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1971 Cutlass Supreme Loss of power
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Jaod
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Jul 11, 2015, 4:17 PM
Post #1 of 8
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1971 Cutlass Supreme Loss of power
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Hi, I need some help. I have a 1971 Oldsmobile Cutlass Supreme with a Rocket 455 7.5L engine. As you know this is a pretty mean engine. Recently, however, I have noticed a severe drop in the engine's power. Used to be I would accidentally peel out of a parking lot if I wasn't paying attention, now I can floor the engine and it accelerates much slower than before. No noticeable symptoms other than the loss of power. Any help would be greatly appreciated.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jul 11, 2015, 10:52 PM
Post #2 of 8
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Re: 1971 Cutlass Supreme Loss of power
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Check valve timing on Olds big blocks with that complaint. TMK it is an interference engine but unlikely to jump a timing chain enough teeth to cause damage. Smooth loss of power a strong clue all at once. That or backfires for no real reason.
Check for a sudden exhaust restriction also with that complaint,
T
(This post was edited by Tom Greenleaf on Jul 11, 2015, 11:02 PM)
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Discretesignals
Ultimate Carjunky
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Jul 12, 2015, 11:05 AM
Post #3 of 8
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Re: 1971 Cutlass Supreme Loss of power
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Check engine light on? 
Has this engine been modified? If so, with what? Does it have misfires, idles rough, or back fires? Have you pulled any spark plugs to see how they are burning?
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jul 12, 2015, 11:06 AM)
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Tom Greenleaf
Ultimate Carjunky
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Jul 12, 2015, 2:20 PM
Post #4 of 8
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Re: 1971 Cutlass Supreme Loss of power
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CEL, DS - crack me up! 1971 Old's didn't even change dash to read "alternator" yet still had red warning light said "GEN."
Jist of this whole question and age of car is going require knowing how close to original things are. OE timing cam gear was nylon but should have been done long ago now. OE exhaust system was double metal pipe* such that inside pipe could collapse and outside show nothing wrong making a wild back pressure unseen by eye but those pipes can't be OE this long later. *Those almost all did that when hitting a puddle by surprise.
In short - what do you have here?
T
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Tom Greenleaf
Ultimate Carjunky
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Jul 12, 2015, 3:57 PM
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Re: 1971 Cutlass Supreme Loss of power
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I saw that. Was also trying to remember the front exhaust on these? I'm forgetting but OE had one crossover pipe and I think passenger's manifold held two pipes? I forget now exactly or if this used a "heat riser" on a spring that forced all exhaust out one side? Dunno what might have been done now to exhaust on this but to me exhaust restriction somehow seems like a reason to check out,
T
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Jaod
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Jul 12, 2015, 7:37 PM
Post #7 of 8
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Re: 1971 Cutlass Supreme Loss of power
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No modifications to the engine, basically all stock as far as I know
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Tom Greenleaf
Ultimate Carjunky
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Jul 12, 2015, 11:32 PM
Post #8 of 8
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Re: 1971 Cutlass Supreme Loss of power
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OK - Hard searching so need to know how much you can identify. 3 common 455 were used, 2V, 4V and 4V HP. It may matter if HP = high performance.
A heat rise is like a choke on end of one side's exhaust manifold used on these originally. What that did is force hot exhaust to cross under but thru intake manifold to warm it up fast. Fine but they could stick and didn't have the power of being warmed up but would quickly from a cold start but if those stayed stuck you lost power and might even knock like bad or way too low octane fuel.
Only one side had them and could be removed, many were TMK. Manifold with one look like this if dang pics show.........
 
^^^^^ like that stuff if pics show - if not try Google Images or Bing Images for Olds heat risers,
The thing on the side should move by hand all the time but don't touch it unless cold! If it has this thing and it doesn't move try to free it up with product like PB carefully. If stuck tight and has this it may need to come apart to free it up or decide to get rid of it which means a different exhaust pipe there - parts just looked for not so easy so I won't keep looking till I know what you have.
That was common especially if a car was left without using it for some time - clearly this car. It could plain break anytime.
It's near impossible that this area of exhaust hasn't been touched in all these years so studs and gaskets may be a reusable type or very rust resistant parts used or not and then it's hard to mess with without torches or beyond chance of not breaking things - YOU need to know overall condition of things like this with pics or a good description.
Do you own a vacuum gauge? IF not get one - cheap enough and real handy anyway but if you are going to DIY things on this car should own one - best the pistol type pump and gauge.
Reason is many items are vacuum controlled even this heat riser could be? Need to know then if so need to test it plus have gauge you can test for exhaust restrictions which I can explain later.
Owned two of these engines, worked on countless but were mostly under 15 years old but close to that. Not "special" cars yet at that age quite yet.
Questions asked are because this was the body of what would be one of the last real American Muscle Cars at least and very desirable for its parts if a boring model like this or less but nice parts for real road burner models many would have all redone exhaust if only to look great long ago.
Would really help to post some pics of this car and just what it is. Believe it or not could be an old lady/man's car or was for style and performance. Any had power that would surprise you now vs anything even non HP engines.
Pics are doable if trouble thru a host site like Photobucket, TinyPics or others if you can get them to show open hood at engine, side, interior w dash, underside of engine with exhaust parts would be great,
T
(This post was edited by Tom Greenleaf on Jul 12, 2015, 11:39 PM)
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