Build 2 is underway. The block is currently being freshened at the machine shop. As a bit of history, this engine was initially built in 2011 as a 427 cid (4.125 x 4.000) with a very lightweight rotating assembly, 12:1 compression, extreme cams, and professionally ported induction system. On a mix of 100 Octane VP and 93 unleaded pump gas the results were 703 bhp @ 6700 rpm. 700 bhp was achieved by 6500 rpm. You can read about that build in HOTB issue 25.
Fast forward 5 years and the engine is undergoing upgrades, hoping to achieve upwards of 770 bhp this time. So, what's changed? I will chronicle this version of the build through this blog from post-machining through to final assembly and dyno testing.
New Ross pistons. 4.130 bore, 14:1 compression, 2.250" steel pins. These pistons are a bit more robust than the featherweight CP pieces from build 1. These weigh in at 433g, up 60g from the CPs, while the retainers and pins make up for some of that. Bobweight is 1624g.
Total Seal AP (Advanced Profiling) steel rings. These are conventional, not gapless. Top and 2nd rings are .043", while the oil ring is a custom std tension 3mm piece. Note the std tension 3mm is still less than the OEM, and the usual high tension 3/16" rings. The 2nd ring is again of the napier design to help with oil control. These rings are a step up from the CP rings last time, and combined with the bore finish should improve ring seal. Keith at Total Seal gave us the exact bore finish to aim for, and the machine shop has a profilometer to ensure we get the peaks and valleys at the right height.
Although the Carrillo 6" tapered beam H-section rods are the same, the bolts have been upgraded to the highest spec material. These are $1000/set bolts, but it is the highest stressed joint in the entire engine, especially at 5000 feet per minute mean piston speed.
Rod bearings are new Clevite V-series. Mains are the same coated OEM bearings as last time.
I'll keep this blog going as the parts come back and get prepared for assembly, including the various build procedures.
Till next time,
Todd
While I'm waiting on the block and components to come back from the machinist, thought I'd start another blog about a few other changes being planned.
On the last engine, we discovered that at the 700hp level the stock fuel supply system was inadequate. We ended up crutching this somewhat with artificially high VE values (>130%!) in the calibration, but never could get enough fuel supply above 5000 rpm. The injectors were upgraded to 30lb/hr Bosch units, but still the fuel supply had a restriction. The fuel pumps (dual Walbro GSS340 units) are more than adequate for 1000bhp.
My theory is that the stock fuel supply plumbing is the likely restriction. Although I haven't measured the ID of the stock fuel rails, the aluminum feed tubes at the tank and at the rail are only about .280" ID, less than 5/16"!
For this next build, I have decided to totally replace the fuel delivery system. The lines, starting from the pumps, will be upgraded to -8 supply, -6 return. This will require some fabrication to the fuel sending unit to cut off the stock tubes and replace with new. I'll also upgrade the "Y" fitting at the same time. The fuel rails themselves will be replaced with new T-6061 extruded aluminum pieces with a full .685" inside diameter.
The stock fuel pressure regulator will be discarded in favor of a Kinsler K-140 high speed adjustable bypass regulator. I believe this is the best regulator on the market. Rail pressure will be set at 75psi to assist with fuel atomization. The Bosch 30lb/hr injectors will flow approximately 42lbs/hr at that pressure. The fuel rails will be plumbed in series, not parallel like the stock system, a factor of the line routing and to make the installation tidier. The supply line will feed one rail (probably the driver's side), with a cross-over line at the front joining the two rails. The regulator will therefore be at the outlet of the other rail (pass side). From what I could tell, that is also how Graham plumbed the GenIII car. Kinsler has advised that there is no performance disadvantage from running the rails in series.
The new system should be more than capable of stable fuel supply all the way to 800bhp and beyond. Once this is proven, I intend to make the system available in kit form to the ZR-1 community if there is interest.
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