Larger Exhaust on a D24 NA?

[DieselScout]

Do D24 NA engines benefit (fuel economy, power) from larger exhausts?

If so, would this work/fit? Or would the header pipe also need to replaced with a larger diameter pipe?
https://www.ipdusa.com/products/2078...lvo-IPD-139511

[v8volvo]

Seems fairly unlikely it would make a major difference. Maybe a little bit of marginal improvement at the very top of the RPM range when exhaust flow is greatest, but most of us don't spend a whole lot of time running our diesels up at those RPMs.

As noted elsewhere, although there may be a few marginal gains that could be achieved by fully optimizing the NA D24 engine, far and away the greatest performance and economy boost would come from converting to a D24T. If your engine is already out of the car it may be a golden opportunity! Although a good running fresh and healthy D24 can be a pleasing engine to operate as well. But any gain from things like bigger exhaust, overbore, cylinder head work, etc, is going to be at most a percent or two improvement. Probably not enough to even really feel. By contrast, changing to a stock D24T engine in a 240 is a difference you would feel in a huge way.

Forced induction through turbocharging seems to be the unquestioned path to improved engine efficiency and power for diesels..... hence the almost total absence of any non-turbocharged diesels produced by OEMs in modern market, i.e. for the last 30 or so years, outside of agricultural/industrial applications (and even there they are rare). I personally cannot speak to the theory of why diesels benefit so hugely from forced induction (like gas engines also do) yet have relatively little potential for power/efficiency gains through other traditional means that usually have great success in adding power without forced induction on gas engines. By those I mean things aimed at volumetric efficiency, like bigger exhaust, intake, camshafts, cylinder head port/polish, bigger valves, etc. But I would speculate part of it may be that the limited diesel engine speed range, usually topping out at 5k RPM or less, leaves minimal opportunity for taking advantage of upgrades like those mentioned above. A gas engine can spin faster and make use of changes that let it move air in (and exhaust out) more efficiently. And its rev range can be increased almost without limit due to the homogenous charge (air and fuel mixed before entering the cylinder) -- the only limit to engine speed is imposed by what the rotating assembly and valvetrain can withstand, and those too can be modified as budget allows to even let a big-block V8 rev to 8000 rpm or more by use of exotic light/strong metals like titanium..... Meanwhile, a diesel engine by contrast is speed-limited not by inlet/outlet gas flow, but rather as I have always understood it, by the diesel combustion process itself -- how quickly the compression ignition cycle can burn the fuel. And perhaps to some limited degree also by the necessarily heavier mass of diesel pistons/rods/crankshaft that cannot really be lightened much due to the diesel compression/combustion forces they are subject to. So even if you could bolt on a massive exhaust, fancy high-flow intake/exhaust manifolds, and an artfully ported and polished cylinder head with high lift camshaft, you'd never get the engine turning fast enough to create the kind of intake/exhaust airflow rates where those things could really make their difference. At least that's the version of it that makes sense to me.

[RedArrow]

Hi forumers! A great thread here, thank you.
May I ask a question related to the exhaust system of the d24t?

Can I use the front muffler/silencer from a gasser Volvo 740 (new) on my td car?
Are the d/td muffler any different from what the gassers use(d)?

I have a very hard time finding a setup for my d24t 740 while plenty of options listed for the gasser Volvos.




I removed the entire exhaust system from my car and now I am trying to figure out a proper setup.

Progress is,
Downpipe got cleaned and painted with high heat paint,
Downpipe connector studs at turbo replaced and I am using new copper nuts, flange gasket,
I replaced all rubber hangers and the clamps too along with the bolts and nuts that connect downpipe to the silencer below the glovebox area, new metal sealing 'donut' ring)...
Silencer unit got removed and everything all the way towards the rear end got removed completely.
(Not yet junked except for the rear muffler that rotted out and all piping is toast as well. I kept the front muffler=silencer for now, mainly for reference but the inlet and outlet sides of it are both toast, corrosion and heat ate it up, can not reuse without too much of welding and it would still look bad, dented, and it is probably burnt out. I doubt it can clog but there is residue inside of course lol, blck. )
The rear muffler was a bosal unit (have numbers photographed) and the front silencer was also a bosal unit that says ''volvo 760 turbo- turbodiesel''.


After the removal,

Some experiments followed with the old parts, several variations were tested etc
(downpipe with silencer plus some short pipe
downpipe without silencer with longer pipe
downpipe without silencer but with piping all the way to the back
downpipe with short sidepipes out at the side
downpipe with silencer and short sidepipe out on side
etc)

With mostly all of those experiments, I found the car being too loud for my liking and the power output is literally not changing much no matter what you do.
Maybe the WOT power is a tiny bit better with the all-out straightpipe without the muffler And without the silencer (front muffler)and short piping till appr the rear doors... but it sounded like a dump truck and the vibrations/droning/loudness inside were not pleasant at all.

Also tried removing silencer unit and used rear muffler only but it did drone as well, and it was also loud.



I now prefer the factory setup or something very similar, in look, in size, in length and in routing.


Can I use anything from the gasser (FRONT MUFFLER/SILENCER, REAR MUFFLER)
(yes i know the axle-over pipe and the tailpipe is the same , and i bought those already)

What is the main difference (if any) between the oem gasoline and d/td powered 740 and 760 cars` exhaust system?

Does it really matter what I use? Also, I gotta have both 'mufflers' in NY state, I guess.



MARKINGS ON THE UNITS:


Front silencer unit:


B O S A L
287-947 ALU
EEG-8-84 / 424 - 5303
VOLVO 760 TURBO - TURBO DIESEL


Rear muffler:


B O S A L
235-949 ALU

36 26 NR 6 --this entire line is barely readable, probably not correctly registered!

EEG B (?or 8?) 84/424 5304


NOte: Despite days of searcing, I haven`t seen any silencer units that have a STRAIGHT pipe section like the one I removed, you can see it in my pictures.

This link shows some units and interestingly the cars with different engines share the same rear muffler , AND even the silencer/front muffler. I am confused by this info.)
https://medias-norauto.fr/pdf/Eclate...osal-15784.pdf

Thank you!

[ngoma]

What you are calling the front "silencer" I think is referred to as a resonator.

Mine also needs renewing. I did pull one from a gasser at the JY as it looked similar. Probably will mount right up using the same hangers etc. Some differences:

1) Inlet flange is not the same orientation/location to mate up to the D24T DP so will need to be cut somewhere along the straight run and welded to a good piece from D24T section. Might be tricky to maintain the correct angle and geometry.

2) Diameter at the resonator can inlet and outlet appeared to be slightly smaller than the existing one on my car, but the pipe further out appeared to measure out the same. Hard to accurately measure because it is ovalized. Not sure it matters much overall?

Rear muffler and associated over-axle and tailpipe sections appear to be same as gasser.

OTOH a capable muffler shop should be able to fit in a generic resonator and fab up the two ends to mate up with what you have.

For sure use hi-temp anti-seize on the nuts/bolts/studs.

[RedArrow]

Thank you for the quick response. I found a seller that states the silencer he has fits a td 760. There`s one way to figure out, I plan to meet him in person to compare it to the one on the car (will be tricky). Many other websites also happen to list the very same item for the turbo 760 (6cyl gasser)and the turbodiesel d24t 760. I am not sure they used the same part but who knows? It is very hard to figure it all out. I wish it all just fit without tinkering. The car was a gasser originally so maybe it has all the places for a gasser exhaust and any unit will fit? I have no idea yet.

In the meantime I found this for good reference.
https://www.skandix.de/en/installati...01422/2000332/

There`s no 'good piece' of the rotten d24t silencer section piping that is currently on, so I will need to see what to do with a new unit to achieve a good fit. I really do not want to get into having to weld it (that`s partly why I prefer the stock system which should be plug-and-play plus adding clamps at certain factory places.)

None of the resonator/silencer units I found show the straight section that the d24t page displays.
It looks like that the one I removed is probably an original d24t part, judging from the straight section between downpipe and silencer/resonator.

[ngoma]

Originally Posted by RedArrow

I plan to meet him in person to compare it to the one on the car (will be tricky).

Shouldn't be too difficult. You can slide the piece up alongside the existing under the car and get a good visual on matching the length, connection locations/angles, and hanger mounts. Should be obvious. *Might* want to jack up that side of the car for easier access so bring your floor jack and stands. Bring tape measure and possible calipers as well.

Originally Posted by RedArrow

The car was a gasser originally so maybe it has all the places for a gasser exhaust and any unit will fit? I have no idea yet.

Doubt that Volvo stamped different floor pans for different engine models. Don't worry about that.