Total novice here. I've no intentions of turning my car into a drag racer or anything. Just wondering if there is something I can do to increase performance (both for highway cruising and general horsing around) without also increasing fuel consumption or making the engine more brittle, or vice versa, a way of increasing fuel efficiency without making it lazier.

From what I can gather from reading around a bit, and correct me if I'm wrong, switching from stock manifolds to aftermarket headers is one way of achieving this. If so how much of a noticeable difference would such an upgrade make? What are the diminishing returns between short, medium and long ones? Would they perform well with the remaining stock exhaust pipes?

An EFI kit sounds like a decent upgrade as well. How much of a difference does it make though?

Open to suggestions. Thanks.
Edit: Oh and I'm also wondering how paranoid I should be about filling E10 on this car. The only alternative fuel available in my country is 98 octane, which I have to drive 120km away from home for.

 

Around here all we have is E-10 and I've been using it in all of my vehicles for the past 15+ years with no issues. You need modern rubber fuel hoses and accelerator pump in the carb, though (you didn't say what carb you have).

You need to provide more information about your car. 1975 was a very bad year for performance as GM was trying whatever they could to meet emissions standards.

The 1975 originally had single exhaust with a very restrictive catalytic converter, so switching to duals with either no or high flow converter will really help (if not already done).

That year car also came with a highway gear rearend. Like any car, swapping to lower rear gears is the best and easiest way to improve performance (if not already done - again, you need to give us more info about your setup).

 

As far as I'm aware everything is stock, as it came out of the factory. Is there a difference in the parts used by different suffixes? Mine's a "supreme".
I'll probably get to replacing those hoses and seals eventually. For now I guess I'll keep filling 98.

I dunno about the converter but the car has two pipes, one on each side, just like every other 75 Cutlass I've ever seen in pictures. If you're telling me this is not stock configuration then I guess it must've been modded at some point.
I'll have a closer look and take some pictures come Friday. If there happens to be a converter on there I can probably just remove and replace it with pipes, right? The car is getting a bi-annual inspection this August but I doubt anybody around these parts know (or care) what emission standards an old American car is supposed to adhere to. The "Emissions" section in the car's digital registry is all blank as well.

Wouldn't this necessitate more fuel consumption though? I'm trying to avoid that.
There's no setup. As far as I'm aware it's pretty much a stock car.

 

Yes, steeper gears would use more fuel.

Aftermarket EFI and headers are pretty drastic changes. The easiest improvement to do to your car for better performance is dual exhaust. Check under your Cutlass and see if it has duals all the way from the manifolds to the tailpipes or if it uses the OE Oldsmobile crossover that splits later.

 

I have a 75 Olds with a 455. The car was restored when I bought it and the engine had been rebuilt totally stock. It had W/Z manifolds on it and some really loud mufflers. I changed the mufflers to Dunomax Super Turbos and put a pair of high flow cats on it. The car still has the 2:56 highway gears in it so it is still a little sluggish off the line. When you are on the highway it will run 80 and 90 and not even breath hard. If I came upon a 3:23 posi I would buy it in a minute. The quadrojet on these cars is a one year carb and is not one ot the best. I had mine rebuilt and it is okay but there are better models and they are not Edelbrocks. Dual exhaust and a good tuneup are the best things you can do for what you are looking for. Headers are a pain and I read too many horror stories about EFI units. This is just my $0.02.

 

I disagree with the header assessment. Long tubes are an easy 30hp and better fuel economy. Get a name brand set, install them, bang them up, remove them and send them out for ceramic coating. In fact, even if you don't do this, I suggest having the manifolds coated in and out. Place in Jonesboro, GA did a set for my truck and held up great to daily driving for 40,000 miles or so when I took 'em off.

Aluminum intake manifold would take 30lb off the front end alone in weight and improve performance and fuel economy. That's about where it would stop before you get into a set of gears, rocker arms, valve springs, camshaft.

 

A good set of dual will probably give 20 horsepower over the restrictive single exhaust with the catalytic converter. I would not go to the trouble and expense of long tube headers for another 10 hp. But then that is just me. He might save 30 lbs with and aluminum manifold but there is not way he will feel 30 lbs in ths car and the manifold will flow little if any better than the stock manifold. His car, his money if that is what he wants to do.

 

There is nothing easy about installing headers.

Real dual exhaust with somewhat free flowing mufflers would help. I wouldn't do very much more. Perhaps a non-emissions quadrajet. The car has low compression and a low numerical rear axle ratio which both will prevent it from easily improving the performance.

 

I can tell you from first hand experience, there is NO difference in performance or economy by switching to EFI. Assuming the carb is tuned correctly, the engine doesn’t really care what kind of induction you have.

As others mentioned, the biggest bang for the buck will be exhaust. Put a good dual exhaust on it, that’s probably an easy 25-30hp improvement with no engine change. Unless you go into the engine for additional modifications, skip the headers. The engine is already choked with the lazy cam timing, until it can breath better on the intake side there will be no improvement with the exhaust side.

Make sure the engine is tuned correctly. Ignition timing in the dark years of the auto industry was pretty lazy. Be prepared for some trial and error to figure out what the engine likes. Don’t listen to anyone who says to get rid of the Q-Jet!!! Best all around carb ever made.

The next biggest improvement would be a gear swap and an overdrive transmission. I’m betting your car has a TH350, a 2004R swap is about the easiest trans swap you can do. Put some 3.73 gears in the back, install an overdrive, it will basically cruise on the highway at the same rpm you are now, with much more get up and go. Win win.

 

I don't have specs for 1975 engines, but looking at the 1971-1972 specs shows a 25 HP difference between the single exhaust and dual exhaust versions of the same engine.

I would imagine even better gains would be achieved by replacing a single exhaust, restrictive pellet-style catalytic converter system with true dual exhaust with either no cats or modern high-flow cats.

 

I checked the exhaust; It's two separate pipes. No intersecting. Perhaps it's had some parts changed out after all if that's not a default configuration.
I also noticed there's some "Comp cams" covers bolted onto the block. Gonna have to do a close inspection and see if I can figure out what I'm dealing with here.

If I were to do something with the exhaust, tell me why I wouldn't simply skip all the catalytic converter and muffler stuff and just weld myself a big straight pipe? I bet it sounds badass, and I don't plan on using this car for long-distance travel. It'd be cheap too.
And how is installing headers a challenge? If it's just because I have to uninstall a bunch of stuff for access then that's probably not an issue. I'm likely to do that anyway at some point for surface rust removal and painting.

That gear & transmission swap sounds promising. I'm gonna have to first identify what I've currently got installed. Would I find that out by crawling beneath the car and finding an alphanumerical descriptor of some kind? I doubt a look inside the coupe would tell one much.

 

Especially if you do a TBI unit. Waste of money.

 

Are you saying it has dual exhaust with no catalytic converter? If so, then it has been modified from the factory setup. That would be good as it’s one less thing for you to do.

I would never advise straight pipes.


You can ID the transmission by the shape of the pan and the number of bolts. Yours should be a TH400, assuming the 455 in the car is original factory equipment.

 

Went out and confirmed there are indeed no catalytic converters on those pipes. Only mufflers.
I also attempted to ID the transmission but all I accomplished was getting my hair full of oil (fixed a substantial oil leak from the oil pressure switch this week but the floor is still oily).
Identifying the transmission will likely have to wait until I've built my new garage, so that's on hold. I'll be fixing an exhaust leak between the right manifold and pipe today though. Will hopefully give me a nicer sound.

Yes but why. Remember I don't know anything.

Edit: By the way I've got these open camshaft vents. Typically looking at other cars they've got them tubed into the carburetor(?). Should I do something about this?

 

The first pic is your pcv [positive crankcase ventilation]and should run to your carb base the second is a breather that should run to air cleaner.

 

I'll look for some hoses and clamps next time I'm in the city.
What are the benefits to hooking this up though?

 

Less oil vapor under your hood, and less emissions.

As for no muffler, it will be quite loud which will attract police and tickets. It will run poorly because the mufflers provide back pressure which the engine requires in it's current setup.

I believe you won't get much improvement by doing anything with the exhaust.

I also don't believe you know enough about the engine to determine whether a non-emissions quadrajet will help, so I would skip that.

The easiest thing, and it's not easy, would be to swap to a compatible transmission with overdrive (I think you need to have some kind of switch or computer to turn on the over drive, perhaps a toggle switch on the dash) AND a better rear axle ratio. It would also make an immediate significant difference without having to touch the engine. Even if you touched the engine, you'd need to do this anyway. Although if you invested a lot to increase the power, you'd need a stronger transmission.

 

Hm, so basically all I have to do is hook up the PCV, change the waterpump (new one came with the car), fix an exhaust leak (today's goal), maybe consider tuning the carburetor at some point, and somewhere down the road look at a gear/transmission upgrade depending on what's already there.
This car is turning out to be in better shape than I had hoped, considering I got it for next to nothing. This has been very beneficial so thanks to everybody for contributing.

It looks like this by the way



There's some giant rust bulges beneath the vinyl top, some matte paint spots from poor paint repair, some tiny rust bubbles in the typical places, and holes in the bumpers, but nothing structural. The underside is completely rust-free.
I've tacked on some new opera window trims since this picture was taken, and I've got the windshield trims ready in my shed.
Gonna get to work on removing the vinyl top once I've got my garage up.

 

That don’t look like the original engine. It’s got an early pre egr intake and either C or G heads

 

Holy crap, in what country do you live? That has definitely been messed with. I love it though!

 

nothing to do with the country. I can see a C or a G on the head and the old style intake.

if it’s matching intake, heads and block…looks like it’s a C headed early 455?

 

Well, I think we are discovering that is not an accurate statement.
True dual exhaust with no catalytic converter (not factory).

Give us some more pictures of the intake as it appears to be an aftermarket aluminum intake manifold (not factory)..

Those "Comp Cams" valve covers appear to be factory valve covers with some decals attached. Nothing special there..

 

In response to your question: "Easy upgrades for a stock 7.5L 455 1975 Cutlass?"

Based on your pictures that show at least 3 different type of spark plug wires, I'd suggest a basic tuneup. New cap, rotor, spark plugs and wires.
Once you get that done go through and check all your vacuum lines and correct any issues. Finally adjust carburetor and timing as per the Chassis Service Manual.

 

I would put a cam down a cylinder to see what dish the piston has..the top end of the engine is a lot older than the year of the car

a compression test wouldn’t hurt either

 

^^^THIS^^^

Make sure you connect your PCV hose too. Early cars that came before PCV had a down draft tube that vented the crankcase to the atmosphere. Deleting it and installing a valve cover breather is just shooting yourself in the foot.

 

Yes, I jumped the gun on that one. Was expecting the whole car to be old, basic and worn out due to the price.
I appear to have gotten quite lucky.

Here's a picture of that manifold. Tried to get closer but the camera'd just blur.
















Got some of the carburetor and engine in general as well. Not quite sure where that PCV hose from the drivers side is supposed to go in. The place that looks like a receptacle is sealed.

I'm in northern Norway by the way.
I'll get to looking at those other things mentioned in due time. I have a new water pump and some spark plugs lying around.

 

Those GA heads are 1972 specific. Another sign this car is not factory original.

 

Make sure the PCV valve (from your passenger's side valve cover) is connected to manifold vacuum. That's the large port at the base of your carburetor that has maximum vacuum at idle.

The breather elbow on your driver's side valve cover is supposed to go to the underside of your air cleaner. Most aftermarket air cleaners have a nipple that will fit your breather hose.

 

Your exhaust manifold's are #1 and #4. These are small block 330/350 manifolds.

What's the casting # on the engine block?

 

The cast is 396021F.

I've found one idle port on the carburetor. Gonna assume that's the one.

 

Greetings. I've spent all winter building a garage so my car project was put on hold.
Anyways, turns out the intake for the PCV on the carburetor was clogged or something, causing pressure to build up in the engine, blowing the head gasket pretty severely, so the car's been sitting since last summer.
To make matters worse, this spring I started the car and parked it in my new garage, then as soon as I stopped the transmission got jammed in park, so I've gotta do something about that as well.
Here are some pictures. I just removed the block this evening. The son-in-law of the original owner tracked me down out of curiosity and gave me a picture of how it looked originally (attached).
First thing tomorrow I'm heading to the city to buy some oil-absorbent.

 

Oh and if somebody happens to have a paper with all the right torque settings for the block that'd be swell.
The roof of course looks like this. Gonna make it a plain black, no leather.

 

That cannot happen. The head gaskets seal the combustion chambers (where the air-fuel mixture ignites and generates high pressure), and the PCV is connected to the area outside of the combustion chambers (where there is little or no pressure).

If the head gasket blew, it was due to something other than the PCV system.

 

Doesn't it make sense for the crankcase to build pressure if the PCV system doesn't let out any air? The radiator also started spewing out liquid around the same time I hooked up the PCV hose. Were I a thinking man I'd of course have been more alarmed and reversed it to see if things changed. In any case I'm going with those pop-on filters next time. They look cooler anyway.

 

You have earlier Ga heads than the year of the car. The intake manifold is even earlier, it’s pre egr/emissions. The trans is a turbo 350.

a plugged PCV won’t blow a head gasket

 

Cool if that's the case. Means the thing blowing might not have been entirely my fault.

 

This is pretty much the first thing to come up when googling "bad pcv", and it maps onto my experience perfectly though.

"If the PCV valve fails, you might notice the following symptoms: excessive oil consumption, rough idling/stalling, oil leaks, sludge, and an illuminated check engine light. It's not advisable to drive with a bad PCV valve because it can cause the gaskets to blow"

 

what do you mean by the thing blowing?

 

The head gasket getting ruined.

 

gaskets, not head gaskets. you don’t understand the basics of internal combustion engines.

I cant help you …I give up.

googling for you is dangerous