Max HP on Honda block?

**RollingThunder** · June 15, 2014, 08:23 PM

So the 3.5R is making 350 hp on a K20, which I assume is safe and reliable or the factory in England would not offer it. But this got me wondering -- what is the max SAFE and RELIABLE hp one could expect from a boosted k24 without changes to the internals? I have not heard of any issues with the factory supercharged option at 300 hp, but wondering how much more is possible without sacrificing the reliability of the Atom which is one of its selling points?

**wafflemaster** · June 15, 2014, 08:46 PM

Some of the Civic guys are getting into the 400s on stock internals, but I'm not sure I would call that safe. I think 350 would be a reliable "daily driver" number to shoot for. You just have to watch the fueling and timing so that you don't melt the pistons during long periods of high-load.

Forged internals and stiffer valve springs should allow for 400s no problem.

**RollingThunder** · June 16, 2014, 05:04 AM

Thanks. I should clarify that I was thinking of the reliability from a track perspective, not the street. Obviously the track is harder on cars so how far can one go on the k24 without some form of an engine build?

**DBeach** · June 16, 2014, 02:25 PM

At PRI last December, HPD told me that they expect at least 2 years before rebuild on the HPD race engines they use in the Grand-Am and World Challenge series. They also said that a rebuild was about $4,000.00.

**jeff8407** · June 16, 2014, 02:57 PM

The "weak link" in the Honda engines are the pistons, especially when boost is taken into consideration.

**McFred** · June 16, 2014, 03:19 PM

Originally Posted by RollingThunder

So the 3.5R is making 350 hp on a K20, which I assume is safe and reliable or the factory in England would not offer it.

I think you're confused by numbers between this side of the Atlantic and the other. The Brits get a hard on over brake horsepower and people from the US generally speak horsepower at the wheel. So "350bhp" to them is "300whp" to us. 300whp is about 350bhp after the generally accepted 15% drivetrain loss is tabulated. That said 300 horsepower at the wheel is cake for a a Honda K20A and can usually be achieved with a wee rotrex at ~12 psi. You can have pretty aggressive timing and keep your cast pistons so long as it's well tuned and your IATs stay low.

There are people in excess of 400whp K24's with rotrex super chargers using aftercoolers or E85. That's like ~475 brake horsepower for those who speak the Queen's english. I would agree that that's probably pushing the edge of reliability. Probably one of the best places to look for what people are doing to get those numbers is K20A.org. You'll have to wade through a lot of junk to get the info though then probably have to take a lot of that with a grain of salt.

**RollingThunder** · June 16, 2014, 04:23 PM

Originally Posted by McFred

I think you're confused by numbers between this side of the Atlantic and the other. The Brits get a hard on over brake horsepower and people from the US generally speak horsepower at the wheel. So "350bhp" to them is "300whp" to us. 300whp is about 350bhp after the generally accepted 15% drivetrain loss is tabulated. That said 300 horsepower at the wheel is cake for a a Honda K20A and can usually be achieved with a wee rotrex at ~12 psi. You can have pretty aggressive timing and keep your cast pistons so long as it's well tuned and your IATs stay low.

There are people in excess of 400whp K24's with rotrex super chargers using aftercoolers or E85. That's like ~475 brake horsepower for those who speak the Queen's english. I would agree that that's probably pushing the edge of reliability. Probably one of the best places to look for what people are doing to get those numbers is K20A.org. You'll have to wade through a lot of junk to get the info though then probably have to take a lot of that with a grain of salt.

Thanks McFred. I understand the difference between wheel hp and brake hp. I was referring to hp at the crank for a single point of reference as that is the measurement used by TMI and England to my knowledge. The supercharged American version is 300 hp at the crank, not the wheels as I understand it. The 3.5r is now around 350 hp at the crank. But given both these HP figures are substantially more than the stock Honda engine hp as it sits in a Civic, for example, I am just trying to get a sense of how far the hp can be pushed without changing the internals.

**wafflemaster** · June 21, 2014, 08:08 AM

Here's what my stock Atom 3 with the k24 is putting down to the wheels:

ImageUploadedByTapatalk1403359611.832770.jpg

213hp. This is on my Mustang MD500, 2 pulls overlaid. You can see there there is a bit of room for improvement in the tune to smooth out the torque curve a bit.

**atom ant** · June 22, 2014, 03:50 PM

Several Atom "300" dyno at 243-248 whp, a quick search on youtube will show the dyno pull videos. This is with the factory supercharger (stage 1, 7psi). I just finished the dyno on my stage 2 (10psi) measuring 278-280 whp. A reverse calculation will show around 18% drivetrain loss, this would yield 341 hp for the stage 2 setup. I believe anything higher than that on the K24 would be a crap shoot.
A spare frankenstein motor is being build (K24 block with K20 head, same race motor used by Honda racing). The same stage 2 super charger should yield over 400 hp reliably.

**FourFather** · June 23, 2014, 08:35 AM

I would think that, given equal rear wheel horsepower, a turbo engine will be less stressed internally, because it does not have to make the extra horsepower that it takes to turn a crankshaft driven supercharger.

It has been said that the maximum horsepower an Indycar engine makes, is not enough to spin a Top Fuel supercharger the way we run them.

Using heat energy that would otherwise be wasted, to turbosupercharge an engine, is likely a more energy-efficient way to go, and should produce longer engine life for a given horsepower level, don't you think?

Eddie