Carb Synch/Brake Questions

[Limitless]

After reading past threads relative to my question on this site and others for information I am not quite satisfied. I apologize for improper forum etiquette if I should have resurrected an old thread instead of starting a new one.

My car:

I have a 71 240z. Everything is stock, l24 motor, dual hitachi sidedraft carbs, etc.

Carb Question:

I am in the process of syncing my carbs with a Synchrometer. After talking to those knowledgeable in the field they stated that as long as the airflow readings are the same for both carbs, I would be fine. I wanted to know if there is an optimal reading in which I should achieve for each individual carb in kg/hr. By evaluation using my ears, my engine sounded the best at around 12 kg/hr for each carb.

Brake question:

My right rear wheel locked up due to the wheel cylinder seizing. After conversing with the gentleman at Z-specialties I was informed a new wheel cylinder would cost $110. I was also informed most of the rear brake parts are either discontinued or extremely rare. Thus I have become tempted to change my rear breaks into disc brakes (as many already have).

My main concern comes from which other cars are the most compatible to do the swap with. Other threads state things such as the 280zx or Toyota 4x4. Out of all my options which would be the easiest, cheapest, or have the best performance?

Currently I found a complete rear axle from a 300zx. Would this be a compatible swap?

Lastly,

Is the front brake system in the 71 240z's commonly swapped out due to the same reasons as the rear brake system?

Again I want to apologize for creating a new thread based on topics discussed numerous times before. I would just like my specific issues to be covered before making any purchases. Thank you.

Edited August 29, 2010 by Limitless

[mlc240z]

On the right rear cylinder and hardware kit, RockAuto has them for $63/$7 (aftermarket rebuilds), MotorSport Auto for $83/$20 (Last time I bought OEM).

[olzed]

The front brake calipers can be removed and Toyota 4x4 four pot calipers fitted to improve the front brakes. Vented front discs can also be fitted to improve cooling. As a rule, unless you do performance driving, the standard brakes are very good. Maybe a new set of pads for the front is all thats needed.

Motorsport Auto sell kits to do these alterations, or you can gather parts from car parts shops and do the changes this way. On my 72 240 we did a driver training day at a local track and after a number of quick stops the brakes were cooking and not pulling the car up. Having some engineering knowledge I was able to gather parts from PicaPart and put together my own performance front brakes. Toyota 4x4 calipers and vented discs from a Mitsi station wagon.

Total cost about $150.

If you are happy with the front brakes leave them alone till they need attention. Just check for leaking fluid.

Edited August 29, 2010 by olzed

[lbpdz]

I am reading what you have posted, and have you thought about rebuilding your current parts also as an option, or just want to move into the performance world.

I have had excellent success hand honing the wheel cylinders (For some crazy reason I want to keep the drum brakes.

In which ever way you go, start from the outside and work your way in (do my current rims have enough clearance to make this happen), followed by what parts will give me the results I am looking for. I tend to like to keep mine stock as possible, and will either build or farm out a job or two..

[Bruce Palmer]

Kg is a weight measure, right? Weight of what per hour are you measuring?

Anyway, it's early and apparently I'm not fully tracking yet.

Balancing the carbs is just that, getting them set so they open at the same rate. Beyond that, they are variable venturies and flow only what the engine (read air pump) will draw.

[Gary in NJ]

Kg is a weight measure, right? Weight of what per hour are you measuring?

Anyway, it's early and apparently I'm not fully tracking yet.

Balancing the carbs is just that, getting them set so they open at the same rate. Beyond that, they are variable venturies and flow only what the engine (read air pump) will draw.

The weight would be kg/hr of air.

Bruce is correct, there isn't an optimum figure as our carbs are variable venturis. What is important is that they open in unison, hence the use of a uni-sync rather then a synchrometer.

[LeonV]

What is important is that they open in unison, hence the use of a uni-sync rather then a synchrometer.

That doesn't make any sense to me. A synchrometer (assuming you mean the one usually advertised for Webers) works great with these carbs. The tool used doesn't really make a difference, it's all about doing the syncing procedure correctly.

Edited August 29, 2010 by LeonV

[Gary in NJ]

That doesn't make any sense to me. A synchrometer (assuming you mean the one usually advertised for Webers) works great with these carbs. The tool used doesn't really make a difference, it's all about doing the syncing procedure correctly.

The point is you don't tune to carbs to achieve a particular flow (measured in kg/h or lbs/h) but to have the same flow. You can use any carb sync tool, but the flow values are only used for reference to compare the flow of the other carb.

[Limitless]

Thank you all for the responses,

Carbs:

Regarding the carbs I will just make sure they are matching as you all stated.

Brakes:

I am still baffled that the wheel cylinders are so expensive, so I am pretty much set on swapping the brake system out towards the performance route. Some of you suggested rebuilding the wheel cylinder, but that just doesn't seem attractive to me. Also all of the other components seem to be rare as well. I just think that swapping out the brakes will be a cure to the problem and not a band-aid.

Would you guys agree that the Toyota 4x4 brake swap is one of the more cost-efficient? In terms of installation and product availability (For replacing parts in the future).

Also, does anyone have an estimate on how much I will be spending to do the swap?(Just the rear for now).

Thank you all.

[LeonV]

The point is you don't tune to carbs to achieve a particular flow (measured in kg/h or lbs/h) but to have the same flow. You can use any carb sync tool, but the flow values are only used for reference to compare the flow of the other carb.

Sure, but you don't need to say "unisyn rather than a syncrometer" because you are inferring that you can't use a Weber style syncrometer on the Hitachi carbs. I actually prefer the syncrometer because it lets you take readings without completely disrupting airflow to the carb. It's definitely more user friendly.

[LeonV]

OP,

As far as I know, the 4X4 calipers are used on front "upgrades" only. Those are some pretty big calipers to put in the back if that's the plan. I think that you can just fix the rear drums more easily and price effectively than changing to a completely different system.

The stock brakes are more than good enough for the task, plus they keep the unsprung weight down compared to the "upgraded" brakes. If you're looking for performance, put in some Porterfield pads and shoes and you're good to go! It will be so much simpler and I doubt you'd regret the performance of properly maintained Z brakes with some good friction material.

[Gary in NJ]

The syncrometer I use for my motorcycles gets connected to vacuum ports on the carbs. How do you connect those to your Z's SU's? I only have one vacuum port on my front carb (connected to the vac advance).

Edited August 30, 2010 by Gary in NJ