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Quick Intro to the project I’m building - not a Miata/MX5, but a 1979 Mazda 323 (you call it a GLC) - rear wheel drive, live axle hatch, powered by a VVT-head BP. Chassis was chosen to suit class rules here in Oz and will be a circuit racing car.
The key issue with the class rules I am running is that, for turbo applications, you need to run a 36mm inlet restrictor in the throat of the turbo. This limits realistic maximum power to somewhere slightly north of 300whp. It also means that to generate lap speed against the heavy v8 cars we race against, you have to run significant static compression (11:1 plus) with e85 and massive boost as the turbo spools to generate big torque to get you off the corner. We are running an EFR6758 and the goal is around 28-32psi at around 4200-4600rpm. From there, whether you like it or not, boost drops off progressively as rpm builds, due to the restrictor. Practical redline, due to the restrictor, is limited to around 6800rpm, though you can rev them as high as you like... just they make no power and you may as well shift to get back into the higher boost torque band.
So your cylinder pressures are bloody huge. Guys here in Australia have been running the BP with some success over many years in other chassis - notably the 808/RX3 platform, which has demonstrated performance benefits of the restricted turbo piston engine over aspirated Bridgeport rotors. The trade off has been reliability.
We have done our best to build an engine that will take the boost. The bottom end is as strong as we can make it, down to billet mains, etc.. The only thing we haven’t done yet is a billet crank, but we are pretty sure running the low redline that the crank will handle it.
Head gaskets have been the main issue for other competitors. ARP studs and Cometics were not cutting it. The shop with the most experience over here reverted to drilling and tapping the block for 1/2’ studs, machining the bosses on the heads down, and running 100ft/lbs or more of head torque. This has generally held the fort, but then resulted in cracked heads and sometimes cracking of the block, particularly in the stud journal around the water pump gallery at the front of the block.
We have gone to 1/2’ studs and running a Cometic, but at around 75-80ft lbs to try and preserve the head (Keegan CNC). I am fairly sure though that we will eventually start popping gaskets.
For our next engine, we will probably look to o-ring the block - but I’d like a short term solution for this particular engine, which is showing promise on the dyno, if the gasket leaks.
So to the question - is anyone aware of a company that makes an off-the-shelf stainless split ring or fire ring gasket for the BP? Something like what SCE Gaskets or Nava Linea make for other engines? If not, I may reach out to these companies and see if they will custom make something - but that will be $$$$ I’m guessing.
Thanks! 3 years of pain but definitely getting close. I may put together a build threat at some point if I find the time. Otherwise, hit up Gary White Racing on FB and scroll back through, you should find some history there.
In case anyone is interested, Nava Linea can do a fire ring gasket for 160 Euros each (plus duties and postage from Italy), but they are 1.6mm thick which is going to reduce our static compression a bit (we are running a 0.030” Cometic and engine was machined for this gasket).
Maybe if there is no other option. I may arrange a run of gaskets. If anyone is interested, drop me a line within the next few days and I’ll bump the order up.
Interesting for sure. Curious, how did you end up with the 6758? Did you try the 6258? With your application, I could see where there may be some real benefits.
Interesting for sure. Curious, how did you end up with the 6758? Did you try the 6258? With your application, I could see where there may be some real benefits.
Some of my competitors are running 6258s. They spool quicker, but the 6758 spools fast enough to produce heaps of torque with my gearing - enough for this little chassis, which is very light. And with the higher efficiency, my hope was that we may see a little more up high, as well as less temp gain on the intake charge.
But yeah, I may end up trying a 6258, certainly if I have issues keeping it singing. My last car in this category was a Datsun 1200 with a turbocharged CA18, running an older Garrett disco potato. It was dead below 4400rpm but still had a shift point around 6800rpm due to restrictor. It was fairly easy to keep in the happy boost range with a 5 speed. The 6758 spools heaps better than the Garrett, so should be fine... we will see though.
Innovative machine makes \ copper gaskets/fire rings for the 1.8, I think. They did for the 1.6, and they worked really well on a rally car i helped build. Maybe then can do what you need.
So I have commissioned a small run of Nava Linea stainless steel fire ring gaskets. I had them custom made 1mm thick. I had to order 5 to make it worth their while, and I needed an Italian-speaking friend to help as in interpreter... but we got there in the end.
I have 5, and will likely need at least 3 myself over the coming year or two. If anyone is out there having issues lifting heads on a BP at 28psi plus, and interested in trying one of these, then hit me up 👍
Warning though - these gaskets were very, very pricey.
01-26-2020, 04:46 PM
Split Ring / Fire Ring Head Gaskets for BP?
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