Slide valve attention

[Henry Schmidt]

We recently had the "pleasure" of inspecting a set of reproduction slide valves that apparently came from Italy. On first inspection, they appeared to be pretty good.
When we disassembled them we found a number of issues.
First thought was "why bother" but as we dug deeper, the issues seemed easily rectified.
First, too much side play: It turns out that the bearings that prevent side to side movement have no adjustment. We were able to remedy this situation by replacing the clamping hardware and slotting the rail.
Marginal slide function: We found that the rail that provide the bearing surface for the lateral movement were unbelievably rough. Hand lapping cured that.
Missing bearings: missing bearings were sourced but because all the bearings were Chinese, they were replace with Austrian made Steyr bearings.
The last this was simply the intake size: I have always believed that Porsche over-ported their small race engines. IMHO the 43mm RSR was a mistake. These slides are 43mm so we made a 38mm removable sleeve that would make these slides more suitable for 3.2 and smaller engines. Now that this process is complete, the test set are for sale.
We will also be offering this service to anyone who finds themselves with a set of these slides.

[winders]

Slide valve, or guillotine valve as they are often called in Europe, ITBs get a lot of oohs and aahs but they really are not that great in reality. Read here:

https://www.racecar-engineering.com/articles/f1/technology-explained-f1-throttles/

Slide valves are the way to go if you need to use them for originality or if you have a restriction on the diameter of the ITB and the increased airflow at wide open throttle versus a butterfly setup is worth dealing with the slide valve shortcomings.

Otherwise go with butterflies. Or, if you have the money, get barrel ITBs. The AT Power "shaftless butterfly" ITBs are a great way to go.

[Henry Schmidt]

Old Porsches are rarely about "state of the art" technology.
We've been putting slides on street car for years. See Wanye's first "911 Rebuild" cover. That's a slide engine we built for the street 25+ years ago.
Slides have wow appeal and they work just fine. They are not the best option for most but if this is the desired aesthetics, we can make affordable options work as designed.

[Henry Schmidt]

8000 rpm 2.8 short stroke, street motor that ran on street gas, started easily and idled great.

[Henry Schmidt]

Red Sled

Slip Sliding Away in a Carrera RS Replica
Article and Photos by Randy Wells

“The combination of sprint cams and slide-valve injection is not really a street-friendly combination,” Jerry Murray explains as I prepare to test drive his blood red 2.8 liter shod early 911. Undeterred, I strap myself into the perfectly positioned race bucket and turn the key. The motor awakens from its afternoon nap accompanied by a raucous swell of air-cooled flat six goodness. I blip the responsive throttle knowing that a lot of revs will be needed to get rolling thanks to the Kevlar clutch and aluminum flywheel out back. As we gently ease into traffic the engine sneezes a bit, almost as though it’s out of tune. “It took us a long time to get the car dialed in for the street,” Jerry remarks as we pick up speed. “I sometimes need to lubricate the throttle bodies before getting started. If I don’t, the slides can stick open.“ This is not exactly a comforting thought as we are already accelerating down the backstretch leaving Laguna Seca Raceway. But resistance is futile, and it’s foot to the floor at the first clear opening. That’s when everything starts happening very quickly.

Forget about being melted into your seatback with the long steady pull from a modern engine. This beast snaps your spine so hard it will pop the buttons off your lederhosen. Even with 8500 rpm available, constant vigilance is required to hit shift points that come up uncomfortably fast with the close-ratio gear set. “I probably inadvertently over-rev this car more than any other I’ve owned,” says Austrian born / LA based Murray. “Thankfully, Supertec built me a bullet-proof motor”. It’s at this point that I’m grateful they also added big AP brakes on all four corners. As I throw out the anchors for a rapidly approaching bend it becomes abundantly clear - the only thing that parallels this car’s acceleration is its ability to stop.

“The Can/Am style calipers with 12” rotors and twin master cylinders were used on 917’s, but eventually made their way to 911 racers seeking an edge.” Jerry’s lips are moving, but the screaming racket coming from the open intake stacks and sport muffler is drowning out everything except the one thought that I might die and go to heaven today. After another attempt at the land speed record it’s hard on the binders again. This slows our pace just enough to start the ride all over again at the next corner. A quick turn of the wheel, roll on the throttle, skate along that thin line between traction and no traction, catch the slide with some opposite lock, then be glad the limited slip differential does its job. Cars that were right beside us are dispatched to the rear view mirror in a heartbeat as the tractor-like pull from this impossibly torquey motor propels us continually forward. I tell myself I could get used to this - all the while fully aware that I’m dangerously close to breaking the speed limit and expanding my carbon footprint beyond what is considered politically correct.

We are rapidly approaching our destination, so I make one more sub-sonic pass to ensure the experience is indelibly imprinted on my brain. When we finally slow down enough to catch our breath, I realize the car’s ride has been firm in the corners and reasonably supple on the straights. On smooth surfaces it’s supremely planted and sticks like glue, but irregularities like cracks, seams and pavement scoring can make this 911 a handful. Jerry’s understated delivery continues, “It definitely reacts to everything on the road, for better or worse, so you need to stay on top of this car.” As we unbuckle, he tells me more about what went into his special 911, “I bought the car about ten years ago as a 1972 RS replica built by Mark Kittinger at Black Forest. It had the upholstery, RS flares and bright red paint job you see today; along with a 2.7 RS spec MFI motor. The first thing we did was take the car to Henry Schmidt at Supertec in Fallbrook, Ca. I bit the bullet and asked Henry to build a motor that was out of the ordinary. We went with a short stroke 2.8L with twin plugs and MFI.”

The engine is the soul of any car and this one is unquestionably a work of art: NOS 3.0L RSR case, 66mm crank, Carrillo rods, 95mm 9.8:1 Cosworth pistons, race springs, 964 oil pump, 40/38 mm ports, RSR sprint cams, 935 twin fuel pumps, twin plug ignition with twin 935 8 pin Bosch CD boxes, and those wild sliders which are replicas of the ones used on 910 Porsches campaigned in the early 60s. Jerry explains the reasoning behind this unusual choice of induction, “Slide valve injection is not usually seen on a street car because it’s difficult to modulate the throttle and it’s prone to binding up from road grit. I never would have thought of this myself, but I turned Henry loose to create a special motor and he came up with some really neat stuff.” Certainly, this motor looks as good as it sounds - with handmade aluminum intakes topped by wire mesh screens and twin plug wires & 935 fuel lines delicately wrapping around the fiberglass shrouded engine. To finish it off, a dual outlet sport muffler exits under the rear overriders.

In addition to the motor, Henry at Supertec spent quite a bit of time considering the transmission, suspension and braking aspects of the car. A late 915 gearbox was chosen for its greater strength and was equipped with an aluminum flywheel, limited slip and hill climb gear set with a tall 5th gear for freeway cruising. “That top gear is the only aspect of this setup that is really not suitable for the track”, says Jerry. “The reduction in RPM between 4th and 5th takes me out of the power band. But for the street, I can’t recall when I needed to keep the revs up during that transition.” The suspension was totally redone front to rear featuring 935 coil over struts, Eibach 250 lb springs in front, 380 lb in rear, Sachs shocks all around (shortened in front to receive mono balls), ERP spring plates, and highly adjustable Charlie sway bars. “The shocks were heavily reworked by the race team we got them from, so I have no idea how they are valved. All I know is that they work exceedingly well, but are not suited for those with loose fillings,” Jerry says. In addition, roller bearing spring retainers were implemented, as were turbo tie rods. Brakes are the aforementioned A.P. four piston calipers with 917 style rotors, twin master cylinders and a balance bar. Considering all the racing components on this 911, you would think it spends all its time at the track. But its primarily use is for driving to and from car events. Still, the rock chips on the front bumper confirm that this is no garage queen – even if it has been shown at the Quail Concours in Monterey, California.

....edit....
Many years later, when the decision was made to have an early 911-based hotrod built, he wanted to take a different approach. Creating a cool sounding RS clone would not be enough – the ideal would be to use original factory or vintage racing parts when possible and blend those with a few more modern ones to create a unique experience. Jerry reveals his reasoning, “It’s all about driving the cars, and making modifications to enhance your enjoyment. It’s the same now as when these cars were new. Enthusiasts and racers were always experimenting, trying something different. It doesn’t matter to me if all the parts weren’t factory options, as long as the majority of them are period-correct.” The building of this car continues to be an ongoing process rather than an end point. Jerry and Henry would start work on the ‘72 911, then find a new component and adjust their direction accordingly. It wasn't until the motor finally took shape that they decided the old suspension and brakes were not going to handle the horsepower. Additional hood lighting is just another example of a treatment that illustrates the underlying principle behind this car’s distinguished build.

....edit....

Jerry freely admits that with an estimated 300 hp in a 2200 lb. chassis his custom 911 is over-built for the street and the skills of a novice. “I graduated from Skip Barber and a few other schools, and thought myself competent to handle what this car has to offer,” he confesses. “That was until we ran into the late Milt Minter at Buttonwillow Raceway. He was gracious enough to take this car out for a shakedown lap with me in the passenger seat. It was absolutely terrifying, and equally humbling when he later admitted only driving 8/10ths since it was an unfamiliar car.” Awareness of the capabilities of his one-of-a-kind coupe has only made Murray more appreciative of the German marque, “I’ve been very fortunate to have had some wonderful cars, but my favorites have always been Porsches”. Clearly this wickedly fast and beautiful “Red Sled” is a testament to that loyal devotion, and air cooled goodness is in Jerry’s blood. Uncle Wilhelm would undoubtedly be proud.

[faapgar]

I have Slide Valves on a 2.8.It was refreshing to hear about Milt Minter driving your car.One of the most underrated drivers of that era.In 1976 I was crew chief for a brand new 934 that Paul Miller had bought.We went to Watkins Glen for the 1st race.Paul and his brother Kenper had practiced in the car for two days.The hired driver was Milt Minter who showed and after 3 laps was 2.5 seconds quicker a lap.He said after the back straight going down to the left hander into the valley the car would snap oversteer.I had driven the track many times and suggested to put a tie wrap on the shock to check travel.Well the ride height was too low and the shock was bottoming.With that change he was even quicker.He was a guy you throw in a car and he could wring the best from it.Any way I have 45mm slides on a 2.8 built on 76 Turbo case.Love it.Ciao Fred

[Henry Schmidt]

Originally Posted by faapgar

I have Slide Valves on a 2.8.It was refreshing to hear about Milt Minter driving your car.One of the most underrated drivers of that era.In 1976 I was crew chief for a brand new 934 that Paul Miller had bought.We went to Watkins Glen for the 1st race.Paul and his brother Kenper had practiced in the car for two days.The hired driver was Milt Minter who showed and after 3 laps was 2.5 seconds quicker a lap.He said after the back straight going down to the left hander into the valley the car would snap oversteer.I had driven the track many times and suggested to put a tie wrap on the shock to check travel.Well the ride height was too low and the shock was bottoming.With that change he was even quicker.He was a guy you throw in a car and he could wring the best from it.Any way I have 45mm slides on a 2.8 built on 76 Turbo case.Love it.Ciao Fred

I knew Milty for years. Great driver but also a great guy. We met on the track with a close encounter. We qualified ahead of his car and as he moved through the field, I got in his way coming out of turn nine at Willow Springs. We were both in 914s and he dove under me half way through the corner, striped the side of my car and blew by. In the pits, we spoke and he didn't even know we touched. The orange on the side of my black and red car proved me right. He apologized and gave me some pointers on rotating through high speed corners. Friendly for years after that.

[jpnovak]

Great Stories!

I just wish these type of throttles were more affordable. I realize the cost of small batch manufacturing but unfortunately these are out of the budget.

[Henry Schmidt]

Originally Posted by jpnovak

Great Stories!

I just wish these type of throttles were more affordable. I realize the cost of small batch manufacturing but unfortunately these are out of the budget.

These sliders could be had for about $6,500.
We bought them to evaluate the product and I'd rather not have it sitting on the shelf.

[stownsen914]

Even though it seems slides may not be the best option performance-wise, they sure are cool. Hope to get a set on the vintage race 911 at some point, like it had back in the day.

[winders]

Yes, they are very cool and sexy. If you have a vintage car that came with them, or you want your car to be period correct, or you have a Historic race car that requires them, they are the only way to go.

I was just saying that you would not want to use them on a build for PCA GT3 race car or for a 964 or 993 street car as they are not best option in those cases as there are better options. Most people do not know that slide valve ITBs are not the best option from a drivability standpoint.

[r lane]

I have a set of those and they are pretty and probably work well enough for me. Am building a 3.6 and will probably trasfer them to that engine. I was at Laguna Seca, fall of 76 with a car driven by George Dyer. I remember 2 934s were there, one driven by Hurley Haywood I think and the other one by Milt. Was wet on either test or race day, Milt would come onto the straight and in the middle of a puddle put it sideways, lift for a nano and back on it trailing flame and backfire. Parked it on the side of the track during the race, CD box had loosened, fell into the throttle linkage, all the fun he could stand. Climbed the fence, collected my friend Billy Cook who was free at the time as our car was out, and headed for a groupe of beer drinking buddies he referred to as the Fresno Indians. Not that racing today isn't top notch, but I think back then, more interesting and colorful.

[winders]

Originally Posted by r lane

Am building a 3.6 and will probably trasfer them to that engine

What size are they at the slide?

[r lane]

43.5mm. They are presently on a 3.0, 265 at the wheels. Response all through the range feels great, but then I don't have something else to relate to. Well that is not totally true, I do have another engine, but with less compression. It has a set of 2.2 stacks that I taper bored and put in 40mm butterflies. That motor has not been to the dyno, but seems to pull similar rpms at specific points on the track

[Henry Schmidt]

As mentioned in the original post, we make a removable spacer that reduces the port size from 43mm to 38mm. They allow for a more appropriate port match for smaller engines where port velocity is critical.

[BURN-BROS]

Nice Work Henry!

[Jeff Alton]

Beautiful!