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GM has a new DOCH flat-plane crank engine for the Z06

Seems like this does not have balance shafts or VVT? Odd. I'll bet it fills an engine bay, DOHC V-engines are massive compare to rods.

Also, 'vette had a DOHC V8 option in the early 90's.
 
larboc said:
Seems like this does not have balance shafts or VVT? Odd. I'll bet it fills an engine bay, DOHC V-engines are massive compare to rods.

Also, 'vette had a DOHC V8 option in the early 90's.
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Wasn't that an engine built by Mercury Marine?
 
JR4X said:
I almost tagged you. What year was your experiment dual plenum intake engine being tested?
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'89 was the first year they had it in production cars. Right now I have it set to open the short runners at about 3500-4000 RPM, you can definitely hear and feel a big change when that transition happens. Almost like VTEC kicking in . I'd be curious to put it on a dyno and see what that looks like on a graph, and if there's much advantage to tweaking that RPM setting.

I was rebuilding my SHO engine at around the same time that dude on the old board was working on his LT5, and all the DOHC stuff looked almost identical. Not surprising as both engines were developed at about the same time and even though Yamaha did my valvetrain vs Lotus, in the late 80s there probably were only a few ways to make that work without developing completely new components. I was able to get valve shims for mine from the local Yamaha motorcycle shop.
 
Been running the race version since going to the C8.R for the 2020 season. 5.5L is the largest na engine size allowed in gt2 spec, hence the engine size choice. There's a reason the Europeans downsize it and boost em. Shake more than a hitachi wand.
 
87manche said:
If you're gonna fix it, fix it.
GM has finally caught up to the euro v8's of 25 years ago that all had 4 cams and variable valve timing and variable length intake runners.

next thing you know they'll figure out turbochargers like everyone else.
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How many of those 25 YO eurotrash V8 4cam vvt, plastic intake manifold, plastic evap and vacuum hosed POS' are on the road now without a CEL, oil leaks, or shittastic electrical issues?
 
Hubbler said:
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Bless you all for designing, building and racing these cars. But I could not make it even halfway through that video. The capper wre the shoes that the design chief was wearing.
 
Hubbler said:
There's a reason the Europeans downsize it and boost em. Shake more than a hitachi wand.
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I wondered why this is a thing.

Pretty good vid explaining this. I've seen this guy's channel before. This one is old.

 
Any idea why the injectors spray in from the exhaust side? Seems like a good way to detonate off a hot exhaust valve.....
Screenshot_20211029-100044_Chrome.jpg
 
Johnny Longrifle said:
How many of those 25 YO eurotrash V8 4cam vvt, plastic intake manifold, plastic evap and vacuum hosed POS' are on the road now without a CEL, oil leaks, or shittastic electrical issues?
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and how are electrical and evap problems related to engine design and durability?

and if you think that a complex american V8 is going to fare any better, well I got disappointing news for you, it's not.
add complexity, add failure points. Now a chevy engine has 4 miles of timing chain and a bunch of plastic guides, just like a BMW one.

OllieNZ said:
Any idea why the injectors spray in from the exhaust side? Seems like a good way to detonate off a hot exhaust valve.....
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direct injection. Think of it more like a diesel. You're putting the fuel in the cylinder exactly when you want it to go boom
 
87manche said:
direct injection. Think of it more like a diesel. You're putting the fuel in the cylinder exactly when you want it to go boom
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Not at all. Injection occurs much earlier so the fuel/air mixture has time to homogenize. Typically during the intake stroke. As far as placement in this engine IDK, but it could be to get better mixing because its counter to the airflow. Could also just be for packaging.
 
Norm said:
It's a different beast from past GM designs, it will be interesting to see if they hold up. 8500 RPM redline :eek:


At 90k for base model, it's not going to be cheap. Wasn't the c8 base price supposed to be 60k :confused:
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It’s ok. Plenty of people that don’t mind waiting in the 6+ month waiting list. Power sells. Just like the 392 Rubicon. Ordering was placed on hold until 2022.
 
larboc said:
Not at all. Injection occurs much earlier so the fuel/air mixture has time to homogenize. Typically during the intake stroke. As far as placement in this engine IDK, but it could be to get better mixing because its counter to the airflow. Could also just be for packaging.
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but still after that exhaust valve is closed right?

you know a whole lot more than most.
schools us.
I was under the impression that it was still later than any kind of port injection where you may have fuel entering with valve overlap and a partially open exhaust port.
 
87manche said:
but still after that exhaust valve is closed right?

you know a whole lot more than most.
schools us.
I was under the impression that it was still later than any kind of port injection where you may have fuel entering with valve overlap and a partially open exhaust port.
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The big advantage of GDI over PFI is the charge cooling effect of the fuel vaporizing as it mixes with hot residual gasses, drawing more mass of air into the combustion chamber and slightly helping knock limits. In normal part load operation a GDI engine will start injecting in the early portion of the intake stroke so in general the exhaust valve should be fully closed before raw fuel has a chance to reach it (not the case during catalyst light off though!). The vaporizing fuel cools off the residual gasses in the cylinder to suck in more air before the intake valve closes. With a PFI engine, the fuel is sprayed onto the closed intake valve so it's more likely to only mix with the fresh air which is already cool rather than hitting the hot trapped residuals so the cooling effect while the intake valve is still open isn't nearly as effective. The amount of air/fuel that can short circuit out the exhaust port is very small for a half way modern EPA compliant camshaft during normal part load operation, regardless of injection strategy.

A big drawback of GDI is the reduced time for all the fuel to completely vaporize before ignition and less time for the fuel/air/residuals to mix before ignition so you get little pockets of overly rich fuel burning slowly. Doesn't hurt torque performance, but results in smoke especially at high loads. I'll see if I can find a public image to share, but if you look at GDI style combustion with a high speed camera in cylinder or a combustion vessel, you'll see little specs of yellow which when slowed down look just like a tiny version of setting raw gas on fire in your driveway. Smokey, yellow, cold flame.
 
larboc said:
The big advantage of GDI over PFI is the charge cooling effect of the fuel vaporizing as it mixes with hot residual gasses, drawing more mass of air into the combustion chamber and slightly helping knock limits. In normal part load operation a GDI engine will start injecting in the early portion of the intake stroke so in general the exhaust valve should be fully closed before raw fuel has a chance to reach it (not the case during catalyst light off though!). The vaporizing fuel cools off the residual gasses in the cylinder to suck in more air before the intake valve closes. With a PFI engine, the fuel is sprayed onto the closed intake valve so it's more likely to only mix with the fresh air which is already cool rather than hitting the hot trapped residuals so the cooling effect while the intake valve is still open isn't nearly as effective. The amount of air/fuel that can short circuit out the exhaust port is very small for a half way modern EPA compliant camshaft during normal part load operation, regardless of injection strategy.

A big drawback of GDI is the reduced time for all the fuel to completely vaporize before ignition and less time for the fuel/air/residuals to mix before ignition so you get little pockets of overly rich fuel burning slowly. Doesn't hurt torque performance, but results in smoke especially at high loads. I'll see if I can find a public image to share, but if you look at GDI style combustion with a high speed camera in cylinder or a combustion vessel, you'll see little specs of yellow which when slowed down look just like a tiny version of setting raw gas on fire in your driveway. Smokey, yellow, cold flame.
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all very interesting.

Is this partially why I see ecoboost f150s smoking like trains at WOT?
 
OllieNZ said:
Any idea why the injectors spray in from the exhaust side? Seems like a good way to detonate off a hot exhaust valve.....
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I'm almost wondering if it could be to the contrary of this, using the fuel to cool the exhaust valve to avoid PI events? Total guess.
 
87manche said:
all very interesting.

Is this partially why I see ecoboost f150s smoking like trains at WOT?
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Nothing partial about it. Choo choo!
I think the general consensus is that GPF's are the future, or go back to PFI once regulations catch up. Doesn't seem like it can be reduced enough in cylinder.
 
larboc said:
Nothing partial about it. Choo choo!
I think the general consensus is that GPF's are the future, or go back to PFI once regulations catch up. Doesn't seem like it can be reduced enough in cylinder.
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First I saw it I thought the truck was broken. I was like *no way that passed emissions", but every one smokes when you get it.
 
newer trucks will also go rich when the engine is pulling hard like a load up a grade.. This protects the convertors..
 
Truckedup said:
newer trucks will also go rich when the engine is pulling hard like a load up a grade.. This protects the convertors..
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Thats been a thing on anything with a cat or close turbo for a long time. Epa and carb will be making that a nono fairly soon. Power enrichment has already be regulated out AFAIK.
 
I mean, it's cool and all, but if I joined irate 3 years ago with a 93 Lincoln mark8 and 100k of r & d money and started asking questions, I'd be unveiling a 600hp 8k NA V8 too:laughing:
 
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