How to Build a Honda Prelude Racecar Part 10

Gearing up for the 2020s

Posted by Roger on December 28, 2019

Although the 4th generation Honda Prelude is a few years shy of celebrating its 30th birthday, we are learning new things about the car every time it goes out on track. The StudioVRM Racing Team is spending this winter making some major setup changes based on some of the things we learned these past two seasons.

So we thought we would share some of what we learned while the Prelude spends the cold winter months receiving upgrades in the shop.

 

Extracting More Power from the H23A1

As many of you know, we are in the small minority of racers powered by the the non-VTEC H23A1. When we had our engine failure this summer, we contemplated switching to the higher revving H22 or following the majority of Honda club racers with a K24 swap. But after a number of discussions with our resident powertrain wizard, we decided to stick with the H23A1. Both of us felt that there was unfinished business, particularly around the head and intake, neither of which had been heavily modified since the car's transition to the SCCA Super Touring Under class. Plus, since we will be able to re-use any undamaged parts, the costs to rebuild the H23 would be around 40% less than what it would to build a new H22 to a similar spec.

 

More Top-End Flow

We learned early on that there is a lot of power to be unlocked in the H23A1's non-VTEC head. When the Prelude was racing in the Improved Touring class, powertrain wizard Robert Oliver was able to glean a solid 12hp across the entire powerband just by cleaning and gasket matching the port openings.

Now that we are racing under the much more permissive Super Touring ruleset, we will be doing more extensive modifications than ever before. Robert is reshaping the intake and exhaust ports substantially and making some tweaks to the valve seats of our new head. In order to help get an even flow of fast-moving air into the ports, Bad Guys Worldwide is also working over our stock intake manifold on their high-tech CNC mill.

Preliminary reports from our two engine experts revealed struggles with this unique challenge. Cole at Bad Guys Worldwide had to abandon his usual approach for porting H series manifolds due to the unique shape of the H23A1 manifold. Meanwhile, Robert found himself removing a surprising amount of material to get the port shapes that he wanted from the spare head.

Thankfully, Cole and Robert are among the best in their respective trades. We remain confident that they will be able to overcome these challenges and the team will be able to reward them with a strong showing at the track.

 

Better Bottom-End Oiling

As it turns out, even the non-VTEC H23A1 isn't immune to oil starvation. We aren't about to let that happen again, so the focus this time will be on keeping the bottom end well oiled.

This motor will be built on a gently used H23 block, which was cleaned and decked by a local machine shop prior to us acquiring it. The powertrain wizard will give the FRM bores a very light hone to ensure that the new OEM Honda rings seat evenly against the cylinder walls.

We will be installing a Kaizenspeed balance shaft removal kit on a new OEM Honda oil pump to ensure consistent oil pressures through the engine's powerband. A baffled Moroso road race pan will raise the oil capacity to 5.5 quarts and provide some much needed protection from oil slosh from high-G cornering. And last but not least, all of this will be backed up by an Accusump in the event of a sudden loss of oil pressure.

 

Worthwhile Transmission Work

During the 2018 off-season, we replaced the OEM 4.266:1 final drive with an affordable 4.64:1 unit from MFactory. The difference was dramatic. Despite moving up to a larger diameter 17" wheel, the car felt more willing to accelerate out of every corner and down every straight. Closing up the gear ratios also eliminated those corners where we felt like we should be somewhere between 3rd and 4th gears.

When we were building the car for Improved Touring S, we had assumed that the torquey 2.3L motor would have enough low-end grunt that it would eliminate the need for a taller final drive. Looking back, we now realize that it should have been the first modifications we made when we were getting into the drivetrain.

 

Suspension and Alignment

While our race-valved Tein dampers and Swift springs continue to provide a good compromise of response and compliance, we did make a few tweaks during the 2018 and 2019 seasons to help our cornering performance.

One of these tweaks was to raise the front spring rate from 12kg-f/mm to 14kg-f/mm in order to get faster transient response through fast S-turns and sudden left-right transitions. This seemed to help through the back sections of NJ Motorsports Park and Summit Point Raceway, albeit at the expense of the razor-sharp corner entries that we had enjoyed in past years.

To compensate for this, we changed our approach to the alignment as well. Our 2019 alignment eliminated the front toe-out in favor of a small amount of rear toe-out, and increases the amount of camber on the car. In 2019, the StudioVRM Prelude raced with the following alignment settings:

Toe

  • Front: 0 degrees
  • Rear: 0.2 degrees total toe out

Camber

  • Front Left: -3.1 degrees
  • Front Right: -3.2 degrees
  • Rear Left: -2.0 degrees
  • Rear Right: -2.2 degrees

We also realized that adding a spacer between the upper control arms and the chassis would give us an additional 0.25 to 0.5 degrees of negative camber when the rear suspension was compressed. So we ordered a set of M18 fender washers from McMaster-Carr and installed them on the rear control arm anchors to gain some much-needed dynamic camber in the rear.

The result is a car that would take left-right transitions much more quickly than in the past, so we were no longer losing dogfights in the tighter infield at NJMP. While the car doesn't feel as willing to steer into the apex as it had in previous seasons, it still rotates willingly thanks to the small amount of rear toe-out.

Despite these improvements, we do see room for improvement. During our last race, the car felt suspiciously like it was riding on the outside edges of the rear tyres through slow corners. This suspicion was later confirmed by some alarmingly uneven tread temperatures from the tyre pyrometer. We plan to address this by replacing the rear camber adjusters with these Moog adjustable ball joints so we can the rear camber to -3 degrees on both rear wheels. This should give the Prelude better tread utilization while retaining the crisp, forgiving handling that we have enjoyed in these past few seasons.

 

Big Wheels and Wide Tyres

It didn't take long for the Prelude's newfound power and agility to completely overwhelm its 225mm wide Hoosier R7s. It was time to move up to 245mm front tyres, and as a consequence, time to move up to 17" wheels.

As expected, the 1" increase in tyre diameter did hurt acceleration a bit compared to our old 15" setup. But the benefits far outweighed that little drawback. Thanks to the stigma of running large wheels on an older 4x114.3 Hondas, 17" wheels are readily available and for cheap. We acquired a set of brand new 17x8 race wheels for half the cost of our custom-drilled 15" Team Dynamics Pro Race 1.2s.

We also noticed that our brakes were consistently running 30 degrees cooler than they had been previously. It seems that increasing the clearance between the brake rotor and wheel rim made a measurable difference in brake temperature.

After experimenting with sizes and compounds (and receiving some much-appreciated advice from our friends at Maximum Attack Motorsports) we decided to run Hoosier R7s in 245/40R17 at the front and 225/45R17 at the rear. The narrow rear tyres work surprisingly well, warming quickly and staying grippy through the duration of a 40 minute sprint race. Although this does mean that we now have to carry two different sizes of tyre to each race, the difference in lap times convinced us that this was the right way to go.

 

What's Next?

The long winter has just begun for us. In all likelihood, the snow will have started to melt before the 2020 model StudioVRM Prelude is ready for its track debut.

If all goes well, our bright green machine will be out testing by early April and will have its race debut shortly after. Schedules and details to come within the coming weeks and months.

All we know is that we can't wait for spring to come.

See you at the track.

~R