Crappy 1/4 mile slip

[jerrad]

One thing to add, with street tires on the car will start spinning at around 45mph while leaning into the throttle, with the slicks it obviously doesn't. Does anyone think that like a clutch, when the tires spin you get little slip at the convertor because the tires are the weak link?

Does that make since to anyone but me?

 

[BMF_Racing]

One thing to add, with street tires on the car will start spinning at around 45mph while leaning into the throttle, with the slicks it obviously doesn't. Does anyone think that like a clutch, when the tires spin you get little slip at the convertor because the tires are the weak link?

Does that make since to anyone but me?

Slippage will increase with load, hence if there is tire spin is present the slippage % will go down. Same goes for if you were to shift the car into OD, it will raise the slippage due to the extra load and not to mention the RPM's are dropped down to where some of the peak TQ is present, which also does not help the slippage cause.

 

[jerrad]

I think thats whats happening. On the street it feels like a tottaly different monster than the te44. I guess a convertor is in the works.

 

[Razor]

If you have an engine with 50K miles and you change the heads, the newer heads will have less leakage than the OEM ones. Kinda like taking an engine and giving the heads a valve job.. the car will run better.

If the car was tuned for 108 and you put different heads it has to be retuned. As it would if you changed the cam.. it has to be retuned. Any changes to the way the air is handled through the motor.. it needs to be retuned.

At 90 MPH in the 1/8 and 108 in the 1/4 there are issues. The car should run easy 114-116 in the 1/4 with a 90 mph 1/8 mile mark.. this is if everything is working like it should, car is tuned correctly. This assummes no heavy leakdown from worn rings, cam that is partially wiped out, etc..

Maybe its just me.. I usually do the cam before heads. But with a roller, the height can be an issue with stock guides. And most do heads and cam at the same time. Even in the aftermarket.

Slipping converter is easy with a Tach. Look for RPM drop between shifts. If its too loose it wont drop RPM's. If it drops RPM's hard then more than likely its too tight. A 500 rpm drop is normal. Shift at 5300 and it goes down to 4800.. every gear. If the converter is slipping(loose) you shift at 5300 and it goes to 5200.

I have seen fast cars with loose converters.. they sound like its one gear all the way down the track.

Jerrad, buy a tach and put it where you can see it. Or get a power logger/direct scan and record the run. Look for RPM drop. You may also look into getting a leakdown performed on the engine to make sure your cylinders are healthy. You want to see all the cylinders even. Motors will miles will have higher leakdowns.. but as long as its even, you should be fine. I'll let you search how to perform a leakdown. I would say use the scanmaster for RPM but its very hard to do as the refresh rate is hard to see exactly whats going on.

Good luck.

 

[jerrad]

Thanks Razor. I was planning on doing a compression check but I guess a leak down is in the plans now too.

 

[Razor]

Thanks Razor. I was planning on doing a compression check but I guess a leak down is in the plans now too.

Both will tell you if you have a ring/cylinder issue.

The cam.. is another deal. You can pull the valve covers and see how the rockers open.. a simple slide ruler can be used on intake and exhuast rockers. This is how I usually can tell when cams are wiped out. The cam should open the valves about .5 inch when the motor is spun over.

If all checks ok.. back to basics on tuning.

 

[jerrad]

Compression test results:
Driver side front to rear: Front=152 Middle=151 Rear=151
Passanger side front to rear: Front=148 Middle=145 Rear= 150

Looks like the compression is good.
Wasn't able to get the leak down test done.

 

[johnnyttype]

Well, after hitting test and tune road, the car shifted at 4475 at 65mph with a 26" tire. The calculator shows 55% slippage but that is based on the quarter, anyone guess what it would really be?

youre gonna have to do this test again, on a long straight road or at the track though! you need to have the car in drive and the RPM reading comes from the top of third gear, not when it shifts to third. You should be well above 90mph(closer to 109mph since that was your trap speed in drive at the end of the track) when you take the RPM reading for the top of third gear. this will give you a better slippage number.

i doubt the converter is the issue, my vote is that the combo is mismatched and in need of a healthy cam!

im guessing here, but this is my theory: car traps at 109mph, probably about 10% converter slippage in drive... this equates to about 5300rpm at the trap, and the stock cams powerband drops off drastically at about 5000rpm if not sooner, hence my vote on a nice cam:smile: hope this makes sense

 

[Dusty Bradford]

will do. :biggrin: yeah it spools like no other with the t-brake and DBB.

It does that with the restalled converter?? What rpm are you seeing at 0# boost?

 

[BMF_Racing]

It does that with the restalled converter?? What rpm are you seeing at 0# boost?

Yep, (it take no time at all to fill the little stock intake and heads with boost)

I will check 0# tonight on the brake ... 24# is at 3100 to 3200rpm but thats in drive.




Sorry to high-jack the thread.

 

[BMF_Racing]

It does that with the restalled converter?? What rpm are you seeing at 0# boost?

Ok, its at 0psi at 2350 to 2400 rpm everytime. good/bad/ok

 

[Dusty Bradford]

I agree, I'm having an issue with the convertor slipping now. On my pass I was at 5500rpm @ 1000ft and went trough at the same 5500 (stock unopened engine). Best mph was 114.98 but should be better if I can get the slippage down.

I'm leaning more towards a camshaft, valve spring issue and your post confirms that.

A loose converter will not hold an engine back. Your converter started out as a 2800, we restalled it to a 2400 and that's what your seeing on the stall test. If your engine is reaching 5500 rpm and can't accelerate past that, your out of cam and/or valvespring.

The good thing is you know you can spool very easily with a 2400 stall. If your new converter will go another 400 rpm tighter, you may be ok. If you don't plan to change cams I'd look into a converter to handle WOT locking. You need to keep rpms down to 5000-5200 yet spool a 67mm.

 

[BMF_Racing]

I'm leaning more towards a camshaft, valve spring issue and your post confirms that.

A loose converter will not hold an engine back. Your converter started out as a 2800, we restalled it to a 2400 and that's what your seeing on the stall test. If your engine is reaching 5500 rpm and can't accelerate past that, your out of cam and/or valvespring.

The good thing is you know you can spool very easily with a 2400 stall. If your new converter will go another 400 rpm tighter, you may be ok. If you don't plan to change cams I'd look into a converter to handle WOT locking. You need to keep rpms down to 5000-5200 yet spool a 67mm.

I Agree, but I have a 109mph at 1000 ft @ 5500 rpm with 3.42 & 27.1" tire. (19% slippage) Hoping to get around 9 or 10% and should be ok then. I guess I will see.

I got about a yr to worry about the bigger motor (building a de-tuned TSM motor). As long as I get a sub 10% slippage rate we should be good.

 

[Blazer406]

Well, after hitting test and tune road, the car shifted at 4475 at 65mph with a 26" tire. The calculator shows 55% slippage but that is based on the quarter, anyone guess what it would really be?

You need to do it with a datalog.... and at the track.... the track gives an accurate MPH at the traps... you get your RPM's off the datalog just as you let off.... assuming you let off right after the traps..... then run your numbers in the calculator....

It would be difficult to get usable results from watching speed and RPMS..... IMHO.

In God I trust.... others must provide data!

 

[jerrad]

You need to do it with a datalog.... and at the track.... the track gives an accurate MPH at the traps... you get your RPM's off the datalog just as you let off.... assuming you let off right after the traps..... then run your numbers in the calculator....

It would be difficult to get usable results from watching speed and RPMS..... IMHO.

In God I trust.... others must provide data!

I like that. :biggrin:

What do you think about doing it on a dyno? There is one about 30 minutes from my house while the track is 2 hours from the house.:frown:

 

[Blazer406]

I like that. :biggrin:

What do you think about doing it on a dyno? There is one about 30 minutes from my house while the track is 2 hours from the house.:frown:

If the dyno can give you a good (simulated) MPH... and you get a good log somehow (DS or Powerlogger)..... of the RPM's..... it might be fine..... on a dyno.... maybe visual ID of the RPM's when you let off will be adequate...

Biggest difference... is the car will be loaded harder at the track.... due to wind resistance on our brick shaped cars.... might skew the results a little... but the dyno will be better than nothing....

 

[Dusty Bradford]

I Agree, but I have a 109mph at 1000 ft @ 5500 rpm with 3.42 & 27.1" tire. (19% slippage) Hoping to get around 9 or 10% and should be ok then. I guess I will see.

I got about a yr to worry about the bigger motor (building a de-tuned TSM motor). As long as I get a sub 10% slippage rate we should be good.

I agree with that as well. It's just wierd that a converter that only goes 2400 rpm at 0# will slip that much..it's unusual. You'd almost have to have a 2000 rpm stall to get the efficiency down. to match the rpm range of the engine. With the engine laying over up top, it's almost like the converter isn't fully coupling after the gear changes.

What's the rpm dropping to at the gear change?

 

[jerrad]

Went and farted around a little bit. I upped the boost to 24/25 and the 02's were at 734, 0 knock and the egt was 1526.
My egt's look a little fat but the 02's look a little lean. Should I add a little bit of fuel?

 

[Blazer406]

Went and farted around a little bit. I upped the boost to 24/25 and the 02's were at 734, 0 knock and the egt was 1526.
My egt's look a little fat but the 02's look a little lean. Should I add a little bit of fuel?

As long as you don't have knock.... then no... I wouldn't touch the fuel....

If you are running at the track.... then let her rip.....

If that is the DD tune.... I might fatten it up otherwise......

What is the timing again?

You running pump gas and alky?

 

[jerrad]

I can't remember the timing, it's whatever Eric puts in the alky chip. I'm thinking around 23*

Yes pump and alky.

Going to the dyno tomorrow to see what rpm/mph I am so hopefully we can figure out if the convertor is too loose.