SLC 24 Howard Jones

Howard Jones

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Did a track day at COTA yesterday with Edge Adicts. This is my favorite group. The run groups are well sorted and the whole day is really run well. Really nice people, especially Karen who is the boss.

So some observations. The day was a perfect one in the mid-70s and full sun with very little wind. Just really nice. The track started very cold with overnight temps in the 30s but by 10 am it had heated up nicely. I had signed up rather late so I ended up in the yellow group which is one slower than I have been running with them. Karen said I could change if I needed to but I told her I wanted to run the morning at about 80% with all the new stuff on the car so I would let her know. That turned out to be a good choice, The two morning sessions were a good fit and everybody went home early after mid-day so the afternoon sessions were pretty sparce. No real need to change groups as it turned out.

I changed to a larger front caliper piston size. About 4 sq/in to a bit over 5 sq/ins. The car always seamed a bit overbiased to the rear but really it felt under-braked on the front. The new calipers radically changed that and now the car really stops well. As good as a GT3 Porsche I would say. I also put some new pads in the front. I used the polymatrix B pads up to now but I found a new BP28 pad that is very close to the poly-B pad torque curve so I tried them. I think they are very similar so for now I am satisfied. We will see on a Texas hot day next year. Brakes done, check.

Gearbox clutch and cooling. The original setup without a cooler and pump heated up the GRBX oil to 200F after 30 minutes on a mild day. Turning on the pump took 20F right out of the oil in about 2 laps. The new clutch fiction disk works as advertised. No sign of slipping or any fitment issue. This is a good solution for 600-650 ft/lb engines using a G50 and the turbo pressure plate. Pretty good upgrade for not a lot of money. It is a bit on/off so maybe not the best choice of a streetcar but it was a perfect solution to my more powerful motor. So that works, Check.

New driveshafts, in the spring I broke a CV and ended up changing over from the odd 36 splined driveshafts to the now-common 28 spline ones. These come with 300M axels CV joints and ventilated boots, These are the upgraded road race version of their high-end axles. Fit right in .bolted up and torqued to spec, No issues, all good, check.

Motor.................ya its got more power. A lot more. The plan to use third gear for corner exits instead of doing one more shift up and down to 2nd with more power really works. I can stay right with the Porsches now until I catch them and pass them on the straights. We will see next year when I run with better drivers in my preferred Red run group. But I believe I have a proof of concept now.

I am also seeing at least another 10mph top speed. I really think it will be pretty easy to see 150 on COTA's back straight now. The higher corner exit acceleration really makes a higher top speed possible.

This engine really ran well all day with no issues at all. Water temps were right at the programmed 190F, oil at about 220F, and oil pressure 70-80 or so all day. It is amazing how well having a pro engine builder do a motor works. Not cheap but worth it. Thank you Samson Racing Engines, New Braunfels Tx. It's nice to know all I need to do to make nearly another 80Hp is to change the tune and put a bigger carb on it if I want to.

New tires, I didn't put them on. I had them there but I just didn't feel the need to use them. As it was, Toyo wants the first heat cycle on new tires to be one hot series of laps and then let them rest for 48 hours, So I would have needed to change them between sessions and run the last one of the day with them. By then It was getting late in the day and the air temps were going down, I was tired and happy with the progress and just didn't feel it. Next time.

I will say that the old Hoosiers are shot, done, dead. This motor will spin them at will even when hot. I spun the car twice on slow corner exits. The rears just light up now whereas with the other motor, I could just mat it and go, None of that anymore. I have to DRIVE the car now.

I have to say that if this car had 800Hp I wouldn't like it. Just too hard to be smooth and precise. However, I believe these cars with 550HP and on slicks are GT3 fast hands down. After that It all up to the skill of the driver.

I think I have video. I'll check the camera tonight and see if it all worked. If so we will have video.

Cheers, Merry Christmas.
 
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Randy V

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Fabulous report Howard! I could just imagine the eyeball sucking G’s when you got on the brakes hard…
Curious if you lost much pedal height with the larger calipers?
 

Howard Jones

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Randy, that is a good question. The calipers I have in the car now are forged Wilwood Superlight radial mount 4-piston. 5.18 Sq/In piston area and 2.46 Sq/In in the rear. I used the radial adapter mounts on the front and they fit perfectly without modifying anything.

I used the 13.06 X 1.25 two-piece on the front and the 12.88 X 1.25 rotors on the rear. The new caliper will accommodate 14-inch diameter rotors so when I wear out the fronts I will change them to the bigger size.

The masters are both .7 and I liked the length of the stroke before, now the stroke (pedal movement) is marginally longer and I may change the front to .75 but I am happy to leave them as is for now. Pedal "feel" is kinda a driver preference thing. I don't like a rock-hard pedal. I like some movement but not a lot. With the smaller front caliper piston area the car just felt like the brakes worked but was overall under braked. It stopped good but not great. It would lock the tires if I wanted to but only at the extreme end of pedal effort. Now I would say that the good spot of the pedal stroke is just about right when really stopping hard but with enough travel left to modulate the brake effort. This is especially so as the aero load bleeds off from 150 down to about 125mph or so and the pedal effort needs to be eased so as to not lock the front tires. A lot of deceleration can be done at the highest speed when the car is aero-loaded. But I tend to 80% the braking most of the time but only really hit them hard after a pass. I am looking forward to the next time I drive the car with new tires on it. Wahoo!

Brakes are the hardest thing to get perfect IMHO. I am really close now.

I can also add that I tried a different pad on the front, I think I like them, we'll see when I put the new tires on.


I had the 6-pot caliper on the front before (bottom)





 

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Randy V

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Sounds great!!!If you want to recover some of that lost pedal height - 2# Residual valves work wonders and I have used them many times to do exactly that....
 
Randy,
Are you saying the residuals can reduce a given amount of pedal travel? Both Howard and I have the Wilwood residuals currently.
 

Randy V

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Randy,
Are you saying the residuals can reduce a given amount of pedal travel? Both Howard and I have the Wilwood residuals currently.
Yes - that's exactly what I'm saying. The first pump of the brakes of for the day will take a longer stroke, but from there on the residual valve will keep that first pump volume in the system for quite some time. Hours, typically...
If you already have residual valves and the second, third, fourth pumps are all the same as the first pump, your residual valves may be leaking back and not maintaining that 2# in the system.
 

Howard Jones

Supporter
What I am talking about is this. The ratio of the master cylinder size to the caliper piston size influences the perceived amount of pedal movement required to transition from foot-off the pedal to full brake effort. A larger size master will feel like a harder pedal than a smaller master size will with the same size caliper and it will require more leg effort to achieve the same brake effort as felt by the driver.

My car has no bleeding problems and no pad knockback problems. The peddle feels the same every time I use it. No pump-up or anything like that. It's that I like a slightly less firm peddle than some other people. I feel like it helps me with modulation.

I have driven a car that had so hard of a peddle that it was hard to concentrate on modulation of the brakes because I was pushing on the peddle so hard. The car stopped great, but it was just too much leg effort for me, that all.

So yeah, the residual valves serve a purpose. They keep the pad slightly in contact with the rotor so that you don't have to make that distance up every time you apply the brakes in a car that has very short brake lines, low-mounted reservoirs, and/or master cylinders in relation to the height of the calipers, or a pad knock back condition.

Oh, and the camera didn't work..............fuck. I'm going to get a GoPro. Just another thing to learn to do I guess, Sorry.
 
Howard yours has been an incredibly enlightening build (or would it be more accurate to say it's an evolution at this point) to read, and I hope you're having a merry Christmas and get some time in the shop.
 

Howard Jones

Supporter
Russ. This was the point I made to Fran when I bought the car. I told him all I wanted was the chassis, bodywork, and the necessary parts to get it rolling out of the trailer with steering. I was interested in building a track-only car. I believe I was the first to do that and he was excited to help me. Thanks again, Fran. What I wanted to do was immerse myself in the development of an aero-sensitive racecar. Sort of a homemade Daytona prototype and an SLC seemed like something I could do and then develop.

Well....................I kinda did it. But the car got better and faster on pretty much the inverse of the curve that I got older and slower. Now I have a GT-3 quick car that I really can't drive that fast. So I have adopted a new goal. Simply drive the car at the best possible fun speed, remain in the appropriate run group, and enjoy what I have until the day comes when I don't enjoy the hobby anymore.

Would I do it if I was 50 again? Things have changed a lot. Mainly the new cars that would be a target have become so advanced technically that it is really beyond the ability of most people (including me) to do with a home-built car in that class. But if I did I would use a power train right out of a modern mid-engined GT car with a sequential gearbox and 500HP or more. An SLC, RCR 917 or a GTR might even be the choice. That way all the electronics would be done for me in advance. Everything else is pretty much straightforward race car stuff.

The thing that would give me pause is the budget. If I discounted the duplication inherent in the development costs and bought the right thing the first time I could build my car today for $125K and be sure to do it right the first time. There is no labor in that price except professional race engine and gearbox building and maybe a roll cage construction. The rest I can do but that is a lot of money for a toy and it might send me in the direction of a used racecar. By the way, that's right in the ballpark for a used P3 car. It's also a lot less than a new Porsche GT-3R.
 
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Howard Jones

Supporter
A bit more on the new front calipers. This time I bought them with the new high-temperature pistons. I have had Wilwood calipers experience piston seizing before due to the piston getting so hot it expands in the bore to the point that it seizes. The guys at Willwood recommend these new pistons to prevent this. Info on that is below and highly recommended for track cars. Especially on the front.

 

Howard Jones

Supporter
Ran the car again at COTA on March 3rd. Again with Edge Addicts. The goal for the day was to try and get a full understanding of brake balance, make a decision on the BP28 versus the older Wilwood C pad on the front, and scrub in the new tires during the last secession of the day.

Brake balance: I think I am as close as I am going to get to "correct". As it turns out about one full rotation of the dial towards the front seems to be optimal. I had previously had 21/2 full turns into the front from centered. That was what I considered the maximum adjustment I wanted to use. I centered the balance bar in the garage before I went back to the track this time so I would know where I was starting from. I have said previously that these balance bar systems need to be used to ONLY fine-tune brake balance and to be careful not to over-travel the mechanical bits to avoid jamming the pivot parts in an attempt to compensate for an inherent miss balance hydraulic condition. You can't fix bad piston size selection with them.

Pads: The BP28s seem to be more heat-linear than the Cs. The C pads would really ramp up the friction coefficient when they reached hot. My guess is that was about 500-600F. You could really feel them come on when they got a certain temp. The BP28 seems to bite as much as the Cs but they reach the same level of friction in a more linear manner. The car stops pretty well now and I found myself going at least 50-75 feet deeper into the brake zones than before. The only thing left to make better is to use 14-inch diameter rotors on the front when the 13.06-diameter ones I am using now are worn out. I also am going to talk to Wilwwod about pads when I get to it. I am interested in the BP30 and BP40 pads in comparison to what I am using now.

Tires: Well, well, well. New tires are better, They are so much better that I don't know what to say. Remember that Toyo wants one heat cycle and then put them away for at least 48 hours. So I could only run them once at the end of the day. They felt so different that it was a little overwhelming and I just never got confident enough to really take them up to the grip limit. The other thing is this car will put at least 4 pounds into the tires as they heat up. At the end of the day when the track is fairly hot it will be more like 6. So the drill is to take them out heat them up and then bleed them off back to 28PSI where they will stabilise for the rest of the day usually. I could not run them again and so since they ended up at 31PSI that in itself will make the car a bit weird to drive. It really only will tolerate 26-28PSI. Next time I will give them a go.

Lap times: I bought a SOLO2 and it seemed like the default settings were what I wanted. But the drive from the paddock spot to the grid fooled it into thinking that was a session or something like that. I believed I was going to get all laps for the day in memory but I only got a few single-lap sessions or very low-speed laps with a few here and there as well as the unloading time on the afternoon before. Shit! new and digital defeats old and simple again. Makes me want to duct tape a stopwatch to the steering wheel.

The few I did get were one of the morning sessions 2:54, 2:42, 2:40, 238, 2:38 and two laps at the end of the day at 2:37, and an encouraging 2:35 on new tires. The best previous lap has been 2:36. Gotta read the manual. That is something I really hate to do.

Next up is to buy a video recorder with a remote on/off. Does anybody recommend a SIMPLE to use camera with a record on/off push button remote control I can use to start the recording as I leave the grid and turn it off as I leave the track? That's all I need it to do. Nothing expensive and not full of features I don't need or want to learn. I'm old and analog.
 
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Neil

Supporter
Ran the car again at COTA on March 3rd. Again with Edge Addicts. The goal for the day was to try and get a full understanding of brake balance, make a decision on the BP28 versus the older Wilwood C pad on the front, and scrub in the new tires during the last secession of the day.

Brake balance: I think I am as close as I am going to get to "correct". As it turns out about one full rotation of the dial towards the front seems to be optimal. I had previously had 21/2 full turns into the front from centered. That was what I considered the maximum adjustment I wanted to use. I centered the balance bar in the garage before I went back to the track this time so I would know where I was starting from. I have said previously that these balance bar systems need to be used to ONLY fine-tune brake balance and to be careful not to over-travel the mechanical bits to avoid jamming the pivot parts in an attempt to compensate for an inherent miss balance hydraulic condition. You can't fix bad piston size selection with them.

Pads: The BP28s seem to be more heat-linear than the Cs. The C pads would really ramp up the friction coefficient when they reached hot. My guess is that was about 500-600F. You could really feel them come on when they got a certain temp. The BP28 seems to bite as much as the Cs but they reach the same level of friction in a more linear manner. The car stops pretty well now and I found myself going at least 50-75 feet deeper into the brake zones than before. The only thing left to make better is to use 14-inch diameter rotors on the front when the 13.06-diameter ones I am using now are worn out. I also am going to talk to Wilwwod about pads when I get to it. I am interested in the BP30 and BP40 pads in comparison to what I am using now.

Tires: Well, well, well. New tires are better, They are so much better that I don't know what to say. Remember that Toyo wants one heat cycle and then put them away for at least 48 hours. So I could only run them once at the end of the day. They felt so different that it was a little overwhelming and I just never got confident enough to really take them up to the grip limit. The other thing is this car will put at least 4 pounds into the tires as they heat up. At the end of the day when the track is fairly hot it will be more like 6. So the drill is to take them out heat them up and then bleed them off back to 28PSI where they will stabilise for the rest of the day usually. I could not run them again and so since they ended up at 31PSI that in itself will make the car a bit weird to drive. It really only will tolerate 26-28PSI. Next time I will give them a go.

Lap times: I bought a SOLO2 and it seemed like the default settings were what I wanted. But the drive from the paddock spot to the grid fooled it into thinking that was a session or something like that. I believed I was going to get all laps for the day in memory but I only got a few single-lap sessions or very low-speed laps with a few here and there as well as the unloading time on the afternoon before. Shit! new and digital defeats old and simple again. Makes me want to duct tape a stopwatch to the steering wheel.

The few I did get were one of the morning sessions 2:54, 2:42, 2:40, 238, 2:38 and two laps at the end of the day at 2:37, and an encouraging 2:35 on new tires. The best previous lap has been 2:36. Gotta read the manual. That is something I really hate to do.

Next up is to buy a video recorder with a remote on/off. Does anybody recommend a SIMPLE to use camera with a record on/off push button remote control I can use to start the recording as I leave the grid and turn it off as I leave the track? That's all I need it to do. Nothing expensive and not full of features I don't need or want to learn. I'm old and analog.
"...during the last secession of the day...." That must have been a Southern track, Howard. :D
 
We use BP30/40s on the Sprint car. 40 on LF, 30 on Rear. The 40s grab on application - desirable on the Sprint car LF as it helps turn the car. Both work well cold and hot.
 

Howard Jones

Supporter
Frank, thank you for that. I also tried the 40s, I used them on the front to try and overcome the lack of front caliper clamping force but what I got was a really aggressive on/off feel with little progressiveness. I have run Wilwood "B" pads a lot and I really like their progressive grip/heat curve. It might be the Bs suit my driving style and run lengths. Would you know if the BP30s are similar to the B's. The BP28s seem to be somewhat similar. I'll know more after the next outing.
 
Sorry, never ran "B"s. Have tried a few non-Wilwood pads in our Wilwoods. Only thing good I can say about any of those is they are cheaper and the local shop always has them on the shelf.
 

Howard Jones

Supporter
Thanks for that Frank. I said in the past that I was going to call Wilwood and talk to a "technical" person and not a salesperson. I did that and the fellow was very helpful. He asked a lot of questions about my car and what I did with it. I really wanted to know which of the current lineup best duplicated the "B" pads I am familiar with and he said the BP30 would be his choice.

On the BP28s. He told me that they are designed to be used on stainless steel and titanium rotors but also can be safely used on the Iron rotors I have on my car. They have a lower friction coefficient than the "B's" when used on Iron and higher FC if used on strainless/titanium. He recommended I change to the BP30 and not use the BP28s.

The truth is, I relied on the FC/temp charts too much and made a mistake buying the 28's. I should have called Willwood first. Another thing I learned the hard way.
 
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