Hugh's 1987 505 STX V6 Project

6 minute(s) of a 40 minute read

This is pure gold; thanks for your thoughts, John. I gotta admit I wasn't familiar with the "bent-six" term although I guess it's obvious really. My goals for this and the other 505 build are pretty modest: 200-250 hp, mostly because I don't want to re-engineer the entire driveline. The stock BA10/5 transmission will reliably handle about 220 lb-ft maximum torque so that's the most I'm after. I've been considering just dropping the 2.5 Turbo PRV setup from an Alpine GTA into this STX and run VEMS or Megasquirt on it. Apparently this arrangement will fit the 505 engine bay. For the (later) Danielson-spec 505 project my Holy Grail is minimum weight, so I'll probably go with a normally aspirated PRV built to rev and breathe really well, like Danielson themselves did. But like any of my project ideas, these continue to evolve...

Were Volvo the only ones to offer the cross-bolted bottom end in production form? And were the odd-fire cranks cast iron then? I wasn't aware of either of these details.

I never considered the PRV bottom end to be underbuilt; it always looked pretty strong to my eye and of course I've never heard of a main bearing failure in any PRV. The cross-bolted mains just sounded like an interesting detail for a higher-output engine. Peugeot successfully extracted 680 hp from the PRV using twin turbos and intercoolers, while running it up to 8200 rpm. I'm not sure what bottom end arrangement they went with but clearly the engine is plenty strong. They used a special DOHC 4-valve head in that application.

"Make it a 3.4..." You mean 3.4L? Would that mean the Premier/Monaco crank with an offset grind and the heads and liners from the same car? As for headers, I think I'll just have them custom-made. I doubt the Peugeot exhaust manifolds are much better than the Volvo units.

8-17-2016

A 605 is on my wish list, but I'll have to import one from France I suspect, as I've never seen one on these shores.

A little update on the STX though:  The Nardi wheel and hub are on their way, and I'll post pics as soon as they show up.  The style I ordered is pictured below:

I will not complete the interior until I get my last 505s imported from the US, as my plan is to use the very best blue dash I have in this car, and put the second-best one in the STI.  Right now I'm not sure which those are.  Both cars will get dash mats, which I've already got.  I think I'd mentioned before that I plan to rebuild and re-engineer the shift linkage to improve the feel and shorten the throws.  In addition to that I will see how feasible it is to place the whole assembly a bit further aft, as I've always felt that the reach to fifth gear was a little long from my preferred driving position.  It might wind up being a completely custom assembly.  We will see.

Progress was very slow while I was busy with the flight school's yearly Air Cadet contract, but now that's wrapped up and with the onset of cooler weather in September I will have more time and better conditions to move ahead.  I have partially fitted the body kit and the new mud guards (pictures below) as well as the new driving lights.  I am looking at some sort of lip (Rhino Lip or similar) for the bottom of the air dam, and something similar to bridge the gap between the bumper and the top of the air dam, purely for aesthetic reasons.  I'm looking for a seamless, factory look for the tucked bumpers. Note that in these pictures I've trimmed the front bumper slightly so that it sits flush, which looks much better.  The part I removed was a section of the inner molding that fits around a metal guide on each side.  The remaining structure is rigid enough that it should not warp or droop. Once all is sorted out and I'm happy with the fit I'll get the body kit cleaned up and painted body colour.  I'll probably do the same with the air dam as it could use refinishing.  The patina on the rest of the car will have to stay for the time being as I can't afford to have it repainted completely right now.

Engine-wise, the project has evolved somewhat.  Phase I will be basically status quo, with the existing engine staying put.  I'll adjust the valves, clean up the snake's nest of hoses and wires in the engine bay, paint the valve covers, and not a lot else at this point.  I want the car on the road before too much more time goes by.  Phase II will involve a turbocharged PRV, either a 200 hp 2.5 from an Alpine GTA, or possibly the 250 hp 3.0 from an A610, or a custom build using what I have available (with appropriate internal mods of course as John Lane recommends).  Either way, a turbocharged PRV is the endgame in this car, which will make it (in my opinion) the ultimate expression of the 505 STX.  By contrast, I think the Danielson-spec Series I 505 build I've talked about elsewhere will be a high-revving normally-aspirated version.