Engine and Transmission Tech

There are several ways to do this, most involve a good bit of machining. I have spent quite a few hours comparing recipes with calculators found here.

United Engine & Machine

Way back in 2005, I was looking for a better piston for the 3.9. I stumbled across the Chevy 305 piston. Back then, I just wanted a piston & rod that would work with the 3.9. Kevin Jackson & I had some exchanges on the V8 email list. He was looking for pistons, too. He wound up using the 305 pistons with a 5.85" rod on a 4.2L crank. He built it, it runs great.

Now, I am trying to keep machining costs down. So I am juggling using the stock 3.7 bore with rods that hopefully won't have to be narrowed & heads & block that won't have to be skimmed. Not working out, so far. :)

I moved the relevant posts from the TA Head thread over to this new thread. Some are just shown as quotes.



Edited 4 time(s). Last edit at 06/23/2016 11:18AM by MGBV8.

Carl, You will have more quench with the later Rover heads 28cc chamber than the 300 Buick 58cc open chamber. I read something a while back where they recommend a dish about the same size as the chamber, oval shape. Piston at zero deck. I've searched high and low for a piston for the 4.2 crank. you need about 1.45 compression height for a 6" Chevy rod combo. For 6.125" rod the Buick 3300 V6 is close. EDIT: had 350 rod length. The 75-77 oddfire 231 V6 has the same length as the 300 V8 at 5.96. It has the later capscrew design. You would need a compression height piston of 1.485. This .040 over 3.66 3.3 Chrysler piston has the dish I'm talking about and 1.255 compression height.




Edited 6 time(s). Last edit at 06/12/2016 12:30PM by mgb260.

Thanks Paul. I was trying to figure out Carl's combo with 4.2 crank. Zero deck with .010 decking. 3300 Buick V6 pistons and 6 1/8" Chevy rods. For the price I would use NASCAR take outs and have crank turned to Honda journal size. Or use the Lunati adapter rod bearings to use more common and cheaper 2.1 SBC rods on 2.0 small journal crank size. I think with your stroker combo You would want aftermarket capscrew rods and probably have to clearance the block in a few places.




Edited 2 time(s). Last edit at 06/10/2016 10:28PM by mgb260.

Quote:

Posted by: mgb260
Date: June 22, 2016 09:21AM

Carl, Years ago I built a 215 with the same Crower cam as you have with 300 heads, using the stock 11 to 1 advertised pistons(closer to 10.5) and steel shim head gasket. Compression was around 9.5 probably. You want a flat top piston or at least a shallow dish with that big chamber. I'd be tempted to use the 75-77 Buick 231 oddfire capscrew rods. Length 5.96. Same bearings as 215. That design is good to 600HP in a 350. The only thing I would do is sand the sides and shotpeen. You need around 1.485 compression height. Ford 2.3 HSC 4 cylinder flat top .030 would be .010 over for you. 200 Ford six has a small dish. Both have 1.5 compression height. You could mill .015 for zero deck. With your cam they recommend 10 to 1 compression.

Quote:

Posted by: mgb260
Date: June 22, 2016 05:26PM

I ran the numbers on a compression calculator and with zero deck flat top pistons I get 9.2 with composite gasket and 9.7 with steel shim. When I did mine years ago I did have the block and heads surfaced to make sure they were flat, which probably helped, as the stock Buick pistons are not zero deck but down in the hole a little. Carl could mill the 300 heads .030 and be just right. My motor was strong but I was disappointed in that the built Buick V6 was about the same in the Jeep. It was bigger at 231 compared to the 215 though. Just a little too small displacement for me. If I build one it will probably be a 4.6.

Edited 1 time(s). Last edit at 06/23/2016 10:55AM by MGBV8.

Quote:

Posted by: BlownMGB-V8
Date: June 22, 2016 09:54AM

That sounds like a good combination. I needed a 13cc dish for 10.6:1 with the 300 heads on a 340 so you should be able to use a flat top. An alternative to milling the pistons might be to stack a steel shim gasket with a composition one for .050" thickness. That'd give you .035 clearance (squish), if that seems too close you might be able to put a shim gasket on both sides of the composite one for .045"

Jim

Quote:

Posted by: BlownMGB-V8
Date: June 23, 2016 01:18AM

Careful with those still shim gaskets though, wouldn't want the pistons kissing the heads. Conventional wisdom seems to indicate .040" is about the right clearance, so a composite gasket, shaved heads and zero deck the pistons and that's not bad. Sounds like a workable combination.

Quote:

Posted by: mgb260
Date: June 23, 2016 08:48AM

Yeah, I wouldn't use steel shim gaskets for zero deck pistons. I just punched in the different gasket thickness in the compression calculator to see the difference in compression ratio.

Quote:

Posted by: MGBV8
Date: June 23, 2016 09:19AM

With those huge chambers, I am curious how far down the valves drop. Is piston to valve clearance even an issue?

Quote:

Posted by: BlownMGB-V8
Date: June 23, 2016 09:43AM

Valve clearance won't be an issue at all. With .500" lift, .050" head gaskets and pistons reaching .008" above the deck I still have 1/4" of valve clearance to the pistons with a 13cc dish which is not much more than 1/16" deep.

Jim

Great! Maybe one less thing to worry about.

Carl, On Chris Gill's 300 stroker(350 crank) build we cut costs on the 300 heads by using slightly larger valves that use the stock seats. 80's 2.8 Chevy V6, 1.72 intake and 1.42 exhaust and Z28 Chevy valve springs. You should either use locktited studs or steel inserts for the rocker arm hold down threads. On my old build I had new seats and 1.74 intake ad 1.50 exhaust Ford 2.3 SOHC valve and Chevy Z28 springs. I tried talking Chris into Alex's Parts beehive springs but the crank machineing cut too much into the budget.