GT Thunder TRX90 National Engine Review

[Pappy]

Ever since the fine folks at Racer Productions made it final that the youth riders would have a home at the GNCC event's, I was wanting to build our TRX90 into something competitive. Being pretty close to the folks at GT Thunder made it really easy to make a decision on who would get the engine.

Laz Sommers, owner and head wrench of GT Thunder is not only a business man, he is a racer first and that usually means you are going to get something that works and not just a bunch of expensive parts and a big bill!

I had decided that I would leave the engine up to Laz and the specs would be at his sole discretion. At the opening round of the GNCC Youth season, he handed me an engine and we promptly installed it the week following the race. The little 90 had been transformed into something that could stay with any other mini quad in the straights , yet had plenty of grunt and mild manners to keep things honest in the woods. Unfortunatley, the engine was 114 cc and even tho several participants have swayed back and forth on the rules, we decided not to run that engine.(RP states that no engines over 90cc)

So, back to square one, another call was made and the engine shipped back to GT Thunder. I explained my situation and we decided to make a 90cc engine that complied with the rules.

The TRX90 engine was treated to a full port job and the head fully inspected and all needed parts were replaced. A new stock cyclinder was then turned into a true 90cc along with a cam to aid in the quest for more power. A slightly higher compression piston would net us more power and the bottom end was deemed in decent shape and left alone. So after no more then 3 weeks, we were ready to try this animal again.

[Pappy]

The engine was installed and break in was completed and first impressions were that it was faster then stock, but not quite what the 114cc engine was capable of. Laz had sent along a larger carburator, but a custom cable will need to fashioned before we can install it.

Being way past the point of common sense, we decided to take this quad racing and see what would happen. The only thing we changed to the driveline was a 1 tooth larger front sprocket. Every thing else was swapped over from our other stock 90.

The first race netted us with the holeshot and more then enough power to keep us out front against some very talented young racers. A mistake in a very rocky section cost us a class win on the first race the bike had attended. The damage to teh quad was repaired and the very next day we hit another local race, securing a second holeshot and the ability to lead more the half the race. Soggy front brakes cost us an overall but not a class win!

[Pappy]

With a weekend full of racing complete, it was time to inspect the quad and engine for any damage. The oil was full and no apparent damage to the engine, but we were not fully satisfied with what we had.

After tightening almost every bolt, repairing tires and rims, we decided to tackle an issue with the stock carb. There was several tweaks and adjustments made and finally the little 90 started showing she had more life in her then we were giving it credit for.

A top speed run was made and in our longest straight away we clocked the quad at 43 mph. That is not too bad for stock rear gearing, and from racing the TRX90 we knew where some more speed was hidding. A quick rear sprocket change and we went back to testing. Top speed exceeded 46 mph but to be honest, I had to let off the chase quad or hit a fence:p I know this is not a dyno, but it is as real world as I can get.

Further testing this combo on our GNCC style track netted us with exactly what we were after. The quad pulls from teh basement and tops out past a point most youth riders will ever need in the style of racing we participate in.

Dyno time will follow, as will the results from the larger carb once it has been installed and properly tuned on the dyno.

GT Thunder gets an A+++ from us in not only customer service, but in the confidence thier engine has given us.