The flat tops with this kit have valve reliefs and should be fine butt you really have to check clearances at assembly to make sure all is good.

I bought a pretty basic Scat kit with cast steel crank, I-beam cap screw rods and forged pistons. All quality USA parts, bearings, etc. including ARP rod bolts. The Scat kits are a good value I think.

...A good day at the McStang garage...!


 

I guess I'm a little confused after reading all of this. If your goal is to improve braking performance with a 15" diameter wheel restriction by switching from the 68 single piston factory discs to some 4-piston caliper setup I think you're on the wrong track. For street use I'd argue that the only thing that will really make a noticeable difference is running a bigger diameter rotor, which you won't be able to do with 15" wheels, or upgrading pads and rotors. A modern multi-piston setup has advantages in racing applications (where many other variables need to be considered and addressed besides just caliper design) but for the street a well designed single piston caliper with quality rotors and pads will work equally well under most circumstances.

I've got 13.2" / 11.75" 2011-14 Mustang GT brakes on my 66 with MustangSteve bracket kits (easy-peasy both ends btw). Calipers and rotors are factory take-offs that I picked up cheap in 2013 and installed with good Hawk pads and it stops like a bug hitting a windshield. 17" min. wheel requirement though (and not all those will clear the calipers).

When my daily driver needed new brakes I upgraded pads and installed PowerStop drilled and slotted rotors, properly bedded they've been a noticeable improvement over the OEM parts with no other changes. I've got 50k + spirited driving on the rotors and it's hard to tell by looking at them, under the foot they're still smooth and silky....I'd buy them again. Calipers haven't been touched since the car left the factory.

I'd suggest a pad and rotor upgrade as best bang for the buck if you don't want to change a bunch of other stuff and run larger diameter wheels.

https://www.powerstop.com/product/power-stop-drilled-slotted-rotors/#y=1968&mk=FORD&mo=MUSTANG&ss=with%20427%20Eng

5/64" is 1.98mm - that's pretty skinny. Seriously tho', I know they're talking about the darkside at the following link but quality of workmanship speaks to me and this kind of stuff prolly makes the biggest difference where the details add up.

Classic : https://www.youtube.com/watch?v=XdSUKSlUgUY

TKOPerformance wrote:

I wouldn't worry to much about the axles.  If they are old my concern would be a fatigue related failure, not a failure from being 28 vs. 31 spline.  We ran 28 spline axles in 8.8s many times without issue.  Traction is what kills them, which you don't have.  Heck, in the GM 7.5" 10 bolt 28 spline axles were an upgrade from the stock 26!  If the axles are old maybe just get a new set of Yukon, Moser, etc. in 28 spline.

Bolted is correct about overall 1st gear ratio.  In a typical V8 that winds to maybe 6,000RPM you definitely don't want to exceed 11:1 and if its only maybe 5,500 stick to 10:1 or 9:1.  Otherwise first is like a granny low in a dump truck.  I used to see guys race Fox bodies with 4.10s and they had to shift almost right out of the hole.  First in the T5 was 3.35:1, so overall they were at 13.7:1!  They'd need 4th at the end of the track and cross the line at some stupid low RPM.  The car would actually run faster with a 3.55 gear.  Better 60', and cross the line at 6,000RPM in 3rd. 
 

28 splines being tough enough is what I was mainly concerned about. With so much 'information' available these days it's sometimes hard to separate the bench racing talk from real experience. I have a line on a 4-pinion 8" Truetrac in an 'extra rib' case that I think I'll pull the trigger on. Axles looked to be in very good shape when I inspected them a few years ago, this car was a single owner job in great shape that I doubt ever got driven hard. Maybe I'll wait and see if anything breaks... I like zipping around more than draggin'.

Fun with numbers - (think these are pretty close)

With a standard T5z gear set and 3.50 rear 1st would be about 10.3:1. Breaking it down with a 25.5" tire:
1st @ 44mph = 5980
2nd @ 66 = 5900
3rd @ 100 = 6180
4th @ 130 = 6000
5th - Cruisin' at 120 = 3490

With a standard T5z gear set and 3.25 rear 1st would be about 9.6:1. Breaking it down with a 25.5" tire:
1st @ 46mph = 5810
2nd @ 72 = 5980
3r

The 66 is getting a healthy 331 and T5Z. Wondering what to do about the 8" rear end. It's a street car with performance underpinnings that I plan on auto-crossing for fun now and then.

I don't intend to be doing any clutch dumps and there are beefier 8" center sections out there that can supposedly take some decent abuse but there's not much to do about the axles that I can see so I think upgrading to a 9" is something I can't get away with not doing if I don't want to get stuck somewhere someday. I don't want to do an 8.8 or anything like that.

Swapping to a 9" means I need the whole package, housing, axles and center section and at this point in my project I think it makes sense to spend a few extra dollars on a 'drop-in' setup. Has anyone dealt with Quick Performance or Speedway motors? For about the same price as Speedway, QP will replace the Trac-Lok with an Eaton Truetrac which seems like a better choice.

On the fence for gear ratio, leaning towards 3.50 (2.95 1st gear and 25.5" tires) vs. 3.70:1.

TKOPerformance wrote:

Lastly, I would stick with shorty headers.  Long tubes tend to have a real flat spot in the middle of the torque curve, which is where you need power the most on the street and autocross.  Long tubes are better for drag racing and all out power, but you want average torque. 
 

When I first started getting parts together for an engine update for my 66 I was planning on dropping in a refreshed mostly stock 5.0 but I've changed my mind about that. I think the shorties made sense for a setup like that. Another reason for going with the shorties was easier fit - I'm going to be using MustangSteve's cable clutch setup with the swap from C4 to T5 and have a Borgeson box installed.

That said everything I've read (and not just on the interwebs) suggests that well designed long tubes with appropriately sized primaries will positively impact torque across the curve and definitely pull more power. I am concerned that the small shorties I have will bottle neck the motor I'm building now.

Rudi wrote:

Don’t forget to use a ARP heavy duty oil pump drive shaft.

I do have the ARP shaft. No pencils please. -

In regards to an all new performance 331 hydraulic roller build I'm wondering what people think about oil pumps. I've got a Melling 68HV but have seen comments like the following while reading around recently. Seems to make some sense, anything to it?

"If you're using standard clearances, use a standard pump. Otherwise, all a high volume pump does is push oil through the bypass, take extra (wasted) HP to run, and puts more strain on the pump shaft/distributor/cam gear."
 

Well that's a giant bummer but seems more like rotten chance than anything else. I mean how many engines, buildings, whatever you can think of ... are put together either under the influence of beer or the umbrella of ignorance and still manage to keep it together? Balancing, ... huh? If you did it at all you were already ahead of the pack.

Great. More please.