RickB Posted March 12, 2001 Share Posted March 12, 2001 I was thinking Kevin could answer this but thought it may benefit others and myself to post this on a forum. Anybody else who can pitch in please do... >> Kevin...did you calculate my tire size vs. trap speed rpm? I have an engine knock and I am curious as to how high I might have revved it the other night. 205/55/14's, 1/4 mile trap speed 110.8 I can measure the actual heighth of the tires tonight if needed. Thanks for coming out, it was good to meet you! I'll post this as a thread as well for everyones benefit. RickB ------------------ RickB@DragRacer.com 280V8 http://www.rickb.racemail.com Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted March 12, 2001 Share Posted March 12, 2001 RickB, you did not state what your final drive is but guessing it is a 3.54, I calculate the RPM to be 5900. ------------------ Scottie 71 240GN-Z Scottie's GNZ Quote Link to comment Share on other sites More sharing options...
RickB Posted March 12, 2001 Author Share Posted March 12, 2001 Thanks Scottie... yes, that is my final drive ratio. that's a reasonable RPM though past my torque band as I have a small cam. ------------------ RickB@DragRacer.com 280V8 http://www.rickb.racemail.com [This message has been edited by RickB (edited March 12, 2001).] Quote Link to comment Share on other sites More sharing options...
GrayZee Posted March 12, 2001 Share Posted March 12, 2001 This site should answer your question: http://www.geocities.com/z_design_studio/ Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted March 14, 2001 Share Posted March 14, 2001 MPH x trans.ratio x rear ratio x 336 (divided by) tire height = RPM If this isn't the formula you needed it still may help someone. Quote Link to comment Share on other sites More sharing options...
RickB Posted March 14, 2001 Author Share Posted March 14, 2001 thanks all...BTW, cool link ------------------ RickB@DragRacer.com 280V8 http://www.rickb.racemail.com Quote Link to comment Share on other sites More sharing options...
Racin_Jason Posted March 14, 2001 Share Posted March 14, 2001 GrayZee that link is AWESOME! I've been looking for something thats simple and accurate such as that for along time. THANKS ALOT! Jason Now I have to go cry because my predictions of high RPM at freeway speeds with a th350 3speed auto are MORE than justified...anyone want to donate a 200r-4 or 700r-4 to a needy recipient?? Im a nice guy...really Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted March 14, 2001 Share Posted March 14, 2001 Rick, Sorry I didnt see this earlier Rick, the weekend, Monday & Tuesday were rather busy for me. The formula Austringer gave is the same I use. RPM = MPH x Gear Ratio x 336 (Divided) by Tire Diameter. Your Tire Diameter came to 22.8" tall; that gave me 5788rpm's you were making when you clipped the 1/4 traps. For those of you whose Tach's work but not your Speedo's you can use this formula: MPH = RPM x Tire Diameter/Gear Ratio x 336 There is also a formula for those who are thinking of changing their tire sizes & are interested in knowing what effect the new size would make. This formula is: Actual MPH = New Tire Diameter/Old Tire Diameter x Indicated MPH Lets say Rick wanted to go to (Which I know he does as he told me so) a 215/60/14. First you have to get the Tire Diameter in Inches...this comes to a 23.3" Tire. Taking the Formula for "Tire Diameter Change" into mind, that would be: Actual MPH = 23.3/22.8 x 110.8 The answer is 113.2 Actual MPH. So Rick, that tire change would give you a 113.2 mph instead of the 110.8 mph. If you want to know what RPM you'ld be at w/the new tire size doing 110.8; simply work the RPM formula....I came up w/5664rpm's. Earlier you ran 5788 & w/the new tire size at 110.8 your rpm's are now at 5664; only an RPM difference of 124. Not very much! Consider going up to a 15" in tire size for racing? Lets say something mild...a 235/60/15 (May need Wheel Flares?); anyway that comes to a Diameter of 26.1" Run the formula for RPM's at your 110.8 speed & your RPM's now change to 5056rpm's; I'ld say w/the 26.1" tires you are now more in your Cam's Peak Power Range & should give you a better/safer 1/4 trap speed! Now, if you end up going thru your engine, due to your most untimely Knock, & beef up the engine w/new cam, forged pistons...and maybe alluminum cyl.heads....your peak power range will change & we'll have to play w/the formulas again. Isnt it fun playing w/these #'s & it doesnt cost anything: its free? Any other questions...let us know. Kevin, (Yes,Still an Inliner) PS: For those of you who are interested; we can take these formulas one step further. If you want to know what Gear Ratio's you need for the 1/4 trap (Overall gear Ratio-that is) you can use this formula: Overall Gear Ratio = Tire Diameter/340 x RPM/MPH [This message has been edited by Kevin Shasteen (edited March 14, 2001).] Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted March 14, 2001 Share Posted March 14, 2001 Kevin and Rick B, I have 235/60/15's on centerlines. RickB you have seen my purple z it's a 71. No flares needed. Just thought I would let you know. Mike Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted March 14, 2001 Share Posted March 14, 2001 Rick, I wanted to mention/suggest you watch your "Mean Piston Speed". If I remember correctly you mentioned your engine was basically a stock engine; exceptions being your Intake/Carb & the Nitrous(?); correct! Take into mind the differences in Mean Piston Speed: Calculated @ Feet Per Minute (FPM) 1) Early Flatheads...no more than 2500fpm 2) Early V8's........no more than 3000fpm Current Eng's-With Advances in Metalurgy 1) Cast Crank/Pistons...no more than 3500fpm 2) Forged Crank/Pistons & Heavy Duty Rods..no more than 3800/4000fpm 3) All out Kenny Bernstein Race Car...5000/6000 if only ran at a few sec's You can figure Mean Piston Speed w/this formula: Piston Speed in FPM = Stroke Inches x RPM/6 That put your death noll run of 110.8mph/5788rpm's @ 3357fpm...definately inching up on its maximum. Combine that w/the higher stress of Nitrous & having ran quite a few runs down the 1/4traps & your stock set up probably ran its course! Time to Upgrade buddy! Good Luck & Have Fun. Kevin, (Yes,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted March 14, 2001 Share Posted March 14, 2001 quote: Originally posted by zfan: Kevin and Rick B, I have 235/60/15's on centerlines. RickB you have seen my purple z it's a 71. No flares needed. Just thought I would let you know. Mike Mike, What size rim are you using; 4 lug or 5 lug? Have you done any suspension mod's to the struts? Curious I am as I would definately like to go to a larger tire but wasnt sure as I'm not a body man...didnt really want to go to flares just yet! Kevin, (Yes,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted March 14, 2001 Share Posted March 14, 2001 If it makes you feel any better, I am facing the same problem. I am running a 3.54 with 275/50-15 DRs (26") and at 5300RPMs in 3rd, I get 114mph and therefore have to shift into o/d. Problem is that my o/d is .67:1 and it drops me down to about 3700 causing the chip to switch to a different mode where it advances the timing and leans out the fuel until I get back above 4000. I need to go through the traps in 3rd and need a 3.36 AND taller tire to make it pass 120mph. You have such a short tire to begin with, giving you up to 2" in diameter to play with. A pair of 225/50-15 would get you an inch in diameter and you could throw them on some Swastikas or something cheap. My 26" tire already gives me more of a rake than I want. I need to get some more solid runs logged then work with the chip maker to see if there is anything he can do below 4000 in o/d. ------------------ Scottie 71 240GN-Z Scottie's GNZ Quote Link to comment Share on other sites More sharing options...
RickB Posted March 14, 2001 Author Share Posted March 14, 2001 Yep...it seems that tires tend to jump in size from the point i am at now. I would prefer not to go all the way to a 26". BTW, I know that the turbo 6's are low rpm torque motors Also, did you hear the Greg Kring bought a Stage 2 motored car! He went a 11.30 something run at 129 mph on street radial TA's, pump gas and 15#'s boost! On slicks he went a 10.06@138 if i am quoting him right!!! ------------------ RickB@DragRacer.com 280V8 http://www.rickb.racemail.com Quote Link to comment Share on other sites More sharing options...
RickB Posted March 15, 2001 Author Share Posted March 15, 2001 Thanks guys... Yep, I've seen zfan Mike's car (very sharp and clean BTW, see my pics on my website). Yeah, I need some 15" rims.. ------------------ RickB@DragRacer.com 280V8 http://www.rickb.racemail.com Quote Link to comment Share on other sites More sharing options...
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