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Cadillac 1979 coupe deville
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Discussion Starter #1
I rebuilt a 472 (72) put the 1969 10.5:1 pistons in the .030 over bore.
put the larger valves 2.19/1.84
put the #5 mts cam
hei total advance curved to 36
timeing at 5 btc
had caburator rebuilt and the guy said he set to run rich.
the engine knocks ,ping ,etc , will not run on 92 octane .I'm mixing to about 96 octane and it still knocked going up a big hill.
you stock 68 ,69 (rebuilt or low miles) guys are you running on 92 ?
have anyone else have a similar engine build? what are you running on?
is this the wrong cam for a high compression engine?
I need help because throwing money at the problem is get dead. I want to run on 92 octane.

o it is strong as s-hell but I need to be able to go to the local shell!
 

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'85 Fleetwood FWD
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Maybe your piston/deck height is affecting the quench area. Maybe some detonation is what's going on. Have you tried backing the initial timing off a couple degrees?. The timing mark on the damper may not be accurate, unless you used a piston stop to verify it. If not verified, the BTC timing may be more than what you are reading at the pointer. Try backing the initial timing off about 3 degrees and see if it helps.

The other possibility ( I think) could be that the cam is ground for a lower comp ratio, like the intake valve closes sooner and makes for higher cylinder pressure.
 

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Cadillac 1979 coupe deville
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Discussion Starter #3
thanks
but can i expect a 1969 472 to run on 92 octane?
I would like to get as much feed back from 1969 , 68 owner as possible therefore I know it is being done.
then I will know the cam is causing the detonation
theresfore replace it with a stock cam and be done
 

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Cadillac 1979 coupe deville
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Discussion Starter #4
here is the info on the cam I put in the engine

MTS #5 Series Grinds
RPM range: 1,000 - 4,500 / Advertised duration range: 258-266* / Duration @ .050” range: 208-215* /
Valve lift range: .495-.510”.
#5 grinds are an excellent choice to replace 1974 and newer smog-controlled stock cams. #5 grinds are an updated
version of the “Hottest” cam grind used by Cadillac in their production engines. The 1973 Cad engines were
equipped with a stock cam that had specs in this range. These cams run more lift and duration than the 1968-72 and
1974-79 original cams. Stock-type idle with excellent economy and a good gain over the smog cam. Works
excellent with the stock TH400 transmission shift points. Just leave it in drive, smash the gas, and let the tranny
shift by itself. Peak cruise RPM for efficiency is 2,200-2,500.



I do not know how the stock cam specs.
 

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95 FWB 81SDV 96 FWB 94 Fleetwood
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I have a similar motor ... I have a 1970 472 with 68-69 .040 over pistons, oversize valves and the cam is 224 @ .050 on a 114lsa... but I'm fuel injected.. I have no problem on 93 octane.. I agree with SteelyBill , and check what he has said...
 

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'85 Fleetwood FWD
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I wouldn't go so far as to use a stock cam. Sounds like the one drmanard has works fine. There still may be some other item to check. I'm always suspect of stock high-mileage dampers. They can move on the rubber damping material, putting the ignition timing mark off somewhat. (been there) The engine should run on 92 octane I would think, if cam and ignition timing are OK. Retarding the cam timing around 4 degrees may also help (?)

Just a suggestion......hope you figure it out OK

BILL
 

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Cadillac 1979 coupe deville
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Discussion Starter #7 (Edited)
THANKS,
I worked with it today, started playing with the timeing , I got it reading 2atdc and it seemed to run fine (after adjusting idle screw a little).
I think you got something because, before today; the starter could not crank the engine over when it got warm. at 2 atdc it turns right over when warm.
I can't say it will run on premium yet because the current mix is around 96 octane, but that timing marker was not right.

at 2 atdc it should be backfiring, right?

please keep this thread going " Can your 1968-1970 BBCAD RUN ON 93/92 octane?" I want to get a good selection of high compression owners.
thanks
 

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'85 Fleetwood FWD
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If your engine was bucking the starter, it's a sure sign of the ignition timing being too far advanced. I personally would retard the distributor a little at a time until it doesn't buck the starter, ignoring the timing mark on the damper. I use the timing mark for reference when I get the thing to run good without spark knock, and put my own mark on the damper for future checks.
Is the timing tab on the front cover original?? Some engines have timing tab/pointers that are sheet metal and can be deformed easily, causing error. Don't know how yours is made.

Hope this helps a bit......

BILL
 

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Cadillac 1979 coupe deville
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Discussion Starter #11
it is the stock marker from when it had points.the marker is not at "A" quality, either

piston stop? don't know , will research!
to make sure this theory is correct.
 

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'69 Fleetwood Brougham, '76 Fleetwood Limousine
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The stock '69 472 has a cam with a duration of 312/308 degrees intake/exhaust. Lift is .440/.454 intake/exhaust.

The (stock) 472 in my '69 Fleetwood Brougham was pinging when I bought it. A shop did a few things (distributor work, bigger jets in the carb) and it helped a lot. It still pings slightly at full throttle. I use 92 octane + octane boost. I've read that changing to colder spark plugs helps prevent pinging.

What these high-compression 472s really need is 98-100 octane gasoline (you know, real gasoline!).
 

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'85 Fleetwood FWD
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Many folks who tune for best street performance advise advanced timing settings just barely at the "ping" at full throttle acceleration .
Today's gas sure doesn't help any when older higher compression engines like and need good fuel. The so-called octane booster additives just add to the cost of driving, from a practical standpoint.
It's impractical to run high compression these days. My 500 build is at 9.2 , and I wouldn't care for it to be any higher.
 

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95 FWB 81SDV 96 FWB 94 Fleetwood
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make sure the distributor centrifical advance is working right .. the weights are free and the springs are connected and not broken.. and make sure the vacume advance is working and not leaking.... both these advances can cause problems like you are having...
 

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'85 Fleetwood FWD
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Seems like you need to check everything you and others can think of. You will get it figured out.

When I looked at your cam duration again, it seems to me that the longer duration cam is fine for the compression you have. If it's a performance cam, the intake event should be OK from what I can figure out. Ignition system may still be the problem.
 

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1969 Coupe DeVille, 1972 Sedan DeVille
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I know it's not entirely relevant, but I usually run 93 in my stock '69 and _regular_ so far anyways, in my stock '72. Am I crazy to be doing that? They both seem to run fine. I thought I had used regular in the '69 as well, but don't remember, as it's been a while since that car ran great. I guess there are big differences from '69 to '72. With HEI, shouldn't your timing be at 10 to 12 BTDC? Could your timing, as read by timing light, be way out of whack? I was thinking of putting a MTS #5 or #10 grind cam in, now I am scared.
 

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'85 Fleetwood FWD
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The HEI ignition would not affect timing, just a hotter spark. The performance cams have more over-lap, and usually recommend what compression ratio you should have. Best way is to talk to the dealer like MTS, and get their recommendations. They should know what you need. Sometimes that's quicker than getting all the opinions here ( like mine for instance:bigroll:)
 

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Cadillac 1979 coupe deville
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Discussion Starter #20
update
put 92 octane in the tank, removed the vacuum advance , set the intial timing to 9 btdc, test drove the car . no knocking, no pinging,etc. I will get an adjustiable vacuum advance, to tune her in almost perfect.if not run without vacuum advance.
 
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