Rear drivetrain strength
Thread Starter
Pro
Joined: Jul 2005
Posts: 517
Likes: 7
From: Peoria IL
Rear drivetrain strength
OK, I'll admit this is probably an example of "bad planning" but I've started preparing a 400hp engine for my C3 and I have no idea whether or not the IRS is a strong enough design to support this power level. I have searched this forum, but the overwhelming majority of you are far more "off the hook" than what I'm building. The transmission is a TH350 soon to receive a shift kit, modulator valve, filter & governor programming kit. I plan to shift at 5800 RPM.
This is purely a street toy, however I will take it to the track on the occasional day that my friends go too. I have a 520hp Camaro that I'm finishing up too for my "serious" toy (TH400, 9" rear, etc) so I won't be tempted to do much more than this with the 'vette in the future. I have no interest in putting nitrous, etc. in the car in the future.
The rear end in the car is well maintained but 100% stock configuration. It's a '76, and I believe the gear ratio is 3.08 (to be checked in coming days).
My main question is this: Should I be worried about the rear suspension/differential, half shafts, etc?
By the way, where is the build sheet usually hidden?
This is purely a street toy, however I will take it to the track on the occasional day that my friends go too. I have a 520hp Camaro that I'm finishing up too for my "serious" toy (TH400, 9" rear, etc) so I won't be tempted to do much more than this with the 'vette in the future. I have no interest in putting nitrous, etc. in the car in the future.
The rear end in the car is well maintained but 100% stock configuration. It's a '76, and I believe the gear ratio is 3.08 (to be checked in coming days).
My main question is this: Should I be worried about the rear suspension/differential, half shafts, etc?
By the way, where is the build sheet usually hidden?
Le Mans Master
Joined: Apr 2001
Posts: 5,000
Likes: 1
From: Minneapolis, Mn USA
The Van Steel catalog claims the IRS developed for the 63 (iron rear) is capable to support 500HP. I suppose this is with tire technology of 1963 as well.
Anyone else heard such a rumor?
Anyone else heard such a rumor?
Thread Starter
Pro
Joined: Jul 2005
Posts: 517
Likes: 7
From: Peoria IL
Hmmm, but slicks in '63 did OK, didn't they? I'm not sure if I'm exceeding the design limits or not- I also don't know if my '76 IRS design is different than the earlier BBC 4-speed C3's. Will I be taxing it badly?
Drifting
Joined: Sep 2001
Posts: 1,427
Likes: 1
From: Boxford Mass
With stock tires, you have nothing to worry about. They will break loose before any damage occurs (to a point). If you get into slicks, wider tires, etc... well its the traction that tends to break things.
I'm also running a 400 with a stock rear suspension for now.
I'm also running a 400 with a stock rear suspension for now.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
500 HP is about the max for a Chevy 12-bolt (solid axle) with an 8.875" ring. The stock IRS and diff. with the 8.375 incher would snap something with any traction at all and 500 HP, in my opinion.
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Le Mans Master
Joined: May 2002
Posts: 5,086
Likes: 786
From: Lebanon Township New Jersey
You're not using the original 32 year old U joints, are you? At least change all 6 with Spicer solid units. If you are going to use drag radials you shoud have the center section rebuilt, and get rid of those 3.08 gears.
Safety Car
Joined: Oct 2006
Posts: 3,930
Likes: 15
From: Calgary Alberta
Thread Starter
Pro
Joined: Jul 2005
Posts: 517
Likes: 7
From: Peoria IL
Thinking out loud:
Unless I'm on the track and using drag radials, it should be perfectly capable of doing a rolling burnout through all three gears with 400hp. Changing the gears won't make it any faster off the line on the street, and the 3.08 gears should give the halfshafts and U-joints an easier life, shouldn't they?
This is a pure street machine in every respect, I'm not building it for the track. I'm not saying I'll never take it down the strip once or twice, but that's not its intent. If drag radials will just tear up the differential, I won't use them.
U-joints sound like an excellent idea. Who sells the solid ones? How do I figure out the right part numbers?
Unless I'm on the track and using drag radials, it should be perfectly capable of doing a rolling burnout through all three gears with 400hp. Changing the gears won't make it any faster off the line on the street, and the 3.08 gears should give the halfshafts and U-joints an easier life, shouldn't they?
This is a pure street machine in every respect, I'm not building it for the track. I'm not saying I'll never take it down the strip once or twice, but that's not its intent. If drag radials will just tear up the differential, I won't use them.
U-joints sound like an excellent idea. Who sells the solid ones? How do I figure out the right part numbers?
Safety Car
Joined: Oct 2006
Posts: 3,930
Likes: 15
From: Calgary Alberta
Thinking out loud:
Unless I'm on the track and using drag radials, it should be perfectly capable of doing a rolling burnout through all three gears with 400hp. Changing the gears won't make it any faster off the line on the street, and the 3.08 gears should give the halfshafts and U-joints an easier life, shouldn't they?
This is a pure street machine in every respect, I'm not building it for the track. I'm not saying I'll never take it down the strip once or twice, but that's not its intent. If drag radials will just tear up the differential, I won't use them.
U-joints sound like an excellent idea. Who sells the solid ones? How do I figure out the right part numbers?
Unless I'm on the track and using drag radials, it should be perfectly capable of doing a rolling burnout through all three gears with 400hp. Changing the gears won't make it any faster off the line on the street, and the 3.08 gears should give the halfshafts and U-joints an easier life, shouldn't they?
This is a pure street machine in every respect, I'm not building it for the track. I'm not saying I'll never take it down the strip once or twice, but that's not its intent. If drag radials will just tear up the differential, I won't use them.
U-joints sound like an excellent idea. Who sells the solid ones? How do I figure out the right part numbers?
Le Mans Master
Joined: Jul 2000
Posts: 6,664
Likes: 162
From: columbia city in
OK, I'll admit this is probably an example of "bad planning" but I've started preparing a 400hp engine for my C3 and I have no idea whether or not the IRS is a strong enough design to support this power level. I have searched this forum, but the overwhelming majority of you are far more "off the hook" than what I'm building. The transmission is a TH350 soon to receive a shift kit, modulator valve, filter & governor programming kit. I plan to shift at 5800 RPM.
This is purely a street toy, however I will take it to the track on the occasional day that my friends go too. I have a 520hp Camaro that I'm finishing up too for my "serious" toy (TH400, 9" rear, etc) so I won't be tempted to do much more than this with the 'vette in the future. I have no interest in putting nitrous, etc. in the car in the future.
The rear end in the car is well maintained but 100% stock configuration. It's a '76, and I believe the gear ratio is 3.08 (to be checked in coming days).
My main question is this: Should I be worried about the rear suspension/differential, half shafts, etc?
By the way, where is the build sheet usually hidden?
This is purely a street toy, however I will take it to the track on the occasional day that my friends go too. I have a 520hp Camaro that I'm finishing up too for my "serious" toy (TH400, 9" rear, etc) so I won't be tempted to do much more than this with the 'vette in the future. I have no interest in putting nitrous, etc. in the car in the future.
The rear end in the car is well maintained but 100% stock configuration. It's a '76, and I believe the gear ratio is 3.08 (to be checked in coming days).
My main question is this: Should I be worried about the rear suspension/differential, half shafts, etc?
By the way, where is the build sheet usually hidden?
Burning Brakes
Joined: Oct 2007
Posts: 816
Likes: 107
Are you talking 400hp at the flywheel or the tire there is a big difference there. If you are talking about a 400hp at the flywheel and your running an auto trans I think you will be just fine with the stock rear. Even if you ran 500 at the flywheel I think you would be fine as long as the car was not being pounded every weekend with slicks.
What converter are you running? If you are less than a 3k convereter I would not worry about the rear with an auto trans, you would never get the car to leave hard enough to break it IMHO.
What converter are you running? If you are less than a 3k convereter I would not worry about the rear with an auto trans, you would never get the car to leave hard enough to break it IMHO.
Thread Starter
Pro
Joined: Jul 2005
Posts: 517
Likes: 7
From: Peoria IL
Good point, I should have specified- 400-420hp at the flywheel. I'm running the stock Corvette converter. I'm told it's typically a good quality 2000-2200 or so stall converter in Corvettes from GM. Again, it's just a street car. The transmission is the original TH350.
Advanced
Joined: Jul 2008
Posts: 93
Likes: 0
From: Soperton Georgia
You probably need to worry about the turbo 350 more than the rear.
Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,990
From: Connecticut, USA
While the condition of vette diffs varied from one to another they share some common weak links. Your 76, if still untouched, has a good posi case with good spiders and lousy clutches. The side yokes will have endplay and the RG bolts may be the flange head type vs the older and better shoulder bolts with hardened washers.
You can build a pretty strong vette 10 bolt by tuning the posi,polishing it, installing a steel cap if you're going to launch the car,a solid sleeve, ARP RG bolts, and hardened spiders, although most st cars don't require them. Will it last forever, all depends on your usage, for a street car making a few passes it should be great, for a 600+HP drag car then you're better off with the 12 bolt.
You can find out how I do all this work and maybe do it yourself by looking up the threads. You'll need access to a mill and grinder though if plan on installing a steel cap,solid sleeve and maybe tuning the posi.
You can build a pretty strong vette 10 bolt by tuning the posi,polishing it, installing a steel cap if you're going to launch the car,a solid sleeve, ARP RG bolts, and hardened spiders, although most st cars don't require them. Will it last forever, all depends on your usage, for a street car making a few passes it should be great, for a 600+HP drag car then you're better off with the 12 bolt.
You can find out how I do all this work and maybe do it yourself by looking up the threads. You'll need access to a mill and grinder though if plan on installing a steel cap,solid sleeve and maybe tuning the posi.
Racer
Joined: Aug 2007
Posts: 267
Likes: 0
From: Brinnon Washington
While the condition of vette diffs varied from one to another they share some common weak links. Your 76, if still untouched, has a good posi case with good spiders and lousy clutches. The side yokes will have endplay and the RG bolts may be the flange head type vs the older and better shoulder bolts with hardened washers.
You can build a pretty strong vette 10 bolt by tuning the posi,polishing it, installing a steel cap if you're going to launch the car,a solid sleeve, ARP RG bolts, and hardened spiders, although most st cars don't require them. Will it last forever, all depends on your usage, for a street car making a few passes it should be great, for a 600+HP drag car then you're better off with the 12 bolt.
You can find out how I do all this work and maybe do it yourself by looking up the threads. You'll need access to a mill and grinder though if plan on installing a steel cap,solid sleeve and maybe tuning the posi.
You can build a pretty strong vette 10 bolt by tuning the posi,polishing it, installing a steel cap if you're going to launch the car,a solid sleeve, ARP RG bolts, and hardened spiders, although most st cars don't require them. Will it last forever, all depends on your usage, for a street car making a few passes it should be great, for a 600+HP drag car then you're better off with the 12 bolt.
You can find out how I do all this work and maybe do it yourself by looking up the threads. You'll need access to a mill and grinder though if plan on installing a steel cap,solid sleeve and maybe tuning the posi.
Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,990
From: Connecticut, USA
I have seen stock engined cars pushed hard that wrecked the posi clutches. All in all the 63-79's aren't bad but there were changes thru the years that need to be addressed when rebuilding. Like any job, this can be done fast and cheap or fully detailed, much more labor intensive and better built.
Sorry, just answering the question not trying to hijack.