Swapping A-body shorty headers and exhaust to M-body

[MoparKidD-4]

I've been reading some other threads on here saying that A-body headers tend to fit best on M-bodies; I was taking a look at the '88 5th Ave I'm going to buy and it might have just been my eyes but the passenger side inner fender looks quite a bit closer to the exhaust manifold than I remember on my Duster...? Since they are shorty headers (Hedman Tight Tubes) which exit down and end right at the oil pan rail I fab'd my own down pipes which snaked over the steering linkage in my Duster; shouldn't these also fit because there are no torsion bars to get in the way, or is the steering linkage in a different location than on A-bodies? Also I don't want to bother with doing a "clean" full exhaust with a Y and large single tailpipe I really want to make it a side-exit exhaust with the tips right in front of the rear wheels. Has anyone done this on their M-body? Due to emissions laws in CO I will need to run a cat on each side but those aren't too expensive nowadays and probably will work better than the horrible old triple-cat system these cars came with. I know I will need to block off the air injection holes in the heads as well since it has an air pump.

 

[BudW]

I have blocked the cylinder head ports more times than I can count – mainly for installing newer heads on older cars.

I had the details written down on a file on my computer – but due to not saving data and hard drive failures – I no longer have that data.

There is an Allen head set screw, which will fit the port size wonderfully. Just get a tap for the ports and thread them to match the set screw threads, spend a bit of time tapping and screwing (15 min, maybe), and you are good. Just make sure the set screw is under the surface of the exhaust manifold flange.

Also, the seat screws are un-doable, so if you decide to go back with exhaust manifolds, you can.


Note: the engine is offset to passenger side about 3 inches, or so, on all rear wheel Chrysler vehicles made in North America from ’93 and down. It allows for steering gear clearance and helps with propeller shaft angles/vibration.
BudW

 

[MiradaMegacab]

Tap the injection holes 1/4"X20 and use Allen head grub screws

 

[MoparKidD-4]

Cool thanks guys, I was looking at the pass. side header last night it's definitely tighter to the block than I originally thought I think it should fit. I also have a set of Magnum heads I took off my busted 360 that seem to be in fine shape, I'm tempted to swap those on at some point but I would need to deal with the pushrod oiling situation (Magnum lifters and hollow pushrods?). That may actually be an overall better way to go because I also already have an Edelbrock Magnum Air-Gap intake off the same engine, I won't need to buy another 4-bbl LA intake.

I forgot how much more stuff there is above the engine on these later-model cars too, smog pump and A/C compressor and vacuum lines, oh my! lol

 

[MoparKidD-4]

So what about the steering linkage? Is it in the same place as the A-bodies in relation to where the engine sits?

 

[MoparKidD-4]

I have blocked the cylinder head ports more times than I can count – mainly for installing newer heads on older cars.

I had the details written down on a file on my computer – but due to not saving data and hard drive failures – I no longer have that data.

There is an Allen head set screw, which will fit the port size wonderfully. Just get a tap for the ports and thread them to match the set screw threads, spend a bit of time tapping and screwing (15 min, maybe), and you are good. Just make sure the set screw is under the surface of the exhaust manifold flange.

Also, the seat screws are un-doable, so if you decide to go back with exhaust manifolds, you can.


Note: the engine is offset to passenger side about 3 inches, or so, on all rear wheel Chrysler vehicles made in North America from ’93 and down. It allows for steering gear clearance and helps with propeller shaft angles/vibration.
BudW

Hey Bud, so just wondering I'm getting the feeling that this can only be done with the heads off the car...? I'm not sure if there's enough room to accurately get a tap between the head and inner fenders just looking under there myself. Also the downpipes coming off the manifolds look to be at least 2" (bigger than the older 318 manifolds I've seen) meaning the outlets must be a decent size right? I'm debating if it's worth the trouble to plug those ports just to put shorty headers on, if they won't make a noticeable difference in power or MPG compared to duals off the stock manifolds (I'm aware it's a stock 318, not a whole lot of potential without at least a cam). But then I'll have to fab up downpipes to come off those whereas I already have a set made up for the shorty headers.

Khalid Z.

 

[7T8 Custom]

Those ports can be tapped and plugged with the heads on the engine and the engine in the car. I`ve been there/done that.

 

[BudW]

You have plenty of room, in car, to tap and plug those ports. I’ve done a lot (but mostly with engine out).
I would have no problem doing them in car.

Now your question of

I'm debating if it's worth the trouble to plug those ports just to put shorty headers on, if they won't make a noticeable difference in power or MPG compared to duals off the stock manifolds

I can’t answer that question.

In my opinion (which you can toss as far as you want to) what to do with a 318 2-bbl car.

The Carter BBD / Holley 2280/6280 carburetor’s only flow about 200 CFM (or 250 CFM, depending on who you ask) total, (two venturi’s at ~1.0 inch, each/throttle blades are 1¼ inch each).

If you upgraded to a 4-bbl, I can see how headers will help in a lot of different ways.

Personally, I don’t recommend changing anything for just about any one change you make to a stock 318 2-bbl) will hurt its low end (where you need it most).

My stock (318 2-bbl) '77 wagon has a killer hole shot - sense it has 3.23 gears in it. Once you get past the stop light then you have nothing, for engine has ran out of steam. BUT, boy is that hole shot fun.
Not enough power to spin the tires (so WOT all the way).

I had considered a few things to make things a bit more fun (ie: 4-bbl, dual exhaust, heaters (or 340/360 exhaust manifolds) and so on), and each one of those things will kill my low end.
What it will do is once I do all of that, with correct camshaft, is the "low end torque" is now "high end power" and I won’t have the hole shot capability anymore (so, not as big of a smile).

My recommendation is to look at gear ratio. I think that might be the ticket you are looking for (not saying others won't, but I would recommend to try ratio, first).

Getting rid of the 2.2 ratio gears is a “must do”.
3.2 (or 2.9) is best, 2.6 is good to OK).
2.2’s (which is what you currently have) are for the worms (and they can have my 2.2’s once I change them).
BudW

 

[Monkeyed]

Just my 2 cents, and at the risk of alienating myself..., my idea of a fun car is tall gears and high rpm power. To me, that's the definition of a "sleeper", at least on the streets, in real world driving, where certain circles know a car and driver by reputation. There are guys that will know a car as a slug even for a stock 2bbl 318. They'll seek you out and try to humiliate you at the stop lights, which is all well and good for them when they get the jump on you. But I love watching their faces fall when the car starts to hit it's stride and I sloowwlly reel 'em in before blowing past them. Then everyone has a good laugh at their expense and I like to imagine they learned a valuable lesson lol.

That and I like the dual purpose of a car that can't get out of it's own way, a lazy cruiser, but you know you can wind it up and it'll GO! if you feel like it... Again, that's just me. I'd rather have a flying start Autobahn road-race course, with long sweeping curves, than a 1/4 mile at a time, or even hairpin to hairpin type.

To each their own, I guess.

 

[kkritsilas]

Just my 2 cents, and at the risk of alienating myself..., my idea of a fun car is tall gears and high rpm power. To me, that's the definition of a "sleeper", at least on the streets, in real world driving, where certain circles know a car and driver by reputation. There are guys that will know a car as a slug even for a stock 2bbl 318. They'll seek you out and try to humiliate you at the stop lights, which is all well and good for them when they get the jump on you. But I love watching their faces fall when the car starts to hit it's stride and I sloowwlly reel 'em in before blowing past them. Then everyone has a good laugh at their expense and I like to imagine they learned a valuable lesson lol.

That and I like the dual purpose of a car that can't get out of it's own way, a lazy cruiser, but you know you can wind it up and it'll GO! if you feel like it... Again, that's just me. I'd rather have a flying start Autobahn road-race course, with long sweeping curves, than a 1/4 mile at a time, or even hairpin to hairpin type.

To each their own, I guess.

As you said, to each their own. A car that is slow to get up and go is not pleasant to drive daily. In the case where you drive in the city, in most cases, you never get to the rpm point where the engine really starts to make power, and like you, while this may not be a popular opinion, cars are not to be raced on public streets, whether it be a block at a time or an 1/8 or a 1/4 mile at a time. Racing is for tracks. Same goes for driving at really high speeds on highways.

Ever notice how often 50 foot times are quoted? Every wonder why? It is because the 60 foot times are a good indication of how much low end torque and traction a car has. For most street driven cars, it is a more important number than 1/4 mile times, as most street races don't go 1/4 mile.

What kind of distance are we talking about while "when the car starts to hit it's stride and I sloowwlly reel 'em in before blowing past them"? In most city driving, those types of things happen a block at a time, and the car with the low end torque generally wins. Race will be over before your car "starts to hit its stride".

I don't deny that people are street racing. They, however, should not be any impression that they are doing anything that is less than brain dead. People who do this are putting themselves and the public at risk, risk that could be avoided if you just went to a track. That is what tracks are for, or are they afraid to face the reality of what the timeslips at the track will show?

I don't like single purpose cars, by which I mean cars that are optimized for only one thing, be it low end torque, high end power, 1/4 mile runs, etc. In the real world, a car must accelerate well, must cruise at highway speeds without giving you a headache due to road noise or exhaust drone, go around corners well, stop "RIGHT NOW", have a comfortable ride, all while getting good gas mileage, have a comfortable interior, room for people and stuff, and be cheap to maintain.

I think way too many people have been watching Street Outlaws on Discovery Channel. Note that the cars on that are full out race cars, not street cars. When the car cannot be driven on the street, requires a garage full of mechanics to look after it, and hundreds of thousands of dollars to build, we have left any semblance of a street car a long distance in the rear view mirror.

 

[MoparKidD-4]

Thanks for the replies guys good stuff there... I'm familiar with the trade-off between low-end and high-end power, the 360 I built for my Duster was a torque MONSTER due to the high cylinder pressures (high comp + small cam) but that was also its undoing; one of the pistons fractured a chunk off after years of abuse with borderline detonation so I learned my lesson there (ALWAYS match your cam to the rest of your engine combo!!).

My goals with this car are to make it a pleasurable highway cruiser; I'm not concerned with hole shots and 60' times that's what my Duster is for (actually I'm building it for road racing TBH). Since I live in Colorado there is a plethora of old Jeeps around and my ideal plan is to swap in an 8.25 rear out of a Cherokee with 3.07 gears (target ratio is 2.8-3.1). I also definitely will be converting it to 4-bbl with a smaller 500-600 cfm Edelbrock/Carter or Street Avenger Holley carb, or a Thermoquad if I can find enough parts to build a complete one lol (I have 2 cores currently). I am impressed with how much grunt this thing has given the awful 2.21 rear ratio and I'm willing to give up a smidge of off-idle grunt to have more power everywhere else in the RPM range.

I think I will stick with the stock manifolds because if I put the headers I have onto this car then I will need to get another set when I finish building the other 318 I have for my Duster. I was not looking forward to fabbing another set of downpipes but looking under this 5th Avenue the lack of torsion bars running down the sides gives a LOT more room to route exhaust piping.

Does anyone know off-hand the inside diameter of the outlets on those factory 1988 318 manifolds? I'm hoping it's at least 2"...

 

[BudW]

Hum (while scratching his hairy chin), “race cars”, Oklahoma City, single purpose cars . . . Street Outlaws (Discovery Channel) . . . Oklahoma City. It all rings a bell, somehow . . .

By the way on weekends (late at night) you can hear the “street racing” pretty much all night long. I have no idea where at and by the time I get there, the event may have gone elsewhere.

The last time I have been to any official (or un-official) timed acceleration contest was in 1984. This was with my ’67 Satellite with a 340 and 3.23’s. Not quite tuned up at this time (and a bit more car than engine).

FWIW, the top slip says 15.55 sec, 89 MPH. Bottom slip says 15.38 sec. My only other time slip went AWOL (but in same time range).


Getting back to point, 95% of my driving is in city with some in-city highway usage. I need city gears, period.

Unless you do 95% highway miles (JustWondering comes to mind) then I can see 2.2 gears being best – but I still think, even for fuel mileage reasons, having lower gears (higher numerically) is better for city driving and better for fuel mileage (which goes against logic).
BudW

 

[BudW]

I had a pair of exhaust manifolds from a ’84 Gran Fury 318 4-bbl police car, which has the 360 ports and larger exit hole. They are missing due to a moving error (lost forever) and the box might be on the side of road somewhere (IDK).

IF I was to guess, I would guess an M-body 318 2-bbl manifold exit to be 2” (maybe smaller) and 318 4-bbl police manifold exit to be 2¼” – but that is only a guess.

I will be changing my exhaust (including the Y-pipe) on my ’86 5th Ave, soon, and I can get measurements on it, then – but that might be a month or two away.

I like the idea on the Cherokee differential. I do have a lot of Jeep gear ratio information, so if you know what year Cherokee, I can give you what ratio’s they had that year. Most of them have a number engraved on them somewhere and that number will tell you everything about that differential – if you know where to find it at (and if it’s not under dirt/grease/rust).
The only thing I don’t have is measurements on them, yet.

On your TQ. I have about 85+ TQ’s in my garage. I don’t know why I have that many – but I do. Some of them are for parts only – so I might have the parts you need. Send me a PM with your carburetor number(s) and I’ll get back with you. I have also rebuilt more TQ’s than most people have ever seen.

I might have a possible (cheap) exhaust solution, as well.
BudW

 

[MoparKidD-4]

I had a pair of exhaust manifolds from a ’84 Gran Fury 318 4-bbl police car, which has the 360 ports and larger exit hole. They are missing due to a moving error (lost forever) and the box might be on the side of road somewhere (IDK).

IF I was to guess, I would guess an M-body 318 2-bbl manifold exit to be 2” (maybe smaller) and 318 4-bbl police manifold exit to be 2¼” – but that is only a guess.

I will be changing my exhaust (including the Y-pipe) on my ’86 5th Ave, soon, and I can get measurements on it, then – but that might be a month or two away.

I like the idea on the Cherokee differential. I do have a lot of Jeep gear ratio information, so if you know what year Cherokee, I can give you what ratio’s they had that year. Most of them have a number engraved on them somewhere and that number will tell you everything about that differential – if you know where to find it at (and if it’s not under dirt/grease/rust).
The only thing I don’t have is measurements on them, yet.

On your TQ. I have about 85+ TQ’s in my garage. I don’t know why I have that many – but I do. Some of them are for parts only – so I might have the parts you need. Send me a PM with your carburetor number(s) and I’ll get back with you. I have also rebuilt more TQ’s than most people have ever seen.

I might have a possible (cheap) exhaust solution, as well.
BudW

Niiice, I will definitely keep you in mind for a TQ once I start gathering parts for the 4-bbl swap. I have a '93 Cherokee myself which I did a gear swap on (had 3.07s originally, changed to 3.55s) so I'm pretty familiar with those and from another thread I found on this forum the dimensions are basically spot-on; all that needs to be done is the spring perches flipped and moved a bit and possibly swap the brakes over (pretty sure the M-body drums are bigger than the XJ Cherokee). The only catch is that as far as I know the only Jeeps that had 3.07 gears were the stick-shift models which are like 5% of all XJs sold.

Regarding the exhaust manifolds I do know the older 318 manifolds are 1-7/8" outlets which is a joke, I was hoping these ones were a bit bigger because the downpipes on these M-bodies are noticeably bigger than the "drinking straws" that came off the original 318 in my '70 Duster.

 

[MoparKidD-4]

I think I found my answer... I'm gonna stick with the manifolds

 

[BudW]

I like things quiet, real quiet.
Maybe because I'm getting older, IDK.

Family don't complain as much, your ears don't buzz after a long drive, the local police is seen less frequently.
Its a win-win-win, to me.

 

[Monkeyed]

As you said, to each their own. A car that is slow to get up and go is not pleasant to drive daily. In the case where you drive in the city, in most cases, you never get to the rpm point where the engine really starts to make power, and like you, while this may not be a popular opinion, cars are not to be raced on public streets, whether it be a block at a time or an 1/8 or a 1/4 mile at a time. Racing is for tracks. Same goes for driving at really high speeds on highways.

Ever notice how often 50 foot times are quoted? Every wonder why? It is because the 60 foot times are a good indication of how much low end torque and traction a car has. For most street driven cars, it is a more important number than 1/4 mile times, as most street races don't go 1/4 mile.

What kind of distance are we talking about while "when the car starts to hit it's stride and I sloowwlly reel 'em in before blowing past them"? In most city driving, those types of things happen a block at a time, and the car with the low end torque generally wins. Race will be over before your car "starts to hit its stride".

I don't deny that people are street racing. They, however, should not be any impression that they are doing anything that is less than brain dead. People who do this are putting themselves and the public at risk, risk that could be avoided if you just went to a track. That is what tracks are for, or are they afraid to face the reality of what the timeslips at the track will show?

I don't like single purpose cars, by which I mean cars that are optimized for only one thing, be it low end torque, high end power, 1/4 mile runs, etc. In the real world, a car must accelerate well, must cruise at highway speeds without giving you a headache due to road noise or exhaust drone, go around corners well, stop "RIGHT NOW", have a comfortable ride, all while getting good gas mileage, have a comfortable interior, room for people and stuff, and be cheap to maintain.

I think way too many people have been watching Street Outlaws on Discovery Channel. Note that the cars on that are full out race cars, not street cars. When the car cannot be driven on the street, requires a garage full of mechanics to look after it, and hundreds of thousands of dollars to build, we have left any semblance of a street car a long distance in the rear view mirror.

I've never seen Street Outlaws. You are way over-analyzing it. I agree that a car should be able to do it all, but there are always compromises. I like having something that's different than what everyone else does. Not to be different, but because I like to try things out for myself and see what I like, and it usually isn't what everyone else agrees is "right". I'm more comfortable in a car that is revving low on the highway than in one that is buzzing to the rafters at 50. I like one that can idle at 6-700 rpm and doesn't need to turn 1,200 to keep from stalling. I love a torquey engine, but I don't like one that can't rev past 2,500 without falling on it's face. I don't like pushing it past 4,000 so you may have a different idea of what I'm talking about. I think people who gather in the middle of the night on a road to organize an illegal street race are morons. I agree with you there. I really could give a crap less about what a timeslip tells me, other than it's an interesting bit of conversation piece. I get some people will thump their chest and say the race is won after 50 feet, doesn't really bother me. "Race" 1,000 miles, that will impress me more.

Wasn't trying to rile your feathers. I have a lot of respect for what it takes to build a fast car, or any car for that matter. Just stating what I enjoy, and trying to tell him not to get discouraged from trying something different.

 

[MoparKidD-4]

You guys on here are definitely a different crowd than over at FABO lol... nothing wrong with that and it makes sense, FMJs aren't typically used for street machine builds. They sure are more comfy than A-bodies, and that's precisely why I got my 5th Avenue as opposed to an older A or B-body (also much cheaper, and newer).

@Monkeyed The 360 in my Duster would pull to about 5000 and hit valve float at 5500, and I thought that was low. Target redline for the 318 build to put in the Duster now is minimum 6000 RPM, aaand it will eventually be turbocharged as well with 8-12 lbs of boost

I like time slips because they give you the most accurate real-world power and performance numbers; I prefer taking my car to the strip and calculating HP based off trap speed as opposed to going to a chassis dyno and spending $150+ just for a few pulls. But like I said road racing is my true calling, way too much downtime in drag racing; 14 seconds of intense fun followed by 20-30 minutes of waiting in line... no thanks

I'm going the un-classy route with exhaust on the 5th Ave. and just having it dump in front of the rear wheels. Muffler choice will be important though, I'm only 26 so I still like noise lol but drone is unacceptable. I really love Dynomax Ultra-Flo mufflers as they have the perfect balance of sound but they aren't cheap, it's tough to justify putting a $160 set of mufflers on a $700 car.

 

[BudW]

14 seconds of intense fun followed by 20-30 minutes of waiting in line... no thanks

Refer to my earlier post (post #12). I’ve been to the drag strip twice (one run one visit and two the other visit) – and not been back, sense, exactly because what you mentioned above.

it's tough to justify putting a $160 set of mufflers on a $700 car.

I usually tell people my 5th Ave is worth $300 - but sense I have no plans on selling it, the cost doesn't matter, much.


I’ve been reading up on exhaust drone and ran across this website
Note: I didn't mean to bring page here - i guess I broke the link somehow.

This is the ticket. Now with that said, getting the correct exhaust combination is best – but some of us don’t have the money we need to get it done correctly, the first time.

My wagon has a bad drone at about 2000 RPM.
My diesel pickup does as well. Now my pickup was purchased with exhaust modified. The previous owner removed the 55 gallon drum muffler (OK, closer to 30 gallon drum . . .), then installed 5 inch straight exhaust on it. The truck is not loud (you can’t tell it has no muffler) but the drone at 1800-2000 RPM will drive you batty.

My pickup has plenty of room under it for such an exhaust modification. My wagon – not so much.

I was thinking about something like this. It should fit under the car OK, I think.

BudW

 

[kkritsilas]

I've never seen Street Outlaws. You are way over-analyzing it. I agree that a car should be able to do it all, but there are always compromises. I like having something that's different than what everyone else does. Not to be different, but because I like to try things out for myself and see what I like, and it usually isn't what everyone else agrees is "right". I'm more comfortable in a car that is revving low on the highway than in one that is buzzing to the rafters at 50. I like one that can idle at 6-700 rpm and doesn't need to turn 1,200 to keep from stalling. I love a torquey engine, but I don't like one that can't rev past 2,500 without falling on it's face. I don't like pushing it past 4,000 so you may have a different idea of what I'm talking about. I think people who gather in the middle of the night on a road to organize an illegal street race are morons. I agree with you there. I really could give a crap less about what a timeslip tells me, other than it's an interesting bit of conversation piece. I get some people will thump their chest and say the race is won after 50 feet, doesn't really bother me. "Race" 1,000 miles, that will impress me more.

Wasn't trying to rile your feathers. I have a lot of respect for what it takes to build a fast car, or any car for that matter. Just stating what I enjoy, and trying to tell him not to get discouraged from trying something different.

You are the one who was talking about "driving around" people when your :car "....hits its stride...". To me, that implies street racing. So do other things in the original post. You're the one talking about putting people in their place when they don't show any respect for your car. All your words, not mine.

You can have a car that is running reasonable RPM on the highway, and still has good low end if the car is built properly (reference to OD automatic/A500/A518). It will idle at 700 RPM, it will get good gas mileage. As for "falling flat on its face at 2500 RPM", unless you are trying to recreate a taxi package engine, that isn't going to happen. As for revving past 4,000, in a properly built engine, that shouldn't be an issue, either. Past 5500 may be, but there isn't really a valid reason to rev an engine that high in almost any street driven situation (unless street racing, of course(..

I have no reason to get time slips, nor do I care what somebody else's says. What I mean by going to the track is to get the racing off of the street, and do it in a controlled, safe, environment that won't expose the general public to potential accidents. Some people use the track to tune their cars, to to see if some change was an improvement or not. More power to them, it is as valid a way as making a dyno run.

if you want to put a Bonneville salt flats racer, fine on the street, fine. If you you want to drive a tractor pull competitor, also fine (assumeing you can get it registered). You can drive a fuel dragster (again, assuming you can get it registered), also fine. However, do not be under any impression that any of them will be well suited for street use. Street cars must strice a multiple variable balance. This is what I was talking abour regarding cars being able to do all things well. You are willing to give up low end torque for higher top speed, that is your choice. However, as above, do not be under any false delusion that this is a good, or to most folks, desirable characteristic. People want cars that move out well at the stop light, can get up to 80-90 mpj, and be all around enjoyable to drive cars. This is why I never "got" the Pro Street cars, and I still don't get the entire facination with drag racing; it is too one dimensional.

I don't really care if somebody has a 9, 10, 11, or 23 second times in the quarter mile. Tell me how much you enjoy your car, and how it works as a daily driver. Tell me what you did to get into the shape it is in, what you want to do going forward.