High Compression 3.2L Engine Build

Oct 30, 2016
For those of you who have been following my build thread, you've already seen some of my plans for this engine, as well as all the past plans that were either interrupted or I changed my mind about. I'll spare you the gritty details and sad backstory here.

At the time of this writing I'm waiting on the pistons to come back from having coatings applied, waiting on wrist pins to get DLC coated, then I'll send the block off to have it honed out another 0.0006" to hit target clearance with the pistons, then finally have the rotating assembly balanced.


The plan is a 3.2L engine based on a 3.0L block with wet sleeves bored to 93mm. I chose 93mm since pistons are widely available from a variety of manufacturers and it gives me a lot of room for rebuilds in the future at 93.5, 94, or 95. Sleeves - especially MID sleeves - are extremely expensive to have installed in a C30 so I don't want to have to do it again anytime soon. The pistons I've selected are actually 20g lighter than the factory pistons so combined with the OEM titanium connecting rods the rotating assembly will be lighter than a 3.0L rotating assembly. Throw a lightweight flywheel on top of that, and this should be a very rev happy engine.
  • High mileage 3.0L block (core purchased from @Venom2049 who was extremely helpful in delivering it to the machine shop)
  • 3.0L crankshaft (from the original engine in my car)
  • Darton MID sleeves bored to 93mm
  • Timeserts for head bolts
  • ARP head studs
  • ARP main studs
  • ARP rod bolts
  • Factory titanium connecting rods, weight matched and balanced end to end.
  • Toda 93mm 12:1cr forged pistons, weight matched, tops smoothed, ceramic thermal barrier coating.
  • Toda wrist pins, DLC coated by Calico Coatings
  • Toda oil pump gear
  • Toda main bearings
  • ATI super damper
  • Factory oil pan with CRF baffle
  • Eventually: Dry sump system custom built by @Mark911 (post break in and assuming engine is running well)

I have two sets of heads to choose from, a set of heads built and ported by Endyn about 10 years ago that I picked up on Facebook market, or a set of heads I sent off to Bad Guys Worldwide for his porting service. Both have full Supertech valvetrains with the 36mm intake valves so ideally I'll have both flow tested and see which one shows the most promising results. Not sure what I'll do with the leftover set of heads, maybe find a bad C30 block and turn it into a 3.1L to complete my collection and have a 3.0, 3.1, and 3.2.
  • Toda Spec A camshafts
  • Toda adjustable cam gears
  • Toda timing belt
  • Toda beehive ("egg shaped") valve springs
  • Supertech bronze valve guides
  • Supertech 36mm intake valves
  • Supertech 30mm inconel exhaust valves
  • CRF locking timing belt tensioner
  • RFY billet cam plugs
  • New OEM rocker arm assemblies to guarantee proper run in with the cams.
  • Deburred and vapor blasted
  • Cam tunnels lightly honed for oil retention (little to no dimensional change)

@A.S. Motorsport billet ITB system with 50mm throttles, trumpet length TBD.


To be revealed...

Engine Management

Chipped factory ECU running a hybrid MAP/TPS based load calculation algorithm based on Megasquirt "ITB mode", as discussed in my build thread.


I have a buddy who does vapor blasting on the side so I've had him do pretty much everything that will easily fit in his cabinet. I'm only having stuff done that can be thoroughly cleaned of abrasive media afterwards. Here's a few examples.



One of the more time consuming projects here has been deburring the block both inside AND outside. There's lots of ridges and sharp spots and I wanted to knock them all down and maybe vapor blast the block too.



After (not blasted yet)


In addition, I took some ideas from @Mac Attack and smoothed out the sharp edges of all the main caps especially around the oil holes.


I fabricated these 2 tapered delrin rods on my lathe and cut M11x1.5 threads onto them to help align the cylinder heads during installation and prevent gouging the delicate aluminum surface on the sharp edges of the dowel pins


The Endyn heads were pretty dirty when they showed up. They had also been installed on their previous engine with MLS gaskets and copper spray which is a bit of a no no so needed a good cleaning before going for vapor blasting then to the machine shop.


Fair amount of grinding in the bowls underneath the oversize 36mm valves. You can also see quite a bit of smoothing in the chambers and the area around the outside of the valves has been smoothed a lot. The cylinder heads were also surfaced on an old belt sander type resurfacing machine which is kind of an archaic method. The heads are at a local shop now (the guy who rebuilt the heads that are in my car now and did a beautiful job) getting worked over and checked for any issues and will be properly surfaced on a fly cutter and come back looking like a mirror. The valve job still looks great, the story was these heads were only run for a few hundred miles before the motor spun a rod bearing. They'll be pressure tested to see how well they actually seal though and then recut if needed.



After vapor blasting the outside looks incredible.




Sharp edges on the cam caps cleaned up as well. Once I get the heads back I'm going to do break them down fully and do a few quick passes with an 800 grit flex hone in the cam tunnels to add a nice crosshatch pattern for oil retention. C30s aren't particularly friendly to their cam caps so this is just a bit of extra insurance for turning north of 8000rpm, this method has helped on other engines with similar issues and shouldn't change cam clearance by any meaningful amount, but I'll measure with a dial bore gauge before and after to be sure.


12 brand new OEM rocker arm sets, given the price of NSX cams, I don't want to take any chances with wiped lobes or rocker pads so brand new rocker assemblies to get the best possible results with the Toda cams. I spent a long time trying to figure out possible ways to refinish rocker pads but since they are ground together as a set and to a specific radius curve (and that curve is different on the middle rocker) I decided OEM was the only solution. If your rocker pads look perfect this is unnecessary but mine had a bit more wear than I was comfortable running.


Port work on the Bad Guys heads, he cut the valve guides off which I don't particularly like but says he's never had any issues with doing this even on street motors.



Prepping the Toda pistons for ceramic thermal barrier top coat. I wanted to have them fully ceramic anodized then have top coat and skirt coats applied but the guy who was applying the coatings said he didn't want to try to remove the Toda skirt coating since it's adhered very well and would feel a lot better just doing the top coat. There was lots of very sharp edges from machining the valve pockets so I used a small file, 600 grit sandpaper, and very fine steel wool to knock the edges down and clean everything up. This isn't just for looks, sharp edges don't shed heat well and can create hot spots on the piston and cause detonation. Doing this can actually let you get away with a few extra degrees of timing in knock limited motors and just provides more safety margin in engines that reach MBT before then, and since I'm running a fairly high compression ratio I think is worth the time investment.


Check out the domes on these 12.1:1 pistons.


Toda Spec A cams. I would have liked to do B or even C cams for the extra duration on the middle lobe but those have a crazy amount of lift (11mm) on the primary and secondary (non-vtec) lobes so would really hammer on the valvetrain even in regular driving.


That's all for now, will post more photos as this progresses. Next thing is to finalize the main clearances after I had to order more bearings due to a problematic batch that had inconsistent thicknesses, I have the bearings but still need to go through the process of torquing up the bottom end and double checking everything.
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May 14, 2014
Wow. Cant wait to hear this thing and see some vids after it's all done. I remember Endyn (The old guy) making crazy power with B series stuff back in the day, but didn't know he did any NSX heads. Will be interesting to see his work compared to Bad Guys stuff as he always puts out great head work too.
Jul 27, 2007
Denver, CO
What’s your target HP/torque numbers?
And do you plan on using pumped 91 octane fuel?
I think John just wants a smooth, reliable running engine LOL. :)

Seriously though, the C30A has some limitations inherent in the design. 3.0L engines max out around 400 peak HP with a full ITB/VTEC-Killer Cams race engine setup. That was the spec for the LeMans GT2 engines. The 3.5L engines used in JGTC GT500 class racing ran around 500 peak hp. In both cases, the engine was spinning close to 9,000 rpm.

Once he gets it dialed in with tuning, my sense is we'll see 340-370 out of it, but a lot of that depends on the dyno, atmospheric conditions that day, etc. Regardless of the number, that NSX will be a fearsome car to drive. Night and day difference from stock, that's for sure. I'm excited to see where it goes!
Oct 30, 2016
I'm trying not to get too invested in a number since frankly C30 builds always end up a bit underwhelming. Mid 300s would be nice, but my local dyno shop is a rather notorious heartbreaker so I'll be ecstatic if I can even break 300 on it. I'm more concerned with trying to stretch the usable torque curve out to 8500-9000rpm than I am with peak HP.

Texas has 93 everywhere so 12:1 should be perfectly safe to run, and once the head gasket thickness is selected for proper piston to head clearance at the quench pads I'm hoping to be around 11.8-11.9 for a bit more safety margin. I'll probably do some logging with 91 to see if any changes need to be made to the tune before I inevitably end up at a gas station 900 miles from home that doesn't have 93.
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Jul 28, 2022
Bay Area, CA
Mid 300’s sounds like a safe goal. Agreed, should be amazing. Back in the days I modified our Polaris 650 PWCs. First mod was increased compression as well as crazy set of expansion exhausts. It took an increase head gaskets as well to stop creating holes in the top of a piston. I’m all about reliability. What’s the equation? Pick two between performance, cost and reliability the third gets exponentially worse!
Oct 30, 2016
Reliability is part of the reason I chose the Toda pistons, as far as aftermarket suppliers go they have an excellent reputation. I believe they are a 4032 alloy so allow for tighter clearances and less wear on the bores than the more widely available 2618 options. I'm planning on running them at around 0.0027" clearance, compared to the 0.0035+ the Wiseco option calls for, for example. They are also very light, 378g each compared to 398g for factory 90mm cast pistons and 411g for the Wiseco 93mm pistons, since boost is out of the question with a compression ratio this high the pistons can be lightened considerably.E

Edit: I heard back from the machinist whos going through the heads and apparently he's almost done. He found the valve guide clearance to actually be tighter than he likes to run which is excellent, he was just able to hone them a bit to desired clearance. I was worried that the guides would be too loose and have to be knocked out which is an expensive and slightly risky process. He also timeserted a few exhaust stud holes that had stripped. I'm not sure if he recut the valves or not, I suppose I'll find out when I get the bill.
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Oct 30, 2016
I've spent the better part of a month trying to track down a good set of titanium connecting rods for this build and I think I finally got them. I'm still waiting on the last one to arrive but I made the unpleasant discovery that oftentimes the rods in a C30 are not at all close in weight.

After pushing the wrist pins out and weighing the rods I found them to be 484.1g, 484.9g, 482.9g, 484.1g, 483.9g, 516.5g. That's nearly a 33g split from heaviest to lightest! In one engine! According to @Kaz-kzukNA1 this is a known issue, and given how long C30s last it seems to be benign, but the plan for these rods is to grind them to perfectly weight match and balance them end to end, and that simply can't be done with that much of a weight imbalance. I was fortunately able to find a 6th rod close enough to make everything work out, huge thanks to @acuhon.

Pushing the wrist pins out was easier than I expected, I just used my Harbor freight vice and some sockets. The wrist pins are a fairly standard 22x57mm (0.866x2.245") and have a 0.0011" interference fit in the small ends of the rods with 0.0009" clearance in the pistons, in case anyone was wondering.


The rods themselves have a lot of sharp machined edges especially around the bolt holes where the material is thin, so I smoothed and chamfered the edges a bit to help resist cracking. Lots more of this to come.



I can't decide how I want to handle the small ends though. There's 3 ways to do this: interference fit wrist pins as the engine came from the factory, bronze bushings as most do with C30 rebuilds, or no bushings with DLC wrist pins.

I'm going with DLC coated wrist pins regardless since it's just cheap insurance to have when shooting for 9k. Bushings are okay but it weakens the small end of the rod and is another sensitive machining operation to potentially be done incorrectly. No bushings with a DLC pin is done in race motors fairly often but is pretty rare in street motors so there's little to no information about how this holds up over high mileage, and I'd love to get 50,000 miles out of this engine.

I'm exploring the possibility of running the rods as Honda originally intended with an interference fit wrist pin. This method has worked for hundreds of thousands of miles hitting 8200rpm all the time so I think Honda was on to something here. In theory I could just have the pistons honed to match the factory clearance of 0.0009", heat the end of the rod to 250C or so, and slip the pin in. The DLC coating should take care of any issues that could arise from the extra 800rpm but I've never heard of anyone doing this before so I need to do a lot of research as well as call Calico Coatings (company applying the DLC) and ask if they can think of any reason this might not work.

Update: I called Calico Coatings this morning and they said they have a lot of customers that press DLC pins into the rods, and just to make sure the small end bore is very smooth so the pressing process doesn't hurt the coating on the pin. I think this is what I'm going to do.

Update 2: I came across this service bulletin for S2000 connecting rods on the SoS website. If the S2K steel rods can be run just fine with no bushing and DLC pins then there is an OEM precedent for running a DLC pin in an unbushed steel rod for high RPM applications. (added as an attachment in case the link goes bad in the future)

Update 3: I called CP Carrillo today and asked if a DLC pin could be floated in an unbushed titanium rod and they said absolutely not.


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Oct 30, 2016
Interesting development, I was tired of getting OEM main bearings where the thicknesses were all over the place so I rolled the dice on Toda main bearings. (Fun fact: the only engine bearings Toda sells across their entire product line is C30/C32 main bearings.) They are also exorbitantly expensive at about $50/shell but ultimately that only amounts to an extra $250 compared to using OEM bearing shells and if you can buy less of them setting up your clearances since the tolerances are spot on then I don't think the cost difference is meaningful in the scheme of things. I bought them from greenline.jp and they arrived in 6 days. I tried to order 2 Toda timing belts from them too but was told they were out of stock with no production scheduled yet, so I paid a lot more than that for one from an Ebay seller.

A bit of background information: Honda typically uses 2 bearing suppliers, Taiho and Daido. Daido bearings tend to be in the high performance engines and Taiho bearings typically show up in the lower performing commuter engines but this isn't a hard rule, but it does sort of indicate that Daido are the "high end" bearings and Taiho are the "low end" bearings. In the NSX however we see a lot of Taiho bearings, then Honda switched to Daido for the C32 rod bearings.

C30/C32 main bearings: Taiho
C30 rod bearings: Taiho
C32 rod bearings: Daido
C30/C32 thrust washers: Daido

Toda sells the main bearings in the same color codes (thicknesses) as Honda does which is nice, and I assumed they would just be Honda Taiho bearings with maybe some magic JDM coating applied. Nominal thickness is 2.500mm with each color bracket being 0.004mm.


If measuring with a micrometer that reads in inches like most of us do here in the USA you can expect to find pink~0.09820", yellow~0.09835", green~0.09850", brown~0.09865", and black~0.09880".

Toda bearing on the left, OEM bearing on the right.


I was pleasantly surprised to find that the Toda bearings have a Daido stamp on the back. (Toda/Daido on the left, OEM/Taiho on the right)


If you zoom in, you can see that the surface finish is a lot smoother with finer machining marks, and based on my measurements, the Toda bearings also have ~10% more load bearing surface area due the less aggressive chamfering so these bearings should have a slightly higher load bearing capacity than the OEM Honda bearings for a given clearance. You can even see a faint marking in the middle of the bearing from the bearing thickness being measured with a tube end micrometer, so nice to know that Toda is actually measuring the parts before sending them out the door.

As far as hardness goes, I don't have an empirical way to measure, but these feel pretty soft like OEM just based on scratching at a corner with my fingernail. They are not hard like what you'd expect from an ACL or Clevite race bearing. I ordered 13 bearings instead of 8 so I'd have room to adjust clearances a bit so I'll have a couple left over to sacrifice to science, I wonder if any shops around here have equipment to measure hardness.


Based on my measurements with a Mitutoyo ball end mic, out of the 13 Toda/Daido bearings I purchased, 11 of them are nearly perfectly within their color band with 2 being off by 1. Compare that to my last order from Honda a few months ago, where out of 10 bearings, only 2 were correctly labeled/colored.

The Toda "egg shape" (beehive?) valve springs showed up too, at $500 for the set and reusing the OEM seats and retainers it's a cheaper option than Supertech for running high lift cams, and a single spring saves weight in the valvetrain. I didn't mean to turn into a Toda fanboy but at this point I have almost their entire NSX parts catalog in this engine.
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Oct 30, 2016
Before setting up my final main clearance I decided to go ahead and check the engine block main tunnel alignment. It should have been perfect since this block was line honed, but I found that one saddle was off by about 0.0010-0.0015" which is completely unacceptable. In addition to this, the main bores are too wide at the parting lines by 0.0030" and the main tunnel has about 0.0010" taper from end to end.

If it was only taper and OOR I would probably just run it but that combined with the misalignment pushes me over the edge of "this needs to be fixed". I suspect all of these issues were present in the block before any machining even took place since the block itself has over 200k miles on it. I had figured that asking the shop to line hone the block would have taken care of these problems, but from the looks of things they didn't trim the main caps at all and just ran the hone right in after installing the ARP main studs. Just line boring again would correct the taper and misalignment but not the out of round, and it would move the crankshaft up in the block and risk throwing off the alignment of the oil pump and transmission input shaft.

This has created quite the can of worms. I think the ideal fix here is to have a few thousandths of an inch of copper electroplated onto the main saddles in the block, install new billet main caps (thanks @foundry3 for supplying the new billet caps), then have the main tunnel line bored back to the factory spec of 69.00mm. This should restore the perfectly round and straight main tunnel in a hopefully permanent way without introducing any new residual stresses into the block.

Plating onto aluminum can be tricky but is often done in aviation applications where a bearing housing bore has gone out of spec and I was able to find a shop that thinks they can do it and quoted $1200 for the service, which is pricey but seems far better than the alternatives.