No matter how perfectly straight and round it may be when it is machined, a cylinder bore will change shape when cylinder heads are installed and when the engine reaches normal operating temperatures. During a presentation at the 2002 PRI Show, the subject of “Hot Honing” caused a tremendous stir of excitement among performance engine builders who were looking for it to provide straighter cylinder bores, reducing oil consumption, blowby, wear and engine friction.
“The concept of heating the block with a simulated head plate and then honing the cylinder bore to achieve a round bore has been evaluated by race engine builders over the years,” explained Harold McCormick of C-K Technologies. “We don’t claim anything that hasn’t been looked at in one form or another in the past. What we feel we brought to this industry was a very organized method of putting together and validating a system – and it can be a very challenging and expensive route.”
In terms of friction reduction, hot honing offers a 1-2 percent improvement. Plus, explains McCormick, the side benefits are real. “Without the lumps and bumps in the cylinder bore you can run a closer piston-to-bore clearance. We’ve seen cases where the engine builder was having a serious piston scuffing issue. By straightening the bore out we were able to eliminate that,” McCormick says.
In addition, he explains, the process allows you to decrease the tension of the rings. “You maintain oil consumption, you get some improvement in friction by any incremental reduction in tension you can make,” McCormick says.
The method developed by C-K Engineering and Sunnen Products Co. delivers on its promises, say experts – but is that promise still demanded by engine builders?
“Even within the performance engine building industry, hot honing is very much a niche market application,” says Sunnen’s Tim Meara. “It provides a real benefit to engines that experience thermal distortion, but it will never be something that a PER will need to do. Even the typical CER won’t see a benefit – it’s more for the high end/high performance applications.”
So if the typical reader of this magazine won’t benefit from the process, why are $20,000 hot honing units still being sold to so many engine builders? Because for certain applications, it can provide a definite edge.
That application is engines that see elevated temperatures for extended periods of time. “On any given Sunday,” McCormick explains, “probably 35 of the 43 teams racing in NASCAR competition will be running with hot-honed engines.”
While many of NASCAR’s top engine builders realize the procedure’s benefits, Meara says other types of racers do as well. “It really leaves you with two classes of racing: endurance road racing and off-road racing like the Baja 1000, or other long races run at extreme temperatures and distances, and circle track racing including sprint car racing.”
McCormick says “The only thing we haven’t seen much interest in yet is high-performance boat racing. We think there could be benefits there, but we haven’t been able to link up with anyone and evaluate it yet. We should be able to show horsepower improvements there.”
Meara says that, for all of the performance involved in drag racing, hot honing is not necessarily a valuable speed trick. “Some drag racers are doing hot honing but it all depends on the block. In some of the stock eliminator classes, where they have to use stock blocks, they’re looking for every advantage they can find. The key is, you need to know whether you’re getting thermal distortion.”
However, McCormick says the need for hot honing may occasionally be overtaken by its allure.
“We’ve also started seeing some interest from Pro Stock drag racers, which is a funny story, because when we look at the data we’ve collected, the cylinder temperatures really don’t get that high,” McCormick says. “A team called us expressing interest in the procedure, but we actually discouraged them from making the investment until after we worked with them a bit.”
McCormick says, “We did a block for them and they must have thought there was some improvement, because they came back and ordered a unit.”
McCormick says that because hot honing’s benefits may not be as evident to drag racers as in some other types of racing, his guess is that much of the improvement seen comes from the torque plates developed for use with the system. “The torques plates we have developed are verified to have exactly the same distortion characteristics as the cylinder head. My guess is they’re seeing improvements from that.
“It’s certainly a possibility that some people are buying a system they don’t really need – many of them could probably get by with a well-designed set of torque plates,” he says.
“The really interesting thing is that now we’ve been getting orders for hot honing units from other Pro-Stock racers, an application we certainly didn’t expect. It may be because things are so competitive in the racing community that if one team does something and sees an improvement everyone else feels they need to do it, too.”
The idea of hot honing isn’t new, reiterates McCormick. “Bill ‘Grumpy’ Jenkens says he did it back in the late ’50s, early ’60s,” he says. “But we’ve gone the extra mile. There was a fair amount of investment involved to get what we felt would give a quality result – it’s not cheap and it hasn’t been easy.”
Other methods of warming an engine block before honing have been tried, but they don’t produce enough heat to keep the blocks at temperature while they’re being honed. Says Meara, “Sometimes people figure they’ll be able to use a hot water heater. With a cast iron block, that hot water heater can’t recover fast enough to keep the block at temperature. I can’t even get through a shower with enough hot water, so heating a 200 lb. block to 220° F is impossible. The hot hone unit pulls 50 amps – it’s like using a welder – it needs to have that much heat put to it.”
The benefits of hot honing have been proven and McCormick admits that he has looked at ways to broaden its appeal to the rest of the industry. Try as he might, though, the benefits will be seen in the engines that are naturally much more expensive. That, Meara says, means engine builders might be better off looking elsewhere for horsepower improvements.
“The way I look at it is this: this procedure offers a 1 to 2 percent gain,” Meara says. “Have you used up every potential improvement you can get everywhere else? It can definitely help if you’re experiencing sealing issues, but there may be other ways you can make bigger gains faster.”
