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Posted by: Tdskip Sep 20 2021, 01:02 PM

Several twists and turns I’m getting close to getting that XN turbo big bore engine back to me. This is the one that had a very elaborate homebrew turbo set up turns out was only running on three out of four cylinders when I did the initial teardown. I ended up having to swap the case out for another one because when it was rebuilt for the first time it was developing crazy high will pressure hand given all the unknowns and some funkiness with it that we discovered we decided it would be better to just use another case

Shop let me know going in the carbs I gave them would be snappy and responsive but probably leave horsepower on the table. The shop also noted that this was not run using optimized headers and exhaust is probably a bit restrictive for this sort of build.

Thing that really jumps out to me here is that the engine is making lotta torch, or at least seems to be a lot of work, down low and had a very usable or p.m. That, to my son white uneducated eyes, suggest that should be fun for regular street use. What do you all think?

Posted by: SirAndy Sep 20 2021, 01:12 PM

Shift at 4500 rpm for max acceleration ...

Posted by: Tdskip Sep 20 2021, 01:19 PM

Andy! Hope you are doing well.

Yes, as this is currently set up does not seem like there will be much point to ringing lots of RPMs out of it.

Posted by: jd74914 Sep 20 2021, 02:07 PM

Did you keep the original heads?

Seems like the it's quite restricted given how flat that curve is.

I'm not totally in the flat torque curve makes it more fun camp though-you tend to end up with rough neck-snapping type of shifts* because your tractive force (what the tire is actually putting to the pavement) curve gets pretty wacky. Later tonight I'll see if I can pull your curve into a spreadsheet to show.

*when shifting agressively

Posted by: mepstein Sep 20 2021, 02:15 PM

Not necessarily. You may want to go a bit over the max so when you shift, the next gear is closer to the max. It will depend how close the gears are and what you are trying to accomplish.

Posted by: rhodyguy Sep 20 2021, 02:27 PM

What is the displacement of this engine? Still normally aspirated?

Posted by: Tdskip Sep 20 2021, 02:48 PM

Thanks for all the responses and discussion. This is a big engine, plus or -2.7 L in the heads were redone. I’m probably running out of fuel and being held back by the restrictive exhaust, but a bit surprised honestly that there wasn’t more horsepower there with all that said.

Posted by: SirAndy Sep 20 2021, 04:18 PM

Max *torque* is what you are after. You'll drop about 500 rpm on a quick shift, so shifting at 4500 will put him right back at the torque sweet spot.

Posted by: windforfun Sep 20 2021, 04:40 PM

https://www.caranddriver.com/news/a15347872/horsepower-vs-torque-whats-the-difference/

Posted by: Tdskip Sep 21 2021, 07:34 AM

Thanks - apparently will have the first 914 Diesel engine (based on torque vs HP)

Posted by: Chris914n6 Sep 21 2021, 01:51 PM

Shop was right about the carbs, you ran out of air. Should be a 160-180 hp motor.

Posted by: rhodyguy Sep 21 2021, 01:56 PM

Esp if they have 28?MM Venturi. Spring for some headers too.

Posted by: VaccaRabite Sep 21 2021, 02:31 PM

You have a LOT left on the table here. That would have been a good pull for a 2056. Whatever carbs you are using, they need to be bigger. Exhaust will be the next restriction, but you clearly need more fuel and air.
Zach

Posted by: JmuRiz Sep 22 2021, 07:33 PM

Something is wrong with the graph, how does it not cross at 5250 RPM?

Posted by: targa72e Sep 22 2021, 07:59 PM

data is not correct in graph. If you have 162Ft/lbs at 4250RPM then you have 131HP. HP should be about 130HP from 4250-5250 based on torque numbers listed. Something is not right with data.

John

Posted by: PlaysWithCars Sep 22 2021, 11:07 PM

Simple equation relates the two and something about the data presented doesn't add up.

Power = Torque * RPM / 5252

Posted by: Rufus Oct 1 2021, 06:11 PM

Agree with the others. Something’s fishy about the torque and power readings not being equal (the curves should cross) at 5252 rpm assuming torque is measured in lb-ft and power in hp and they’re numerically on the same scale.

JMHO, but I wouldn’t use the curves, or pay for the dyno testing until presented with data that makes sense. These curves don’t.

FWIW: this’s the 1st thing I look at as most of my career involved engine performance / emissions development & testing.

Posted by: Rufus Oct 1 2021, 06:36 PM

Shift at 4500 rpm for maximum acceleration?

Nope. Shifting near peak torque engine speed will leave a lot of acceleration “on the table”. (Remember you want maximum torque to the rear wheels; not "upstream" of the tranny … each gear multiplies input torque differently based on ratio.) For maximum acceleration you always at least want to rev to peak power (unless for some bizarre reason that’s above redline or there’s a concern about mechanical weakness). Optimum shift points can’t be accurately determined without first knowing gear spacing. For optimum acceleration, the power and torque to the final drive (any point “downstream” of the transmission) at the shift rpm equal the power and torque available to the final drive at that vehicle speed in the next higher gear (@ WOT of course). Optimum shift points are determined from the available power / torque at the final drive as a function of vehicle speed for each gear. The points where available power & torque in one gear fall below that available in the next gear is the optimum shift point. Often optimum shift points are over the peak power rpm (assuming redline permits). Because gear spacing is not necessarily the same from shift to shift in a given gear set, optimum shift points can vary from one shift to another.

Maybe not the best example, but a random chart from an old college textbook will show the idea. Note that “propeller shaft rpm” is final drive rpm not erpm, and is proportional to vehicle speed. The peak power and torque values differ from gear to gear due to slightly different throughput efficiencies based on gear ratio. The differences in peak torque are additionally related to the different torque multiplications of gears.

So what about the curves not crossing in the chart? One must assume the curves end at engine redline. Therefore torque and power available for acceleration will immediately drop after each shift. This could be avoided with narrower spacing / more gears. The goal being to maximize “area under the curve(s)”.

If vehicle aerodynamic drag (in hp) is plotted on the same chart as final drive power, top speed is predicted by the point where drag crosses available power.

Posted by: Rufus Oct 1 2021, 10:40 PM

Quoting Tdskip: “… a very elaborate homebrew turbo set up …”

It’s not clear what this means, especially “homebrew”. But if it still has a turbo, I hope someone knowledgeable/ experienced has had a hand in it. Matching a turbo & engine is kinda complex and theoretical. If not done correctly, problems like driveability, etc can result.

Here’s a link with a little info on turbo mapping:
https://www.garrettmotion.com/wp-content/uploads/2019/10/GAM_Turbo-Tech-103_Expert-1.pdf

I’m not experienced in turbo matching, but was close enough to it at my last employer to know it’s definitely not a one-size-fits-all proposition.

Posted by: Tdskip Oct 2 2021, 06:01 AM

Good morning, the turbo set up was removed, this engine is naturally aspirated now. Sorry if that wasn’t as clear as it should have been.

Posted by: Tdskip Oct 2 2021, 06:06 AM

Thanks for all who spotted this issue, this was the first dyno run that I’ve seen and I did not spot that there might be a data issue problem.

130hp would be around where I would expected it to be.

The shop does a run with every engine they build but there was an oil leak that they found so they are going to redo the build and rerun it.

I should get an updated dyno read out and will post that.

THANK YOU ALL for the eyes and thoughts on this, appreciate the education.

Posted by: Gatornapper Oct 2 2021, 06:55 AM

While we are displaying Dyno readings, anyone have a Dyno reading for HP/torque curve for a stock 2.0?

Would love to see that for many reasons......

TIA,

GN