1.4L Teardown/Modification

[cndctrdj]

Also a stiffer valve spring is needed when working with high boost

 

[Preloader]

Boost definitely magnifies the issue.

But also helps combat the issue of time. My horsepower plan involves making use of revs up to 7k. At those engine speeds, valves open and close so fast that, without the assistance of boost, air/fuel has a very small window to enter the chamber. N/a engines require a lot of flow work to encourage air/fuel to enter in such a limited amount of time.

In a boosted application, such flow work is not required (athough it doesnt hurt). This is why I'm sprung on turbo and am never going back to n/a.

 

[ChrisJ]

Boost definitely magnifies the issue.

But also helps combat the issue of time. My horsepower plan involves making use of revs up to 7k. At those engine speeds, valves open and close so fast that, without the assistance of boost, air/fuel has a very small window to enter the chamber. N/a engines require a lot of flow work to encourage air/fuel to enter in such a limited amount of time.

In a boosted application, such flow work is not required (athough it doesnt hurt). This is why I'm sprung on turbo and am never going back to n/a.

Oh cmon thats nothing compared to older F1 engines running at 18K+
7-9K is pretty common really if you include motorcycle engines.

 

[Preloader]

Many modern race and sportbike engines are happy to rev passed 7k. The point is the economy 1.4 was not engineered to flow well passed 6k.

 

[AJH]

Well, if I read correctly our 1.4 is an oversquare design (stroke is longer than the bore is wide) which means it probably won't want to rev like a honda. The longer the stroke the faster the piston speed. Just like with the valvetrain the piston is traveling 0 inches per second at bottom dead center, it accelerates like mad as until it reaches the center of the stroke where it starts to de-accelerates like mad until it reaches top dead center of the stroke when it is traveling 0 inches per second. If you have two engines revving to the exact same RPM the piston speed will be faster the longer the stroke. Once again we must remember that force= mass x acceleration. (F=Ma) so the internal forces working against our oversquare 1.4 are much greater than those on an undersquare engine. You can have situations where the crankshaft and engine block start flexing, causing the engine to lose oil pressure at the crankshaft, which quickly leads to spun main bearings. (Old Pontiac 400, and 455 cu/in used to do this) if the forces are extreme or the parts not strong enough the force can pull the connecting rod apart. The piston keeps moving up, the rod goes back down, minus all or part of the piston. Next time it comes around it might punch a hole in the engine block, but the motor is junk.
Have you calculated the piston speed at 7k+rpm?
So why did Chevy put an oversquare engine in our Sonic? Well, while the design doesn't lend itself to stratospheric revving it does deliver more more torque, and torque is good!
Torque is really good.

 

[River_Rat]

I think you mean undersquare. Regardless, over vs under square is only one consideration. To answer the question of why gm went with this particular ratio, I would hazard a guess to say that it was probably to accomplish the goal of creating a low displacement engine (under 1.4 liters) without sacrificing low to mid range torque. This was probably why they chose what some might consider an undersized turbo as well. I think it is an effective design so far as that is concerned.

Still, at 3.25 inches, the 1.4 has a shorter stroke than many of these high revving hondas. Now look at the bore of this design at 2.85 inches. How does such a diminutive piston affect f=Ma? One might think that such a tiny piston would significantly reduce mass, thus mitigating, to a greater or lesser extent, the increased acceleration that results from a longer stroke.

In any event, we are talking about a relatively minor bump in the operating range, and this increase is being accompanied by rods and pistons that should be stronger than stock.

 

[Preloader]

Boner inducing Piston physics. Great stuff.

Agreed, the difference in piston acceleration between 6k and 7k multiplies forces aggressively. The tensile forces on the rods as pistons approach TDC is where events became scary.

From what I've read, specs on OEM internals are accurate for their application. That is to say the forged internals on our 1.4 were engineered, tested and rated for tensile and compression forces up to 6.5k, but will quickly lose the capacity to support forces above that.

This is why I have no intention of winding my stock block up to 7k. Instead I am having uprated forged pistons and rods built for my race duty 1.4 build.

And even then, if exposed to hyper-7k revs often, I'm prepared to do rebuilds every 15-20k mi. Budget tuners, don't try this at home.

 

[Preloader]

On a comical note..... I shipped a piston and rod to DDMW in the very same box my Ultragage came in. opcorn:

 

[$ub$onic]

Hahahaha. Fantastic

 

[ChrisJ]

Boner inducing Piston physics. Great stuff.

Agreed, the difference in piston acceleration between 6k and 7k multiplies forces aggressively. The tensile forces on the rods as pistons approach TDC is where events became scary.

From what I've read, specs on OEM internals are accurate for their application. That is to say the forged internals on our 1.4 were engineered, tested and rated for tensile and compression forces up to 6.5k, but will quickly lose the capacity to support forces above that.

This is why I have no intention of winding my stock block up to 7k. Instead I am having uprated forged pistons and rods built for my race duty 1.4 build.

And even then, if exposed to hyper-7k revs often, I'm prepared to do rebuilds every 15-20k mi. Budget tuners, don't try this at home.

I recall the issue with undersquare being breathing. When you have a larger bore vs stroke it breaths better at higher rpms. Of course, this is going back to when I was into the SBC and people were comparing SBC 305 vs 302, 327 and 350. Perhaps 4 valve per cyl is a totally different animal.

 

[AJH]

I think you mean undersquare. Regardless, over vs under square is only one consideration. To answer the question of why gm went with this particular ratio, I would hazard a guess to say that it was probably to accomplish the goal of creating a low displacement engine (under 1.4 liters) without sacrificing low to mid range torque. This was probably why they chose what some might consider an undersized turbo as well. I think it is an effective design so far as that is concerned.

Still, at 3.25 inches, the 1.4 has a shorter stroke than many of these high revving hondas. Now look at the bore of this design at 2.85 inches. How does such a diminutive piston affect f=Ma? One might think that such a tiny piston would significantly reduce mass, thus mitigating, to a greater or lesser extent, the increased acceleration that results from a longer stroke.

In any event, we are talking about a relatively minor bump in the operating range, and this increase is being accompanied by rods and pistons that should be stronger than stock.

Dang, I always get over and undersquare mixed up...
Well, one of the problems with a small bore is you can't fit very very big valves in the head, which limits flow at high RPM.
For sure they chose to build the 1.4 for torque, because that is what you need day to day.

 

[laborsmith]

On a comical note..... I shipped a piston and rod to DDMW in the very same box my Ultragage came in. opcorn:

So much irony and so much coolness.

Any potential puns intended.


Laborsmith

 

[theenico]

In all the over square vs. under square banter, no one mentioned rod ratio. It's the rod's length with respect to the crankshaft's stroke that determines the acceleration characteristics of the piston. Bore vs stroke has NOTHING to do with piston speed. The over under debate is one that drives me nuts.

Bigger bore just makes room for larger valves and makes the flame front have to go further.

So Pre, did you measure the center to center length of the rod?

Found a decent write up on rod ratio:

http://planetminis.com/forums/performance/164681-rod-stroke-ratio-fully-explained.html

If you guys actually take the time to read it, you'll notice that bore is missing from all the calculations used to determine piston speed. Oh yeah, that's because it is unrelated. I think I may have already mentioned that earlier. [/end rant]

 

[Preloader]

I hardly have adequate equipment for precise measurements, but Dave will mic and auto cad them for me. I'm going with direct upgraded replacements. I won't be changing anything, including CR.

The stock piston already has a 3 piece oil control ring and I assume a moly top ring, and I'll be requesting the same for my replacements.

I will also be procuring ARP fasteners soon as well.

There is clearly no room for larger intake valves, I just hope a cam re grind doesn't extend the open duration of my wallet too much.

 

[theenico]

It'd just be interesting to know what the stock rod ratio is and how close to the "ideal" 1.75:1 it is. That is the automotive ideal BTW. Some motorcycles and F1 cars use ratios higher than 2:1.

Some more homework:

Rod to Stroke Ratio - Tech - Honda Tuning Magazine

http://www.motoiq.com/MagazineArticles/ID/1996/Does-Length-Matter.aspx

 

[Preloader]

Ill throw a tape on it in the morning for a ballpark ratio. And I'll throw up some more detailed pics of the rods/pistons too.

 

[River_Rat]

I'll just clean this up

 

[Preloader]

OK.... My interest got peaked and I had to get some numbers up.

Please note that these are in eyeballed sixteenth's.... Completely barbaric in the world of engine mathematics, but at least will shed a little light on the discussion.

Rod C-C: 5.1875"

Crank Stroke C-C: 3.25"

RS Rod Ratio~ 1.6:1 relatively close to the "ideal" 1.75? Or is that way off?

Is this the "diamond coating" that's already worn through at 14k miles?

Hefty crown, and sexy skirt:

 

[Preloader]

Being that the ratio is lower than 1.75:1, does that classify the rods as "short"?

Aggressive angle causing piston side loading..... Bad.

Longer stop at TDC for better AFM burning.... Good.

 

[theenico]

That's cool and all, but I certainly didn't intend to imply that bore had any impact on piston acceleration or velocity. Rather, I was just pointing out that smaller bore equals less mass flailing about at the end of the rod so far as that relates to the force equation, which really has very little to do anything.

Anyway, I think it might be a step too far to say that bore vs stroke has NOTHING to do with it. For a given displacement, bore and stroke have something of an inverse relationship. I think that we are all in agreement that stroke does, indeed, have a place in determining piston acceleration/velocity. Generally, an undersquare engine is going to have higher piston acceleration/velocity than an oversquare engine of the same displacement.

I wasn't replying to your post. I should have quoted for context. Either way, it bugs me when people throw around bore-stroke ratio when talking about piston speeds. Take the 1.4T for example, if I replace the stock rod with a longer one, I have changed the acceleration characteristics of the piston. The bore-piston ratio didn't change, but the rod-length to stroke ratio did.

This is the post I was replying to, and now that I've reread it, I have to say I mostly agree with it too since it talks only about stroke in the context of piston speed. Occasionally reading comprehension even nails me. Sorry guys.

Well, if I read correctly our 1.4 is an oversquare design (stroke is longer than the bore is wide) which means it probably won't want to rev like a honda. The longer the stroke the faster the piston speed. Just like with the valvetrain the piston is traveling 0 inches per second at bottom dead center, it accelerates like mad as until it reaches the center of the stroke where it starts to de-accelerates like mad until it reaches top dead center of the stroke when it is traveling 0 inches per second. If you have two engines revving to the exact same RPM the piston speed will be faster the longer the stroke. Once again we must remember that force= mass x acceleration. (F=Ma) so the internal forces working against our oversquare 1.4 are much greater than those on an undersquare engine. You can have situations where the crankshaft and engine block start flexing, causing the engine to lose oil pressure at the crankshaft, which quickly leads to spun main bearings. (Old Pontiac 400, and 455 cu/in used to do this) if the forces are extreme or the parts not strong enough the force can pull the connecting rod apart. The piston keeps moving up, the rod goes back down, minus all or part of the piston. Next time it comes around it might punch a hole in the engine block, but the motor is junk.
Have you calculated the piston speed at 7k+rpm?
So why did Chevy put an oversquare engine in our Sonic? Well, while the design doesn't lend itself to stratospheric revving it does deliver more more torque, and torque is good!
Torque is really good.

It still stands however that even though the stroke is a factor that effects piston speed, the inclusion of rod length is the other factor used to determine piston speeds.

Over-square and under-square is just the bore-stroke ratio. Changing the size of the bore doesn't change piston speed.

All I ask is that people stop using over/under square in discussions about piston speed.