Coast RPM...kinda long

sst7250 · 01-27-2009, 01:00 AM

I have a question that maybe you guys can help me with. It will proabaly get a little long winded but I an new to this and feel a bit of backround cant hurt so here goes.

I have been trying to run S/ST for the last two years. Due to a few issues I have not been able to make any races at all other than brackets. Last year I was getting close and finally got my combo dialed in ok for a novice I guess. I had a coast RPM of 4800 with my old engine a 572" Hemi. It made max power(840) at 7000 and max torque(750)at 5400 rpm. It seemed to work well and showed good promise, it went 10.90 at 149/150. Well that engine had an unfortunate and catastrophic failure a few weeks before I was planning on my first S/ST race.

Well fast forward to today. I have my new engine(520") in the car and have been getting ready and sorting out the bugs. I always like to get the car sorted out on full power before I slow it down. Just the old heads up racer in me I guess, plus I like to see what the old pig can do. I probably went a bit overboard and now have more than I needed. It makes peak HP(1041)at 7600 and peak torque(776)at 6300.

My engine, while it makes good HP numbers for what it is it has a completely different power band than the old one. On the dyno it was not subjected to RPM lower than 5500 and I can tell you it is a real pig at anything below that, as the wrong converter confirmed for me. So here is my question. What do you experienced guys think would be a good starting point for coast RPM. I think I understand the dynamics of coast RPM but am concerned if I drop it down that low that I will have issues coming off the stop. This new engine really pulls hard from about 6100 and up. My converter stalls at 6300, so I would assume if I come off the stop at 4800 it will immediately flash to 6300 and I could have some tire spin?

I am just looking for experienced opinions on this. I have asked around with some of the local guys I know and am juts seeking others opinions. We plan on trying to get out there this weekend and testing to see what we get, track and weather conditions permitting. HELP A NEWBIE out here guys

Lou SG2340 · 01-27-2009, 08:01 AM

I assume coast RPM is RPM on the stop. I would try for 4100 to 4500 RPM.The convertor will flash to stall speed when you come off the stop. Shifting by time & being in high gear when you come off the stop will help alot with wheel spin . The higher the RPM on the stop, the longer you will have to be on the stop to slow your car down.

Dave Steltz · 01-27-2009, 10:38 AM

What Lou said...get on the stop by .2 or so, shift on time to high gear, cruise (coast) set at about 4200, then off and go...the rpm will climb up to close to your stall speed and away you go...this will minimize any tire spin...

You didnt mention what TS you have, most will agree that an under-carb will make the car much more consistant and air powered is better, cause you can slow down the speed that the blades open and give you a smooth transition...

The one thing you might battle is the length of time on the stop, most guys I know with similar power will be on the stop for 4 secs at least...

sst7250 · 01-27-2009, 11:37 AM

Thanks for the replies so far. I forgot to ad the type of stop. I have a Dedenbear TS5A and a Mega 450 box. Also a Dedenbear air shifter on the car and I agree shifting on the stop is the plan. Keep the info coming I am all ears. Looks like the consensus so far is about what I was going maybe a bit lower RPM.

01-27-2009, 01:00 AM	#1
sst7250 Member Join Date: Jan 2009 Location: Las Vegas, NV Posts: 179 Likes: 9 Liked 40 Times in 29 Posts	Coast RPM...kinda long I have a question that maybe you guys can help me with. It will proabaly get a little long winded but I an new to this and feel a bit of backround cant hurt so here goes. I have been trying to run S/ST for the last two years. Due to a few issues I have not been able to make any races at all other than brackets. Last year I was getting close and finally got my combo dialed in ok for a novice I guess. I had a coast RPM of 4800 with my old engine a 572" Hemi. It made max power(840) at 7000 and max torque(750)at 5400 rpm. It seemed to work well and showed good promise, it went 10.90 at 149/150. Well that engine had an unfortunate and catastrophic failure a few weeks before I was planning on my first S/ST race. Well fast forward to today. I have my new engine(520") in the car and have been getting ready and sorting out the bugs. I always like to get the car sorted out on full power before I slow it down. Just the old heads up racer in me I guess, plus I like to see what the old pig can do. I probably went a bit overboard and now have more than I needed. It makes peak HP(1041)at 7600 and peak torque(776)at 6300. My engine, while it makes good HP numbers for what it is it has a completely different power band than the old one. On the dyno it was not subjected to RPM lower than 5500 and I can tell you it is a real pig at anything below that, as the wrong converter confirmed for me. So here is my question. What do you experienced guys think would be a good starting point for coast RPM. I think I understand the dynamics of coast RPM but am concerned if I drop it down that low that I will have issues coming off the stop. This new engine really pulls hard from about 6100 and up. My converter stalls at 6300, so I would assume if I come off the stop at 4800 it will immediately flash to 6300 and I could have some tire spin? I am just looking for experienced opinions on this. I have asked around with some of the local guys I know and am juts seeking others opinions. We plan on trying to get out there this weekend and testing to see what we get, track and weather conditions permitting. HELP A NEWBIE out here guys

01-27-2009, 08:01 AM	#2
Lou SG2340 Member Join Date: May 2008 Location: Disputanta Va (30 minutes from VMP) Posts: 122 Likes: 0 Liked 0 Times in 0 Posts	Re: Coast RPM...kinda long I assume coast RPM is RPM on the stop. I would try for 4100 to 4500 RPM.The convertor will flash to stall speed when you come off the stop. Shifting by time & being in high gear when you come off the stop will help alot with wheel spin . The higher the RPM on the stop, the longer you will have to be on the stop to slow your car down.

01-27-2009, 10:38 AM	#3
Dave Steltz Member Join Date: Nov 2003 Posts: 323 Likes: 0 Liked 0 Times in 0 Posts	Re: Coast RPM...kinda long What Lou said...get on the stop by .2 or so, shift on time to high gear, cruise (coast) set at about 4200, then off and go...the rpm will climb up to close to your stall speed and away you go...this will minimize any tire spin... You didnt mention what TS you have, most will agree that an under-carb will make the car much more consistant and air powered is better, cause you can slow down the speed that the blades open and give you a smooth transition... The one thing you might battle is the length of time on the stop, most guys I know with similar power will be on the stop for 4 secs at least... __________________ Dave Steltz 135G SG/SP/SST BIAECH Racing Team

01-27-2009, 11:37 AM	#4
sst7250 Member Join Date: Jan 2009 Location: Las Vegas, NV Posts: 179 Likes: 9 Liked 40 Times in 29 Posts	Re: Coast RPM...kinda long Thanks for the replies so far. I forgot to ad the type of stop. I have a Dedenbear TS5A and a Mega 450 box. Also a Dedenbear air shifter on the car and I agree shifting on the stop is the plan. Keep the info coming I am all ears. Looks like the consensus so far is about what I was going maybe a bit lower RPM.