General Chat
Q:
The Tech articles written by David Reher and posted on Reher-Morrisons web site (also published in the National Dragster) are very good reading for any car enthusiast. Good information is contained in all the articles he writes, but the thing I find most intersting about them is the common sense approach taken by David Reher and the folks at Reher-Morrison Racing engines.
Some of you may have already read some of the articles over there, and for those who haven't and are unaware of them, you will enjoy them. For those of you who have seen posts like this from me in the past, this is not for you......this is intended to spark some interest from those who have missed in the past and wouldn't have a clue to search for this in the archives.
Here is a really good one regarding RPMs and why it can be a good thing to spin them up tight. Enjoy.
http://www.rehermorrison.com/techTalk/47.htm
All of the articles can be found at:
http://www.rehermorrison.com/techTalk/indexStart.htm
Tech Talk Article 47
"Raising the Redline: Why RPM Matters"
by David Reher
Looking back at the 2004 season, I can attribute much of the performance improvement in Pro Stock to faster engine speeds. It’s difficult to believe that 500cid Pro Stock engines now routinely turn 10,000 rpm, but the truth is plain to see on the data recorders and on the time slips.
The trend toward higher and higher engine speeds was also evident in NASCAR stock car racing until the rulemakers applied the brakes with new restrictions on rearend and transmission gear ratios. Now the growing interest in fast bracket racing, Top Sportsman, and Top Comp eliminators is bringing this same high-rpm technology to sportsman drag racers.
Why does turning an engine higher make a race car run faster? This is my final column of the year, so I’ll offer my ideas and hope that they give racers something to think about over the winter break.
The simple explanation is that raising rpm effectively increases an engine’s displacement. This might seem nonsensical because the volume displaced by the pistons doesn’t change, but consider the effects of filling and emptying the cylinders faster in real time. An internal combustion engine is an air pump, and if we turn that pump faster, we can theoretically burn more fuel in a given amount of time and consequently produce more power. For example, an eight-cylinder engine running at 6,000 rpm fires its cylinders 24,000 times in one minute (assuming perfect combustion). Increase the engine’s speed to 8,000 rpm and it will fire 32,000 times per minute, a 33 percent increase. The volume of air and fuel that moves through the engine is now equivalent to an engine with a much larger displacement. There are also 8,000 additional power pulses per minute transmitted to the crankshaft that can be harnessed to turn the wheels and accelerate the car.
Raising engine speed is analogous to supercharging or turbocharging a motor; the goal is to increase the volume of air and fuel that moves through the engine. The airflow is increased with a forced induction system by pressurizing the intake system; in a naturally aspirated engine, the airflow is increased by raising rpm. If done correctly, both approaches will increase power.
A higher revving engine also permits the use of a numerically higher gear ratio to multiply the engine’s torque all the way down the drag strip. Let’s say an engine that produces 1,000 horsepower at 7,000 rpm is paired with a 4.56:1 rearend gear ratio. If this engine is then modified to produce 1,000 horsepower at 8,000 rpm, it can now pull a 4.88:1 or 5:14:1 rearend gear without running out of rpm before reaching the finish line. The numerically higher gear ratio gives the engine a mechanical advantage by multiplying its torque by a greater number to accelerate the car faster – in effect, it has a longer lever to move the mass.
I learned this lesson many years ago when I started drag racing. I raced my little 302cid Camaro against 426 Hemis and 440cid Max Wedge Mopars. The big-inch engines had thunderous low-end power, but my high-revving 302 with a 4.88:1 rear gear would just kill them because they were all done at 5,800 rpm. My small-block had much less torque and horsepower, but I could multiply the power it had with a steeper gear ratio. The same principle applies to racing a Pro Stock or a Top Sportsman dragster. By turning more rpm, we can use a greater gear ratio to produce more mechanical advantage to accelerate the car.
There are limits to engine speed, of course. Higher rpm increases parasitic losses from friction and windage. The stability of the valvetrain also restricts engine rpm. However, with the technology developed in NASCAR and in Pro Stock, racers are learning how to build engines that operate reliably at high rpm. Research and development on valve materials, springs, rocker arms, and pushrods are now being applied to serious sportsman drag racing engines. In fact, I wish that I had some of the parts that we now install in our high-horsepower sportsman engines for our Pro Stock program a few years ago!
While increasing rpm is generally a good thing for a racing engine, it also puts more responsibility on the owner. A high-rpm combination requires more vigilance and more maintenance than a low-rpm motor. It’s important to check the valve lash frequently and to look for early warning signs such as weak or broken valve springs. Neglecting these parts in a high-rpm racing engine can produce some very expensive problems.
Raising an engine’s operating range also requires complementary changes in the drivetrain and chassis. A high-rpm sportsman engine really needs a high-stall torque converter to realize its potential. With an automatic transmission, the engine speed should ideally drop 1,000 to 1,300 rpm after a gear change. For example, if the converter stalls at 6,700 rpm, the engine should be shifted at around 8,000 rpm. Shifting this engine at 7,000 rpm would simply put the engine back on the converter, causing the converter to operate inefficiently and wasting horsepower by heating the transmission fluid.
I’m excited about the emerging trend toward fast sportsman drag racing. I enjoy working with customers who want to go fast because it gives me an opportunity to deliver the benefits of our Pro Stock R&D to other racers. Not every racer wants or needs a high-rpm engine, but if the goal is to have a fast car, raising the redline is a proven approach.
Ken
'82ZX n/a 2+2
'02 Sportster XL1200C
A:
so basically, it's in the saying, it's all about gearing?
there goes that "little four banger" sh*t ;-)
stan
1972 240Z, L28, R200, MSD (fuel system rework)
1991 CRX SI, many many mods
1982 280ZXT (engine and wheels are staying, everything else is going to the junkyard)
A:
So Ken,
Just what is the technology that NASCAR teams have developed to allow pushrod engines to hit those big RPM numbers? How do they keep the valves from floating and how do they keep the bottom end together?
A:
Plus, when the engines "let go," the show gets even better for the spectators - KA BLOOEY!
Rusty but running.
Polish cell phone and two tubes of Aluma-seal.
And, now we are historic.
A:
He doesn't discuss the specific "here's how we do it" in the article, but I suspect a good deal of that information is in the two books published by R-M. He has written two books, one on bottom end, and one on upper engine. Granted, you will need to absorb the information on a 'concept' level since their business is Big Blocks and high revving Small Blocks. Best thing about it is, all crankshafts turn 360 degrees, and all four cycle engines have four cycles....application of concept is where you will reap rewards. If you have the spare 'Jack' they offer an engine school as well conducted on site at R-M Racing Engines facility in Arlington Texas.
The good thing about R-M is that they have built engines for NASCAR, and Craftsman Truck as well as NHRA Drag Racing from Sportsman on up to Pro Stock. Davids partner Bruce Allen was the builder of the Indy 500 Buick V6 engine that sat on pole for the '85 race. Bruce was working at McLaren Racing Engines at the time and came to the R-M team after Lee Shepard was killed in a testing accident.
These guys know motors.
Ken
'82ZX n/a 2+2
'02 Sportster XL1200C
A:
"A high-rpm combination requires more vigilance and more maintenance than a low-rpm motor."
-Honda seems to have figured out how to do this
He also failed to mention that engines with shorter strokes, are easier to rev as well.
"With an automatic transmission, the engine speed should ideally drop 1,000 to 1,300 rpm after a gear change. For example, if the converter stalls at 6,700 rpm, the engine should be shifted at around 8,000 rpm. Shifting this engine at 7,000 rpm would simply put the engine back on the converter, causing the converter to operate inefficiently and wasting horsepower by heating the transmission fluid. "
-or maybe..say, stop being a pu$$y, learn how to drive, and put a manual in there (unless you are physically unable). Sorry, had to vent.
God must love stupid people, he made SOOOOO many of them!
A:
hey mike. he made reference to the shorter stronke engines revving faster in the opening paragraph when he talked about beating guys with his 302.
My guardian angel has twin turbos. . .
1995 Cobalt Green NA
1988 Maroon 300ZX NA (sold)
A:
years ago i had a built 413 wedge i put in a 70 challenger with 4spd and a 4:10 lock rearend-- i cant count how many chevy 327 s blow trying to beat me in 1/4 mile. not once in well over 400 races was i beat. i cant possible beleive his 302 would have come close to a big block mopar with proper gearing. if it had all the dragters wouldve had chevy engines( they didnt)
but all in all it is a interesting article and he his right about higher rpms. my tach went to 10,000 and i peged it many times. never blew the engine after around 95,000miles i finally sold it to a mechanic freind who rebuilt and shipped it out to new york. my mistake
____________________________________
1980 280ZX coupe
2001 maxima
1994 F150 4x4 van works custom truck
170000 and never needed mech repairs
1996 ford explorer -they cant all be good