SURBO ON A RACE GO KART

Mike, owner and driver of kart
(Mike first used the Surbo on his 2007 Kia Cerato CVVT 1.6)

This is Mike's kart, with a 125cc 1-cylinder, 2-stroke Aprila engine. The original power of this engine was 28 bhp at 14000 rpm, and with its own weight at 90 kg, and Mike's at 83 kg, the power per ton was 28/{(90+83)/1000}=161.85 bhp per ton. The Surbo has been observed to give 30% more acceleration power (as shown on a 125 bhp Civic ESi with Surbo beating a 160 bhp Civic VTi), and so the kart with Surbo could have 161.85x1.3= 210.4 bhp per ton. Compare this to the 265 bhp per 1450 kg of a 2004 WRX 2.0 STi, which is 182.75 bhp per ton, and it is clear that this kart is not a toy.

The kart had been in Johore Malaysia, so it was not possible for me to fit the Surbo on directly. Mike had taken the air filter case to me, and I incorporated a small cone filter in place of the shredded sponge filter inside the filter case, put the Surbo in the grey pipe and included adaptors. It was up to Mike and his mechanic David to clip the setup onto the throttle body of the carburetor. I turned up only 10 minutes from the start of the race and there was no time for adjustments.

Mike finished in 4th place, out of 7 karts. I talked to Mike and decided to tweak the Surbo system, as there were 2 air purge tubes from the carburetor, which we had left alone for the 11am race. I connected the 2 purge lines to 2 taps on a T joint (silvery part shown in pic below, which I had taken from home in between the 2 races). Also, the Surbo setup was not sealed at the throttle body and that caused a pressure leak. I applied silicone to be sure. Mike had the option to run with taps closed (full air compression from Surbo) or with one or both slightly open. David was concerned with retaining some of the purging as it was part of the 2-stroke engine design, but it would take away some of the air pressure from the Surbo. With both taps closed, David agreed that the sound the kart engine was making was a high-compression sound, as he suspended the rear end of the kart, and let the rear wheels spin freely.

4pm race: there was new-found power in the kart with the Surbo blowing fully, but so much that Mike could not step on the throttle through the corners as the throttle became too sensitive. The rear driving wheels would skid if he opened the throttle, so he had to be careful around the corners. He took this as a practice session as it was like a new kart, which was different in handling. He will be putting the kart through more testing on the straighter tracks in Johore later. I will be supporting the kart development in every way I can, including installing an electronic fingertip purge control so that excessive boost can be taken away before corners, and full boost applied on the straights. Also, an electronic vacuum gauge will be added to help trigger the Surbo for max power at part throttle, thus keeping much spare vacuum in the engine to ensure rev extension. There is no electronic rev limiter on the kart, but just an adjustable mechanical stop on the throttle spring.

EMAIL FROM MIKE DAYS AFTER

Once again thanks for helping at the track, i'll probably be testing it again end of the month when we catch up with some other karters. the device really can make much difference to the kart, even more than in a car, i'm keen to incorporate it into the kart but must first tame it down a little, otherwise i can't turn into corners, hope some setting on the chasis can help. David was saying he'll also try it on some of his old engines which have already lost some compression, will keep you in touch of the progress.

Mike

Mike and I decided later that the purge on-off control should be linked to the brake pedal. That is, when the brakes are applied, the purge would expel the Surbo's air pressure, and when the brake pedal is released, the purging would end and the Surbo would make its pressure again. Mike will implement this on his kart and any news will be reported here.

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