Sorry to bring this back up, but does anyone have the specs on the F20B DOHC VTEC motor from the Accord SiR-T/Troneo? Like the Rod length and Rod/Stroke? Same sort of information? Thanks

 

Import Review- I disagree on your theroy of the stroker motors making less peak HP. What determins how a car makes power on the top end is how well the head, intake, TB, header, and cams can flow air. The stroker will make more all around torque than a non-stroked engine. More torque results in a quicker ET. If you can make the same ammount of HP with a stroker as a non-stroked engine at a lower RPM, then you don't have to work the engine as hard. The rest comes from correct gearing to fully maximize the powerband.

 

making less peak HP can result for many things ... I know this first hand form my race motor. Putting r/s ratio aside, the porting, camshaft profile and header design plays an important part. The bottom line is you will need a magnifying glass to see the difference between a 1.58 r/r and a 1.62 as an example. Many builders/racers, like myself will take the extra rod ratio with no sacrifice to stroke, this will help put the power on the very top end of the curve will the motor is doing more work in less time, the essential part of accelerating.

so 150 in torque is ALL you guys are pulling ? shame on you

I know of an east coast race motor that has much much more TQ than that ... in a b-series motor

Greg

 

Greg,

as always brief, to the point, and insightful.

I take it that to mean in the above statement that you prefer using longer rods with deck height added (Clarica Guy). Do you have to run any special gear ratios with those motors?

When you opt for a longer rod, the hypotenuse of the triangle changes. You can then calculate for each crank angle, the side load force and piston speeds for a given stroke. It's a rather insightful exercise on what the differences are for stock length rod vs a longer rod.

You need a bit of high school triginometry and an Excel speadsheet. It's quite interesting to see how piston speeds change during filling, during squeezing, and during the power stroke at the ATDC crank angles considered to be the sweet spot for peak cylinder pressures.

it really does confirm your notion that the power is moved up top where you want it in a small displacement, high winding, normally aspirated motor.

 

With this thread being 3 pages long, I kinda skimmed through it, so I appologies if this has been brought up before.

Has anyone discussed the effects of R/S ratio on piston dwell time at TDC & BDC along with piston speed away from TDC (outrunning the flame front)? Or are these also other design parameters that Honda 'didn't really care about', as texan had said in page 2?

 

Actually I did discuss it in another thread here, and it's certainly not something I claim Honda doesn't care about. But they also care about packaging concerns and a thousand other engine parameters, and it's still my opinion that one does not design an engine around slight differences in r/s ratio. As an example, let's take a B16a (what with it's "perfect" r/s ratio) and stroke it 4mm. We'll do it two ways, with and without preserving r/s ratio.

B16A stock stroke: 1.74:1 r/s ratio
maximum piston speed@ 8500 RPM: 7064.1 fpm
mean piston speed @ 8500 RPM: 4316.58 fpm
maximum rod angularity: 16.7 degrees

B16A 81.4 mm stroke: 1.64:1 r/s
maximum piston speed@ 8500 RPM: 7461.8 fpm
mean piston speed @ 8500 RPM: 4540.42 fpm
maximum rod angularity: 17.75 degrees

B16A 81.4 mm stroke w/ 9.6mm deck plate: 1.74:1 r/s
maximum piston speed@ 8500 RPM: 7427.7 fpm
mean piston speed @ 8500 RPM: 4540.42 fpm
maximum rod angularity: 16.7 degrees

And now a piaston velocity and position plot ATDC of the two stroked combos...


Wow, big diffferences eh? We've added a custom deck plate, had to get a set of custom rods, altered cam timing to the point we definitely need to re-index the top end, and all for .5% lower maximum piston speeds and .9 degrees less angularity. You have to get at least 40 degrees ATDC to even see that both lines don't perfectly fit on each other, and at their maximum difference we get a piston that's all of about 0.5-1 mm further down an 81.4mm stroke.

Now if you think that is going to show up in meaningful terms, either in reliability, power output, optimal cam timing, etc., I'd like to know why. Because here it's clear to see that while increased stroke has a significant impact upon piston location and speed, the r/s ratio diffrerences do not create enough movement for us to concern ourselves with.

 

michael,
we have calculated approximately the same tranny gear ratios needed with a 1.7x vs a 1.6x r/r, we change slick size to help compensate with offset ratio.

As for r/r comparison, the power output seen for (with the same ramp rate cam profile in the same block) two given ratios shows that the higher r/r will carry the tq curve longer and increase hp at the same time the curve flatness begins later so hence the reduced "midrange" torque for higher r/r, this is similar to moving your cam gears to "shift" power, but not as aplified because dwell time and piston speed comes into play wiht a longer rod, whereas simply moving centerline doe snot change the crankshaft dynamics on the motor, just timing on the airflow.


eechris,
good observation on the flame front speed relative to piston speed, but for the piston to outrun the flame travel you would need a 1.3x ratio at 9Krpm at which point the rod will come out the side of the block, seen this happened to couple guys already who were antsy for displacement but didnt give a crap about their pistons speed.


texas,
I agree with you, I do not think one should add a deck plate to gain r/r as there is more than enough room to move the wristpin to get that. However, if you purely wanted displacement (via stroke and deckplate) it would be the only path to take worth making sense. The similar observation can be made as to why did Apex go through what they did to make their motor spin clockwise, I certainly did not see the $/benefit on that but I guess to each his own ...

... also, on your graph, the slope of both bellies of the curves is actually telling you something, did you notice what ?

Greg

 

Didn't apex make the motor spin clockwise so they could run a custom 6 speed tranny? If they hadn't the car would have run the wrong way.

 

So here's a question... Would it be good to stroke a B18C motor with B16 head and run 12:1 compression with JUN III OR would it be better to bore it to 84mm, 13:1 compression with JUN III??? I've been told that the stroker would put out some nice HP, I don't remember the TQ... but the bore would be nice TQ AND HP!!! Oh yeah, apply this to road racing and not 1320.... I'm thinking boring would be the better of the two, but then again I'm not sure.....

 

A few more sticks to add to the fire. Maybe Honda had to resort to their fancy superslick piston coatings to get high RPM`s and longevity out of mediocre R/S designs. If you make more power and get more friction, how much of the additional power is being used to warm the atmosphere instead of getting to the crank?
Im interested in 2L low end torque, great longevity, low 13`s street and decent fuel economy in a 5G hatch. The Dart/Payne Honda block has a higher deck (+.55") and 84.5mm bore for around $2100. I intend to add an ITR crank which will give me ~ 1950cc`s and the same R/S as the B16 (~1.74). At cruise my AirFuelRatio target is 14.5/1. If my finances hold out, Ive spoken to a custom gear manufacturer about a .5 fifth gear ratio. I`ll let you know how it all works. By the way, those stroker kits are obscenely priced.

 

Yes they are. Boring to 84-85mm on a NA machine seems allot smarter to me.

 

Hey guys just to let you know what I'm doing. I'm destroking my H23 VTEC for the exact purpose that you guys are discussing.

The H23 VTEC had

87mm bore
95mm stroke
1.49 RS/R
2.258cc

Here's what the tuned curves looked like


Now maybe you more intelligent peeps can analyze the curves, but I notice that even with stage3 cams that are supposed to be making power to 9000rpms the car just runs out of steam at 7000rpms. The storker just isn't getting enough air up there.

No I got my hands on an F20B crank, so my setup is going to be

87mm bore
88mm stroke
1.65 RS/R
2093cc

Can somebody run through the calculations for piston speeds and make the graphs? I want to compare it with the 90.7mm H22a crank to see how much of an improvement I'm making. I'm thinking this setup can make some crazy power on the top end and still have a great torque curve. Like a superbored out B16

 

So would it be possible to bore and stroke, with decent reliability on a b16? maybe make it a 1.9?

 

I don't know about that, I don't think the B16 block is tall enough to do it reliably...but I know jack about the B16

 

well im also gettin ready to build an engine and on your topic hear i was wondering how u mite feal about boring and sleaving a vtech 60 or 80 if i can get it and stroking it but it will not be an NA moter

 

im going to find a supercharger for it and run the secondary fuel system that edelbrock has availeble im not a big fan of turbos

 

jesus christ necro from hell.
and learn to spell check.

 

ya i know my spellings a little rouph lol