Why high RPM's on the oval tack? - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 05-15-2007, 07:42 PM
On the learning curve.
 
Join Date: Feb 2007
Location: Nova Scotia
Posts: 236
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Why high RPM's on the oval tack?

Hi everyone,

Ok so I was looking in another thread and and asked a question and I was told it was due to the fact that circle track cars like high rpm's. I was wondering why? I realise that hp is usually made at the top of your power curve but torque is made at the lower middle {depending on application/engine}.

So wouldnt you want the torque to be able to pass someone? Which would usually mean lower rpms, correct? Ive been looking at some speed formulas and they seem to pretty much say that the more rpm you have the more speed is available but since oval tracks arent typically that long wouldnt you want the torque to be able to pass someone? ....Ok Im confused someone please shed some light for me.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 05-15-2007, 08:06 PM
DeathRattle's Avatar
Some Punk Kid
 
Last photo:
Join Date: Oct 2006
Location: Michigan
Age: 28
Posts: 787
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Comes down to technology(today) and rules of the racing organization.
If you need to have 352,377,400,350 whatever, cubes thats what you get to make power with. Also I believe rear gears can also be dictated to the field.
You would have to run some weird(high overdrive) gears to keep the engine speed down and vehicle speed up, and I dont think its allowed in most competition levels or any for that matter.
Back in the day they didn't turn 9-10k with the modified production engines because the technology wasn't there. It is now, so they can do the tremendous RPMs and keep it stable.
I bet johnsongrass could tell you a lot better/detailed info on current and days of old specs as he actually does this stuff.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 05-15-2007, 08:10 PM
On the learning curve.
 
Join Date: Feb 2007
Location: Nova Scotia
Posts: 236
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
So your saying there is no real reason to it? Just that technology allows them too so they do it?

Steve
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 05-15-2007, 08:25 PM
DeathRattle's Avatar
Some Punk Kid
 
Last photo:
Join Date: Oct 2006
Location: Michigan
Age: 28
Posts: 787
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Well if your allowed a 1:1 final and a 3.55:1 rear gear and you want to go 160mph that engine is going to scream.
And some classes specify rear gears.
Could be lower or higher, which would intern change the peak RPM range and peak MPH of the field is capable of. Then its just up to you to make the most power with your cam/compression/timing/etc
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 05-15-2007, 08:29 PM
On the learning curve.
 
Join Date: Feb 2007
Location: Nova Scotia
Posts: 236
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Right and technically the more rpm the more speed? Then when you make more power {more so torque} that will give the passing power you need while maintaining your high speed? Am I correct so far?

Steve
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 05-15-2007, 08:35 PM
DeathRattle's Avatar
Some Punk Kid
 
Last photo:
Join Date: Oct 2006
Location: Michigan
Age: 28
Posts: 787
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Well lets say an engine is turnin 6000(peak power,safe(stable)) and going 150-160MPH

assume same gear ratio's

now the engine is spinning 9000 and going 180-190MPH.

And its not just the stroke that changes the total overall engine speed. The valvetrain has the biggest say in what you will get away with.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 05-15-2007, 08:39 PM
On the learning curve.
 
Join Date: Feb 2007
Location: Nova Scotia
Posts: 236
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Ok now I have two more questions. These engines, while one is turning 6000 and the other is turning 9000. Do they have the same power? If the 6000rpm has 600hp/tq does the 9000rpm also have 600hp/tq? My point is does the rpm difference influence the speed or is it the power that comes with those rpm?

Now what factors of the valvetrain limit how far an engine can rev?

Thanks Steve
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 05-15-2007, 08:56 PM
Blazin72's Avatar
You got a leaky spark tube...
 
Last wiki edit: Rearend removal
Last journal entry: General Lee
Last photo:
Join Date: Jul 2005
Location: Union, WA
Age: 32
Posts: 2,868
Wiki Edits: 19

Thanks: 0
Thanked 2 Times in 2 Posts
Engine size is a factor. The best way to increase the power potential of an engine is to add cubic inches, increase the rpm potential or force more air down its throat (which I would think could be related to adding cubic inches).The big blocks they ran in NASCAR 40 years ago were somewhere around 70-80 cubes larger than the 358ci they are limited to today. How many N/A 358ci V8s do you see making 750hp at 6000 or 6500 rpm? The Honda S2000 engine is a good example, when they first came out they had 2.0L (120ci) engines that were rated at 240hp at 8900 rpm. The later versions continued to make 240hp but bumped displacement up to 2.2L (131ci) and the power peak dropped to 7800rpm.

Here is a related question I asked a few months ago:
Big bore vs. Long stroke
Quote:
Originally Posted by steveyb4342
Now what factors of the valvetrain limit how far an engine can rev?
Weight is a huge factor, the ability of the spring to force the valve shut and hold it shut at high rpm. Since things happen so incredibly fast at 8000 rpm the camshaft has to open the valves far enough and long enough to allow the cylinder to draw in enough air/fuel to make power in those rpms. And as we all know cams designed for that kind of use aren't conducive to low rpm duty.

Useless info: Did you know an engine spinning at 8000 rpm completes the four stroke cycle about 67 times per second? The intake stroke on an engine spinning at 8000 rpm only lasts about .007 seconds.

Last edited by Blazin72; 05-15-2007 at 10:23 PM. Reason: Added useless info...
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 05-15-2007, 08:57 PM
DeathRattle's Avatar
Some Punk Kid
 
Last photo:
Join Date: Oct 2006
Location: Michigan
Age: 28
Posts: 787
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Very high duration cam. Tight/high spring rate valve springs (dual - triple) to close the valves very fast. Also additional measures to keep oil on the coils to cool them off. Anything to prevent floating the valves and spring failure from heat. Takes lots of money, and I am pretty sure the component lifespan is not as long.
The faster spinning engine will make more power with same bore/stroke.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 05-15-2007, 09:22 PM
Registered User
 
Last wiki edit: Wheelbase database Last photo:
Join Date: Jan 2007
Location: Virginia
Posts: 3,618
Wiki Edits: 1

Thanks: 6
Thanked 163 Times in 150 Posts
Blazin72 hit the nail right on the head. The more air you move through the motor, the more horsepower you make. A larger engine moves more air, so all else being equal, it makes more power. Forced induction is another way. Virtually all racing series are displacement limited, and other technologies like porting, valve sizes, and carb size are also mandated by the governing body. The only way to make more power with a fixed displacement and these restrictions is to rev higher.

Unfortunately, it's now time for a little math:

A 358 cu in engine at 7000 RPM moves about 725 cubic feet of air per minute through the engine (358/1728 = .207 cu ft of displacement, 0.207 x 7000 / 2 =725 cfm. Note the 7000 is divided by 2 since there is only one intake stroke for every two revs). Now this same engine at 8000 RPM moves 828 cubic feet per minute and ideally should make about 14% more horsepower. Yes, these are idealized numbers and the reality of port flow, restrictor plates, mixture distribution, etc, etc all have effects, but this is why higher RPM is better. Note that this 358 at 8000 RPM moves as much air - and all else being equal should make as much power - as a 427 at 6700 RPM.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 05-15-2007, 10:32 PM
Member
 
Join Date: Dec 2004
Location: Madison, WI
Posts: 1,885
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
It is mainly a function of circle track cars running a lap in the same gear, and a limited amount of rear gear options, given the track diameter is fixed. You design a circle track engine to peak RPM at the end of the straight and make the highest amount of torque (and therefore horsepower) at the RPM the car will be coming out of the corner at. This gets you out of the corner hard and pulls throughout the straight for continuous and maximum acceleration. To make an engine run hard from the exit of the corner to the end of the straight, with one gear, requires and engine that will continue to make power into the upper RPM band, as compared to a stock type motor.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 05-16-2007, 12:20 AM
Registered User
 
Join Date: May 2007
Location: Saint John,N.B.,Canada
Posts: 46
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Oval Track RPM's

Blazin72 was very close to the correct answer to your question. They adjust the final gear ratio to the track that they race on to keep the engine in the right powerband. RickWI was even closer to the right answer! They build the engine to suit the track that it is run on. Yes it is designed to make max torque coming out of the corner and max HP at the end of the straight away. What you may not understand is that the basic engine building rules for the street that you are use to don't apply on the race track! These engines have the camshaft ground specifically to suit the application that the engine will be used in. The heads are ported and intake and exhaust manifolds/headers ported to suit the particular application where this engine will be used. My Kudoos to RickWI for suggesting the proper answer to this question! All I did was expand on it. Thanks, RickWI, Yours, westfaliaguy.
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 05-16-2007, 02:26 PM
Registered User
 
Last photo:
Join Date: Apr 2007
Location: Seattle, Wa
Posts: 7,025
Wiki Edits: 0

Thanks: 4
Thanked 516 Times in 436 Posts
Quote:
Originally Posted by steveyb4342
Hi everyone,

Ok so I was looking in another thread and and asked a question and I was told it was due to the fact that circle track cars like high rpm's. I was wondering why? I realise that hp is usually made at the top of your power curve but torque is made at the lower middle {depending on application/engine}.

So wouldnt you want the torque to be able to pass someone? Which would usually mean lower rpms, correct? Ive been looking at some speed formulas and they seem to pretty much say that the more rpm you have the more speed is available but since oval tracks arent typically that long wouldnt you want the torque to be able to pass someone? ....Ok Im confused someone please shed some light for me.
It's a matter of design efficiency. Horsepower is a measure of torque in time, this is what does work. Torque by itself is simply a force. An engine in a race car turning at 9000 RPM develops far more horsepower (therefore, does more work) than the same size engine turning at 6000 RPM. To do the same amount of work at 6000 RPM would take a larger motor. These are the underlying physics of the situation. A larger motor takes more space, adds weight and in and of itself requires even more power to get the job done. A good example of this is drag racing shortly after World War 2. At that time there were a lot of big military airplane engines on the market, like the Rolls Royce Merlin. Of course the fast guys thought the fast way to beat a little old Chrysler Hemi powered drag car would be to build a car big enough to hold one of these 2,000 horsepower airplane motors. It didn't work, the power needed is geometric function of weight and drag. With the physically huge engine, the weight and drag penalties went up way faster than the power and the things weren't competitive.

So when the rules constrain the size of the machine, there is some optimum physically sized engine. In the classes you refer to, the small block Chev, Ford or Chrysler long ago became recognized as an optimal solution. The improving technology over the past few years has only made these engines even more competitive as RPMs and power has gone up without a corresponding increase in size or weight.

Bogie
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 05-16-2007, 03:53 PM
NAIRB's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Sep 2002
Location: cimarron, ks
Posts: 1,658
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
The answer to this question is quite simple, and we need not confuse it with too much discourse.

We want as much torque at as much RPM as we can produce, and we want to be able to harness it, and apply it to the ground.

Modern stock cars are far more advanced from a chassis stand point and we have gotten much better at applying that to the track. This is why we are seeing larger engines, turning more RPM than we used to see. The chassis technology of the old days and with the old tires, would allow this to happen, but we can now get away with it.

A 301 Chevy in the old days would turn as many RPM as most modern engines we are seeing now, but obviously, the larger engines produce more power.
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 05-17-2007, 12:28 PM
On the learning curve.
 
Join Date: Feb 2007
Location: Nova Scotia
Posts: 236
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Hey everyone! Sorry for taking so long to reply, Ive been trying to get the engine out of my car . Anyways, I think understand now and Id just like to say I really appreciate all your answers. ....Now to try and make my test bed 305 rev like wild and make power lol. For those of you who dont already know, I picked up an old 305 and I have been applying all the little things I learn to the engine. I do it all myself mainly because I dont want to spend my car $$ on it and I dont care if it blows up. Its a really good learning tool! I am in the process of machineing a set of pistons and connecting rods for it, Im not trying to make big power or anything I just wanna see if itll work. lol. Anyways Thanks alot!

Steve
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
high volume and high pressure oil pumps can destroy cam and distributor gears! Knobie Engine 75 02-13-2011 03:22 PM
too high rpm help jcdaly Transmission - Rearend 25 01-31-2005 09:03 PM
Altima RPMs drop while driving suddenly, can't maintain speed, can't start sometimes elukas Electrical 1 10-07-2004 03:31 PM
Permatex High Tack same as gasgacinch? brian400ex Engine 4 02-13-2003 08:13 PM
erplexing rpms madhat Engine 2 01-12-2003 05:53 PM


All times are GMT -6. The time now is 12:57 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.