squarles67

Have you noticed any difference in power with the downpipe change?

slocaddy

No, power wise feels the same, blows the tires off just as it did before,
Only reason I did the 5" to begin with was just cause I could, and I thought it would be "cool"..........yea not cool........

I think I will chop up the rest of the 5" stuff and make myself a "race" exhaust that dumps out behind the front tire under the pass side fender, maybe it will shoot fire!!!!

forcd ind

iTrader: (7)

How much clearance did you gain going to oval pipe, I was thinking of that for my 4" where the floor is tight.

Project GatTagO

iTrader: (7)

Based on that calculator, critical speed is about 4300rpm (using 3.5" diameter, 0.250 wall thickness, and 72" length, aluminum material)...That's not very high!

What is your R&P ratio, and tire height?

Andrew

slocaddy

I did measure length of drive shaft, it's 69" u joint center to center. Gears are 3.73, and tire height is 28"

slocaddy

It's only 2" high now, worked out great.
when it was 5" I only got it down to 3"

Project GatTagO

iTrader: (7)

With the new information and assuming .250" wall thickness of the driveshaft tube, critical speed is just under 4700rpm. With your gear and 28" tall tires, you will reach that driveshaft critical speed at 105mph.

I definitely wouldn't put this thing on a chassis dyno. Dyno runs are done in direct drive (1:1 on whatever transmission you are using), so at 6500 engine RPM, the driveshaft speed will be, well, 6500RPM at a theoretical vehicle speed of 147 mph.

Keep all that in mind when you're doing highway pulls!

Andrew

Here is a tech bulletin from Mark Williams, but it does not go as high as 69"

https://www.markwilliams.com/servicebull/sb0049.pdf

slocaddy

Interesting, that the car is limited to 105 right now, and that's the calculation you came up with......

Project GatTagO

iTrader: (7)

How is the car limited to 105mph?

Andrew

slocaddy

Not sure, it was a surprise to me when I went to Mexico and accelerated quite brisk and it basicly felt like I shut it off.....did it 3 times and each time it was at 105......
Now, I'm not saying that the Speedo is calibrated correctly, but it is limited none the less......

Bad Apache

Most factory PCM's have a built in speed limiter based on the original vehicle/tires. By coincidence, my buddies 2500hd stops dead at 105mph.

slocaddy

Yea, it was quite the surprise, I thought "well, I didn't hear anything go boom"..........

Bad Apache

I have a damaged driveshaft from a '99 K1500. Let me measure the thickness. I seem to remember it being much thinner than the guestimated 1/4 thickness. Not sure how much difference that would make in the calculations.

Bad Apache

Better late then never. 5" diameter and .075 wall thickness. It's a larger diameter than yours, but gives you an idea how thin the aluminum is.

slocaddy

So what's the remedy? 2 peice drive shaft? Steel?

If I had done a two peice, that could have changed what I had to do my floor/trans tunnel .........

Don't want to have to stay under 105 on Mexican roads..........

BudRacing

iTrader: (3)

I'd go 2 piece if I were you. With a turbo, you'll want to test this things limits at some point. The limit of the driveshaft is not something you want to find out, though.

squarles67

I'd call a driveshaft company like PST and ask them.

As I understand it the larger the diameter the higher the critical speed. The strength and weight of the material also affects the calculation.

Bad Apache

^^^ X2. They'll get you straightened out. The built-in limiter needs disabled also. Your driveshaft situation has me wondering about mine. Mine is steel. Wonder if it would be close to the right length for your car? I'll try to measure it and let you know. Then you could salvage yard one up.

slocaddy

Lol! That's damn near every drive in this thing

SQRBODYLSFREEK

Looking good, glad to see you're still going!! Question for you though - do you still have the old 500 and trans?? Accessories?? My plans have changed slightly in that I need to get it a running and driving car ASAP so I can start enjoying it. I decided a running driving project will be best for now. Let me know!! I may be interested in getting some stuff from you....