Planning to redo the motor, trans, rear and suspension of my 2 dr '81 Diplomat. Presently a /6. Moving toward 318 or 360 with about 400 streetable HP(A/C/PS/PB), 2.74 904 and "B" body 8 3/4 with 3.55 gear. For front suspension, other than a Koni gas shock and aluminum K spacers, what else do I need to keep the front end tight and track well? Anything to know about installing a 3/4" rear sway bar with the 8 3/4 rear? With how slow the aftermarket is right now and the low priority of the FJM, I'll have to assume 1-2 years before all the parts are available.
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- Thread starter CM360
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M_Body_Coupe
Well-Known Member
Not sure if you have all the motor parts already, but I would recommend going the stroker route! Heck, all other things considered you are gaining an easy 40-50 cubes, and at that power level that's easy 50hp extra, and more likely 75 actually. The biggest expense here is the stroker crank...otherwise the pistons you would be getting (presumably) new for either build anyways.
Front suspension wise you could go to the thicker 11/16" tie-rod setup. Factory is 9/16", while the fleet/HD stuff was 11/16". Aftermarket now has some pretty sexy looking parts out there and I'm guessing since these things aren't exactly flying off the shelves you may have an easier time finding these.
I would certainly re-do all the soft parts, so bushings, etc. Move up to poly if need be.
Can't say much about the 8-3/4" and sway bar unless you're retaining the ISO setup, which vast majority of folks are dead set against. I did keep it, moved to POLY ISO replacements, back end is pretty stiff making for great road manners, but due to the overall street config my 1/4 mile 60' times are horrific as I have no real body weight transfer. So you need to pick your goal and do everything possible to RULE that domain!! lol
Front suspension wise you could go to the thicker 11/16" tie-rod setup. Factory is 9/16", while the fleet/HD stuff was 11/16". Aftermarket now has some pretty sexy looking parts out there and I'm guessing since these things aren't exactly flying off the shelves you may have an easier time finding these.
I would certainly re-do all the soft parts, so bushings, etc. Move up to poly if need be.
Can't say much about the 8-3/4" and sway bar unless you're retaining the ISO setup, which vast majority of folks are dead set against. I did keep it, moved to POLY ISO replacements, back end is pretty stiff making for great road manners, but due to the overall street config my 1/4 mile 60' times are horrific as I have no real body weight transfer. So you need to pick your goal and do everything possible to RULE that domain!! lol
My last 360 build, I made 20 HP less than the prior stroker build, using same heads, intake and carb. The extra $1800.00 spent on the stroker kit ain't worth it for 20 HP. Just want a DD with good road manners. People depend on modern car technology to stop them from having accidents. Better brakes and suspension and tires help their poor driving skills. A 40 year old car can't cut it but I'm willing to try to get it somewhere in the ball park.
M_Body_Coupe
Well-Known Member
Fair...but that just means the stroker combo wasn't the right fit. In other words, maybe the heads, maybe the intake, the carb, or the cam didn't allow the stroker power potential to come through. After all, more cubes means more fuel, more power.
Alright, got it. That's a pretty clear goal. You know, you mentioned brakes...you bet, spend a little time looking for the larger 11.75" discs, they do make a difference (you'll need the larger caliper adapter as well). I have those on my coupe and the butt-meter did register a difference. I also used the fleet brake pads, specifically AC/Delco #17D84M. I am sure the aftermarket has alternatives as well, most likely better performing ones as well.
For this to be a well mannered DD ride you will need to keep your cam profile fairly civilized...have you picked anything yet? I'm thinking max of 220-225 @0.050 duration, and maybe even with a wider LSA?
400HP is a pretty easy goal to hit with a stock stroke 360, but a stroker will will make that same power with a milder cam and compression all the while doing it earlier in the RPM range. It's the quintessential build for a ballsy driver in all aspects except gas mileage.
I'm running a 230@50 roller cam in my 512 with a tight converter and 3.54 gears. Part throttle torque response from the motor is amazing.
Does your build involve new pistons and rods? If so, you can toss a cast crank stroker kit at it and be nearly a wash in money between the two. A cast crank kit would be a lot cheaper and would live happily in a motor making 450HP. Most guys don't need these higher dollar forged kits. The blocks will give out before the rotating kit.
If you're reusing the stock pistons and rods then it starts not to make as much sense money wise.
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For handling the absolute weakest link in these cars is the torsion bars. The factory only made a single rate bar for all models and it is woefully inadequate. With Firm Feel never producing the bars the next best thing is to run a moderate spring rate with the largest anti-sway bars you can get. FF does sell 1.25" and 7/8" sway bars. I'll be upgrading to these this summer. The factory cop bars I have can't seem to keep up with the added weight in the nose of my car since the big block swap.
Actually, would you be interested in them? I'm never going to build another F/J/M, so it makes little sense for me to hold onto them. They would be perfect for a lighter coupe with a small block.
Mounting the rear while doing an ISO delete is easy. FF sells the plates to do it and this is the route I took.
The biggest improvement in handling for the least amount of money would be frame ties and sway bars.
I'm running a 230@50 roller cam in my 512 with a tight converter and 3.54 gears. Part throttle torque response from the motor is amazing.
Does your build involve new pistons and rods? If so, you can toss a cast crank stroker kit at it and be nearly a wash in money between the two. A cast crank kit would be a lot cheaper and would live happily in a motor making 450HP. Most guys don't need these higher dollar forged kits. The blocks will give out before the rotating kit.
If you're reusing the stock pistons and rods then it starts not to make as much sense money wise.
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For handling the absolute weakest link in these cars is the torsion bars. The factory only made a single rate bar for all models and it is woefully inadequate. With Firm Feel never producing the bars the next best thing is to run a moderate spring rate with the largest anti-sway bars you can get. FF does sell 1.25" and 7/8" sway bars. I'll be upgrading to these this summer. The factory cop bars I have can't seem to keep up with the added weight in the nose of my car since the big block swap.
Actually, would you be interested in them? I'm never going to build another F/J/M, so it makes little sense for me to hold onto them. They would be perfect for a lighter coupe with a small block.
Mounting the rear while doing an ISO delete is easy. FF sells the plates to do it and this is the route I took.
The biggest improvement in handling for the least amount of money would be frame ties and sway bars.
