Data Recorder Shows 300 rpm 'droop' After Car Launches???

Don Whitmore · 06-14-2012, 09:10 AM

All...thanks for the input.

@KRatcliff....what is different that the Comp cars don't see to have the 'droop?'

@BlueOval Ralph...would you go leaner / richer in this area? I forgot to mention it is a fuel injected combo.

Thanks for the help!!

KRatcliff · 06-14-2012, 09:32 AM

I cannot answer the question on the Comp cars due to zero experience with them. I can only surmise that the ones you may have seen may be leaving at a significantly higher RPM, the converter may be smaller (ie 7"), and the engine isn't pulled down as much or at all when the converter fully engages.

I have looked at the graphs of many fuel injected stockers and super stockers. Every one of them had the same hump. Even our super stocker with a carb combo has a hump. Most were 2 step cars, but a few were foot brake stockers.

Any tuning that you do for this event is basically behind a curtain and you are not exactly sure what the A/F ratios are due to the action of the 2 step. I have a certain pattern of attack for that event, but that is just for my stuff and I have a lot to learn before I come close to getting these tunes right.

Listen to the others with more experience than me on this. I was just giving you my experience.

Aaron Keown · 06-14-2012, 10:24 AM

IMHO you don't see it is much in comp simply because of the nature of the beast, which is light, lighter, and lightest. The lighter cars with higher H.P. are naturally not going to be as susceptible to theese things.
But you should deffinately believe these guys are pointing you in the right direction, but in all honesty there are hundreds of things that if not exactly the right pieces or setup correctly that can cause this. I am assuming you are running an LT-1 in either a camaro or firebird from you info (and please correct me if I am wrong and that is not the case) and I have a little bit of experience with those engines and what you are talking about can make or break the way the car performs. Just for example, one of my best customers Jeff Dona was able to go a 1.18 sixty foot at bella rose. Now given, he is in I and you are J but I am guessing pretty close to the same basic combo, now I am not you so I don't know what you consider a "good" sixty foot time, but in my humble opinion I think Jeff's car is one of the best real super stockers off the line that I have ever seen.

FED 387 · 06-14-2012, 11:16 AM

listen to Keowen if its who I am thinking it is he has built some fast stuff--Comp cars will/might/could have either a tiny flat line or a VERY small droop when the car first leaves the line usually its a rapid upward spike or you hope it is---- A Comp engine regardless of size is making at least 2.6 HP per CU IN and then the really good ones make all the way up to almost 3 HP per CU IN.possibly more!!! The starting line RPM 's ,( gearing , car weight etc.factored in) that they are leaving at too are such that the phenomonen(RPM drop) you are seeing is so small or does not even exist.
I think it would be unwise to try to compare a Super Stock engine such as yours with the graphs from a Comp engine based solely on the tremendous performance differential here... My suggestion would be to find and talk to a similiarly classed car owner/driver for their perspective on this... Also if you have a data recorder you should be talking to the manufacturer for his input on what you are seeing. They are constantly talking to racers so they might be able to figure out a bit what it is you need too. FED387

BlueOval Ralph · 06-14-2012, 12:38 PM

A little richer at peak torque if EFI give it a little pump shot

Quote:

Originally Posted by Don Whitmore

All...thanks for the input.

@KRatcliff....what is different that the Comp cars don't see to have the 'droop?'

@BlueOval Ralph...would you go leaner / richer in this area? I forgot to mention it is a fuel injected combo.

Thanks for the help!!

Ed Wright · 06-14-2012, 01:48 PM

Quote:

Originally Posted by BlueOval Ralph

A little richer at peak torque if EFI give it a little pump shot

Mine used to do it when it was too rich "down there". It was simply pulling the engine down. Now only if it turns the tires. 1.3X 60's there's a hump, 1.2X 60's, no hump.

Vic Santos · 06-14-2012, 04:43 PM

Don, I use to have the "hump" in my SS car and got rid of it by working on the Q-Jet. The basic problem is the Q-jet bowl. Its too small and makes the secondaries rich during high G's (launch). It takes a lot of detailed testing to solve this problem. Work on secondary rod shapes and hangers. If you don't have a Q-Jet disregard what I've said except for the "too rich" part.
Vic Santos

Michael Compton · 06-14-2012, 05:08 PM

Having ran a car in traditional Super Stock and now SS/BS (comp style), I have encountered the same exact thing that you are describing. According to everyone I talked to, it is almost like the motor takes a big drink of fuel right off the starting line. If you have AFR meters on the car, you can really see the "rich" issue. Some of it I believe was fuel pressure driven and some of it the jetting we were running.

A couple things that did help my current combo in SS/BS were moving the AFR sensors to the headers and not the collectors to get a better reading and increasing the timing on the starting line and pulling it back down track. Seems that the increased timing on the starting line helps burn the fuel a little better when on the tranny brake and within the first 60 feet.

And I think Kyle might be onto something. My issue has almost gone away since changing to the Quickfuel carb and my new A-1 convertor. Maybe it is a combination of the changes I made over the winter but I still think carb and converter helped tremendously.

06-14-2012, 09:10 AM	#1
Don Whitmore Member Join Date: Aug 2004 Location: Central Illinois Posts: 140 Likes: 0 Liked 0 Times in 0 Posts	Re: Data Recorder Shows 300 rpm 'droop' After Car Launches?? All...thanks for the input. @KRatcliff....what is different that the Comp cars don't see to have the 'droop?' @BlueOval Ralph...would you go leaner / richer in this area? I forgot to mention it is a fuel injected combo. Thanks for the help!!

06-14-2012, 09:32 AM	#2
KRatcliff Senior Member Join Date: Sep 2011 Posts: 766 Likes: 75 Liked 524 Times in 141 Posts	Re: Data Recorder Shows 300 rpm 'droop' After Car Launches?? I cannot answer the question on the Comp cars due to zero experience with them. I can only surmise that the ones you may have seen may be leaving at a significantly higher RPM, the converter may be smaller (ie 7"), and the engine isn't pulled down as much or at all when the converter fully engages. I have looked at the graphs of many fuel injected stockers and super stockers. Every one of them had the same hump. Even our super stocker with a carb combo has a hump. Most were 2 step cars, but a few were foot brake stockers. Any tuning that you do for this event is basically behind a curtain and you are not exactly sure what the A/F ratios are due to the action of the 2 step. I have a certain pattern of attack for that event, but that is just for my stuff and I have a lot to learn before I come close to getting these tunes right. Listen to the others with more experience than me on this. I was just giving you my experience.

06-14-2012, 10:24 AM	#3
Aaron Keown Junior Member Join Date: Mar 2004 Location: 1710 Dutch Lane,Jeffersonville,IN Posts: 63 Likes: 0 Liked 0 Times in 0 Posts	Re: Data Recorder Shows 300 rpm 'droop' After Car Launches?? IMHO you don't see it is much in comp simply because of the nature of the beast, which is light, lighter, and lightest. The lighter cars with higher H.P. are naturally not going to be as susceptible to theese things. But you should deffinately believe these guys are pointing you in the right direction, but in all honesty there are hundreds of things that if not exactly the right pieces or setup correctly that can cause this. I am assuming you are running an LT-1 in either a camaro or firebird from you info (and please correct me if I am wrong and that is not the case) and I have a little bit of experience with those engines and what you are talking about can make or break the way the car performs. Just for example, one of my best customers Jeff Dona was able to go a 1.18 sixty foot at bella rose. Now given, he is in I and you are J but I am guessing pretty close to the same basic combo, now I am not you so I don't know what you consider a "good" sixty foot time, but in my humble opinion I think Jeff's car is one of the best real super stockers off the line that I have ever seen. Last edited by Aaron Keown; 06-14-2012 at 10:26 AM. Reason: spelled off of

06-14-2012, 11:16 AM	#4
FED 387 VIP Member Join Date: Jun 2006 Posts: 3,420 Likes: 529 Liked 333 Times in 180 Posts	Re: Data Recorder Shows 300 rpm 'droop' After Car Launches?? listen to Keowen if its who I am thinking it is he has built some fast stuff--Comp cars will/might/could have either a tiny flat line or a VERY small droop when the car first leaves the line usually its a rapid upward spike or you hope it is---- A Comp engine regardless of size is making at least 2.6 HP per CU IN and then the really good ones make all the way up to almost 3 HP per CU IN.possibly more!!! The starting line RPM 's ,( gearing , car weight etc.factored in) that they are leaving at too are such that the phenomonen(RPM drop) you are seeing is so small or does not even exist. I think it would be unwise to try to compare a Super Stock engine such as yours with the graphs from a Comp engine based solely on the tremendous performance differential here... My suggestion would be to find and talk to a similiarly classed car owner/driver for their perspective on this... Also if you have a data recorder you should be talking to the manufacturer for his input on what you are seeing. They are constantly talking to racers so they might be able to figure out a bit what it is you need too. FED387

06-14-2012, 04:43 PM	#7
Vic Santos Junior Member Join Date: Dec 2008 Posts: 27 Likes: 0 Liked 14 Times in 2 Posts	Re: Data Recorder Shows 300 rpm 'droop' After Car Launches?? Don, I use to have the "hump" in my SS car and got rid of it by working on the Q-Jet. The basic problem is the Q-jet bowl. Its too small and makes the secondaries rich during high G's (launch). It takes a lot of detailed testing to solve this problem. Work on secondary rod shapes and hangers. If you don't have a Q-Jet disregard what I've said except for the "too rich" part. Vic Santos

06-14-2012, 05:08 PM	#8
Michael Compton Member Join Date: Dec 2003 Location: Neosho, MO Posts: 215 Likes: 0 Liked 59 Times in 13 Posts	Re: Data Recorder Shows 300 rpm 'droop' After Car Launches?? Having ran a car in traditional Super Stock and now SS/BS (comp style), I have encountered the same exact thing that you are describing. According to everyone I talked to, it is almost like the motor takes a big drink of fuel right off the starting line. If you have AFR meters on the car, you can really see the "rich" issue. Some of it I believe was fuel pressure driven and some of it the jetting we were running. A couple things that did help my current combo in SS/BS were moving the AFR sensors to the headers and not the collectors to get a better reading and increasing the timing on the starting line and pulling it back down track. Seems that the increased timing on the starting line helps burn the fuel a little better when on the tranny brake and within the first 60 feet. And I think Kyle might be onto something. My issue has almost gone away since changing to the Quickfuel carb and my new A-1 convertor. Maybe it is a combination of the changes I made over the winter but I still think carb and converter helped tremendously.