3kGT vs. Camaro Calipers

[Luke]

The reason for the piston size difference is to prevent pad taper.

Those 3kgt piston sizes are very interesting indeed.
They seem to be much smaller than those of stock galant caliper.

Area wise, they are 56% of the stock caliper piston area.

This means, 3kgt conversion will cause the brake bias to shift significantly to the rear.
Specifically, it will change the front-to-rear brake bias by a factor of 0.61.
( 56% * 12.36 / 10.8 = 0.61 )

IMO, this will cause the car to be unstable as the rear tires will lock up way earlier than the mitsu engineers intended.
Ideally, you'd want the brake bias to shift just slightly to the rear compared to stock.

Here's a chart comparing stopping distance versus brake bias:

http://www.stoptech.com/products/BBK/balance.shtml
http://www.stoptech.com/tech_info/wp_brakebiasandperformance.shtml

Someone correct me if my calculation above is incorrect though..

Quote:
Quote:
What's the piston size of 3kgt calipers ?


I ordered a set in to measure, believe it or not I get two different measurments for the front and rear pistons in the caliper. I get 30.76mm for the front piston and 29.52mm for the rear piston. I've never seen 4pots with variant size caliper pistons, WTF??

 

[Luke]

Ugh.. never mind my previous post..

The piston sizes information from which I based my calculation is incorrect.

According to http://www.stealth316.com/2-brakeupgrade.htm
the 3kgt piston size is 40.4 and 42.8 mm

Redoing the calculation, 3kgt conversion will move the brake bias to front .
Specifically, front-to-rear brake bias will increase by 16%.

IMO, stock setup is usually already more front-biased than optimal ( shortest stopping distance ) because the lawyer/engineer never want unstable rear lockup to occur.
Thus, I believe increasing front-to-rear brake bias even further than stock will actually increase stopping distance.

 

[Luke]

Okay, I went ahead and calculated the front-to-rear brake bias change for all three setup:


[*]3kgt caliper + 12.35" rotor +16%
[*]camaro caliper + 13" mustang cobra rotor +44%
[*]corvette caliper + 13" mustang cobra rotor +2.7%
[/list]

 

Ok, so what if you did a rear caliper replacement on the GVR4 from a 3KGT. Or, mesured everything out and found out if they are the same for our cars. If they are the same as a GVR4, than why couldn't you just replace the GVR4 master cylinder with a 3KGT? And just to really make it more complicated, can you put 3 turbos on our cars?

 

[bazeng]

wow!
interesting stuff!!!

i totally agree with the camaro bias going to the front...

can this be fixed with an adjustable bias valve?

 

Quote:
Ok, so what if you did a rear caliper replacement on the GVR4 from a 3KGT. Or, mesured everything out and found out if they are the same for our cars. If they are the same as a GVR4, than why couldn't you just replace the GVR4 master cylinder with a 3KGT? And just to really make it more complicated, can you put 3 turbos on our cars?



You would lose your ebrake setup if you switched to a 3000GT rear brake caliper. They use drum style rear brake calipers.

3 turbos would be useless... 4 are much more efficient.

 

[skivittlerjimb]

Quote:
i totally agree with the camaro bias going to the front...
can this be fixed with an adjustable bias valve?



Hmmmm, I'm thinking I'll hold off on installing these Camaro calipers until I can find a C5 Vette set. Oh well. Good to know now rather than locking up the fronts at high speeds. 44% is a huge brake bias change. The rears don't do a ton of stopping work now, but at that point they'd pretty much just be along for the ride. It would also make trail braking much more difficult, I would think (not that I'm an expert on trail braking, by any means).

There are plenty of adjustable brake bias valve kits out there, but I'm not sure just how much they could really compensate for this big a change, and it would be a bit of a "Band Aid" fix IMO. Also, my car has ABS deleted, but for folks that still have ABS, I'm not sure if a bias valve would be compatible or not.

-Jim B.
280/1000
1432/2000

 

Quote:
The piston sizes information from which I based my calculation is incorrect.

According to http://www.stealth316.com/2-brakeupgrade.htm
the 3kgt piston size is 40.4 and 42.8 mm




I dont think that is accurate, I'll post pics tonight with the micrometer right on the pistons. I'm sure Hans has got a set of early 90s VR4/TT calipers around, maybe he can check too.

 

[Luke]

Hi Jim:

To make matter more complicated.. even though I am using C5 brake calipers, I am still using the Camaro caliper brackets. The adapter than Ron makes is designed for the Camaro caliper bracket. ( which is non interchangeable with the C5 caliper bracket )

So, basically, you need parts from both camaro and caliper brake setup.
Picture of parts

The good news is that C5 vette calipers can be had for very cheap from www.corvetteforum.com. ( $50-$70 bucks )
The reason why they are so cheap is that many C5 owners upgrade to C5 Z06 calipers.
The only difference between Z06 and non-Z06 calipers is the color. ( Z06's is red )

Anyway, the C5 calipers will give you much much improved brake pedal feel.
The brake pedal is very very firm. ( it is simple physics due to the smaller pistons )
I have driven Audi S4 with stoptech brake upgrade, and the pedal feel is the same.

IMO, it is still a very cost-effective upgrade. We are lucky that the C5 calipers happens to have just the correct piston size to pretty much retain the stock brake balance.

Quote:
Hmmmm, I'm thinking I'll hold off on installing these Camaro calipers until I can find a C5 Vette set.

 

[skivittlerjimb]

Cool, thanks for doing the research and posting the numbers, Luke. The plain jane Camaro/Firebird caliper upgrade may still make sense for a lot of folks, as long as they're willing to accept earlier front lock up and likely faster front pad wear. I'll search around for some C5 calipers. I'm assuming the C5 and Camaro/Firebirds use the same brake pads, yes? What are you going to run for pads?

-Jim B.
280/1000
1432/2000

 

[Luke]

Hi Jim:

You need to use the cheaper /ubbthreads/images/graemlins/smile.gif Camaro/Firebird brake pads.
The Corvette C5 ( more expensive ) brake pads does not fit on the Camaro caliper bracket ( also called pad abutment bracket )

I use Hawk HPS brake pads, with plan to use the HP+ version for track days.

 

[bazeng]

Luke, can i ask you if these calipers are okay.

88-96 C4 Corvettes with J55 option HD 13" rotor

i know they are not c5's
but are the c4's the same spec?

 

[WesS]

sry f* up

 

[Luke]

bazeng: What size are the pistons of J55 C4 caliper ?

I have no idea if it'll fit.. I didn't research the C4 parts, because the Camaro folks only upgrade to the C5 brakes..

 

[bazeng]

Thats okay Luke,
I believe they are smaller although still mounted on a 13" rotor.

I've managed to source a c5 set!
Front and rear!

How would the stock c5 rears hold up on a VR4?
I tried finding specs, but finding it very hard to get numbers from the net.

As for handbrake, what could be done?
any suggestions?
maybe lock up all wheels with the handbrake via a hydrollic handbrake.
??

could that be done?

thanks

 

[Luke]

Hi bazeng:

I also have a set of rear C5 calipers.

Figuring out how to upgrade the rear brakes while retaining the parking brake function is also on my wish list.
If you can figure this out, do let us know