WHY KEEP ENGINE RPMS under 7000rpm - Team Camaro Tech
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post #1 of 51 (permalink) Old Apr 1st, 02, 12:31 PM Thread Starter
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theres been alot of discussion about building high rpm engines lately, lets look at the pros and cons of running an engine over 7000rpm
read the links then the comments please http://www.iao.com/howthing/improhtw.htm
what they are saying is that the faster you spin an engine the less efficient the wet sump oiling system is and the greater the percentage of loss to friction from all sources , now remember this post,
ever wonder why your engines torque curve gets higher with the engines rpm level untill about 4000rpm-5500rpm(DEPENDING ON YOUR COMBO) but fades above that rpm level?
well it depends on several factors, first as long as the cylinders can fill completely you get a good fuel/air burn so you get a good cylinder pressure curve against the piston each time the cylinder fires,THE ENGINES TORQUE CURVE INCREASES WITH THE NUMBER OF EFFECTIVE POWER STROKES PER SECOND, at very low speeds theres not enough air velocity to mix the fuel correctly or produce a effective ram tuneing effect but as the rpms increase the cylinders fill very efficiently untill the rpms reach a point where the cylinders just don,t have the time necessary to flow
enough air through the valves to fill the cylinders , remember a 5000rpm the intake valve out of 720 degs in each cycle opens for about 250degs of effective flow even with a hot roller cam, now thats only about 35% of the time and theres 41.6 intake strokes per second , thats only 1/60th of a second for air to flow into the cylinder, I found this graph that shows the relationship between V.E.(VOLUMETRIC EFFICIENCY) and AN ENGINEs torque CURVE http://www.n2performance.com/lectures/lect1/n2perf5.gif
WHAT THAT GRAPH SHOWS RATHER EFFECTIVELY is that its your engines ability to fill the cylinders that increases your power and the more efficiently you do that the higher the rpm level you can acomplish that at the more power your engine makes, remember the formula for hp is (torque x rpm/ 5252=hp)so moveing the torque curve higher in the rpm range increases hp but look at the curve on the graph carefully.....after the peak torque
is reached the efficiency of the cylinders filling drops off, and as rpms increase its a race between more power strokes per minute trying to raise the power and the increaseingly less effective percentage of cylinder filling dropping the power.
Volumetric Efficiency

The volumetric efficiency of a 4-stroke engine is the relationship between the quantity of intake air and the piston displacement. In other words, volumetric efficiency is the ratio between the charge that actually enters the cylinder and the amount that could enter under ideal conditions. Piston displacement is used since it is difficult to measure the amount of charge that would enter the cylinder under ideal conditions. An engine would have 100% volumetric efficiency if, at atmospheric pressure and normal temperature, an amount of air exactly equal to piston displacement could be drawn into the cylinder. This is not possible, except by supercharging, because the passages through which the air must flow offer a resistance, the force pushing the air into the cylinder is only atmospheric, and the air absorbs heat during the process. Therefore, volumetric efficiency is deter-mined by measuring (with an orifice or venturi type meter) the amount of air taken in by the engine, converting the amount to volume, and comparing this volume to the piston displacement.
this increases untill the torque peak then falls as the rpms increase.

engine red line
piston speed is about at a reasonable max with stock components at 4000 feet per minute, now rpms alone do not have as great an effect as stoke x rpms in figureing piston speed.
example 4000fpm(feet per min.) is 48000 inches per min. if your stroke is 3.48 like in a 350 chevy the piston must go up then down in each dirrection once for each rpm(revolution per min) so 3.48x2=6.96 so 48000/6.96=6896 rpm, in this case the valves are more likely to float before the rod bolts snap from inertial stress, but lets try a 383 that has a 3.75 inch stroke,3.75x2=7.5" so 48000/7.5=6400 rpm max for the rod bolts(about the same as the probable valve float rpm.
btw long term highway cruiseing speeds should be kept to 2000fpm piston speeds for best engine life.
http://www.melling.com/engoil.html
what this is saying is that the faster you spin an engine the harder it is to maintain proper oil pressure and oil volume, thats why dry sump systems are normally used on engines that need to turn over 7000rpms on a regular basis.

now air flow through the cylinder heads also peaks at about a lift equal to 1/3-1/2 the diamiter of the valve and at about 4000-6000rpm depending on the cylinder head flow numbers/engine stroke and displacement and cam timeing, so with all those factors working against spinning an engine to over 7000rpm its realy better to concentrate on building an engine that has a greater efficiency in the 4000rpm-6500rpm range as the parts necassary to run at the higher rpms will double or triple the costs involved while just increasing displacement of efficiency in the 4000rpm-6000rpm range will cost less and will result in an engine thats under less stress and lasts longer.

BTW the 400 can be bored and stroked to about 427-440 cid look here,and NOT ONE OF THESE ENGINES NEEDS TO SPIN OVER 7000rpm,BTW some of these guys are running over 1200hp http://www.theengineshop.com/engine5.shtml http://www.amerspeed.com/engine_prices.htm http://www.shafiroff.com/434_sportsengine.html
http://www.lingenfelter.com/packages/427TT.htm
http://www.golensengineservice.com/e....asp?engine=85
http://www.geocities.com/monty_williams/
http://www.skulte.com/turbo.html
http://www.grapeaperacing.com/GrapeApeRacing/
http://www.turboclub.com/aturbo.htm



[This message has been edited by grumpyvette (edited 04-01-2002).]
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post #2 of 51 (permalink) Old Apr 1st, 02, 04:04 PM
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I have read similar stuff from David Vizard, John Lingenfelter, and John Baechtel.

Some people here don't understand how important it is that you consentrate your torque gains in the area that you spend the most time in, taking the converter flash speed, trans ratio, amount of gears, rear gear ratio, shift point, and shift recovery point into account. They just go...What is that? I don't like typing at great length's and I obviously don't have access to the links you have.

If you could find something that like the header site where you enter the datta and it gives you the time at each RPM point that would be WAY COOL!!!

At this site it would be like parting the clouds.

[This message has been edited by mutant 68 (edited 04-01-2002).]
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post #3 of 51 (permalink) Old Apr 1st, 02, 04:30 PM
 
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You need to throw cam duration in here, too b/c if you look at the various cams as they increase by say 5 degree's going up you will see that all that is really happening is that the cam is shifting the torque curve over on the rpm scale!

That is as long as the engine combination can produce the expected power in the upper rpm's.

I would hazard a bet that if you take two engine combinations, one, a low speed torque one and the other, a high speed horsepower one and gear and tire each so that you can use each's power to it's fullest, AND hold the rpm range the same, say like 1500 to 5500 rpm for the low speed engine and 3000 to 7000rpm for the high speed engine that it would be a wash as to which would win a drag race!!!

I say this because I bet both engines will produce almost identical torque outputs and it is torque that wins races!!!!

Take a look at the old big MOPAR combinations that used ta tear up the streets in the late '60's with 440's, 727 t/f's and 3.23 rear gears and you will see what I mean. As always, IMHO. pdq67



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post #4 of 51 (permalink) Old Apr 1st, 02, 06:18 PM Thread Starter
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post #5 of 51 (permalink) Old Apr 1st, 02, 06:43 PM
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WOW WOW WOW...Hold yer horses. I'd watch it with those phrases around here grumpster

I have been checking out prestage lately. I got it the link from you a wile ago.

[This message has been edited by mutant 68 (edited 04-01-2002).]
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post #6 of 51 (permalink) Old Apr 1st, 02, 11:41 PM
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Great info Grump! Thank you. It's relative to a conversation I had with an old friend the other day. He's arguing with me that I should be building my new 408(all forged bottom end) to go 8000 RPM! I am trying to explain to him that first of all, I have been saving my pennies to build this motor for the past year and a half and just don't want to wind it up that much, secondly, I'm trying to show him that I don't need to take it that high to make decent power for the street, which is where the car will be driven! When will people learn that bigger is not always better! It's the combination that counts!
Thanks again for the info.
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post #7 of 51 (permalink) Old Apr 2nd, 02, 04:11 AM
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We deal with many limitations and principals when we engineer our cars. Like;

1. The first law of thermodynamics..."There aint no free lunch" because speed costs money.

2. The displacement laws such as 5.0 liter maximum engine size. SCCA Trans-Am class racing. Now we build it small and wind it up to the moon. Never would we do this for optimum performance otherwise.

3. The most important law of them all...More's law - more is better than less. 420 cube small blocks that we build to rev 8000 RPM. We use this law over all others until we know better.

Great links Grumpy!

-Mark.


[This message has been edited by stingr69 (edited 04-02-2002).]
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post #8 of 51 (permalink) Old Apr 2nd, 02, 08:33 AM
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Anyone get this one to work?
http://www.prestage.com/carmath/dynochart.asp

It tells me I need to shift my 383 at 7000 RPM - I don't think so!

------------------
68 Camaro, 383 small block with TH350 trans. 11.98's at 111mph and never trailered.

[This message has been edited by Eric68 (edited 04-02-2002).]
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post #9 of 51 (permalink) Old Apr 2nd, 02, 11:35 AM
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PDQ67
I have to say that if you had 2 engines one a low rpm, and a second
high rpm engine making the same torque - the high rpm engine would
win a drag race easy. This is because if the torque of the 2 engines is the
same (say 400ft/lbs), and HP and TQ always cross at 5250rpm, the high
rpm engine would be making more hp as the rpm increases higher:
Say a low rpm 350 makes [email protected] & [email protected] (your average
street 350sbc make about that much)
And a high rpm 350 makes [email protected] & [email protected] (a worked
over street/performance 350sbc with the common: cam/intake/headers)
Both engines make the same tq, but the high rpm 350 makes 50 more hp,
meaning it would win a drag race easy.
When you raise the peak tq rpm higher upper rpm hp increases, this is how
a dyno calculates hp, from the tq measured, and why diesels make great low
end tq and no hp as rpm rises, and "crotch rockets" make little low end tq but
big upper rpm hp. If you look at some dyno graphs you can see what I'm
talking about, the lower the rpm the greater the tq vs. hp, and the higher the
rpm the greater the hp vs.tq This is how most race cars take advantage of
making the most hp possible - by revving then, Formula one engines buzz over
18,000rpm, and they're the most technologically advanced engines on the
planet. If your theory was right they'd only have to turn them 5000rpm.

------------------
67RS CAMARO - STREET CAR, 502 PUMPGAS, HYD. ROLLER, TH350 w/ATI 10" 12-BOLT w/373 ~ ON MOTOR, ET STREETS WITH MUFFLERS.
BEST 1/4: 60FT= 1.63, [email protected], [email protected]
BEST 1/8: 60FT= 1.54, [email protected], ???
-----------
65 BISCAYNE - NO MOTOR OR TRANS - WILL BE 454 SLEEPER
---------
DAILY DRIVER: 91 B4C CAMARO, 305TPI, TREMEC 5-SPD, 342 GEARS, K&N, CRANK PULLEY, EDELBROCK HEADERS, 4" SINGLE EXH., [email protected] 60FT=2.06
SOON TO BE 383 W/ SUPERRAM
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post #10 of 51 (permalink) Old Apr 2nd, 02, 12:31 PM
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Ahhh, I must come to the aid of Mr PDQ67 here . . .

Rafal, I ran both of your hypothetical engines through Dragstrip Plus . . . the low RPM engine runs a 13.11 @ 100.6 mph. The 400 HP engine runs a 13.26 @ 105.1 mph. I assumed a 3000 stall, 3.23 gears, a 3200 lb car, 150 lb driver, slicks, and shift points 200 RPM above peak HP.

How can the lower HP engine possibly win you might ask? Horsepower really has NOTHING to do with your ET - after all, horsepower is a function of torque! You calculate HP starting with torque.

Engine torque, since it is a measure of actual force, can be multiplied by gear ratios, axle ratios, tire diameter, etc and a real number that represents the pressure the tire puts on the pavement. This force on the pavement is what moves and accelerates the car. If the lower HP engine makes more torque in the usable RPM range it will win every time!

Horsepower numbers can just confuse things sometimes IMO.

Case in point I run a TQ set up 383 and run 12.0's at 111 mph. I can beat some cars all day long with 115 mph trap speeds. Of course they all go flying past me past the traps, but who cares - I already won!

------------------
68 Camaro, 383 small block with TH350 trans. 11.98's at 111mph and never trailered.

[This message has been edited by Eric68 (edited 04-02-2002).]
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post #11 of 51 (permalink) Old Apr 2nd, 02, 12:52 PM
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Gene
 
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ERIC68, I think you over simplified the simulation. The high RPM HP engine would want more gear and stall than the low RPM TQ motor.

I had a friend that just recently built a Pontiac 400. He got a lot of advise from a prominent Pontiac engine builder that said use a STOCK converter (approx 1,200 RPM stall) and no higher than 3.23 gears. The higher stall speed wastes the torque generated by the engine at RPMs lower than the stall speed. If you make 500 ft-lbs at idle with a mild cam, you don't need a 3,000 RPM stall.

Play around with the gearing and stall speeds for each engine and then see which combo wins. Maybe the low RPM torque motor is faster. Maybe not.
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post #12 of 51 (permalink) Old Apr 2nd, 02, 12:54 PM
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How about some 4.10 gears for the high rpm engine and a bit more stall too, then by taking full advantage of the rpm band the higher rpm engine will win, the mph shows it has the potential to run some mid to high 12s, if the car is set up right. The lower mph on the low rpm engine shows that a low 13 is about all your going to get out of it.

My buddy chevelle runs [email protected], so that just tells me that the guys your beating dont have their cars set up right or they would be in the mid 11s too.

Then agian I'm not a believer in these computer programs, you should see the error/mismatched parts I get on my combo, not to mention the low 11 times, but not in the real world.

------------------
67RS CAMARO - STREET CAR, 502 PUMPGAS, HYD. ROLLER, TH350 w/ATI 10" 12-BOLT w/373 ~ ON MOTOR, ET STREETS WITH MUFFLERS.
BEST 1/4: 60FT= 1.63, [email protected], [email protected]
BEST 1/8: 60FT= 1.54, [email protected], ???
-----------
65 BISCAYNE - NO MOTOR OR TRANS - WILL BE 454 SLEEPER
---------
DAILY DRIVER: 91 B4C CAMARO, 305TPI, TREMEC 5-SPD, 342 GEARS, K&N, CRANK PULLEY, EDELBROCK HEADERS, 4" SINGLE EXH., [email protected] 60FT=2.06
SOON TO BE 383 W/ SUPERRAM
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post #13 of 51 (permalink) Old Apr 2nd, 02, 01:17 PM
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I say that the mph shows the ET potential for each combo, and
100mph is good for some low 13s, while the 105 is good for some
mid 12s. We can check by looking in a ET/MPH calculator, theres
a certain ET you should be running for a certain MPH, its just that
simple.
Example: a Harley with [email protected] and [email protected] will
only run a 15sec 1/4 mile.
A 750 crotch rocket with [email protected] and [email protected]
will run a 11sec 1/4 mile. (even if we add another person to the 750,
to make weight equal the 750 would be in the 12s easy.
Still a real beating for the Harley.
Another example: a TPI 350 makes around [email protected] - flywheel,
and only maybe [email protected] - flywheel.
Now a new LT1 make around [email protected] - flywheel, but make
around [email protected] flywheel.
Which one do you think gets wipped up on at the stop light all the time.

Believe me I've raced plenty of LT1s when they first came out in my 305
TPI, (which runs about the same as a bonestock LT1) and could actually
pull on some of them in first and second, but once I hit 3rd the TPI just
falls on its face and the LT1 would walk away.


------------------
67RS CAMARO - STREET CAR, 502 PUMPGAS, HYD. ROLLER, TH350 w/ATI 10" 12-BOLT w/373 ~ ON MOTOR, ET STREETS WITH MUFFLERS.
BEST 1/4: 60FT= 1.63, [email protected], [email protected]
BEST 1/8: 60FT= 1.54, [email protected], ???
-----------
65 BISCAYNE - NO MOTOR OR TRANS - WILL BE 454 SLEEPER
---------
DAILY DRIVER: 91 B4C CAMARO, 305TPI, TREMEC 5-SPD, 342 GEARS, K&N, CRANK PULLEY, EDELBROCK HEADERS, 4" SINGLE EXH., [email protected] 60FT=2.06
SOON TO BE 383 W/ SUPERRAM
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post #14 of 51 (permalink) Old Apr 2nd, 02, 02:59 PM
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Actually I think the best reason is pieces of paper with the pictures of dead presidents on them.

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post #15 of 51 (permalink) Old Apr 2nd, 02, 03:16 PM
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Eric
 
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gheatly, OK - 4.10 gears and a 3500 stall gets you nearly a dead heat. TQ motor - 12.88 @ 100.6, HP motor 12.83 @ 105.1.

Which would you rather drive on the street?
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