Scandinavian SL-C build

[Johan]

Another thing. You might need a proportioning valve on the front circuit due to the weight difference. The SL-C is around 60/40 and Camaro I guess close to 48/52. (Rear/Front)

 

[Joel K]

Another thing. You might need a proportioning valve on the front circuit due to the weight difference. The SL-C is around 60/40 and Camaro I guess close to 48/52. (Rear/Front)

Thanks Johan, I was thinking I’m may but haven’t gotten that far yet. Thanks.

 

[Joel K]

For the pump, I got a pressure switch from the junkyard from a Volvo V70 T5.
But some of the pumps have the switch built in. Don’t think the UP50 have one, I can check the part no on Monday.
My measurements of the second hole is 76mm up from the lowest hole and then 32mm between the second and third. Total length of the slave is 108mm. That is around 3.52:1. I made a last minute change of the ratio due to the lower weight of the SL-C compared to the Camaro.
I don’t have the experiance to figure out what ratio will be correct for a light car like ours, so this will be trial and error.
But if you want 3.8:1 you should place the second/middle hole 76% over the bottom hole. That is if your Tilton ratio is 5.0:1.

Thanks again for the info Johan, looks like summit sells a switch to control the Hella air pump so I’ll probably get the combo. Is the pump noisey?

Summit Racing SUM-760155-1 Summit Racing™ Replacement Vacuum Pump Switches | Summit Racing

Free Shipping - Summit Racing™ Replacement Vacuum Pump Switches with qualifying orders of $109. Shop Electrical Switches at Summit Racing.

www.summitracing.com

 

[Cam]

Haven’t had a chance to catch up with build threads, looking great Johan! Good idea on the banjo boot solution, cleaner than the piece-meal version that is typical.

power brakes is one of those things I keep going back and forth on. When I drive the car I don’t find I need it. Not sure if I would feel the same if an emergency situation came up; without ABS I suspect I would just lock up my brakes and I would be better off sticking with manual.

 

[Del]

I 100% agree with Cam. I plan to swap into CTS-V front calipers (assuming they clear the wheel). Admittingly it's only for looks, but I kind of hope I get a little more stopping power too

 

[Johan]

It's too much snow up north to do the inspection so it has to wait a while longer and I'm getting crazy by not doing anything, so I decided to swap to power brakes.
First I mocked it up and had the levers and pushrods lasercut then calculated the approximate ratio of the slave lever. The stock Camaro SS brake pedal is around 3,8:1 and the Tilton pedal a little adjustable but I calculated with 5,3:1.
I ended up with a total ratio of 3,75:1.
It's very tight up front due to my cooling duct so I had to mount the reservoir remotely, I used the old Wilwood and my buddy Calle made a new mount to the MC. Also made new brake line fittings, the Camaro has 1/4" lines and I'm using 3/16".

 

[Johan]

I had to place the steering rack mount on top i.s.o below the rack, due space limited. The final selection of vaccum pump is the Hella UP 5.X, it's designed to independently supply the required vaccum for brake booster and other components such as doorlocks.
I also added a proportioning valve to the rear circuit, however I'm not completely convinced, it might be needed to the front circuit, time and testing will tell.
Pressure testing shows 1200 psi front and 950 psi rear without any adjustment on the valve and so far I've only done road test up to 90 km/h, no high speed test. Front lockes up first (as it should) and I haven't been able to lock the rear.
It's getting really crowded up front now, can't fit much more in there.

 

[Joel K]

I had to place the steering rack mount on top i.s.o below the rack, due space limited. The final selection of vaccum pump is the Hella UP 5.X, it's designed to independently supply the required vaccum for brake booster and other components such as doorlocks.
I also added a proportioning valve to the rear circuit, however I'm not completely convinced, it might be needed to the front circuit, time and testing will tell.
Pressure testing shows 1200 psi front and 950 psi rear without any adjustment on the valve and so far I've only done road test up to 90 km/h, no high speed test. Front lockes up first (as it should) and I haven't been able to lock the rear.
It's getting really crowded up front now, can't fit much more in there.

Nice work Johan, if I am reading your post correctly you have actually driven the car with the power brakes installed? If so, how did the pedal feel with the ratio you selected?

 

[Johan]

Nice work Johan, if I am reading your post correctly you have actually driven the car with the power brakes installed? If so, how did the pedal feel with the ratio you selected?

Nice work Johan, if I am reading your post correctly you have actually driven the car with the power brakes installed? If so, how did the pedal feel with the ratio you selected?

Joel, yes I have driven it with PB but without the front clam. The pedal feels close to perfect, if anything a touch too much ratio, final decision will be after test drive with the front clam on.
It also has a tendensy to lock up fronts well before rear, but as I said I have to test it fully configured/ complete car.
I made a couple extra slave levers without the middle hole if I have to change it.
And the prop valve, I dont think you need, at least not on the rear circuit. More likely that you have to reduce the front pressure.
Here are the measurements. To be exact 3.73:1

 

[Johan]

Update. I spoke to a guy racing 5th gen Camaros. He told me that many proportioning vales reduces the pressure by 20-25% even if turned all the way to zero reduction. So I bypassed the prop valve and the pressure diff (Front/Rear) is now 100 psi.
I’ll test drive as soon the roads dry up, but I think it will be right on. I’ll be back.

 

[Frank Clark]

We have use a number of different valves in different race cars. Yes some always reduce pressure. We used one that controlled between 50%-100%, that's probably what you want if you need a valve.

 

[Johan]

We have use a number of different valves in different race cars. Yes some always reduce pressure. We used one that controlled between 50%-100%, that's probably what you want if you need a valve.

Frank, do you have a brand or part number of any of those valves?

 

[Frank Clark]

The previous one we used was:

Wilwood 260-8420 Lever Style Proportioning Valve

This proportioning valve has six preset adjustment points actuated by moving a lever allowing racers to adjust brake bias during a race without having to "look" where the knob position is. This lever "clicks" into the six positions for positive adjustment and the bright red lever is easily seen...

www.speedwaymotors.com

It gives about 50-100%.

currently using:

Speedway Compact Adjustable Brake Proportioning Valve

Very compact, can be hidden in cars that do not allow adjustable proportioning valves. Color reference scale on valve stem allows fast, accurate setting. Installs in rear brake line and allows you to adjust front-to-rear brake bias to prevent rear brake lock-up under heavy braking. Can be used...

www.speedwaymotors.com

Because it will cut off 100%

Don’t know that either of these are suitable for you, but if you read the descriptions you can see they do describe their functioning well.

 

[Johan]

Update2. After testing without proportioning valve the deceleration was better but I still wasn’t satisfied (front locked up too early) so next step was to install the valve on the front circiut.
Pressure diff is now approximatly 1200psi rear and 950psi front (at the same pedal force) and braking is now very good (front still locked up first).It should be in the ballpark now and next step to finetune the brakes will be to temporarily install accelerometers. I also adjusted the compression on the front shocks to softer to help weight transfer. I don’t know if it has any impact on the deceleration/friction coefficient or if I’m able to see any change on the accelerometers, time will tell. I’ll let you know.
Conclusion, if any of you are thinking of going with power brakes and use the Brembo calipers the stock Camaro SS booster and MC will work fine but you must reduce line pressure on the front. To get the pressure diff I have now (R 1200/F 950) I’m in the middle of the range of my proportioning valve so I can go either way from here.

 

[Joel K]

Terrific feedback Johan, glad you are getting the setup sorted out.

 

[Johan]

One thing that has been bugging me is the as delivered Master Cylinders (Wilwood), they are supposed to be mounted F3/4” and R7/8” according to the Wiki manual.
This setup will give a higher pressure to the front circuit, opposite to the result I have found (even with bias to the front). I always thought that my brakes demanded a very high pedal pressure but that’s ok, the other thing was I had the feeling the front locked up way too early with the result of somewhat poor total brake efficiency. The same feeling when I switched to PB and had a higher line pressure to the front. As you know I switched the proportioning valve to front circuit and is now running approx. 900 psi front and 1200 psi rear. (Opposite to a normal car) The brake retardation is much better and I still haven’t locked up the rear, and that is with quite hard pedal force.
I’m just curious if someone else has done any research of the line pressure and come to the same conclusion.
In a perfect world the best retardation would be just before all four wheels lock up (at the same time) and the friction coefficien goes down but that would be dangerous so we set the front to lock up a little before the rear.
If I knew what I know now (concerning line pressure F/R) , I would swap the MC:s with each other and see if the retardation got better.
I might be wrong, but my testing points that direction.
Any thoughts guys?
Take care and be safe.

 

[Ken Roberts]

Up until now I`ve had the Graz KBA (unmodified) in the car and this saturday I decided to swap to my KVJ (modified drop gear). Everything went smooth until the last thing to tighten, the drive shafts. As it turns out Audi apparently changed the diameter of the bolt circle on the transmission mounting flange from approx 95mm on the KVJ to 93mm on the KBA, so I eighter need new drive shafts to the KVJ or swap back to the KBA. Fortunatly I have another set of 1.04:1 drop gear, so I went ahead and changed it in the KBA.
It went a lot easier this second time around, the Graz was apart in a little over 2 hours.

The driveshaft shop has a adapter plate made available now to address this concern. Only problem is the axleshafts need to be shortened 5/8"

Michael's GT-R Build

Mike why didn’t you just bond the light plate to the back of the foglight housing I believe that is what Kurtiss did on his car

www.gt40s.com

 

[Johan]

It’s a good day today. My SL-C passed the last and final inspection with flying colors.
Thursday before Easter I was up in northern Sweden an did the build inspection, they check pretty much everything, chassi welds, brake retardation, noice, emission to name a few. All good.
And today I made final inspection/registration at the Swedish DOT and it passed without remarks. So I’m a very happy camper today.

Another thing, I’ve said it before, concerning the brakes, last Thursday when we sorted out the retardation with accelerometers I lowered the line pressure even more to the front circuit and best retardation was with 780-800 psi front and 1200psi rear (still lock up front first).
So, I have a hard time understanding the Wiki manual saying 3/4” front MC and 7/8” rear, I’m convinced the brake effiency would be a lot better by switching the MC:s. Weight distribution on my car was approximatly 42%-58% and total weight 2800 lb. Pretty much standard SL-C.(street tail, Graziano). The only thing being a little off is a 25lb fire extinguisher system in the back.
It would be interesting to hear how they came to the conclusion of the master cylinder sizes.
I’m not saying the brakes are bad in any way with the ”wiki” setup but at least my car responds in a much better way with the above setup.
If anyone tries this I would be happy to hear the result.
Regards,
Johan

 

[Joel K]

Congrats Johan, looking forward to some driving reviews.

FYI, there were a couple comments recently in Kurtiss’ GT-R build thread post #180 and #182 he states that the correct setup for for the master cylinders on a GT-R are 3/4” front and rear and the 7/8” is for the clutch.

 

[Cam]

Congrats Johan!