Engineer/math minds HELP!!

[Alky V6]

Yes you are correct , the G force continually drops as the run progresses. I believe mine was down to about .5 Gs near the 1200' mark. Mike

The sim has .446. Close enough for government work.
So what do you think of that hp number? Nuts, huh.

 

[Blazer406]

Making lots of assumptions here:

Acceleration rate between 1.7 and 2 sec is slightly less.

Assuming converter slip gets better with the RPM's going higher. I estimated 11% slip @ 8000 RPM. I assumed the slip decreases to 4% by 8500 RPM. I don't have a feel if the converter will actually couple that well.... but I've seen quite a few people quoting slip numbers in the 3-4% range for their PTC converters....

Tire growth is just figured based off 20% at 200 mph

I get the top of 1st.... you are traveling about 138 mph....still with the 1.8 gearset in the tranny.

And this happens around 2.05 sec.

Distance traveled by the 1/2 shift is now about 208.5 ft. with the above assumptions.

I wonder how much more HP is on tap at 8500 RPM vs the 8000 RPM?

How much boost @ 8500?

When you switch to the higher gearset in 1st for the tranny, how does that affect the acceleration thru the same speeds as the 1.8 gearset? I would assume you will slip less (tires) because you aren't putting as much torque to the ground at a given RPM while in 1st.....

 

[BlownV6]

With the 1.69 gear and 8500 rpm shift point, I have 2.35 sec, 257'. With the slip factor changing with this TC, I'm sure the accuracy of the sim is getting worse as the run progresses out.

Im sure the longer it stays in low and the higher the rpm I turn the tighter the converter slip is going to be , so I suppose there is a chance that it may even travel a bit further and longer than what your showing. Reguardless!!
The additional time and distance traveled in low gear should be a real advantage over the current gear set. Im thinking that thanks to you guys - this is a no brainer!! 1.69 gear set here I come!! Thanks guys!!!!!
Mike

 

[BlownV6]

Ok dont shoot the messanger here!! I see that a 1.65 gear set might also be an option. If you still have your computers warmed up , what would time/distance be for a 1.65 vs the 1.69 you figured?? Thanks Mike

 

[Dusty Bradford]

but I've seen quite a few people quoting slip numbers in the 3-4% range for their PTC converters....

Any converter can couple that well if the combination allows it. My 9.5 can achieve those #'s on 8 second cars and slower. Keep in mind those low slip #'s are at the end of a 1/4 pass. 1/8 slip #'s will be higher.

Mike's converter is performing well above my expectations. Typically blower converters will slip more but they will et better by keeping the rpm up. The blower converters don't need to pull the engine rpm way down in order to keep the boost up.

Just had a customer call back 2 weeks ago after swapping to a 9.5 that wasn't spec'd for his car. It slipped 17% but the combination loved it. This was a higher rev'ing small block with twin 88's. The converter slipped more but the car went faster.

 

[Alky V6]

Any converter can couple that well if the combination allows it. My 9.5 can achieve those #'s on 8 second cars and slower. Keep in mind those low slip #'s are at the end of a 1/4 pass. 1/8 slip #'s will be higher.

Mike's converter is performing well above my expectations. Typically blower converters will slip more but they will et better by keeping the rpm up. The blower converters don't need to pull the engine rpm way down in order to keep the boost up.

Just had a customer call back 2 weeks ago after swapping to a 9.5 that wasn't spec'd for his car. It slipped 17% but the combination loved it. This was a higher rev'ing small block with twin 88's. The converter slipped more but the car went faster.

That's interesting. That seems to be something that showed up in the sim. Trying to just match the top end slip number, I noticed that as I tightened up the spec's, I also had to increase hp in order to keep meeting the target mph. This was showing me that tightening the slip can maybe end up slowing a car. Have you found some cases on the track where this was so?

 

[Alky V6]

Mike. 1.65 with a 8500 rpm shift point. 284' at 2.511 sec.

 

[BlownV6]

And Im sure mine will go faster with the converter looser also, as we discussed. Problem is I havent realy got onto the final tuneup where Im sure Im getting everthing out of the motor that I can. So until I get to that point Im satisfied with what Dusty sent me. I keep making more power and that loosens it up!! Looks like I will be changing low gear sets , that may loosen it up some also. As dusty just said , in my case I dont care what the slip numbers are!! As long as the ET numbers keep getting smaller!!:biggrin:
Thanks for all the help!! Mike

 

[BlownV6]

That's interesting. That seems to be something that showed up in the sim. Trying to just match the top end slip number, I noticed that as I tightened up the spec's, I also had to increase hp in order to keep meeting the target mph. This was showing me that tightening the slip can maybe end up slowing a car. Have you found some cases on the track where this was so?

I think it works kind of the oppisite for a blower car compared to a turbo car. The more RPM I turn the more boost I have period!! And with this big blower it is a parrell line that follows the RPM pretty much exactly. With a turbo that is marginally small for the application the Boost may actually be higher with lower Rpm because the turbo can only supply and Exhaust so much air , so more Rpm just works against itself. In these classes where you are turbo limited I can see where the harder you can couple the converter the faster it may go. Thats just the way I see it!! Mike

 

[BlownV6]

Mike. 1.65 with a 8500 rpm shift point. 284' at 2.511 sec.

Wow , Thanks Donnie!! That would be just awesome!! Almost to the 330' in low gear , I believe that is what the doctor ordered!!! Thanks again Mike

 

[Dusty Bradford]

That's interesting. That seems to be something that showed up in the sim. Trying to just match the top end slip number, I noticed that as I tightened up the spec's, I also had to increase hp in order to keep meeting the target mph. This was showing me that tightening the slip can maybe end up slowing a car. Have you found some cases on the track where this was so?

Yes, it's very possible to slow a car down with a really tight converter. Too many times people get hung up on slip %. This is more an issue on blower cars than it is turbo cars. The turbo cars can generate the same amount of boost at 6000 rpm vs 8000 rpm so they don't mind being lugged down as long as the engine isn't running in too low of a rpm range for the cam.

For example, the car I described has a large cam and turns 8500-9000 rpm. To get a converter to slip 4-5% with 2800+hp would really pull it down on the gear change and the engine would be pulled out of it's usable power band and basically sit there in that range as the converter couples. With the looser converter the rpm will hang in an area where the engine is really making some power and the car will accelerate faster. This is why the top teams don't focus only on slip % but the e.t. They aren't afraid to test many converters to find what the car likes.

The Buick turbo motors don't mind being lugged down so they seem to run good with anywhere from 3-10%.

 

[Alky V6]

Interesting.
Let me throw a theoretical situation out there.
A car with a flat hp curve from 7200 rpm to 7800 rpm is crossing the finish line at 7800 rpm. TC slip is 18%.
Will tightening the TC for the top end so that the car is crossing at say 7500 rpm typically result in a better timeslip? Assuming that the boost level is unchanged between the two converters.
I can see that the tighter TC would provide more range so that the mph could be increased with more boost until the redline (7800 rpm) was again reached, but let's just assume the boost is unchanged.

 

[Dusty Bradford]

Interesting.
Let me throw a theoretical situation out there.
A car with a flat hp curve from 7200 rpm to 7800 rpm is crossing the finish line at 7800 rpm. TC slip is 18%.
Will tightening the TC for the top end so that the car is crossing at say 7500 rpm typically result in a better timeslip? Assuming that the boost level is unchanged between the two converters.
I can see that the tighter TC would provide more range so that the mph could be increased with more boost until the redline (7800 rpm) was again reached, but let's just assume the boost is unchanged.

I would say as long as it's not dropping the engine much under 7200 at the gear change you should see a gain from putting more power to the ground.

 

[Alky V6]

I would say as long as it's not dropping the engine much under 7200 at the gear change you should see a gain from putting more power to the ground.

But, are you putting more power to the ground?
The rpm is different, but being between 7200 rpm and 7800 rpm the power at the flywheel is the same. The TC transfers power, but the TC does not make addition power itself when at speed, ignoring any small amount of torque multiplication that might be occurring, but most likely not.

edit: But then, more TC slippage creates heat, and heat is a loss in hp being transferred through the TC. So a TC with more slippage would lose more hp as it transferred the power through it.

 

[BlownV6]

Update and my final post on this. After discussing the choice between the 1.65 & 1.69 ratios it was determined that the better choice would be the 1.69 simply because it is quite a bit stronger that the 1.65. I purchased two 1.69 gear sets today so that is what I will be working with this next year hopefully!! Depending on the progress of my new cylinder heads. Big thanks for all your input!!! Thanks Mike

 

[Dusty Bradford]

But, are you putting more power to the ground?
The rpm is different, but being between 7200 rpm and 7800 rpm the power at the flywheel is the same. The TC transfers power, but the TC does not make addition power itself when at speed, ignoring any small amount of torque multiplication that might be occurring, but most likely not.

edit: But then, more TC slippage creates heat, and heat is a loss in hp being transferred through the TC. So a TC with more slippage would lose more hp as it transferred the power through it.

That's why the top guys spend a lof of time at the track testing.

Example 1. The TC slips 14% and the rpm never falls under 7000 rpm.

Example 2. The TC slips 8% but the engine is pulled to 6600 rpm. It's possible less power is put to the tires if 6600 is putting the engine in a spot where it isn't happy.

 

[Alky V6]

That's why the top guys spend a lof of time at the track testing.

Example 1. The TC slips 14% and the rpm never falls under 7000 rpm.

Example 2. The TC slips 8% but the engine is pulled to 6600 rpm. It's possible less power is put to the tires if 6600 is putting the engine in a spot where it isn't happy.

So then, each application has its own best target TC slip number. A low TC slip number will not necessarily mean the best timeslip.

 

[Dusty Bradford]

So then, each application has its own best target TC slip number. A low TC slip number will not necessarily mean the best timeslip.

Exactly.

Only way to know is by track testing.

Most of the street car stuff I have done where slip is under 5% are all basically low rpm engines operating in the 5000-5800 range.

I do have some customers with slip under 5% and shifting over 7500 as well. They have what I would consider excessive rpm drop but when it sets records I can't really say it won't work:biggrin:

In the end, there is no cut and dry rule on what is best. Testing tells the true story.

The dyno challenge guys are a good example. One particular car had basically no slip and put down over 1500rwhp. At the track the car was a pig, wouldn't get out of it's own way for 300 feet.

My own car. With a loose converter the car was only .1 slow but it would go down a slick track. Put the tight converter in it and it would pick up that .1, mainly due to the 60' but the track had to be really good. Put the tight converter in and run on a slick track and it was .2 slow.

 

[Alky V6]

Exactly.

Only way to know is by track testing.

Most of the street car stuff I have done where slip is under 5% are all basically low rpm engines operating in the 5000-5800 range.

I do have some customers with slip under 5% and shifting over 7500 as well. They have what I would consider excessive rpm drop but when it sets records I can't really say it won't work:biggrin:

In the end, there is no cut and dry rule on what is best. Testing tells the true story.

The dyno challenge guys are a good example. One particular car had basically no slip and put down over 1500rwhp. At the track the car was a pig, wouldn't get out of it's own way for 300 feet.

My own car. With a loose converter the car was only .1 slow but it would go down a slick track. Put the tight converter in it and it would pick up that .1, mainly due to the 60' but the track had to be really good. Put the tight converter in and run on a slick track and it was .2 slow.

Very interesting.