Dyno Testing Bolt-ons On The 4.0

[ColoJeep]

Right. Problem is I spend zero time at full throttle going up rocks.

-Mac

True , But the lack of power shows up mainly on the highway , I've never had a lack of power off road , a lack of crawl ratio sure , but the engine makes good off road power. Think about how many time you are at full throttle climbing steep highway grades .

 

[NashvilleTJ]

Right. Problem is I spend zero time at full throttle going up rocks.

-Mac

Then you are doing it wrong, Mac.



Wait - That may just be me...

...never mind!

 

[macleanflood]

Pretty sure I have a video clip of @hosejockey61 telling me we'll all be fine going up some steep obstacle in Moab as long as I layed off that Oregon full throttle shit.

-Mac

 

[lBasket]

Pretty sure I have a video clip of @hosejockey61 telling me we'll all be fine going up some steep obstacle in Moab as long as I layed off that Oregon full throttle shit.

-Mac

You were lifting front end a decent bit but that could've been because you had that blown shock

 

[GoldenGorilla]

At full throttle the air spends almost no time in the intake manifold. Engine Masters did an episode on cooling the intake manifold and it made zero difference at full throttle.

I hear you and in my experience agree. It's always a bit tough to translate their results on an engine dyno stand to the real world under a hood.

I built myself a heat shield while putting in my aFe shorty header and have been watching the air temps from time to time out of curiousity. I know your goal is around WOT conditions and that's great to understand. In the real world cruising on highways and driving around town at various throttle positions, the temps are all over the place. I have noticed when the intake is heat soaked it does take 5-15 seconds for the temps to show a drop at full throttle. Could just the sensor is hot. But while highway cruising the temp even at part throttle comes down over time.

I'm also curious about the results of the windstar intake mod. I really don't like the Banks cut a hole in your hood design. I think the stock intake design is a good compromise of pulling the coolest available air from under the hood, but we all know you could cook a pizza under there while rock crawling.

 

[lBasket]

but we all know you could cook a pizza under there while rock crawling.

Or a burrito!

 

[BlueC]

Right. Problem is I spend zero time at full throttle going up rocks.

-Mac

It seems you might be doing it wrong. Maybe you should add a little East Coast to your style.

 

[CharlesHS]

I love the sound that engine makes and I am sure the performance is VERY impressive, but for the amount of money invested in that head and engine along with the installation and tuning; I would have to sell my house to afford the amount of money what was invested in that head and engine.
NOT very practical for most Jeep owners.

 

[Rickyd]

It seems you might be doing it wrong. Maybe you should add a little East Coast to your style.

Definitely my preferred method of wheeling. Unfortunately,with age has come the knowledge I can't afford one of those rigs and better not treat mine like that!

I love the sound that engine makes and I am sure the performance is VERY impressive, but for the amount of money invested in that head and engine along with the installation and tuning; I would have to sell my house to afford the amount of money what was invested in that head and engine.
NOT very practical for most Jeep owners.

Agreed. I would run a turbo long before building a 10,000 rpm motor

 

[GoldenGorilla]

With our modern CNC machines I wonder if it's possible to design a new head for the 4.0.

Move the intake or exhaust to the other side for one... although I think the pushrods get in the way.

-Mac

I think cutting the cooling in it might be the hardest even with a 5 axis CNC.

 

[GoldenGorilla]

Never seen that DOHC 4.0L engine before. If I were serious about a crossflow I6 in the jeep and for some odd reason wanted to keep the jeep block, I'd figure out how go overhead cam at the same time too.

 

[SkylinesSuck]

Thinking of an NA gas motor as an air pump, as is often said, this makes sense. If your stroker has 15% more displacement and volume of pumped air varies linearly with displacement, then you might expect the stroker to produce the power of a stock motor at about 15% less RPM (to the Left). BUT, if your intake setup can provide the airflow, that power should continue to climb with RPM (provided enough fuel) until the motor flys apart.

Seems pretty simple. Am I getting this right?

Kinda?

The theoretical example I was giving was more for understanding the concept sake but wasn't entirely accurate. As somebody already pointed out, it's more of a whole system thing. There are so many variables, even engineers who actually understand this stuff can't just say "it'll make this much power at this rpm" but instead need to spend lots of time on the dyno testing and tweaking.

I will try to find a video I saw testing a different kind of I6 motor I used to play with. They destroyed the crank and rebuilt the motor using everything else exactly the same (same head, cams, intake, etc.) except they stroked it from a 2.6 to a 3.2L IIRC. It made *slightly* more peak hp but at like 800rpm lower or something like that. This was on a high hp turbo car that had already maxed out the turbo, so at this point the turbo was the limiting factor, but the same would mostly apply if your n/a head was the limiting factor.

One difference I can think of though is n/a it's more of a vacuum pump kinda thing. So I guess there is a bit more to gain if you Invision the motor having bigger lungs to pull a little more air through the same straw. But again, it's not a "flows enough" kinda thing as much as a point of diminishing returns. Going from a 2" exhaust to 3" would likely yield a substantial gain. 3" to 4" might give more, but barely.

 

[BlueC]

As somebody already pointed out, it's more of a whole system thing. There are so many variables

Yes. There's so much going on inside an engine, so many frictions and drags that increase exponentially. I find engine theory stuff interesting, like sonic/resonance tuning. Just so much is happening and fast.

I will try to find a video I saw testing a different kind of I6 motor I used to play with. They destroyed the crank and rebuilt the motor using everything else exactly the same (same head, cams, intake, etc.) except they stroked it from a 2.6 to a 3.2L IIRC. It made *slightly* more peak hp but at like 800rpm lower or something like that. This was on a high hp turbo car that had already maxed out the turbo, so at this point the turbo was the limiting factor, but the same would mostly apply if your n/a head was the limiting factor.

I'd like to see that. It's hard to keep everything but the stroke the same, but I'd like to see that comparison.

 

[ColoJeep]

I'd like to see that. It's hard to keep everything but the stroke the same, but I'd like to see that comparison.

Stroke is always an interesting factor , longer stroke increases the leverage of force to the flywheel but it also increases frictional loss , especially as r.p.m. increases. I love to think about this stuff ! It is hard to comprehend that a piston changes direction and goes from a dead stop to full acceleration twice with each rotation of the crank. 6000 r.p.m. = 12,000 changes . 200 changes per second !

 

[BlueC]

I love to think about this stuff ! It is hard to comprehend that a piston changes direction and goes from a dead stop to full acceleration twice with each rotation of the crank.

If you want to get real deep in the weeds there, think about this, with piston speed, at a certain point the rings will begin to hydroplane on a thin film of oil on the cylinder walls and lose friction, but when piston speed slows down below that threshold the rings break through the boundary layer and friction increases back to "normal", and that happens with every stroke when pistons speeds are fast enough. I hope that makes sense, and if your head starts hurting thinking about that, that's normal.

This is about the best representative graphic I could find. Think of the middle as max speed/least friction.

 

[ColoJeep]

If you want to get real deep in the weeds there, think about this, with piston speed, at a certain point the rings will begin to hydroplane on a thin film of oil on the cylinder walls and lose friction, but when piston speed slows down below that threshold the rings break through the boundary layer and friction increases back to "normal", and that happens with every stroke when pistons speeds are fast enough. I hope that makes sense, and if your head starts hurting thinking about that, that's normal.

This is about the best representative graphic I could find. Think of the middle as max speed/least friction.

View attachment 626664

And if that's not enough , let's look at rod length and stroke . The rod ratio , it's effect on piston acceleration rate , critical piston speed , and then piston thrust friction .
The thing that gets me is the speed/time all this happens at . Many events are happening simultaneously and concurrently and quickly , even in our glorified Rambler engines .

 

[GoldenGorilla]

A stroker is almost always going to have a higher compression ratio and that itself will increase power. Most references say 3-4% more hp per unit of additional compression alone assuming the same displacement. The stock 4.0s are in the 8.7-8.8:1 range and most strokers are aiming for 9.3-9.5. These dynamics are why the power isn't just a 15% increase.

 

[Rickyd]

A stroker is almost always going to have a higher compression ratio and that itself will increase power. Most references say 3-4% more hp per unit of additional compression alone assuming the same displacement. The stock 4.0s are in the 8.7-8.8:1 range and most strokers are aiming for 9.3-9.5. These dynamics are why the power isn't just a 15% increase.

Compression is part of it. But not THE reason. Most people do more than add a 258 crank and higher compression pistons when going to the effort of rebuilding a 4.0l based stroker.

 

[jeepguy03]

Definitely cool to see the dyno results, thanks for posting this stuff. My TJ's 4.0L is 100% stock besides some 4 hole injectors the PO installed before I bought it, as well as a magnaflow cat, and some brown down motor mounts I added since the stock ones were shot. The Jeep as a whole is pretty stock (1" lift, 31s) compared to the XJs I built over the years.

Back in the day there was someone on another forum who did all sorts of engine mods to a stock XJ 4.0L to track power increases and mpg changes. It was kinda neat to see what mods actually did improve it, even if a tiny bit, and what other mods made no difference at all.

 

[Brianj5600]

Go here, https://www.speed-talk.com/forum/ There are some applications that need longer rods, but not here. There are tons of smart guys.