nismothunder Posted February 9, 2010 Share Posted February 9, 2010 (edited) Ok hears some simple math for engines...let me put on my lab coat and then well get started... Ok hear are the Questions... 1.How tall a gear shold I run? 2.What is my rpm rev limit,and how can I increase it? 3.Whats the size of my engine now that I have a .040 over bore? 4.If I want to race it in the 1/4 how do I figure out what I should dial my ET as...? First off you need to know... 1.weight of the car. 2.engine size/cubic inchs. 3Tire diameter 4.rear gear ratio 5Bored and strokes of a stock engine of the same type... Maximum Engine Rpm... Stock engines(cast cranks and so on) 21000 % stroke=rpm Heavy duty engines(forged insides) 24,000%stroke=rpm Racing engines(fordged and aluimnum pistons and such) 30,000%stroke=rpm So for a stock 360 dodge it would be... 21,000%3.58=5865 rpm And the shorter the stroke the higher the rpms,if you didnt know Piston Speed... 6%(RPMxstroke)=piston speed. and what the rpm limit it is also just as simple. Stroke%(6xpiston speed)=Rpm limit So a 360 with a 3.58 stroke and maximum rpm of 5,865 rpm would have a piston speed of 3,499 fpm(feet per minute) Figureing torq... Another simple math problem... A 80s 360 v8 is rated at 170hp at 4000rpm you will need to now this,you will be quized class... So its (max hp x 5252)% the rpm which the engine make max hp... So a 360 that makes 170 hp at 4000rpm would make 223lbs at the same point... (170x5252)%4000=223 Ok class now calm down...it now Cubic inchs time...yay!! Ok I know your happy but shut and sit down... and you in the back put you pants back on... Number of cylinders x .7854 x bore x bore x stroke... So a 307 v8 bored .o40 over would be 313 cubic inchs... the problem looks like this 8x .7854 x 3.915x3.913 x 3.25 = 312.9 ci(you round up to 313...) I hope this helps you people that always wanted to know how to figure this stuff out but didnt know how... Thank you,its been great,good night!!! Edited February 9, 2010 by nismothunder Link to comment Share on other sites More sharing options...
MY1PATH Posted February 9, 2010 Share Posted February 9, 2010 (edited) ummm 21,000% 3.58= 751.8.... AAAh wrong symol divde... 21,000/3.58=5865 rpm that puts the vg30 with stock forged internals (24000/3.3) redline @ 7272 sounds about right but my limter stops me @ 6k BUT what about the speed of the valve springs? Edited February 9, 2010 by MY1PATH Link to comment Share on other sites More sharing options...
nismothunder Posted February 9, 2010 Author Share Posted February 9, 2010 No idea on the speed of valve springs,and yeah % is the wrong simble but I couldnt figure out where the divension symble is so I made do with what I had... Link to comment Share on other sites More sharing options...
edicer2 Posted February 9, 2010 Share Posted February 9, 2010 divide symbol is just a a/b so the slash part (/) Link to comment Share on other sites More sharing options...
Nytrosfinder Posted February 10, 2010 Share Posted February 10, 2010 As if I havent done enough math homework today... Link to comment Share on other sites More sharing options...
nismothunder Posted July 3, 2010 Author Share Posted July 3, 2010 A new one,I dont think any of us are running carbs but to get a decent idea of the carb size you need... Cubic inchs X Max rpm / 3456= carb size Cfm(minmul size) So a 3.0 is 189 ci and the rev limiter comes on at 6500 ish. 189 X 6500 / 3456 = 355.46875 CFM. Link to comment Share on other sites More sharing options...
Indigent Posted July 7, 2010 Share Posted July 7, 2010 Just for your reference, the RPM rev limit in the ECU is 6250 RPM. If you ever need to change it, I can help, but it is not for the faint of heart. Link to comment Share on other sites More sharing options...
MY1PATH Posted July 8, 2010 Share Posted July 8, 2010 (edited) Just for your reference, the RPM rev limit in the ECU is 6250 RPM. If you ever need to change it, I can help, but it is not for the faint of heart. On stock internals 7000 is the safe limit. after that you need faster springs. Now are 20 year old springs too fatgiged to still handle that? Somone kicked me when downshifting to 4th.... 2nd gear made the enginge jump some where over 8000 (the needle was burried past the 8) before I got the clutch back in. After the adenaline, having my heart leap thru the windshield and realize nothing had seized, I am still driving... I Couldn't help but how it sounded, I wanted to hear it again but didn't dare try. (I was also scoling my passenger). But having a 7000 limit for $#!ts and giggles would be nice. Edited July 8, 2010 by MY1PATH Link to comment Share on other sites More sharing options...
adamzan Posted July 8, 2010 Share Posted July 8, 2010 I am content with the stock redline tyvm. Link to comment Share on other sites More sharing options...
Indigent Posted July 8, 2010 Share Posted July 8, 2010 I bumped mine to 7000, and some 300zx guys take it to 8000, but they do full bottom up builds... 7000 is nice, and I have had no problems, gives me just a hair more when I really get on it I am running a jdm glora motor, so it isn't all that old. Link to comment Share on other sites More sharing options...
Kingman Posted July 8, 2010 Share Posted July 8, 2010 Hmmm... new 300ZX motor... a 7,000 RPM limiter would be nice. Link to comment Share on other sites More sharing options...
JamesRich Posted July 8, 2010 Share Posted July 8, 2010 Just for your reference, the RPM rev limit in the ECU is 6250 RPM. If you ever need to change it, I can help, but it is not for the faint of heart. How about a little more info on this changing the rev limiter. Are you reprogramming the computer or using resistors to fool it? My pathy doesn't pull much after 3500 rpm so it wouldn't do much good to raise it but would still like to know how. James Link to comment Share on other sites More sharing options...
MY1PATH Posted July 8, 2010 Share Posted July 8, 2010 Hmmm... new 300ZX motor... a 7,000 RPM limiter would be nice. Its the same engine silly. Yes you got one but don't go drivin like a race car once you get it in. Its like old ppl who say they are young becuase they got a heart transplant and the donor was 23 lol. Link to comment Share on other sites More sharing options...
Kingman Posted July 8, 2010 Share Posted July 8, 2010 Its the same engine silly. Yes you got one but don't go drivin like a race car once you get it in. Its like old ppl who say they are young becuase they got a heart transplant and the donor was 23 lol. I know lol. My truck is like my grandpa, new hips and knees and he's good to go! Link to comment Share on other sites More sharing options...
Indigent Posted July 8, 2010 Share Posted July 8, 2010 (edited) I desoldered the ECU ROM and put a DIP socket in it's place. I then bought some EEPROMs and I burn the image to one and stick it in the socket. There are sooo many possibilites once you do this. Changing the REV limit is as easy as modifying a hex value and burning the chip. Let's not threadjack though. Edited July 8, 2010 by Indigent Link to comment Share on other sites More sharing options...
SteeevO Posted July 9, 2010 Share Posted July 9, 2010 This is something i've always wanted to do. Start a new thread?? Link to comment Share on other sites More sharing options...
JamesRich Posted July 9, 2010 Share Posted July 9, 2010 This is something i've always wanted to do. Start a new thread?? +2 I want to know more about the programming, I have uprev software to reprogram my Titan. James Link to comment Share on other sites More sharing options...
Indigent Posted July 12, 2010 Share Posted July 12, 2010 just revive my old thread in the wd21 section about ecu programming. I have done a ton of work on this. I disassembled the ROM code and figured out a bunch of stuff specific to the wd21. Link to comment Share on other sites More sharing options...
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