Way back in the muscle car days, the easiest way to get more power out your engine was to put in a big, lumpy cam and some high-compression pistons. Without the bigger cams, higher compression pistons will get you extra power, but the two of them together usually make for a potent combination.
Last month, we wrote about Mahle's newest pistons for the H22. These true drop-in pistons for a stock block are an incredible breakthrough. The H22's block is all aluminum, with no steel sleeves like other Honda engines have. Instead, Honda casts a carbon-fiber matrix around the cylinder area. The carbon is strong enough to eliminate the need for steel sleeves. Porsche 944 engines are similar. The problem is that forged-aluminum pistons don't like pushing up and down in that all-aluminum bore.
Mahle was the first aftermarket company to take their experience in OEM and racing (including Formula 1) piston manufacturing and develop a forged H22 piston with a coating that is compatible with the H22's cylinder walls. Until the Mahle pistons came along, you had to sleeve your H22 to install forged pistons. Available in low-, stock- and high-compression versions, you can now do a lot more with your stock-block H22 than previously possible.
Talking with Mahle about their new pistons, they told us of a development project that involved a "high-mileage" Prelude with about 70,000 miles. The short version is that they installed their 11.5:1 pistons and a pair of aftermarket Japanese camshafts into this H22 and, with that, horsepower jumped by 30!
Well that sounded like a challenge to us. So with Mahle on board, we set out to duplicate the project with an H22 of our own. The good guys at Superior Racing Development in Tempe, Arizona, helped us locate Dustin Denson, whose '95 Civic coupe had a transplanted H22. Dustin dropped off the car and we started what became a nearly four-month project.
Mahle sent up a set of their drop-in 11.5:1 compression pistons and we started the search for cams. Mahle couldn't remember exactly what Japanese company had supplied the cams, but Brian Crower told us about his Crower cams having been revised with some of the fastest ramp rates available and manufactured with a new hardening process so we were game. Crower sent us a set of Stage 3 cams, springs and revised retainers specially made for these very high-lift cams.
But first things first, we needed to baseline the H22 Civic. Over to Xact Dyno in Tempe, where a group of third-gear pulls on the Dynapack netted us about 156-wheel hp. It seemed low to us and when we called the car's owner about it, he said that had to be wrong. The car had been tuned in January 2005 to 176-wheel hp. Looking at the power curve, (yellow line in dyno chart) we could see that the top end went really flat. Xact had seen this before and figured it was the pistons letting go. Sure enough, a compression check showed low numbers on every cylinder.
Regardless, this engine was about to get new pistons and we set to work at SRD, getting the head off and the old, dying pistons out. Jake at SRD got the head off and instantly saw the problem. Every piston had scored its cylinder wall, creating a lot of leakage. Also, judging by the yellowing on the cam oil-spray bars, it seemed as though the oil had not been changed in quite some time. That's the problem with swap motors; you never really know exactly what you're getting.
With the pistons removed, SRD decided the cylinder wall scoring was too deep to remove with just a bore smoothing and that we'd have to use the .25mm overbore Mahle pistons. Mahle quickly got us a set of their overbore pistons and the block went off to S&S Machine in Mesa, Arizona, for the overbore and cylinder prep process. Just as we explained in the March 2006 issue, this is a critical step and you need to make sure the shop you chose knows how to do it.
After all that, SRD put the engine back together and dropped it into the car. The next step was to set the clearance of the rocker arms. In addition to the rocker clearance, you'll also need to install revised retainers that allow for a higher installed height. The B16A and H22 have notoriously short installed heights (1.320 inches or less). The +.060-inch retainer raises the height, allowing more lift and preventing the retainers from hitting the valveseals. Crower dual valvesprings (good for 8000+ rpm) were installed, as were the raised-height retainers.
Before we could race off to Xact Dyno for tuning, SRD decided that using such a big cam and high-compression pistons required checking the piston-to-valve clearance. Sure enough, the exhaust valves hit the pistons. This Crower cam was a big boy. The good news was we wouldn't wreck anything; the bad news was it all needed to come apart so the pistons could be relief cut. Mahle is keen to mention that the pistons we received were released in small batches and that all future batches will have the necessary clearance relief cut into them. The moral of the story here is to pay to have unknown combos like this checked or you'll really pay later.
Finally, nearly three months into the project, the Mahle/Crower H22 was ready for the dyno to see if we could get the same results as the Mahle R&D crew. Off to Xact Dyno we went and pushed out some pretty crappy numbers. Believe us, there not even worth mentioning. Drawing on Xact's experience and placing a call to Crower gave us an idea.
With big aftermarket cams and pistons, the exact cam center can easily be different than with factory sprockets, especially if the head has been milled. Because Dustin already had adjustable cam gears installed, and because SRD was swamped and two deadlines had already passed for this story, we moved over to UMS Tuning. Tony Szirka, owner of UMS, put a cam degree wheel to the H22 and found that the cams were indeed off from zero on the cam wheels.
Relative to Crower specs, the cam wheel indicated that the exhaust cam was 5 degrees advanced and the intake advanced by 4 degrees. That's quite a bit, but our head did get decked for a truly flat surface, and this is a high performance combo, so it's actually not bad. Like the piston to valve clearance check, this is another must-do performance step to get maximum power. Tony says it's a three-hour job, but you could easily spend that much time on the dyno at way higher rates trying infinite combos and still not get it right. Plus, you run the risk of going too far and whacking a valve into a piston. Thanks to UMS for stopping what they were doing and getting this done.
Back on the dyno AGAIN, torque was massively improved. We had the added advantage of a Hondata s200 to tune everything like we were factory Honda engineers. Tuning on the small cam was going very well; however, switching to the big cam, we were again disappointed. Power climbed steadily to 5500, but then just went flat. After everything on the ignition side was checked and OK'd, Xact decided it had to be the exhaust.
Dustin's car had an OEM compatible DC 4-2-1 header with factory sized collector. It had no cat and a 2.5-inch exhaust, but according to Xact, it was clear the air just wasn't able to get out. SRD to the rescue again. Josh just happened to have an RMF-style 4-into-1 header with a 3-inch collector sitting at home. We quickly grabbed it and bolted it to the H22.
With the much larger header in place, power literally leaped to 198 from 166. It was starting to look like the Mahle guys weren't full of you know what. They just didn't tell us what header was on their car and, after that, it's now brick-in-the-head obvious that a large exhaust is a requirement for the 200-wheel hp club.
So we were 25-wheel hp up from when Dustin's car was healthy, back in January. Thirty-five horsepower was gained from the less-restrictive exhaust, and we knew there was more to be had. The air/fuel ratios were running dangerously lean past 7000 RPM (near 14:1) and the Hondata showed injector duty cycle at 100 percent. If we could get some more fuel to the engine, we would likely get more power.
Cranking on the adjustable fuel pressure regulator until it showed 70 psi at idle got us very little and at that pressure the injectors would soon fail. We had hit yet another wall! A day later and with 470cc/min injectors from Xact, the H22 was getting all the fuel it could swallow. This pushed power to 206. We'd hit the 30 wheel hp gain we'd set out to achieve. But with peak power at only 7200 rpm, we had to wonder if there wasn't more to be had.
Dustin's H22 had a stock intake manifold and we thought that might be the problem. Xact's Dynapack has a built-in pressure sensor, and connecting it to the manifold showed that vacuum was actually increasing with rpm. A sure sign of a restrictive intake. With a borrowed Skunk2 manifold and oversized throttle body, we were set to find more power.
And sure enough we got slapped again. Because this H22 was in Civic and not a Prelude, the manifold wouldn't fit without cutting the firewall-something Dustin did not want to do. Since his stock manifold already had the butterfly system removed, we figured we probably had enough runner volume, but the smallish throttle body may have been holding us back. So we port-matched the stock manifold to the Skunk2 TB and hit the dyno.
The dammed thing actually made less power! Not much less, but less. Manifold vacuum was higher too, which made no sense. Looking at the AEM cold-air intake tubing, we decided it could be the culprit. Disconnecting the tubing and letting the throttle body breath netted a 210-wheel hp run-like we expected.
But excessive vacuum at full throttle was still an issue. At this point, all we could figure was that the factory manifold just wasn't cutting it, and we were two issues overdue, so there was NO time to try anything else. 220-wheel hp could certainly have been possible, and with race gas, perhaps as high as 235 or 240. But, we bettered our achieved goal and the job was over.
On this painfully long journey, we learned some things that will certainly help you readers out-whether you're building an H, B, D or whatever Honda engine. Firstly, big cams need big compression. People are often disappointed with the results of aftermarket cams. Mostly, it's because the stock compression isn't what the cams were designed for. Secondly, high compression pistons must be checked for clearance with big cams. Same thing goes for the valvetrain. The rocker arms on the H22 had to be modified and used along with taller retainers to fit this cam. Letting all these things hit each other at high RPM will destroy more than just those parts.
Additionally, keep in mind that an engine is just an air pump. The cams control the amount of air that gets in and out. With big cams comes the need for better intake and exhaust. A 3-inch exhaust is a requirement for an engine of this size.
Finally, if you're doing all this, it's going to take more fuel. The stock 310cc/min injectors will quickly meet their match. As well, trying to manage all this with a fuel controller is futile. Running high-compression pistons, junk 91-octane fuel and stock timing is like dating twins-it's gonna be fun, but you're gonna get caught and it ain't gonna be pretty. Use a Hondata or something like it.
In the end, it wasn't as simple as Mahle had told us, but this combo is highly effective. The Mahle's have a street price of about $500 and the Crower cams are on sale for $500. The springs and retainers are also about 500 bucks, but with the right exhaust and tuning, this is nearly a 40-wheel hp gain with monstrous torque. There truly is no replacement for displacement.