preignition and detonation are the same

 

Really? When I think detonation, I think of an uncontrolled burn [and possibly mutliple flame fronts colliding with each other]. But when I think pre-ignition, I think of a hot spot in the chamber lighting the mix before its suppose to be.

Here's a link for my reference: J&S SafeGuard.

 

edit... wrong window Great thread tho...


[Modified by X2BOARD, 1:36 PM 6/25/2002]

 

Here are the Honda B block crank's piston speeds:

B16A
77.4 mm 8000 RPM 20.6 meters/sec
8500 RPM 21.9 m/s
9000 RPM 23.2 m/s
9500 RPM 24.5 m/s
10000 RPM 25.8 m/s
B17A
81.4 mm 8000 RPM 21.7 m/s
8500 RPM 23.1 m/s
9000 RPM 24.4 m/s
9500 RPM 25.8 m/s
B18C
87.2 mm 8000 RPM 23.3 m/s
8500 RPM 24.7 m/s
9000 RPM 26.2 m/s
9500 RPM 27.6 m/s
B18A/B18B/B20B
89.0 mm 7500 RPM 22.3 m/s
8000 RPM 23.7 m/s
8500 RPM 25.2 m/s
9000 RPM 26.7 m/s
9500 RPM 28.2 m/s
B20A
95.0 mm 7000 RPM 22.2 m/s
7500 RPM 23.8 m/s
8000 RPM 25.3 m/s
8500 RPM 26.9 m/s
9000 RPM 28.5 m/s

 

you got those from one of the archived threads on http://www.theoldone.com didn't you?

 

To whoever said "Rod/Stroke ratio doesnt mean anything".
I say Stay STOCK! Dont worry about. Engine Geometry means a lot. Some of us just like to think of the unknown.

Im only an engineer for a small shop, I dream about this stuff, but this is where I waste time (nerd). Excuse me for slightly modifying your statement above, I agree with most of it. There can be a factor thrown in there such as "cam duration" (which we all know is actually duration of the valve opening-to-closing).

Yup. Ive always thought of the "Longer Burn" as an advantage. Do you think Nissan would ever change the geometry of the RB26DETT for the Skyline? I think not. More piston dwell time, stufff in more boost, long burn, make enormous amounts of high end torque.

The longer burn due to longer dwell time is not bad. No matter what r/s ratio, for any high heat application (FI, NOS, or NA-endurance) you should do something for the pistons. Such as Coatings, or Piston coolers (oil squirters in vtec block). This keeps the pistons under consistent temperatures instead of rising too much, further preventing detonation. Also, Remember.. Forged Pistons get rid of heat faster than Casted

I knew it all along. Due to the common distruction of the bigger bore B20b/z (compared to the B18a/b), Everybody thought "Bigger bore creates more side loading". Not true. B20b/z cylinder walls are weak compared to the B18a/b.

Its nice to use visuals, especially in this thread ..to clear up the confusion. Check my ACAD...

Drawn to same scale, in both situations connecting rod thrust angle is the same, and I carried the centerline of the connecting rod to the cyl wall.
As you can see, given the same Piston, Rod, Crank, & Deck Height,
Smaller bore has the more side load.

 

I have to agree on pretty much everything except the side load decreasing due to a larger bore. It seems that would only depend on the rod angle. Say the rod angle is 45 degrees. You go through the calculations and you'll see that whatever force pushes down on the piston will be the same as the side force. You can increase the bore 10 times, 20 times, to infinity...the side load will still be the same as the vertical load and will have to be taken up by the cylinder wall. Maybe more piston area means there's less pressure on the cylinder wall, but that's beside the point. The force will remain the same.

Another way to put it: even though the imaginary line you drew going from the rod centerline to the cylinder wall seems to have a lesser effect with a larger bore, the resultant of that imaginary line will be a vertical force and a horizontal force, directly into the cylinder wall. The size of the piston has no effect on that horizontal resultant.

 

You got me thinking. I might be too general here. Time to apply Statics. If only I had my stock internals out of my old B18A, I can draw them to scale on ACAD, find out where thrust angle is most, copy the same drawing over, make it 84mm bore (B20b/z), and apply the vectors to come up with the difference. Thats if there is a difference... I knew in general, since the bigger bore has a piston with more surface area, the load is more distributed than having a piston with less surface area.

 

I dont think the rod angle should change when u increase the bore. u will not change the position of the wrist pin at all with a larger piston. if the wrist pin is in the same place how would the rod angle change?

rod/stroke are the only factors that will effect rod angle. by changing bore u do not change the rod length or the stroke.


[Modified by DIRep972, 1:49 AM 10/15/2002]

 

Just thought I might be able to add something useful.

If you stagger the valve sizing and use the staggered valve timing on the primary and secondary to open the smaller valve first, wouldn't that solve the problem?

The timing relationship b/w the primary and secondary lobes might need to be fine-tuned with custom cams, but isn't the concept of it pretty sound?

BTW, when I say primary and secondary lobes, I mean the non-VTEC lobes.

 

so i asked:

"doesn't the bigger bore of the B20B block IMPROVE its geometry?"

i got pretty much flamed for this question...

but anyways,

bore/stroke ratio is as important as rod/stroke ratios methinks...

t..

 

I agree bore/stroke ratio .

SR20DE(T): 86mm/86mm
RSX K20: 86mm/86mm
93-97' Supra 2JZGTE: 86mm/86mm

All have nearly the same bore & stroke.
Different output curves, because of different r/s ratio & total displacement.

Bore > Stroke = Oversquare
Bore < Stroke = Undersquare

I like to think of Oversquare as HP and Undersquare as: Torque limited before high rpm.
Longer piston travel of the undersquared motor, limits the achievable rpm and power production at the high rpms.

 

I saw the topic come back to the top a while ago, just haven’t had time to read it all and post. And I see a lot of good stuff here. Quick 200k Mile Motor , not sure what made you post to the old topic, but I’m glad to see it at the top. And first, I want to say that that is a good drawing for this thread, and I think I had it backwards in one of my earlier posts, I didn’t go back to read and make sure. But your artistry does a good job of showing how the larger bore decreases side loading, even though the rod ratio does not change numerically. Although, now that I get to thinking about it, this could well be more along the lines of pressure dispersion on the rings rather than completely dictative of the side loading on the cylinder walls themselves. This is what I gather that Lsos was touching on. This could go either way from engine to engine, a lot of factors would come into play I would think, especially the dimensions of the piston ring as well as its seating against the piston itself. This correlates directly to cylinders' ability to oval themselves over time, the more that the piston rings are able to compensate for this, than the less wear that would be apparent over time. (or at least that is what I would think). Piston ring dimensions also can be manipulated to aid in heat dispersal.

Quick 200k Mile Motor , another thing I wanna touch on is what you said about leaving the engine geometry stock. I agree with this for the most part. For a street motor, I have never seen the reason for a deck plate and longer rods. I’m not saying that this isn’t a powerful engine, it just wont fit under the hood. Plus, when you mess with tolerances and geometry specs, the chances of things going wrong drastically increase. Keeping it as close to stock on the street is the best idea. For the most part. What DIRep said about not changing the piston pin location is what I am getting at. While keeping the deck height stock, and relocating the piston pin, increasing rod ratio just a little, this has its rewards.

Art was telling me about some interesting things he had heard regarding NASA and carbon engines. And their exceptional ability for heat dispersion. I’ll see if I can get the link.

Tinkerbell , while I do agree with your statement about b/s ratio, I think you need to add to it “for a street motor” because with the ability to increase deck height then the bore can be matched more to combustion speed once the proper rod ratio for the application is achieved, dictating piston speed and the amount of distance that the flame front has to travel. Bore to stroke ratio is more important on a street motor than rod to stroke ratio is I would think, simply because of the ability to develop a compact, lightweight engine package. Quick 200k Mile Motor , about the undersquare motor having “torque limited before high RPM”, I find this to be a bit vague at best, keeping deck height the same and increasing stroke, to the point of making a motor undersquare will create more and more torque before high RPM due to displacement and piston speed increasing. Just the same as decreasing stroke (and therefore increasing rod ratio and bringing the motor to “perfectly square”) will create the flatter torque curve. Assuming all other specs are kept the same.

Although, the ability to develop a compact lightweight engine and transmission package is also under great scrutiny in the open wheel racing world as well.

And I didn’t know that the new K20A2 was a square motor, thanks for the info.

 

great thread

 

Two questions here, since I'm not picturing it in my head quite the way you've drawn it. First, wouldn't the thrust load be applied equally about a point (the wrist pin) rather than the drawn imaginary line, thus making each side load equal given a set rod angularity? Regardless I still agree with your conclusion, because in my mind the larger bore size also makes for a larger piston ring area over which the force is applied, thus reducing load at any single point.

Secondly, since the thrust load becomes problematic only during high rod angularity which is only seen near 90 degrees ATDC, wouldn't the piston already be far enough down the bore to negate that imaginary line's intersection point being above the deck? With most any Honda 4 cylinder, the piston will be at least 1.5" down the bore when you reach maximum angularity.

Ps- Could the wrist pin centerline to cylinder wall distance ever have an effect on the thrust encountered?

 

I must've confused you on that one. I originally said..

Bore > Stroke = Oversquare
Bore < Stroke = Undersquare

I like to think of Oversquare as HP, and Undersquare as: Torque limited before high rpm.
Longer piston travel of the undersquared motor, limits the achievable rpm and power production at the high rpms.

We're both in agreement that an undersquared motor will produce more torque before high rpm. Check out my recent post in another thread: https://honda-tech.com/zerothread?id=301080&page=3