ranta18

This started from a thread in the drag racing forum....

What kind of maximum piston speeds are you guys running on your drag motors? I'm talking engines making over 260 whp. The stroked and sometimes decked engines.

Take B-series with a 98mm stroke and 156.8mm rod (figuring 1.6 R:S) at 11K rpm = 11,655 ft/min maximum piston speed

Is that how fast you are pushing them? Stock GSR/ITR numbers at 11K rpm show a max piston speed of 10,382 ft/min. Change that to 10K rpm and its 9438 ft/min. 9K rpm (stock ITR redline) is 8494 ft/min.

The graph below shows the comparisons at 11K rpm:



Are you guys going higher than 12K ft/min? Obviously 9500 ft/min is safe because 10K in a built ITR is nothing new. Most pro A/M guys have been known to run 11K also. So somewhere between 10,000 and 12,000 ft/min?

Before you post... THIS IS NOT THE AVERAGE. You have to use the stroke, rod lenght, and rpm to figure this out, not just the stroke and rpm. I'm not talking average or mean speed. Just the maximum. This is the calculator I used: http://2.6liter.com/Calc2.htm

hybrid_vtec

interesting!!


bump for some input!

Combustion Contraption

4,000 fpm is a safe # for mean piston speed with todays metallurgy standards. How much do items like titanium rods, ti peices in the valvetrain, hollow cams and the such increase that #?

hybrid_vtec

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LsVtec92Hatch &raquo;</TD></TR><TR><TD CLASS="quote">4,000 fpm is a safe # for mean piston speed with todays metallurgy standards. How much do items like titanium rods, ti peices in the valvetrain, hollow cams and the such increase that #?</TD></TR></TABLE>


I dont think they increase speed, they lower the rotating mass. However longer rods and longer stroke crank will affect piston speed b/c of the longer distance of travel due to longer stoke. And it is an important factor to consider when building an engine to try to find ways toreduce as much stress as possible on the bottom end components. Balancing the bottem end has helps reduce stress!

ShaunRR

The reduction in mass is the primary thing that allows engines that use those parts to rev higher. It reduces the forces on the parts as they change direction.

ranta18

I don't care about mean piston speeds and when building an engine, you should look at the MAX speed, not the mean. Yes, rod length determines max piston speed. Longer rods help lower the max speed. That is why it is used in the calculations.

Combustion Contraption

I have always been under the assumption that rod length has nothing to do with piston speed, just piston accelerration.

xEnderx

Longer rods with shorter stroke give you less side load and less rod angularity. From what I have learned in my lab experience 4500 is really the absolute "safe" piston speed on a street motor. Limited # of runs drag motors are allowed a bit more leeway. Hell I think the Top Fuel dragster motors approach 6800 fpm on their piston speed.....then again they are only good for one run.

ranta18

Rod length is very part of MAXIMUM piston speed. Not average, but maximum. I'll try to find a link that explains in detail.

xEnderx - Those are all mean/average pistons speeds. 4500 is nothing for a Honda. A stock ITR (87.2mm stroke) turning 9K is 5150 ft/min. The drag motor example I gave above (98 stroke @ 11K) would be 7073 ft/min for the avearge speed.

Maximum speeds... Anyone?

Combustion Contraption

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ranta18 &raquo;</TD></TR><TR><TD CLASS="quote">
Maximum speeds... Anyone?</TD></TR></TABLE>

Be patient, young padawan.

marcin

just some random thought to throw in here.
A proper flame front/burn expands at a certain speed. I wonder if there is an ideal piston velocity which allows you to take the fullest advantage of its expansion rate. Too fast and your outrunning it, too slow and you may be backing up... Since the velocity of the piston changes with rpm, im guessing at some point every motor will run across this scenerio... Wonder if theres a way to figure it out so that you have the ideal piston speed in the operating range of the engine.

just a thought.
m.

ShaunRR

I would think that would depend on a lot of factors, making it diffucult to calculate reliably without some sort of sophisticated computer simulation and extrememly accurate data about the engine.

But who knows, perhaps a simple equation can get it close enough to be useful.

marcin

i agree with what your saying. To realy take into account all the different factors accurately would be difficult. Perhaps there is some sort of general rule...

Wonder how and if peak VE relates to that sweetspot.

any pro engine guys wanna clue us in?
or maybe some hints in the right direction. We can always go out and build motors for 10-20 years to get enough experiance to make some conclusions about what works and what dosent.

thanks.
m.


Modified by dvious hatchie at 4:53 AM 5/14/2005

radteg

good thread and good info man....

Speedz

suscribing

rjay8604

See the one thing i hate about measuring feet per second is it doesn't factor in velocity, as in the change of direction. And even when speed remains constant, a change in direction is also acceleration. The one beautiful thing about the reciprocating movement of the engine is it slows the pistons and rods down in the best possible way, the piston speed is the same as looking at a graph of a sinewave, because they are the same thing. I guarantee rocket has info on this and i am sure other do to. HE has discussed piston speed and flame front travel and how a lower rod/stroke ratio can "outrun" the flame and lose high-rpm power. Also he has talked about the piston dome obstructing incoming airflow and how a flat top piston has optimal cylinder filling. good stuff.

AllMTRWH0R3

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dvious hatchie &raquo;</TD></TR><TR><TD CLASS="quote">just some random thought to throw in here.
A proper flame front/burn expands at a certain speed. I wonder if there is an ideal piston velocity which allows you to take the fullest advantage of its expansion rate. Too fast and your outrunning it, too slow and you may be backing up... Since the velocity of the piston changes with rpm, im guessing at some point every motor will run across this scenerio... Wonder if theres a way to figure it out so that you have the ideal piston speed in the operating range of the engine.

just a thought.
m.</TD></TR></TABLE>

great point.

One thing that also comes to mind that in tuning of a drag motor that each cylinder. How to tune injector pulse to get more breathing for a motor that gets over 5000 fpm per minute. I have tooken my motors pass that just thought I would share a little insight.

xEnderx

Ranta18: Yeah, the majority of my real engine experience has been with old school V8's so I'm a little out of my depth currently with the smaller displacement motors. Still, when you REALLY get down to it a motor is a motor and I should be able to get the hang of the 4 cylinder thing in time. The motors are alot tighter, thats for damn sure.

ranta18

bump for some more info ???

Carlo Gambino

in some old book about v8 motor (dav vizard maybe), 5000 is the maximum with stock rods. but yes as ranta said 5000 ft/min was nothing for honda. my friends D13B (76mm stroke) with big *** camshaft rev almost 5000ft/min ( 10.000 rpm ) and still happy until now.

ranta18

more average piston speed info, just talking about the maximum average speed.

anyone got any on the maximum speed?

MAX_CFM

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ranta18 &raquo;</TD></TR><TR><TD CLASS="quote">more average piston speed info, just talking about the maximum average speed.

anyone got any on the maximum speed?</TD></TR></TABLE>


Your Missing the boat.. Look Else where

Read My other post ......

ranta18

You had said "I dont think honda is a good platform to study the effects of piston Speeds the parts are to light..."

Are you saying that using maximum piston speeds to determine how high to spin the motor is the wrong way to go about it?

Oyvind Ryeng

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ranta18 &raquo;</TD></TR><TR><TD CLASS="quote">Are you saying that using maximum piston speeds to determine how high to spin the motor is the wrong way to go about it?</TD></TR></TABLE>
My personal opinion is that one needs to look at force. Example /w numbers out of my ***: two identical engines, running a constant RPM: one with a 77.4mm stroke on a rod/piston weighing 800 grams is the same force as the one excerted on a 89mm stroke with a rod/piston weighing 500 grams. Also, rod length factors in here, because it affects the rate/speed of acceleration. Agree/disagree?

Combustion Contraption

I agree, but rod length plays more of a role than just the rate of accelleration.