Editing Hopping up the 500 Cadillac

==Overview==
Many things were learned about what to use, what works and what doesn’t after many dyno pulls.

==Findings/tips/tricks==
#The crankshaft can be offset ground 0.300" smaller to the same size as a big block Chevy which yields a 35 cubic inch increase. Coupled with a slight overbore you now have 540 cubic inches, and the ability to use BBC rods. This does not affect longevity but does increase torque. Horsepower does NOT really increase without a change in the heads and cam.
*When this is done you can use 6.800" H-beam Chevy rods which are MUCH stronger and very affordably priced. Cadillac rods will fail above 5000 rpm.
*While 1974-'76 large chamber heads can be used, there is a substantial power increase to be had with 1968-'72 small chamber heads if they are fitted with BB Chevy 2.19" intake and 1.84" exhaust valves. Small chamber heads with big valves and bowl work are worth 25 hp over large chamber heads with big valves and bowl work.
*The BEST heads to use are the new aluminum heads from MTS. When these are Fully Ported by an experienced head porter (like BPE) they are worth about 100 horsepower over a stock head of any type.

[[File:Mts cad head.jpg|thumb|left|600px|MTS custom aluminum 76cc "FR" head, ~$3500/pair ca. 2012]] <br style="clear:both"/> 

*The Edelbrock intake works good on a 500 inch or smaller motor if you don’t exceed 4500 rpm. Larger motors or those with good heads need the new single plane from MTS. Power will NOT drop off like the Edelbrock which is airflow limited. The Edelbrock will make 30-40 ft/lbs more torque under 3500 rpm. The MTS is worth 50 ft/lbs torque and 50 horsepower at 5000 rpm over the Edelbrock.

[[File:Mts single plane intake cad.jpg|thumb||left|600px|MTS single plane aluminum intake manifold]] <br style="clear:both"/>

*The factory Q-jet works good on the Edelbrock. It does NOT seem to work very well on the single plane even with rejetting. Reversion from the huge secondaries on the single plane may be the problem.
*Multiple sizes and types of carburetors were tried. Best torque and horsepower with the large chamber heads was with an out-of-the-box 750 Holley. Best by 20 horsepower. The large chamber heads flowed only 710 cfm MAX measured through the carburetor at 5200 rpm under load on the dyno. Larger carbs up to 1000 cfm were tried and ALL lost horsepower and torque.
*The long stroke Cadillac, whether 4.300" stock or 4.600" stroker, needs plenty of cam. Several cams have been tried. For any type of performance use, a minimum of 234-244 degrees intake duration at 0.050" tappet rise with as much lift as you can get, works well. This cam will peak at 5100 rpm but still have good torque at 3000 rpm. With really good heads, add 10 degrees or 244-254 degrees intake duration. Stock heads and stock valves only need about 220-230 degrees intake duration. Anything bigger will not flow any more air because of head flow limits.
*Engine size does not affect HP as much as torque. Engine size DOES affect torque. Shocking as this sounds, A 350 cubic inch engine with good flowing heads will out horsepower a 550 cubic inch engine with poor flowing heads. The 550 ci engine will out torque the 350 at low to mid RPM. TORQUE is what makes the car go. The Cadillac has poor flowing stock heads so you have to maximize torque and help the horsepower under 5000 rpm. This is why the Cadillac is generally limited to 5000 RPM.
*Stock rocker arm stands are prone to breakage at over 100 lbs of valve spring seat pressure. This light spring pressure limits RPM to about 4600. More radical cams or more rpm require more valve spring pressure. This requires aftermarket rocker arm assemblies. MTS and others have some excellent ones that will take high spring loads. The heavy rocker arms require a minimum of 130 lbs of seat pressure. Beehive conical springs work best to counter the harmonics that cause premature valve float. With a normal non-beehive 130 lb spring we were on the verge of valve float at 5100 rpm. Higher spring pressure can wipe out the cam lobe of the Cadillac cam blank because of its small diameter. Beehive springs can extend this to perhaps 5500-5700 rpm with the same pressure. You better have really good heads to flow enough air at that rpm to still make horsepower at that rpm.
*With aftermarket rocker arms you cannot use stock valve covers. You have to use tall ones for clearance.
*The factory HEI distributor works fine if it is modified slightly. The stock advance curve is about as screwed up as any I have ever seen. For performance engines with over 9:1 compression ratio, the curve that seems to work well is 8 degrees initial and 25 degrees mechanical advance at 3000 rpm. For low compression engines under 9.0:1 CR, use 12-14 degrees of initial advance, and 20-22 degrees mechanical advance all in at 2500 rpm. This will give the motor low speed pep. Plug the vacuum advance. They over-advance and cause pinging. This distributor tip also works well in stock applications.

==Dyno results==
With the wimpy large chamber heads and Pontiac valves the best observed and uncorrected pulls were:
*549 ft/lbs torque @ 3200 rpm, yet still made 502 ft/lbs @ 4600 rpm
*442 hp @ 4500 rpm, and still showing 438 @ 5100 rpm

I worked on Cadillac 500 engines back in the 1980s. By the time I replaced everything wrong inside
these poncho Pontiac motors I had hordes of money in this thing. Frustration set in quickly. These engines have so many bad points it's hard to justify them. They are known to have weak oil pressure that can lead to a rebuild or two after an oil change if you don't prime the oil pump. Only stock pumps exist even today. No hi volume ones yet 28 years later. 3500 dollar heads now a days. Wow. For a lousy 100 hp. I decided to put two of these
engines in my thoughts bucket and then used a big rig turbo on them back in 1989. I linked both together with a custom home made coupler. The car ran in the eights on the street on pump gas. I then boosted the engines up to 36 psi. I broke several rear ends not even getting to run the car much. It even broke a Dana 60 rear. I used alcohol in a kit beneath the pump gas carb. Got them running right. I spent 18 years running these motors with my friends in some of there cars. We eventually switched over to duel Chevy big blocks turboed. Too much low end torque isn't good for parts. The rods had broke next when the car did hook. Then the pistons. I replaced all that just to have both cranks break. The guys at cmd swore the cast cranks could take 3000 hp plus. I laughed on
that one. Cadillac motors aren't special. They are all engines. If you can work on big block chevys, you can
on cads too. Just a few rules to learn. This project Sr 71 as I called it put out 3500 hp  out of the two
engines before the cranks broke on the 4th run. As I say. Dynos  aren't real world and do not tax motors very hard. It's funny when these magazine dynos say things like 1350 hp with stock internals with a turbo. Then
they think it won't break in a car under load. Lol. Forged caddy cranks are hard to get and very costly. If
I saved all my money from the Sr 71 cad project and went with my two tall deck 427.s I'd be at 450 MPh. With my duel Big blocks. 3500 hp at 36 pounds of boost and not with busted cranks. 

Cad to do list if you didn't know.
re,drill. Flex plate at machine shop as they are only drilled for stock junk converters.
replace conn rods with forged.
replace cast pistons. No forged parts in this lux motor.
Improve cad block oiling system and plumb new lines.
buy a non regain thin diam. Cam.
replace entire valvetrain. Or build your own.
pay twice as much money for parts as chevys.
offset grind crank .300 the other way to reduce stroke so engine can make power above 5000 rpm.
hog out cad heads and install bigger taller valves to avoid 3500 heads.
cut timing chain cover in half.
deburr block some burrs are coming off with my fingernails and screwdriver.
cut distributer and still won't fit hei under Camaro hood.
make sure to get proper rear sump pan and pickup used. Very expensive.
pick broken parts out of old oil pan and examine.
hope oil pump shift doesn't fall out again into motor while putting hei back in Again.
cad motor with big stroke will have to Rev higher to keep up with a smaller stroke engine you race against.
get rid of uphill intake manifold.
replace all main and head bolts.
make sure to put every last bolt in oil pump.
don't forget of ring on mile long pickup that looses prime after car sits for a day.
buy custom motor mounts.
make sure oil pump doesn't hit cars suspention.
have fun changing spark plug on booster side of car.

Spend 8000 dollars for 550 hp.