

Thanks Greg.   I love this Forum.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

hirvine