Rear Gear Selection for a 200 MPH GT? Who's done one?

[sheizasosay]

I did it with my car when I had the Procharged 4.6, 734whp, 3.31 gears, and a Liberty built 3650. Once I hit 200 mph, the coolant temps were 240 degrees. Shifting from 4th to 5th is a big drop in RPM so I ran the car to 7500 RPMs in 4th which dropped the RPMs to 5100 in 5th. I lifted at 6200 rpms which was 218 mph. This high speed run overheated the diff and damaged parts.

What all aero did you have on your car to push an S197 to 218mph with 734rwhp? And did you lift at 6200rpms because it wasn't pulling anymore or did you run out of road? This a standing mile type event?

 

[marcspaz]

Wow... lots of great info! Thanks for all the feedback guys! This is exactly the type of info/feedback I was hoping for. I am going to do some product and method research and see which way might be a direction I would like to go.

I am sure I am going to have more questions, but I'm thankful for the responses. Thanks a bunch guys.

Spaz

 

[Marc s]

What all aero did you have on your car to push an S197 to 218mph with 734rwhp? And did you lift at 6200rpms because it wasn't pulling anymore or did you run out of road? This a standing mile type event?

When I did my top speed event, It was on a 5 mile asphalt course. The car quit gaining speed after about 4 miles which was 6200 RPMs. Just before I lifted, the RPMs started to rise again and the car was moving around. There was so much heat and windage in the diff, that my right rear axle seal melted and oil was spraying onto the tire. The gear oil temps were 330 degrees. I had a splitter, APR rear wing set at .75 degree AOA, removed side mirrors with CJ covers, hood vents, taped off all of the seams, and blocked off the brake cooling ducts.

 

[Department Of Boost]

When I did my top speed event, It was on a 5 mile asphalt course. The car quit gaining speed after about 4 miles which was 6200 RPMs. Just before I lifted, the RPMs started to rise again and the car was moving around. There was so much heat and windage in the diff, that my right rear axle seal melted and oil was spraying onto the tire. The gear oil temps were 330 degrees. I had a splitter, APR rear wing set at .75 degree AOA, removed side mirrors with CJ covers, hood vents, taped off all of the seams, and blocked off the brake cooling ducts.

Any idea what it was running at the mile mark?

I was just looking at your sig. I thought your car made something like 660hp (there was a dyno video up somewhere). How did you get it to make 817hp? That's a BIG swing NA.

817 hp Roush/Yates 358ci NASCAR Cup engine

 

[Marc s]

Any idea what it was running at the mile mark?

I was just looking at your sig. I thought your car made something like 660hp (there was a dyno video up somewhere). How did you get it to make 817hp? That's a BIG swing NA.

My last mod motor made just under 750 corrected whp. On this dyno run, the belt slipped at the end of the pull so the hp nosed over. I resolved the belt slip issue but never had the car back on the dyno. Without the belt slip, it probably made more whp but I have know way to confirm it. My current NA engine made 817 at the flywheel on an engine dyno. I never dynoed my NA engine in 4th gear so I don't know what it makes at the ground in high gear. I got the tune dialed in useing 3rd gear because I didn't want the 4th gear tire speed on the dyno.

 

[Department Of Boost]

My current NA engine made 817 at the flywheel on an engine dyno.

Gotcha, I figured you worked off the new standard (rwhp) like everyone else.

 

[sheizasosay]

817rwhp NA from the rear tire out of 347 cubes would be......like Godzilla's dick: scary...yet impressive some how, but still science fiction. There goes goddamn godzilla and his big ole' science fiction penis just wreckin' Tokyo. Then the movie would stop and Godzeerah would take off his mask and be like "it's hot in this suit". I feel like I have referenced a dick too many times for one post.

This thread makes me want to buy aero stuff. I need to get rid of that cowl induction hood. What was I thinking?

 

[Department Of Boost]

My current NA engine made 817 at the flywheel on an engine dyno.

Was that when it was at Roush/Yates?

 

[Marc s]

Was that when it was at Roush/Yates?

It made 775 at the flywheel as delivered to me from Yates in superspeedway restrictor plate trim. I removed the restrictor plate intake and bought a X351 SVO short track/road race manifold from Yates and had it ported, flowed, epoxied, and then flowed again. I also removed the solid flat tappet cam and had it spun on a cam doctor so I could get a cam card. I emailed the cam card over to Crane and had them grind me a solid roller that had the same specs. The intake, 950 cfm carb, and roller cam allowed the engine to produce 817 at 8400 RPMs.

 

[BadPiggy]

It made 775 at the flywheel as delivered to me from Yates in superspeedway restrictor plate trim. I removed the restrictor plate intake and bought a X351 SVO short track/road race manifold from Yates and had it ported, flowed, epoxied, and then flowed again. I also removed the solid flat tappet cam and had it spun on a cam doctor so I could get a cam card. I emailed the cam card over to Crane and had them grind me a solid roller that had the same specs. The intake, 950 cfm carb, and roller cam allowed the engine to produce 817 at 8400 RPMs.

I've seen that epoxy word a few times lately. Care to explain what it is, how it's done, why do it, what areas of the engine you do it to, what it helps...to a novice?

I'm curious to know about it.
Thanks!

 

[Marc s]

I've seen that epoxy word a few times lately. Care to explain what it is, how it's done, why do it, what areas of the engine you do it to, what it helps...to a novice?

I'm curious to know about it.
Thanks!

The short version is to balance the flow between the intake runners, the cross section area of the intake port, and to change the shape of the intake plenum. To get good flow numbers, bigger isn't always better so epoxy is used to reshape the port and/or the port entry. To obtain good HP numbers, sometimes less flow is better because port velocity at a certain RPM is what's really important. The cross section area in relationship to valve diameter versus valve angle is a what generally delivers the best power as long as the camshaft profile is matched too.

 

[Department Of Boost]

The intake, 950 cfm carb, and roller cam allowed the engine to produce 817 at 8400 RPMs.

You put it back on a engine dyno before you put it in the car?