jerseymike

On my '68 98 (455 365hp) it came stock w/ a single exhaust, dual exhaust was an option.

When the time comes for a new exhaust,on a car like this (non high performance like Cutlass or 442) is it worth or advantageous go to a dual exhaust? What advantages are there if any?

Oldsmaniac

Yes it makes a big difference. If you want quiet though I suggest mufflers and resonators.

Rickman48

Could make up to 25-30 hp, depending on your state of tune!
What comes in has to go out, and the easier the better.

ent72olds

I also heard that too big of diameter pipe could be a negative because an engine needs some backpressure. Is this true?

69350rocket

Yes, assuming your engine is mostly stock a dual 2.5 inch setup would do fine.

TripDeuces

Engines do not require back pressure, they need exhaust scavenging but that's a whole different topic. A 2.5 inch system would probably be perfect for your car if using stock exhaust manifolds. I'd expect about a 10-15 hp increase at best with a little bit better mpg depending how you drive it.

jerseymike

thanks for the quick replies everyone. I believe the car already has a 2.5" w/ the single exhaust and just a muffler no resonator,so maybe the dual exhaust could be an option when it's time.

Since this isn't a hi-perf car, in what manner would the extra HP benefit the car? Would it show more on the highway or from a standstill? I don't launch it off the line from red lights or stopsigns,just wondering where the extra horses would be noticible,if at all. I forget what the cars exact weight is (close to 4,000lbs) but it's not light even being a convert.

TripDeuces

You have a 2.25 inch single exhaust. You'd see an increase throughout the rpm band with a high in the mid-range near the torque peak.

jerseymike

hey TripDeuces thanks for the info;

I had to go out and check and you're right on the 2.25 (how did you know that?!)...so you think up grading to the 2.5" duals would be better overall if it's a nice fit? and if it wasn't a nice fit i assuming the stock 2.25 would still have some advantages.

as far as your expalination on the rpm band and midrange info..can you dumb that down alittle? i'm understand somewhat of what you mean just not clearly.

thanks,

mike

redoldsman

If you put a nice set of twin turbos on the car, the biggest advantage is going to be your increased enjoyment in driving the car. It is just going to sound cool and put a smile on you face. It will breath better but you have plenty of power for what you are doing. If it were me, I would probably just keep the 2.25 pipes and use a nice pair of turbo mufflers. I really doubt you could feel any difference in the two sizes. Now if you were modifying the engine, that would be a different story. Just my $0.02.

jerseymike

also just so i can be sure i'm on the same page as you all,are we talking OD's or ID's

i went an double ck'ed i have a 2.25" outter diameter and it's 2 1/8th inner.

since this isn't the origional factory installed system,i don't know what was factory stock.

jerseymike

Hi red, your $0.02 is more than welcome...the car's not a hotrod,just a cruiser,but that doesn't mean she likes to just sit at 65 on the hwy,especially on an open road. At 75 she purrs and asks for more throttle.

BTW what are twin turbos? the exhaust or a brand?

MDchanic

This is the second time in as many days that I've posted a link to a post in this thread.



Your stock 455 with stock carb and TH400 is going to rev no higher than 4,500 RPM and flow no more than 750 CFM through the carb (actually, using a volumetric efficiency of 82%, it looks like it only wants about 500 CFM). A single 2¼" exhaust like you've got will flow about 408 CFM, while duals will flow 816 CFM. Dual 2½" pipes will flow about 1000 CFM, clearly way more flow than you need, and possibly enough to reduce scavenging at low RPM. I think a key question is whether you plan to make any changes in the future that would raise the rev band, in which cast the 2½" would clearly be for you, or whether you want to stick with what you've got, in which case the by-the-book answer might point to the 2¼" pipes. My inclination is to go with the 2½", as the 2¼" just seems small, but I can't argue with the numbers, which tell me otherwise.

With all due respect, I'm afraid I must disagree with Red in this case.

I can see Turbos on an A-body, especially one put together as a hot rod, but I personally just can't stand seeing (hearing) full-size cars with loud exhausts.
These cars were made to glide silently down the road with smooth, honey-like power, and that "ThumpThumpThumpThumpThump" just wrecks that feeling.

Just my own 2¢ .

- Eric

Oldsmaniac

Stock single exhaust was 2 1/4 OD. A 2 1/4 dual system will be fine for your application. I converted a 66 Delta to duals and I could feel the extra power. It was as if the engine just had a tune up or like it had dropped 750 lbs in weight.

Bunser

''A single 2¼" exhaust like you've got will flow about 408 CFM, while duals will flow 816 CFM.''
Sorry, but I disagree. Duals would probably flow about 600ish CFM, if that.

droptopron

Duals look cooler
If you run a resonator it should still be quiet at idle and give you more flow. You are correct that too much flow is no good either. If the factory dual was 2 1/4" I'd go with that.

TripDeuces

I'm glad you did re-post that MDchanic. I had a nice version of that chart somewhere but couldn't find it to post myself. I thought the Torque-Tech sight had one but couldn't find it there either. Thanks

redoldsman

Quote:
Originally Posted by redoldsman
If you put a nice set of twin turbos on the car, the biggest advantage is going to be your increased enjoyment in driving the car. It is just going to sound cool and put a smile on you face.

With all due respect, I'm afraid I must disagree with Red in this case.

I can see Turbos on an A-body, especially one put together as a hot rod, but I personally just can't stand seeing (hearing) full-size cars with loud exhausts.
These cars were made to glide silently down the road with smooth, honey-like power, and that "ThumpThumpThumpThumpThump" just wrecks that feeling.


MD, I appreciate the due respect. It has been my experience there are several different versions of turbo's (jerseymike we are talking muffler type here, not brands). I agree with you 100% that an Olds 98 should not have a loud hotrod sound to it. The Flowmaster 40 Series are LOUD and as Joe P. has pointed out several times, do not really flow that well. I have a set of generic turbos on my 72 Cutlass that produce a very nice mellow sound. Here is a clip of the Dynomax Super Turbo which has a very nice mellow sound. With the right set of mufflers, I repectfully stand by my original statement. Here is the link:

http://www.dynomax.com/soundsofdynom...-turbo-muffler

MDchanic

Hey, Red, I don't want to argue with you, because it's strictly a matter of personal opinion (and besides, you agree with me about the 98s ). I just wanted to give Mike an alternate point if view, so he doesn't feel peer pressure.

I know what you mean about mellow turbos - I've had them on my Chevelle in the past and used to live that slight burble from behind as I rolled along the highway.

I don't like those harsh ones though, unless the motor is really race-tuned.

- Eric

RAMBOW

Do they make reproduction B-body "Dual Exhaust" drivers side exhaust manifolds now?

68 B-body has the steering box & linkages mounted behind the spindles instead of infront like a-bodys...

For single exhaust, the drivers side exhaust manifold aims straight down, and goes under the engine...

Its just about impossible to snake an exhaust pipe over tha steering linkage on that Stock drivers side manifold.

They made "dual" exhaust manifolds for b-body that had the drivers side exit farther back so it would go over the steering arms, but they are pretty rare.

or at least they were back when i had my 68 delmont. Maybe they are around now?

Jaybird

jerseymike & RAMBOW: If you decide to go with a dual exhaust system, Thornton has the left side exhaust manifold that you will need. http://thorntonmusclecars.com/produc...aust-manifolds
I bought one for my 67 Delta 88. It works for me!

cutlassjoe

And...It sounds really good too. I've heard it.

jerseymike

Hello everyone;

thanks for all the help and advice, all the input has been great and it is appreciated very much. I have to say this place is pretty cool. If I do go w/ the duals I might as well stick to the 2.25 system, it seems to be the reasonable thing to do.

It never even dawned on me that I might need a new exhaust manifold,so I have a question about that.

When cutlassjoe said is "sounds really good too", will there be a sound difference (with the replacement) between the current stock single exhaust manifold and the passenger side stock manifold? Let me see if I can clear that up a little; if I install the new manifold to switch over to dual exhaust, will there be a sound difference from the left and right side? I like the way the car sounds now w/ just a muffler, I don't want it to sound like a hot rod or anything. It's not whisper quite, but it's not growling either. It sounds like a 455 w/ a muffler.

I read the write up from the webpage Jaybird posted and it seems like the new (replacement) manifold is a New Old Stock part or a very good reproduction. Is there a preheater mechanism for this that needs to be purchased seperately, I know I'll need new manifold gaskets. I'd probably go the extra step and put new gaskets on each side and replace the the preheaters if it's possible to locate them, any thoughts on those? Not listed in Fusick.

Also considering everything is 44 yrs old, what about new bolts? I'd feel better installing new bolts for the few extra bucks, who knows what condition they will be after trying to get them out. In the last catalog I have from '06 Fusick only lists for '69-'72.

mike

MDchanic

I can't answer your questions about the different sounds, but I can make suggestions about two others.

1. I wouldn't worry about the preheater butterflies. They're really for very cold weather (like below zero), and you won't be driving it when it's that cold out. Yes, they operate at warmer temperatures than that, but you won't notice the difference unless it's very cold out.

2. Yes, you should replace your bolts, unless they look really good. You can probably get bolts that look exactly like the originals for an impressive price from one of the restoration companies, but they're really just regular hardened bolts that you can get down at the corner hardware store. I'd have to go out and check the size - off the top of my head it's ⅜x16 x about 1½", but I could be wrong. Bring the old bolt to match it up.

- Eric

Oldsmaniac

If your manifold has the butterfly damper/preheater it has a bimetallic spring on it. You should be able to move the counterweight by had enough to check to see if it is stuck. the new repro manifold does not have this feature and it is not a problem.

rustyroger

[QUOTE=MDchanic;373375

I can see Turbos on an A-body, especially one put together as a hot rod, but I personally just can't stand seeing (hearing) full-size cars with loud exhausts.
These cars were made to glide silently down the road with smooth, honey-like power, and that "ThumpThumpThumpThumpThump" just wrecks that feeling.

Just my own 2¢ .

- Eric[/QUOTE]

I'm with Eric on this.

IMO loud exhausts only belong on cars that can deliver high performance, a car that sounds like a pro street and can't outrun a Post Office truck is just silly to me. A whisper quiet car that blows away snorting bellowing opposition is something I like to see. It's perfectly feasible but won't come cheap.

You might regret putting a loud system on your car if you want to take it for a long trip, and you may attract unwanted attention from traffic cops too.

Roger.

jerseymike

Hello all, opening up this thread again. First I just got the new driver side exhaust manifold from Thornton to switch to dual exhaust system.

Now about stainless systems. I was given a recommendation for one company that fabs the system,their (dual) price is $1,400 w/ 18ga SSteel. Set includes w/ muffler,and SS clamps.

Sorry don't know if it's proper to post the business names and web sites, if so I'll follow up w/ them so someone can say if they know of their reputations.

After looking around I came across another fab co. whose (dual) price is $775.00 using 14ga (304) SSteel. This company I need to call on Monday to confirm their web pricing and ask a few questions.

Being this is such a big difference in cost and the cheaper of the 2 is the company using a heavier gauge SSteel, what should I be looking out for?

I know 14ga is heavier (overall) per foot,is it too heavy or awkward to work w/ and support?

thanks for any input,

mike

oldcutlass

Here's my humble .02!

Is the underside of your car a showpiece? If not I would just install the new manifold/'s and take it to a good muffler shop and get them to put a nice exhaust on it. The aluminumized pipes of today will outlast your car. There are many options for duals on big cars from mild to wild, make it what you want.

jerseymike

OC, no the undercarriage is not a showpiece, I'm considering the SS because i'm under the impression that it's the best way to go being in NJ,steel has a way of rusting quickly even if it's not exposed to road salt conditions. If there is one thing that irks me is seeing the exhaust rust away but I didn't know that aluminum pipes were quality enough to hold up for years.

mike

oldcutlass

The newer exhaust systems are not as prone to rotting as the old ones were. There are coatings that you can use and they will out last the car. You can get a nice custom, mandrel bent exhaust system for less, By the way stain-less is not stain-free and can get just as ugly under your car.

I'm not telling you how to spend your money, just throwing out a suggestion. I'm originally from NJ, so I remember how the winters are. That is the reason I live in Texas now!

MDchanic

I agree that if it's not a show car, and it is not driven in the salt, you will gain nothing from stainless.

Also, remember that there are different grades of stainless.
There is the stainless that is used for trim, where you find a car completely disintegrated in the woods, but the trim is still bright, and there is the stainless used for modern car exhausts that turns reddish and rusts through after ten or so years, and there are many, many kinds in between as well. Without knowing what kind is being used in the exhaust you're buying, you could be throwing your money away.

- Eric

Nasty455

I've also seen plenty of dyno stats showing 20-30 hp with a good dual system.
The technology today lets you see exactly what each upgrade is worth.
$1000 is about the going rate for 30 Hp it seems.
Once you add up the costs of a system,add mufflers,hangers and hardware,$1000 is a real good estimate.
Go h or x pipe,duals,tailpipes.
The exhaust scavenging helps the engine breath much better,and prevents gasses being drawn back into the combustion chamber.

jerseymike

Nasty, thanks for the info.

There is quite a bit of real estate under the car to make the X or the H. Which config would you recommend and why would a straight run out the back w/ out the X or H be bad or insufficient?

Is there a certain point of location to start to make the transition of the X or H or should I leave that up to the fab guy?

Thanks,

mike