V-12 Engine into 308 Build, over on Grassroots

I messed around with the new valves longer than I planned today. Yesterday I cut the OD and ground the seats to make them look about right but when I measured how they were sitting I had to cut off another .010 and .012. The intakes are pretty critical to get the springs setup right since the cams are .452 lift and the spring are good for .460, but the exhaust lift is only .420 so +/- .010 on installed spring height is just fine. Then setup the shims so cam in and out of the head 3 times to get the clearances right, then start cleaning. Tomorrow more cleaning so everything is ready to go when head gasket stuff arrives. I need to place some other parts orders too, other engine gaskets I'll need, CV boots, and I'd like to switch to smaller master cylinders to reduce the pedal pressure, its ok but I think I'd like it better if it needed a little less force so 3/4" cylinders out, 5/8" cylinders in is the plan.
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Reached out to a buddy with a 348 who just did a tilton pedal box in and logs fluid pressure. He says the rear should be about 50% the front. I have F430 calipers and rotors which are all 4 the same size as are the 348 calipers, rotors smaller? not sure. A 308 used smaller rears both rotor and piston size...so I probably have a pretty unbalance system and I just haven't driven/tested enough to know. I kind of knew that but figured since the F430 is setup that way because it does help under very slick conditions....when I would realistically NEVER drive my car but in theory it could help. I have both a balance bar and an adjustable proportioning valve so it would probably all work out fine once adjusted.

What I did today was order a single 5/8 master I'll install on the front system thinking that will let me start with a much closer to balanced system. It won't drop the pedal pressure as much as I was hoping but I guess once I had to start cranking in the proportioning valve that would have increased the required pedal pressure anyway so its probably a wash.

 

Once I got done thinking about brakes as a way to delay cleaning engine parts I got back to clearing engine parts and I think everything is clean and ready to assemble. I also got the grime out of Ferrari and beveled the cam covers so there should be no more o-ring cutting happening.
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It's called 'patina'

 

Rhymes with vagina

 

I thought a balance bar eliminates the need for a proportioning valve. What do they do together?

 

Nothing. Either have one or the other. Coarse adjustment is made by master cylinder size, then fine adjustment via the balance bar. Of course, the valve is an easier fix - just plumb it into the rear brake line.

 

Ehhh, sort of. Caliper size, master size, balance bar all have the same effect. They set the f/r pressure or force ratio for all conditions.

A proportioning valve varies the f/r balance based on system pressure so to f/r balance changes with pedal pressure. Warm dry afternoon with lots of grip is high pedal pressure and more front bias. Cold wet morning is lower grip, low pedal pressure less front bias. The proportioning valve automatically makes this adjustment. All street cars should have a proportioning valve (modern cars basically use the ABS for the same purpose).

In a race car you usually give the bais adjustment to the driver to fine tune during the event....a balance bar works very well for this.

For me the purpose of the balance bar is to get cold wet system balance right. Then the proportioning valve will automatically adjust the bias for high grip. Without a proportioning valve I would have to setup for high grip and live with suboptimal braking in other conditions.

 

There is a good proportioning valve writeup on the wilwood site
https://shop.wilwood.com/blogs/news/how-does-a-proportioning-valve-work

Here is what the one I have does....it does nothing until it hits the set pressure, then reduced any additional line pressure. So low grip, low pressure you get more rear braking and at higher grip less rear braking letting the system be good at most conditions. The goal is always lock the front first, but not by a lot.


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These explanations of balance bar vs proportioning valve are excellent. Thank you!

I have just installed bigger brakes in a car I am prepping for track days. It is the first time I have put brakes from one car into a different one. I am quite concerned about front/rear brake balance.

 

I am a little OCD I'm told so I am considering modifying the valve for a 50% reduction instead of 57% reduction thinking it will let me get the setup a bit more optimal.......

I'm also rethinking my master cylinder decision and remembering why I matched them when I put this setup together... the valve is already doing too much....hmmmm

 

Empi makes a 50% proportioning valve, pn 16-3157-7, I think I will replace the 57% wilwood while I'm at it.

 

I know that! I was referring to the manually adjustable aftermarket valve, not the factory installed one. I used to race Minis, where the proportioning valve is very important. The early ones used a ball and spring, so I'd have to shorten or pack out the spring to change the balance. The later ones used a little ball on a sort of ramp, that self-adjusted according to the braking G-force, so tilting it changed the bias - cheap solutions in those days. On my last Elan, I designed the caliper piston area to give me 67/33% F/R, which I was going to fine tune with a Tilton proportioning valve, but it was so good, I never bothered.
Edit: Oh, and a balance bar is useless if you haven't got the bias in the right ball-park with disc and caliper piston size first.

 

Yeah, its can make 10% or 20% but it unlikely to make a 50%
I have been pondering a little. on the 308 there is significant front bias baked in the the caliper/rotor sizing. On the 348 the 4 calipers are the same but the rear rotors are a little smaller 10%? Then on the 430 all 4 calipers and rotors are the same, but built in bias at all. They increasingly added more rear brake so I'm wondering if they felt more comfortable getting closer to the limits because the ABS was getting better? Or in reverse what the condition was they were trying to avoid with the older setup that? Wet steep down hill run? dry steep down hill maybe?

Anyway I confirmed the adjuster was full out on the valve, so min pressure to the rears. I'm sure I did that to ensure the fronts lock first before starting testing but it also means max pedal pressure needed. The new masters will drop the pedal force 30% and I can get maybe another 10 or 15% once the bias is property adjusted to let the rears work as hard as they can....in theory. Hopefully everything arrives for the weekend or at least a few days before the head gasket stuff so I can make the changes while waiting instead or it interfering with progress.

 

I am surprised to read that a balance bar only adjusts 10% or 20%. That is a disappointingly small range.

I am using Corvette C4 brakes, which presumably have appropriate piston sizes for a Corvette. The problem is that a C4 Corvette has a weight distribution of 51% front / 49% rear and my car has 42% front / 58% rear. I can't figure if I am going to have too much front or too much rear brake!

 

Corvette brakes will likely have too much front bias to be optimal but that is perfectly safe. The bar itself has limited range but you can swap mastercylinders to get into the bars ability to fine adjust.

You can calculate what you have by measuring the caliper pistons and rotor diameters. Then from there calculate the ratio you want between the masters to get it where you want bias wise. You want about 2/3 front,1/3 rear as a starting point.

 

I got tired of guessing and did some actual math. I calculated axle load as a function of braking G force, then the axle forces to go with, then converted to system pressure, put a 10% reduction on the rear axle to know the front locks first, then optimized with just mastercylinder/balance bar, then added a proportioning valve and re-optimized, then a 2nd valve, then a 3rd. The 3 valve system uses non-standard valve ratios so really just to see. The graph goes to 1.5G so slicks but I let the line cross the safe line after about 1.25G that I figured DOT race tires might give.

Its kind of an assumption on my part that matching the curves is a good thing as it should give shorter stopping distances in suboptimal conditions and also I thing should keep the car better balance comign off the brakes into turns.

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I played some more and fixed a couple not quite right calculations. It looks like 5/8 and 0.7 masters are about perfect then the 50% valve then a 57% valve, and a 3rd 57% if I'm in the mood for perfection, but it does seem like if I can have 13 MAP sensors I should be able to have 3 proportioning valves Image Unavailable, Please Login . The pad cf messes with the valve setup because they work on pressure and pad cf changes system pressure.....so the spread sheet tells me where to set everything for what pad cf number.

Now I need to decide if I need to add transducers and log brakes or just buy a couple gauges to do the setup....I need to go back there the ECU setup info, its been a while and I'm not sure what all is still available and what extra wiring I ran or if I would need a CAN expander or some such.
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It looks like analog inputs AN21 and AN22 are available . Light gray is what AEM used them for and I try to follow when I can going back to when I wasn't sure my program would would correctly and thinking I could reload theirs....I now know only they can load their firmware but it was a good thought.
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And I have 3 2-conductor shielded wires. 1 I want to save for a front CAN line but I could use the others 2 and send 5V and ecu gnd up 1 and the 2 brake pressure signals back in the other. I have 3 unshielded wires too but I like to keep analog signals in shield wires anytime I can and I have them sitting. There is a 4th, I think 3 wire under the dash on the by the steering wheel planned for steering angle.
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Anyway, it looks like front and rear brake pressure transducers are a go and I'm kind of eying CAN accelerometers but I think I'll hold that thought until the car is actually driving and just use a phone app to setup the brakes for now.
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I thought this weekend was brakes......but brakes can wait since the head shims/rings arrived a week early and they look marvelous!
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The pin holes were a little tight
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but now fit. I hadn't ordered the orings knowing thinking there was time, but did last night when I got the shipping notice for the shims and they will be here tomorrow so I can assemble and get it on leak test Saturday maybe
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The heads are on
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The o-rings were not as easy to install as I'd imagined but but the aviation sealant mostly kept them on place
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Then inspect and set the head on. The 518 sealant I used on the coolant pipe test covers needs time to dry before I can pressurize, but I did put in 5 psi to make sure the orings stayed put and that is holding
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nevermind....

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Flame ring?

 

Not sure I understand the question? The copper is intended to be the flame ring, and not intended to seal., just protect the o-ring.

My thought today is since I'm now counting on sealant everywhere but the cylinders, it could be leaking anywhere.....and I have a brand new tube of 518 sealant that now seems ideal. I like the idea of high temp RTV too, but there is no way I can assemble this in 5 minutes. A quick google of slow set RTV upped up form-a-gasket 2a...the thick version of aviation sealant.

I'll start with 518 and see what that does I guess.

 

So I knew the sealant needed time and I didn't wait.....for sure the sealant on the gage plate blew out while I was in side cleaning up. It holds no air now and I hear/feel it at the plate. When I popped the plate off there was a clear channel.
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This means I have at least a temporary reprieve The plate is resealed, hot air gun deployed to speed things along.

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