higher RPMS

kinkyllama · Post by **kinkyllama** » Wed Apr 06, 2005 8:39 pm

Im just woundering to what all the things you should do to your car before reaching higher RPMs... like past redline.

Theres this course at a track near me where my car doesnt have enough power to keep it at the same speed or slightly accelerating on this corner so im forced to downshit and idealy i would keep it at about 7k RPMs but i dont want to blow my engine. What can i do to beef it up against this?

Also.. what happens when you downshift and let the engine slow you down? Do the cyl. still get fuel into them? What negative effects could you get from down shifting to a stop instead of braking?

I kinda wanna buy the ARP bolts from 360dynamics(connecting rod bolts, cyl head studs) just to have a more stronge engine but i would wanna install them myself. Is this something i could do myself without risking screwing something up?

MMamdouh · Post by **MMamdouh** » Wed Apr 06, 2005 11:00 pm

at higher RPM yoget what is called "free float" for the valves whre the cam lube is no longet pushing the valve down yet the valve don't have time to pull back before the piston comes up!

practically you have to bypass the rev limiter on your car and i don't know how then get stronget valve springs to avoid the free float effect... accordinglt you will have to use better cam shaft bearings (not sure if this the correct turm) to handle the extra pressure the new springs will exert on the shaft... in short it is too damn expensive to do that.

as for downshifting: it is practically braking... i use that all the time to ease the pressure off the brakes. and yes the engine still gets fuel during that but not as much as you think... i guess during that the ECU sees that you are off the throttle and the engine RPM is getting down so it will dump just enough fuel to keep the engine at idle. not really sue of that but that is the only logical explanatio... otherwise the engine will keep at higher RPM with your foot off the throttle.

what effects can that have?? if you do it right then nothing will happen... just don't shift when you are too hight in revs or else the engine will violently brake the car and that will put too much strain on the tranny gears and engine mounts.

it is better to poke the throttle pedal in the process of down shifting so that the engine RPM difference is not that big when you engase the lower gear and also apply the brakes... it is better to share the braking load on the engine and brakes that letting one do all the work.

MMamdouh

kinkyllama · Post by **kinkyllama** » Wed Apr 06, 2005 11:16 pm

mmamdouh wrote:at higher RPM yoget what is called "free float" for the valves whre the cam lube is no longet pushing the valve down yet the valve don't have time to pull back before the piston comes up!

practically you have to bypass the rev limiter on your car and i don't know how then get stronget valve springs to avoid the free float effect... accordinglt you will have to use better cam shaft bearings (not sure if this the correct turm) to handle the extra pressure the new springs will exert on the shaft... in short it is too damn expensive to do that.

as for downshifting: it is practically braking... i use that all the time to ease the pressure off the brakes. and yes the engine still gets fuel during that but not as much as you think... i guess during that the ECU sees that you are off the throttle and the engine RPM is getting down so it will dump just enough fuel to keep the engine at idle. not really sue of that but that is the only logical explanatio... otherwise the engine will keep at higher RPM with your foot off the throttle.

what effects can that have?? if you do it right then nothing will happen... just don't shift when you are too hight in revs or else the engine will violently brake the car and that will put too much strain on the tranny gears and engine mounts.

it is better to poke the throttle pedal in the process of down shifting so that the engine RPM difference is not that big when you engase the lower gear and also apply the brakes... it is better to share the braking load on the engine and brakes that letting one do all the work.

MMamdouh

Oh yeah i forgot about the valves... I dont really know why i even asked this question.. with a few more hp i wont even need to go higher rpms cuz ill have just enough power to gain speed on the corner at the bottom of 3rd.

If you downshift to low the rpms go past the limiter.. and you can keep them there if you put your foot on the throttle after downshifting.. it wont gain any RPMs but it stays the same... im not certain on this though.. Its hard to say if i started putting gas into it while it was above the limiter or not. Since i was racing.. on the corner and all i couldnt exactly look down at my rpms but it sounded like it.

I always match the engine RPMs before downshifting... its what of the best things to do, especialy in racing. One guy was going through 4-5 trannys a year but since hes been doing "toe and heel" (matching engine RPMS) he only goes through 2. Plus it keeps your momentum on the turns if you match the RPMs.

Post by **PrecisionBoost** » Thu Apr 07, 2005 2:45 am

You do not want to increase your redline.... you should be shifting well before it right now.... otherwise your not using the power band correctly.

Look at the Dyno sheet from my car... you will see that the power drops like a rock after 5700RPM.

Look at the blue line... this is probably where your car is running (red is with the underdrive pulley)

So if you shift at 5700RPM to 5900RPM you will have the most efficent power transfer. (which will result in quicker lap times)

If you up your RPM to 7000 and shift there you will be making about 30 horsepower at your shift point!!!

Needless to say your speed would really drop off.

What you really need to do is change your gear ratio.... not your redline.

I know intimidator has different final gear ratios.... if you gear it different it will accelerate way quicker but it won't have as high of a top speed.

This will also make the gearing closer together so you won't drop as many RPM during shifts (which will again make you accelerate faster)

The only bad thing is that if you change the final gear ratio and make it accelerate faster you will loose gas mileage and your car will run at way higher RPM's on the highway.

kinkyllama · Post by **kinkyllama** » Thu Apr 07, 2005 3:12 am

I know ive looked at the power band.. ive tried shifting as low as 5600rpms and have tried all sorts of things.. but although i shift right when the power starts to drop off when i get up to the next gear its at a too low of RPM.. i seem to get the best results at about 6300rpms. It defintly pulls ALOT harder when i shift at 6500 rpms than at 5700 but it seams like the best mix is still a little bit after the RPMS drop off.

I know how low of power i have at 7kish rpms but im not able to get into the next gear b/c of the way the corner goes.. im just going to slow down a bit more before i get into the corner.

As for the gear ratios ive considered that but main thing is.. i need that top speed... once i get the corner down well before the straight away ill be reaching 110mph... once i get a little more power under my car im going to need all the top speed i can get... especialy since thats whree you can make up the most time.

I could probably drop a little bit for the top speed cuz ive been over 130mph and (kinda hazy now) but i think i still could go maybe 145 untill the trans tops out which i wont reach on the track unless i about double my power output.

daewooluvr · Post by **daewooluvr** » Thu Apr 07, 2005 4:16 am

This is a problem with your gearing in your transmission not with the amount of rpms.

Post by **PrecisionBoost** » Thu Apr 07, 2005 4:17 am

Well.... I just can't understand what's happening here.... if you have a choice of 7000rpm in one gear or say 5000rpm in the gear above you are allways going to be making more power at 5000rpm.

When you say it pulls harder when shifted at 6300 but I just don't see how that's possible.

At 6300 rpm you are making about 70hp

So if the next gear up is higher than 3300 rpm you will be putting more power to the ground.

If I were you I would get out a calculator and figure out your "optimum" shift points based upon your gear ratios.

DomWoo · Post by **DomWoo** » Thu Apr 07, 2005 4:22 am

then go get your self a programabe shift light and program all the shifts you want

Post by **PrecisionBoost** » Thu Apr 07, 2005 5:08 am

Ok... 195/55/15 tires have a diameter of 23.3"

So for every revolution of the tire your car travels 73.2"

Gear Ratios... final drive is 3.944

1 --> 3.545 Total ratio = 13.98
2 --> 1.952 Total ratio = 7.70
3 --> 1.276 Total ratio = 5.03
4 --> 0.971 Total ratio = 3.83
5 --> 0.763 Total ratio = 3.01

So tire revolutions per minute can be calculated as follows:

Engine RPM / Total Ratio = Tire RPM

To get speed we multiply the revolutions per minute by 60 to get revolutions per hour

Then we take the distance traveled per revolution and divide it by 63360 to find miles per revolution

The result is the speed of the car in miles per hour.

Car speed = (Tire RPM X 60 ) X (73.2" / 63360 )
Car speed = Tire RPM X 0.069318
Car speed = ( Engine RPM X 0.069318 ) / Total Ratio

So.... in 1st gear you can figure your speed out by using the total gear ratio of 13.98

speed @5500RPM in 1st gear = (5500 X0.069318) / 13.98

(A)speed @5500 RPM in 1st gear = 27.3 mph (making 108 whp )
(B)speed @5750 RPM in 1st gear = 28.5 mph (making 100 whp )
(C)speed @6000 RPM in 1st gear = 29.8 mph (making 85 whp )
(D)speed @6250 RPM in 1st gear = 31.0 mph (making 70 whp )
(E)speed @6500 RPM in 1st gear = 32.2 mph (making 40 whp )

Ok..... now lets work backwards and figure out the 1-2 shift

if we shift at 5500 RPM ( 27.3mph) we can use the forumla to figure out what the RPM will drop to when shifting into 2nd gear (total ratio = 7.70)

Car speed = ( Engine RPM X 0.069318 ) / Total Ratio

27.3 mph = ( Engine RPM X 0.069318 ) / 7.70

(A)Engine RPM in 2nd gear @ 27.3 mph = 3033 RPM (making 65 whp )
(B)Engine RPM in 2nd gear @ 28.5 mph = 3166 RPM (making 69 whp )
(C)Engine RPM in 2nd gear @ 29.8 mph = 3305 RPM (making 72 whp )
(C)Engine RPM in 2nd gear @ 31.0 mph = 3443 RPM (making 75 whp )
(D)Engine RPM in 2nd gear @ 32.2 mph = 3577 RPM (making 78 whp )

So if you look at what power was being made in 1st you will find that shifting at anything over 6250 rpm will make your car slower (since your not using all your power band)

Ideally this should be set up in an excel spread sheet with each gear to get the exact perfect shift point.

Lets look further and try to pinpoint the perfect 1-2 shift RPM.... which should be just under 6250 RPM

1st Gear @6200 RPM --> 30.74 mph ( making 70 hp )
2nd gear @30.74 mph --> 3415 RPM (making 73 hp )

These numbers are pretty close... so you will end up with a shift point of about 6200 RPM

Now that you get the general idea you can figure out the ideal shift points at every single gear shift.

You might be led to belive that it pulls harder when shifted closer to Redline but that's most likely due to the illusion of power differencial.

Which is to say you go from making a mere 40whp in 1st gear to a massive 78 whp in 2nd gear.... which makes the car accelerate quickly and jump forward.

If you can feel the shift.... you've shifted too late.

The ideal power transfer happens very smoothly since your making exactly the same power in both gears.

A jump forward only occurs when you've mis-shifted

I know your looking at this and saying "well I said I get the best results at a shift of 6300rpm which is very close to the 6200 calculated here" but this is only due to the massive difference between 1st and 2nd gear.

I will do the next shift point to illustrate my point better.

Post by **PrecisionBoost** » Thu Apr 07, 2005 5:33 am

Here is the optimum 2-3 shift......

Gear Ratios... final drive is 3.944

1 --> 3.545 Total ratio = 13.98
2 --> 1.952 Total ratio = 7.70
3 --> 1.276 Total ratio = 5.03
4 --> 0.971 Total ratio = 3.83
5 --> 0.763 Total ratio = 3.01

Car speed = ( Engine RPM X 0.069318 ) / Total Ratio

speed @5500RPM in 2nd gear = (5500 X0.069318) / 7.70

(A)speed @5500 RPM in 2nd gear = 49.5 mph (making 108 whp )
(B)speed @5750 RPM in 2nd gear = 51.8 mph (making 100 whp )
(C)speed @6000 RPM in 2nd gear = 54.0 mph (making 85 whp )
(D)speed @6250 RPM in 2nd gear = 56.3 mph (making 70 whp )
(E)speed @6500 RPM in 2nd gear = 58.5 mph (making 40 whp )

Car speed = ( Engine RPM X 0.069318 ) / Total Ratio
27.3 mph = ( Engine RPM X 0.069318 ) / 5.03

(A)Engine RPM in 2nd gear @ 49.5 mph = 3591 RPM (making 77 whp )
(B)Engine RPM in 2nd gear @ 51.8 mph = 3759 RPM (making 86 whp )
(C)Engine RPM in 2nd gear @ 54.0 mph = 3918 RPM (making 90 whp )
(C)Engine RPM in 2nd gear @ 56.3 mph = 4085 RPM (making 92 whp )
(D)Engine RPM in 2nd gear @ 58.5 mph = 4245 RPM (making 96 whp )

So the transition point here is were both gears have the same whp which is around 5800 RPM to 5900 RPM

If you took your 2-3 shift all the way to 6300 RPM you would have overshifted by nearly 500RPM

Of course you would get the illusion of power because your only making 70hp in 2nd gear and when you drop your clutch into 3rd your making about 93 hp..... so you would get a surge from the 23hp difference.

If you had two exactly identical cars running side by side..... me shifting at 5850 RPM during the 2-3 and you shifting at 6300 RPM I would pass you like your standing still.

I'm making a constant 90hp during my shift and your only making 70hp.... so given the cars weigh exactly the same I'm going to accelerate faster than you.

Hopefully you understand the concept.... don't be tricked by a surge in power during the shift.... the correct shift will feel smooth like glass.... it's a "sweetspot" you won't forget if you hit the shift point on the button.

Post by **PrecisionBoost** » Thu Apr 07, 2005 5:44 am

Sorry for all the math but this is what a good racer does.... they figure out the exact optimum shift points.

They also plot out the course on a computer and compute the perfect corner entry speed and angle.

Everything can be calculated.... amount of understeer/oversteer.... drift... exit speed... exit angle.

A pro-racer would have every single corner figured out well before a race and they could theoretically calculate their "perfect" lap speed based upon the setup of the vehicle ( tire traction, ashphalt/concrete temperatures )

Then after the race (which they've taped) they can see where they went wrong... where they deviated from their "theoretical" model of the perfect lap.

Sometimes it's a problem with the car and sometimes it's driver error.... but in the end they can correct their mistakes for the next time they race that particular course.

Of course the real racing teams have incredibly expensive modeling software to help them find the optimum lines and entry speeds but you can allways do what you can to calculate as much information as you can.

kinkyllama · Post by **kinkyllama** » Thu Apr 07, 2005 1:16 pm

ahh i see.

Thanks alot man!

Post by **Efratech** » Thu Apr 07, 2005 2:33 pm

great explanation,

kinky' you did mention you had a problem on a corner right?

are you running out of space for the shift? if so you will have to figure out a better line to have a faster corner exit, that way you can shift at the corner exit.

Efrain.

kinkyllama · Post by **kinkyllama** » Thu Apr 07, 2005 4:23 pm

Im not sure anymore.. now since i got new tires (plus softer) my lines going to be alot different so im not sure how i can take the corner.

My front tires were bald and my backs were pretty good. The tread rating was like 380 so they wernt soft. My new ones are 200 tread rating so my lines probably completly changed.... actually damn, i should be able to take the corner now in the middle of 3rd gear instead of bottom (or top of 2nd).

MMamdouh · Post by **MMamdouh** » Thu Apr 07, 2005 5:17 pm

why don't you make a drawing for that turn so we can help out more??

MMamdouh