Viper motor gurus need advice on how to get to 550whp

[Steve M]

I took for granted the 0.75 ratio on the gen 3's 5th gear but it seems to be 0.74, which makes more sense now. My ''tire correction factor'' is now 27.52'' for that 355 ACR tire 50% wear. I triple-checked with the 4th gear and it matches almost perfectly (66mph @ 3,000rpm).

The only thing left that is a little off is the top speed at rev limit (6,250): on the simulator its 77.1 mph @ 2nd gear while I get constant 79mph GPS reading. So either the rev limiter is not precise or the car continues to accelerate a little after cut off...

But anyways, I placed the order for the 4.10 gears to go along my high-rev engine and on the simulator I get 76.3mph @ 6,800rpm, so very similar... And max of 135.8 mph in 4th gear, which is about the max trap speed on 1/4 mile I will be able to go. If I'm lucky, I will be able to set the rev limiter to 7,000rpm for 140mph. I'm not building a drag car at all, but would be interesting to give it a try.
Also, on my local racetrack the maximum I would be able to go on the stretch is about 135-138mph, which is perfect as I will use mostly 3rd and 4th gears.

Yeah, there's all sorts of conflicting info out there on gear ratios, rev limits, etc. For the gear ratio side, you really need the tooth count, which can be hard to come by.

For drag racing, keep in mind that your trap speed is averaged over the last 66 feet of the run. Your instantaneous speed as you cross the finish line will be higher than that trap speed indicated on the time slip...I'll have to see if I can tell from the data and video I have of my runs what that number looks like.

For reference, my car with 3.55s, 335/30-18 Hoosier drag radials, an estimated ~3,650 race weight, and what I'd guess is around 520 at the wheels (never measured) has trapped a best of nearly 131 MPH. If you are expecting significantly more power (and it looks like you are), 4.10s may be too much gear. You can definitely help that by running a 28" tire (like the MT or M&H 345/35-18), but that is a significantly heavier setup than the Hoosiers. An in-between would be a 345/30-19 drag radial. If you are thinking about showing up to the drag strip on something other than a drag radial, don't. You'll end up frustrated at best, and at worst you'll end up in the wall. I was almost taken out by a Mustang on street tires a couple years ago that lost control and crossed the center line...eye opening for sure.

[TKO MOTORSPORTS TEAM]

I took for granted the 0.75 ratio on the gen 3's 5th gear but it seems to be 0.74, which makes more sense now. My ''tire correction factor'' is now 27.52'' for that 355 ACR tire 50% wear. I triple-checked with the 4th gear and it matches almost perfectly (66mph @ 3,000rpm).

The only thing left that is a little off is the top speed at rev limit (6,250): on the simulator its 77.1 mph @ 2nd gear while I get constant 79mph GPS reading. So either the rev limiter is not precise or the car continues to accelerate a little after cut off...

But anyways, I placed the order for the 4.10 gears to go along my high-rev engine and on the simulator I get 76.3mph @ 6,800rpm, so very similar... And max of 135.8 mph in 4th gear, which is about the max trap speed on 1/4 mile I will be able to go. If I'm lucky, I will be able to set the rev limiter to 7,000rpm for 140mph. I'm not building a drag car at all, but would be interesting to give it a try.
Also, on my local racetrack the maximum I would be able to go on the stretch is about 135-138mph, which is perfect as I will use mostly 3rd and 4th gears.

If your within 2 mph and couple hundred RPM below 100mph your are doing pretty good. Top speed estimates you will find your speed will be off. Calculators and formulas are usually " LAB" conditions so no real comp for aero drag, or parasitic drag. Simulators have some comps that make them a little more accurate but not much. Real world testing is the only true data you can trust to see if your #s are on.
At the end of the day unless your qualifying and the top 5 cars are separated by 1-2/ 10ths all these calculations are over kill; BUT if you dig this type of stuff its interesting and fun basic race engineering.

[Aevus]

Yeah, there's all sorts of conflicting info out there on gear ratios, rev limits, etc. For the gear ratio side, you really need the tooth count, which can be hard to come by.

For drag racing, keep in mind that your trap speed is averaged over the last 66 feet of the run. Your instantaneous speed as you cross the finish line will be higher than that trap speed indicated on the time slip...I'll have to see if I can tell from the data and video I have of my runs what that number looks like.

For reference, my car with 3.55s, 335/30-18 Hoosier drag radials, an estimated ~3,650 race weight, and what I'd guess is around 520 at the wheels (never measured) has trapped a best of nearly 131 MPH. If you are expecting significantly more power (and it looks like you are), 4.10s may be too much gear. You can definitely help that by running a 28" tire (like the MT or M&H 345/35-18), but that is a significantly heavier setup than the Hoosiers. An in-between would be a 345/30-19 drag radial. If you are thinking about showing up to the drag strip on something other than a drag radial, don't. You'll end up frustrated at best, and at worst you'll end up in the wall. I was almost taken out by a Mustang on street tires a couple years ago that lost control and crossed the center line...eye opening for sure.

Thanks for the advice Steve, yeah if I were to be serious about drag race I would probably not put 4.10 gears. But since I will use mostly my car on the street and I already have 3.73, I will go to 4.10. Especially since I might lose a bit of torque in the low-end with that upcoming big camshaft..

[Aevus]

BUT if you dig this type of stuff its interesting and fun basic race engineering.

THAT.

[Aevus]

If you are expecting significantly more power (and it looks like you are)

Minimum target is 620whp, hopefully 650whp.

[Dan Cragin]

You will need an external oil pump to run 7000 rpm in a Gen 2 Viper engine.
The production pump cavitates at 6300 rpm.
Kevin at EED has an external pump setup with modified pan. The pan is used
for the sump so a full dry sump system does not need to be used.
You will need updated valvetrain and lifters.

[Aevus]

Dan, I don't think AIllick (OP) is looking for 7,000rpm on his gen 2, I do but on a gen 3.

:-)

[Aevus]

For the oil system, I have the Compe coupe swing arm pan and I just got that installed:

https://store.prefix.com/products/ge...rotor-oil-pump