7.5 or 8.5?

[futten]

im torn between following charlie f1`s experienced advice or my own piece of mind charlie gave me some advice on making my 7.5 stronger like the center bracing a girdle and 28 spline shafts but a secound opinion is appreciated my regal will see like 350 hp and maybe 350 lbs-ft (no on knows sins its NA engine) but also alot of weight reductions to body and a 4 speed manual is a reniforced 7.5 good enough for me?

 

[b4black]

It depends a lot on the tires you run. A street tires that spins easily is much easier on the drivetrain than a set of slicks. If the tires don't break loose, then it's the rear end that might break.

I run a stock 7.5" without concern. I'm not making 350 ft-lbs, but I run drag radials and launch with 9 psi of boost.

If you're going to do a lot of upgrades, you might want to weigh the cost of that versus the cost of a stock 8.5" which can easily hold the power.

 

[futten]

well the engine is a 3.8 that will be high compressin ported etc etc no one knows the end result of hp and torque sins no one has buildt an engine the same way so im hoping charlie is right and the 7.5 will hold and yeah im running street tires

 

[chopped39]

Run it till it breaks.

 

[fuzzyGN]

Are you going to run nitrous? If not, (or even with a small shot) no matter what you do to a N/A 3.8L you will not break the 7.5. With only 231 cubic inches there is only so much power that can be made. I would say that 350 ft/lbs is the very top end and probably very optomistic. I have run a slightly modified N/A 4.1L with a 4speed and a 7.5 rear and it was fine. I hated the clutch wear problem and added pressure plate only added to the problems. Engine thrust bearing longevity is not good with a manual trans but I digress. Weld the tubes to the center section, get a rear end girdle, and for about 200 bucks it will live a really long life. The only reason I am even considering changing mine is because the 7.5 is a C-clip axle and I am pretty sure with the new engine the car will be fast enough to require retainers. Once we get to that level, the upgrade cost does factor in. Yes my car is several hundred pounds lighter than a Regal but with a wheels up trans-brake launch it is still hitting the rear end plenty hard. IMO at your level an 8.5 is cool but a big waste of money.

 

[futten]

as said its hard to say the final result on output i mean when did you last hear of someone building a NA 3.9 to the same extent? 10-11:1 compression ported heads and intake edelbrock intake 600 holley carb and from advice from comp cams and charlie this is the cam spec roller cam blue printed internals

duration exh 230 int 236 050

490 lift

112 seperation

 

[fuzzyGN]

You mean like a 4.1L with 13:1, aluminum heads, solid roller with 260 @ .050 and 620 lift, single plane and a 750 Holley? Oh with 150 shot of nitrous to top it off? Not recently . I am guessing even on the juice only around 500hp. That is still close to 2 hp per cubic inch which is a tall order. I am not trying to discourage you but anything North of 300hp from only 231ci is pretty darn stout and nothing to be ashamed of. Again, the 7.5 will be fine. If you have a burning desire to spend money an 8.5 will also be fine but for me I'd rather spend the money on more speed parts. Or after the West Coast Nationals eye opener, more on safety equipment.

 

[futten]

oh dang! ok im pretty safe in feelin the 7.5 will hold up thanks

 

[charlief1]

Toldja.

 

[futten]

yeah yeah i know just needed some reasuranse sins i have one person sayin it wont hold and one that says it will

 

[fuzzyGN]

Don't remember who but there is one board member with a full weight Regal running mid 11's on a 7.5. He has an intercooled set-up but it is making the cheese to run in the 11's. Not sure what mods (if any) he has done to his but it can be done.