When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hello all. I have a 1971 Oldsmobile 98. Has the 455/TH400...
Every everything has been going really great with the vehicle. Been my daily driver for over a year now and I couldn't be happier. I even get good gas mileage lol.
My question is in regards to exhaust. I've had to change my driver's side exhaust manifold gasket twice now. I think the manifold maybe slightly warped and thus causing it to start leaking prematurely. Rather than taking it to a machine shop to be surfaced, I was wondering if anyone here has any experience with maybe like a short tube header that would bolt up to the factory Y pipe. Any recommendations?
I'm also curious if anyone has ever ran duals on one of these 98's. that may be something I think about doing in the future, for now I just want to get another manifold on it so that it stops the leaking exhaust noise lol.
Pretty sure dual exhaust was standard on the 4bbl 455 engines in those cars. If it has a single exhaust now, it wouldn’t be a big deal for a competent exhaust shop to make a dual exhaust for the car. The transmission crossmember has bumps for 2 exhaust pipes. The biggest hassle would be dealing with years of “environmental loctite” on the current exhaust hardware.
I would think the manifold would have to be pretty badly warped to the gasket to blow out twice in a short period of time. Is the gasket blowing out in the same location? Is the gasket correct?
Dual exhaust was a factory option on these cars and they use the same W and Z exhaust manifolds as the A-body performance cars. Meaning they're available reproduction and are the best way to go. If you try to make duals work with what's on there you'll get into screwy bends around the starter on the driver side and have to plug the crossover port on passenger side.
I guess it's possible for a manifold to be warped enough to start leaking again with a gasket, but I'm wondering if there's some restriction in either crossover pipe or headpipe. The factory exhaust pipe was double-walled and not unheard of for the inner pipe to rot and collapse internally over time.
Factory used graphite grease to seal between exhaust manifolds and head. But those were machined flat before assembly. If you surface the manifold without surfacing the head exhaust flange, might make it worse.
Since you've apparently had the manifold off a few times, next time it's off use a straightedge across the sealing surface to see how far off kilter it is.
Wasn't expecting replies so soon, thanks! Duals are something I'm considering but that's way down the road just figured I'd ask here since I was already on the topic of exhaust. Forgetting duals for a minute though, is there a header that will just bolt on in place of my current manifold and connect to the factory y-pipe?
I'm lucky to have found my Ninety Eight on the second floor of a brick warehouse. It was parked there in 1989 and left there until I purchased it in January 2019... Spending the last 30 years in storage really saved me from having any rust. That being said the car was 18 years old by 1989 but seems to have been well cared for. Hopefully there is no issues with the pipe being collapsed inside. It does seem to breath pretty well. There's a flomaster on there now and it sounds pretty good.
As far as I know it is the correct gasket. It matches up perfectly. I just used the one that is listed for this vehicle at advance Auto parts.
Joe_padavano lead me to another question I have. I keep hearing about the different engine codes, block codes, and cylinder head codes... K heads, J heads, G heads... How can I learn more about my own vehicle to know more about what I actually have? I run my own small repair shop and do all of my own work so it's something I'd be very interested in learning more about. Thanks
Is there anywhere I can learn more about what Oldsmobiles came with what and why?
See the photo above about the VIN derivative stamp. The second character is the model year. The third is the assembly plant. The last six will match the last six of the VIN from the car it was born in.
Back when I was young n poor I welded an outer ear back onto my 68 400. Cast welded slow cooled, nickel rod if I remember.
I surfaced the manifold myself with a large straight cut file. Hey, I had the time. The file was long enough to cover most of the machined surface. Took it a little at a time and checked it against a flat surface. You have to go at each end a little at a time. It worked.
Fit the Felpro gasket behind it problem solved. Went 20K miles before I removed it only to put on a set of 69 400 center divided manifolds AKA WZs.
Still have it on the shelf of original parts for the car.
Or find a machine shop that can surface grind it for 50 bux. Use the gasket either way. Torque it to spec maybe a little less with the anti-seize. Recheck torque a couple of times until the gasket settles in.
Copper high heat or Nuclear grade silver anti-seize is what I put on ALL exhaust fasteners....and everything else I put back together. Never know when your gonna have ta go back in for surgery.
If you're asking about the larger question of what casting numbers and letters go with which model years and applications, there are tables we can point you to. While I hesitate to hold up the Olds FAQ, the block and head casting tables in it are reasonably correct. Some of the other data goes downhill in a hurry, so take it with a grain of salt.
Thanks Joe. I didn't see those pics at first but they are There now. I'll be reading over those links you sent me. Mainly just curious what parts were used on what vehicles and why. For example I've heard the heads on mine have less compression than a 455 from say a cutlass or 442... So maybe in the future it would be realistic to put a different style of heads on for a little better performance.. maybe not lol... Just doing my research
For example I've heard the heads on mine have less compression than a 455 from say a cutlass or 442... So maybe in the future it would be realistic to put a different style of heads on for a little better performance.. maybe not lol... Just doing my research
Unfortunately you heard wrong. On the big block Olds motors, the heads all have the same size combustion chambers, even the smog heads from the mid-70s. Olds varied the compression ratio by changing the depth of the dish in the piston, By 1971, however, all Olds motors were 8.5:1 CR, even the ones in 442s. Changing the heads won't raise that unless you can find aftermarket heads with smaller chambers. Keep in mind that simply changing CR won't make a big difference. You have to match all the parts, starting with the cam. Your 71 motor has a relatively mild cam and small valves. Couple this with a lazy ignition advance curve and you're at a power deficit. Assuming the engine is in good mechanical condition and correctly tuned, start with dual exhaust and ignition timing. Once you have that dialed in, then consider more meaningful changes like cam and CR.
Thanks Joe I appreciate the info. It had a 88,000 mi when I first got it. I've got it up to 106,000 mi now. I'm considering pulling it next year if it starts to give me any issues and just do a general overhaul, but I try to take care of it, and as long as I don't have to pull the engine I won't lol. I'll start with the exhaust like you said. And then see what I can do about the ignition
Thanks Joe I appreciate the info. It had a 88,000 mi when I first got it. I've got it up to 106,000 mi now. I'm considering pulling it next year if it starts to give me any issues and just do a general overhaul, but I try to take care of it, and as long as I don't have to pull the engine I won't lol. I'll start with the exhaust like you said. And then see what I can do about the ignition
With the mileage you have, I’d strongly recommend replacing the timing chain. The cam gear has a nylon coating. A lot of OEM engines used that setup for noise control. Which I suppose works great until the nylon starts to crack and flake off. The nylon chunks fall into the oil pan and plug up the oil pump pickup.
If the timing chain and gears are worn, you might find a noticeable improvement in power just from replacing the timing set. The loose chain will regard cam timing, which will make the engine feel “lazy”.
As others suggested, get the dual exhaust manifolds. Headers will be a much bigger hassle, and with a otherwise stock engine probably won’t gain much over good manifolds.
What is this Y pipe you have mentioned? Olds single exhaust has a pipe coming off the drivers side exhaust, goes under the oil pan the the passenger manifold, then a larger pipe coming off the rear of the pass manifold to the rear of the car. Technically, Olds engines don’t use a Y pipe. The W Z manifolds mentioned earlier have just one outlet each for a true dual exhaust.
If your car has manifolds with just one outlet each with a single exhaust, it sounds like someone over the years fabricated a Y pipe with single exhaust. You may already have decent manifolds on the car.
Beautiful car! It's one of the best Oldsmobile ever made (of course I am biased).
Don't go to headers. I have a set of high quality Hedman Hedders on my 71 98 and they're a PITA. They always blow header gaskets even using locking bolts.
My lord is that a beast. There used to be a 73 Delta 88 down the street, that looks even bigger. Yeah, dual exhaust, a bump in compression and cam will help move so much car if you want a total overhaul. They don't make them like that anymore, if they do, it is called a limousine😁.
Last edited by olds 307 and 403; December 21st, 2020 at 10:29 AM.
Nice 98, in 1989 I bought a meticulously cared for 71 Coupe DeVille with 82,000. They are both built on the same platform, same beautiful comfy rides. I think Olds did a better job with the instrument panels on the 98.
December 18th, 2020, 11:53 AM
