Do 3.55 gears really lower indicated HP?

[Tagoo]

I've been pondering this question as I'm getting ready to do a gear swap on my car (540whp NA still feels a little slow). I've read a bunch of posts where people are quick to say that shorter rear gears reduce the indicated HP on a dyno. If this is true it stands to reason that putting even taller gears (say 2.50:1 gears) would yield a higher HP number. Is that true? Does anyone have actual back to back dyno experience that supports the lower HP assertions?

I could understand transmission gearing making a difference when a ratio other than 1:1 is used. But I just don't get it with rear end gears. If I were to guess, I'd think that shorter gears would exagerate HP on a dyno due to the quicker acceleration. Of course, I'm assuming dynos use acceleration to estimate HP.

Thanks in advance for sharing your knowledge - I'm just trying to get smarter

 

[Black Moon]

I've been pondering this question as I'm getting ready to do a gear swap on my car (540whp NA still feels a little slow). I've read a bunch of posts where people are quick to say that shorter rear gears reduce the indicated HP on a dyno. If this is true it stands to reason that putting even taller gears (say 2.50:1 gears) would yield a higher HP number. Is that true? Does anyone have actual back to back dyno experience that supports the lower HP assertions?

I could understand transmission gearing making a difference when a ratio other than 1:1 is used. But I just don't get it with rear end gears. If I were to guess, I'd think that shorter gears would exagerate HP on a dyno due to the quicker acceleration. Of course, I'm assuming dynos use acceleration to estimate HP.

Thanks in advance for sharing your knowledge - I'm just trying to get smarter

I don't see how it could possibly make a difference.

 

[Russ M]

It does but only seems about 10-15rwhp. The shorter gears have more teeth which in turn causes more parasitic loss, so yes if you go longer gears it will have the opposite effect.

On a side note I would have you seriously consider changing gears, your car may feel quicker but it wont be unless you are on R compound or better tires. If you put gears on a viper with normal wear tires all you are going to do is spin more especially with your power increase.

 

[JonB]

The driveline drag is minimal, probably under 1% additional.

Unless you have sticky-tires, the 0-60 FT might be slower, if its wasted on wheelspin. Lightened Flywheel helps minimize wheelspin as well.

But once its hooked up, [ie by 25 mph?] the car accelerates proportionately quicker in all gears, and slows quicker too. And SQUIRTS out of corners....be careful-er.

Great Bang-4-Buck Mod, probably the BEST

 

[Black Moon]

On a side note I would have you seriously consider changing gears, your car may feel quicker but it wont be unless you are on R compound or better tires. If you put gears on a viper with normal wear tires all you are going to do is spin more especially with your power increase.

I'd have to disagree from personal experience. 355's were a huge difference with PS2's before and after. You could spin the tires easier if you wanted to but if driven correctly you will be happy with the change. Someone would have to prove the power loss to me on a dyno.

 

[BW96snake]

HP = rpm x tq)/5250
You might get less rpm but more tq to the ground but the hp would be the same (with no changes).

There is only a slight loss due to increased friction of the 3:55 ring.

 

[Black Moon]

The driveline drag is minimal, probably under 1% additional.

Unless you have sticky-tires, the 0-60 FT might be slower, if its wasted on wheelspin. Lightened Flywheel helps minimize wheelspin as well.

But once its hooked up, [ie by 25 mph?] the car accelerates proportionately quicker in all gears, and slows quicker too. And SQUIRTS out of corners....be careful-er.

Great Bang-4-Buck Mod, probably the BEST

Jon gave me a great deal on my gears and everything he says is dead on (at least everything he says about the gears) Sorry Jon I had to throw that in. I've been in a ball busting mood all day.
Sal

 

[Black Moon]

I've been pondering this question as I'm getting ready to do a gear swap on my car (540whp NA still feels a little slow). I've read a bunch of posts where people are quick to say that shorter rear gears reduce the indicated HP on a dyno. If this is true it stands to reason that putting even taller gears (say 2.50:1 gears) would yield a higher HP number. Is that true? Does anyone have actual back to back dyno experience that supports the lower HP assertions?

I could understand transmission gearing making a difference when a ratio other than 1:1 is used. But I just don't get it with rear end gears. If I were to guess, I'd think that shorter gears would exagerate HP on a dyno due to the quicker acceleration. Of course, I'm assuming dynos use acceleration to estimate HP.

Thanks in advance for sharing your knowledge - I'm just trying to get smarter

I just put a Paxton on my car and bought a Gen4 complete diff. I may swap it out soon in order to go back to the 307 gear rather than spending another $300 having the gears set up. The 355's are barely broken in with 300-350 miles on them. I will be selling the complete diff. if someone is interested. I know I probably shouldn't say that here since Vendors like Jon can't advertise on threads but I just did so I apologize.

 

[Russ M]

I'd have to disagree from personal experience. 355's were a huge difference with PS2's before and after. You could spin the tires easier if you wanted to but if driven correctly you will be happy with the change. Someone would have to prove the power loss to me on a dyno.

Assuming the driver is competent, learns how to drive the car properly and is good at it I would agree with you. However during real world driving where traction always varies the people with 3.07 have shown to be quicker at least in my experience. Off course there is always people out there that practice practice practice, but they are few and far between.

 

[Black Moon]

Assuming the driver is competent, learns how to drive the car properly and is good at it I would agree with you. However during real world driving where traction always varies the people with 3.07 have shown to be quicker at least in my experience. Off course there is always people out there that practice practice practice, but they are few and far between.

Oh, if you're talking off the line in a drag racing situation then you're correct. I was refering to just hard road driving not from a dead stop.

 

[Russ M]

I just put a Paxton on my car and bought a Gen4 complete diff. I may swap it out soon in order to go back to the 307 gear rather than spending another $300 having the gears set up. The 355's are barely broken in with 300-350 miles on them. I will be selling the complete diff. if someone is interested. I know I probably shouldn't say that here since Vendors like Jon can't advertise on threads but I just did so I apologize.

Gen 4's diffs don't fit Gen 2's, otherwise it would be a smart move.

 

[Tagoo]

On a side note I would have you seriously consider changing gears, your car may feel quicker but it wont be unless you are on R compound or better tires. If you put gears on a viper with normal wear tires all you are going to do is spin more especially with your power increase.

Thanks Russ. I've got drag radials for traction. I'm already going into 4th before the end of the quarter, so there won't be adding another shift. Also, on freeway pulls, the stock gears just don't pull hard until about 4K. Hoping gears will help that.

 

[Rizzo]

From my motorbike days I have to wonder if gear changes make you any faster overall. On a bike its very simple to change gears and \i tried a bunch of different gears to see if any if them made a difference. My buddy and would go out and do a ton of roll ons and see where we would be. Our bikes stock were almost exactly the same up to 150 mph and then mine would pull away. I would go and change the front gear down 1 tooth first and then we would go back and do the same roll ons. We would try everything from different rpms etc. The only difference was in the shift points but at 150 mph we were still side by side. Back to the garage and I would go down 1 more tooth to see what that would do. Same results just different shift points but at the end of the race we would still be side by side. The gear changes made no difference as to how fast I was to 150 mph. I just dont buy
that gear changes make a difference in how fast a car is but thats just from my experiments.

 

[Paul Hawker]

Gear changes can indeed make a difference in 1/4 mile or 1,000 ft times. Depending on how many shifts you make, and what gear you end up at the finish line.

Otherwise most Vipers will accelerate in a similar fashion. Shorter gears will tend to spin tires more.

It has been well documented that the stock gears tend to do best on dyno pulls, with aftermarket gears showing slightly lower max hp. Never saw a really well explained reason of why this occures, but it has shown up many times over the years.

Lower gears certaintly feel faster, the Viper revs faster, makes more noise, and slithers around a bit, just on the edge of traction. Great fun.

 

[dave6666]

I've been pondering this question as I'm getting ready to do a gear swap on my car (540whp NA still feels a little slow). I've read a bunch of posts where people are quick to say that shorter rear gears reduce the indicated HP on a dyno. If this is true it stands to reason that putting even taller gears (say 2.50:1 gears) would yield a higher HP number. Is that true? Does anyone have actual back to back dyno experience that supports the lower HP assertions?

I could understand transmission gearing making a difference when a ratio other than 1:1 is used. But I just don't get it with rear end gears. If I were to guess, I'd think that shorter gears would exagerate HP on a dyno due to the quicker acceleration. Of course, I'm assuming dynos use acceleration to estimate HP.

Thanks in advance for sharing your knowledge - I'm just trying to get smarter

 

[Glen97]

I don't know about the HP numbers but seat of the pants the 355's are a lot more fun!

 

[Russ M]

dave6666,

Gearing is something you always play around with on drag cars, so tbh I cant even remember how many times I have swapped the gearing on my track cars, only problem is they are not vipers. On supras however going from a 3.73 to a 4.11 and then to 4.30's then to 3.90's etc etc was common for me. The dyno numbers change based on what type of gear you have 10 hp was the most I had ever seen, and who knows how much of that was day to day air changes which the correction could not factor out, but I feel fairly confident in my results.

 

[bluesrt]

It does but only seems about 10-15rwhp. The shorter gears have more teeth which in turn causes more parasitic loss, so yes if you go longer gears it will have the opposite effect.

On a side note I would have you seriously consider changing gears, your car may feel quicker but it wont be unless you are on R compound or better tires. If you put gears on a viper with normal wear tires all you are going to do is spin more especially with your power increase.

boss u r getting way to technical here- put some lower gears in it if you want a better power feel- i think thats what the guy is after

 

[Red Snake]

I can't explain the physics or engineering involved but I have had this discussion with my tuner, who has literally dyno'd hundreds of Vipers and other performance vehicles. He told me that installing a shorter gear (numerically higher) will cause the peak hp numbers to read slightly lower on a dyno.

 

[dave6666]

dave6666,

Gearing is something you always play around with on drag cars, so tbh I cant even remember how many times I have swapped the gearing on my track cars, only problem is they are not vipers. On supras however going from a 3.73 to a 4.11 and then to 4.30's then to 3.90's etc etc was common for me. The dyno numbers change based on what type of gear you have 10 hp was the most I had ever seen, and who knows how much of that was day to day air changes which the correction could not factor out, but I feel fairly confident in my results.

Oh I believe all of it w/o proof. It has been said before, I read it, and believe it. I was just trying to get back to the OP's question of prove it to me. I went with the 3.73 for the fun factor. Could care less what it does on the rollers.

 

[Tagoo]

Dave's got it. I was really looking for actual data. As I searched this board for 3.55 info, every thread had people saying "oh ya, 3.55s will totally drop your dyno numbers, dude" <sarcasm>. I really wanted to hear from people who had objective info to share, not just subjective opinion.

Russ and Rizzo gave me exactly what I was looking for. I know my current dyno/ET/Trap numbers. Just trying to fully inform myself before I jump to new gears. Thanks all!

 

[Vital Velocity]

I have the 355 with a paxton, I'd like opinions from those who have had 355 and 307 with paxton cars

 

[SquadX]

I have 355 with paxton and it revs quicker for sure and seems to stay in powerband or get there quicker (alum. flywheel as well). In 5th my car pulls very well. Many times I will cruise in 5th around 60, floor it, and hit 150 fairly quick (without shifting) while on mexican soil.

The flip side, I shift more as I run out of rpms. I think two vipers equal power, one with stock gear and the other 355s, the stocked geared viper would make up ground around the top of 3rd and be even and start to pull in 4th. The stock geared viper would be in 4th while the 355 viper would be in 5th. Im looking to back to stock gearing and was interested in doing something in the 2.90ish range but its not available. Again this is a GTS im referring to, SRT has higher rpm range and would fair better.

Now a 5th and 6th gear swap, i think would really benefit 355s in the high mphs.

Gas mileage will **** but I try not to think about filling up twice in a day of driving, lol.

Hope something I wrote helps.

 

[SquadX]

When Plum and I finally hook up to do some pulls in Mexico, one of us will post as my hp is slightly lower but enough to get some type of comparison.

 

[eucharistos]

please do squadx

 

[Andrew2KRT10]

do it, was the best upgrade i ever did, the car snaps, more responsive, fast ! So what if at the end of the Pocono stretch you have to hit 5th after spraying the whole way, it's worth it

 

[Vipuronr]

So, mind if I jump in here....seeing as I drive my mostly on back roads, occasionally on highways and never on track, do you feel it is worth it to go to 3.55's? If it tends to make the car break loose, is it worth making the change! Car is only slightly modded and no SC/Paxton.

In the "old days' changing the rear end was very common in muscle cars, but they were all about straight-line acceleration.

Thanks!

(CAVEAT: If I've misspelled anything in the above post, I apologize in advance to Dave)

 

[costanZo]

I remember reading if you're running 19s in front and 20s in the rear having 3:73 gears feels like you have 3:45 gears, since that would be the equivalent. I believe Dave stated that.

So if I currently have stock 3:07 gears, what would my gears supposedly be compared to? Considering I'm also running 19" wheels front, and 20" wheels in the rear.

 

[jrod_okc]

When i get my tranny fixed Joel, we will have to go for a friendly run.

 

[JoelW]

I just got a 3.55 set from JonB and they are not quite broken in yet but it is more fun to drive on backroads. 5th gear is now the old 4th gear - give or take a few RPM but 1st thru 4th are much more usable.