Author Topic: What pistons should I use for a 400?  (Read 303 times)

Maxthe222

  • Active Forum Member
  • *
  • Posts: 435
What pistons should I use for a 400?
« on: November 18, 2019, 02:48:21 AM »
So we tried with the stock pistons and rods but some of them have the piston head rings seized and some are too scuffed to use. Although I was against it, it appears the block may have to be bored out 0.030. there is a bit of a lip you can feel around the ring of the holes, so I am now in the market for some pistons and rods (and maybe a camshaft as well I suppose) for the Fire Am. I assume the block hasn't been bored, it doesn't look like it has so I'm assuming I'm going from totally stock bore to 0.030 over. The cheaper the better lol. Considering having the block "blueprinted" while I'm back to this stage.
1979 T/A Y84 WS6
1979 F/A W72 WS6
1971 Formula 400 4-Speed

Maxthe222

  • Active Forum Member
  • *
  • Posts: 435
Re: What pistons should I use for a 400?
« Reply #1 on: November 18, 2019, 06:04:04 AM »
You mean having the decks actually properly and perfectly shaven to be totally level accurate to each chamber? Yeah that's what I was thinking depends on how much disposable income I have over the holiday period
1979 T/A Y84 WS6
1979 F/A W72 WS6
1971 Formula 400 4-Speed

Fbird

  • Active Forum Member
  • *
  • Posts: 108
Re: What pistons should I use for a 400?
« Reply #2 on: November 22, 2019, 07:30:19 AM »
typically do NOT have the block decked until you have your pistons, rods, crank assembly numbers and your head CC's so you can deck it accordingly to achieve your desired CR. To have one trued-up then to only have to go back and deck .020 off costs for 2 operations...$$$
Most machine shops will not do any work on a block without having the assembly components to ensure the numbers work!
For average use...the KB hypertectics have a reasonable review!
I personally would throw a set of TRW slugs in it and be done...
« Last Edit: November 22, 2019, 07:31:51 AM by Fbird »
67 Firebird
1980 Turbo TA (injected 400 now :) )

jonathonar89

  • Oracle Forum Member
  • *
  • Posts: 2013
Re: What pistons should I use for a 400?
« Reply #3 on: November 22, 2019, 09:45:50 AM »
Fbird is right.

As he mentioned, the KB’s are nice.  I had them installed in my 400.  Stock 400 crank/rods...ARP bolts and KB Forged Icon

Maxthe222

  • Active Forum Member
  • *
  • Posts: 435
Re: What pistons should I use for a 400?
« Reply #4 on: November 22, 2019, 02:14:29 PM »
Yes, won't be doing any of that machining for a while now it seems, leaving the motor for after the holidays now, I didn't think I'd get away with using all totally stock components on it.
1979 T/A Y84 WS6
1979 F/A W72 WS6
1971 Formula 400 4-Speed

Re: What pistons should I use for a 400?
« Reply #4 on: November 22, 2019, 02:14:29 PM »

oldskool

  • Oracle Forum Member
  • *
  • Posts: 2298
Re: What pistons should I use for a 400?
« Reply #5 on: November 29, 2019, 08:44:05 PM »
Would not use the "Hypercast" pistons. It has been posted that, unless you use a really big top ring gap, the extra heat will cause piston failure. Has happened many times. VERY few recommend the Hyper pistons.

Only other cast 400 pistons are the dreaded "8-eyebrow" pistons. Low compression and lots of sharp edges on top.

So, the cheapest decent 400 pistons are the Speed Pro L2262F forged pistons, in the oversize you need. The pin height is 1.714. So, some will still need to come off the block, in order to get close to the desired "zero deck height". Ebay usually has the best price. Makes a difference if you order from a seller that doesn't charge tax. Summit, Jegs, & Amazon do now charge tax. There are still some Amazon & Ebay sellers that don't charge tax. A guy on the PY forum said that a law was recently passed, requiring all online sales to include tax. Said he's thinks most sellers will comply by the 1st of the new year. Can't verify this.

Here's a set for $330, shipped, right now.

https://www.ebay.com/itm/Speed-Pro-Forged-Coated-Skirt-Flat-Top-4VR-Pistons-Pontiac-400-Set-8-030/252692906295?hash=item3ad5abc137:g:tIQAAOSw6DtYXCzj:sc:FedExHomeDelivery!71251!US!-1

If you have $600 or so to spend on pistons, you can buy Icons, with a 1.720 pin height. Or, you can buy Auto Tec brand, and have the pins located where you need them.

A cheaper piston option is to go with cast pistons made for a 455 Olds engine. .020 over = .025 over 400 Pontiac size. And .030 over = .035 over 400 Pontiac size. They have a shallow dish. Sell for less than $250 on Ebay.

https://www.ebay.com/itm/Silv-O-Lite-Pistons-for-1968-76-Oldsmobile-455-7-5L-V8-Oversize-20-Set-Of-8/332530255520?epid=1411150205&hash=item4d6c5906a0:g:uaIAAOSwzbxaZ81S

https://www.ebay.com/itm/Olds-455-Pistons-030-oversized-NEW-9-75-to-1-1968-thru-1976-set-of-8/302622167324?hash=item4675afd11c:g:U-cAAOSwg3FUj1g~

Here's even a set of Zollner NOS pistons, for $170 shipped.

https://www.ebay.com/itm/8-Set-Zollner-Engine-Pistons-for-1968-1976-Oldsmobile-455-7-5L-V8-020-Oversize/143451838798?hash=item216665594e:g:JTQAAOSwg9Rd211l:sc:FedExHomeDelivery!71251!US!-1

"...so I am now in the market for some pistons and rods..."

If you want new rods. The cheapest I know of are the RPM H-beams, @ $400, assuming they don't charge tax.

At the time of this post, they are $400 shipped. No tax or shipping charges added.

http://www.racingpartsmaximum.com/sae4340steelhbeam-2.html

Jegs sells the Eagle SIR6625PP-8 rods for $370. That includes shipping, but not tax. They DO now charge tax. But,they are also showing a $20 off deal, for some purchases, over $250. So, if that applies to these Eagle rods, that will make 'em slightly cheaper than the RPM H-beams. But, the H-beams are lighter & stronger.

https://www.jegs.com/i/Eagle/356/SIR6625PP/10002/-1





« Last Edit: November 29, 2019, 10:14:55 PM by oldskool »

oldskool

  • Oracle Forum Member
  • *
  • Posts: 2298
Re: What pistons should I use for a 400?
« Reply #6 on: December 03, 2019, 08:32:16 AM »
So we tried with the stock pistons and rods but some of them have the piston head rings seized and some are too scuffed to use. Although I was against it, it appears the block may have to be bored out 0.030. there is a bit of a lip you can feel around the ring of the holes, so I am now in the market for some pistons and rods (and maybe a camshaft as well I suppose) for the Fire Am. I assume the block hasn't been bored, it doesn't look like it has so I'm assuming I'm going from totally stock bore to 0.030 over. The cheaper the better lol. Considering having the block "blueprinted" while I'm back to this stage.

If you go with 6X heads, I recommend Speed Pro L2262F forged pistons, as the cheapest DECENT pistons you can buy. Will need to have some cut off the block deck, in order to get the piston tops up to near zero deck height.

Most good engine builders will first square up the block deck with the crank centerline.

Another way to go, is to use L2323F.030 forged 455 Olds pistons. These have an 18cc dish. They'd be great to use with some 72-80cc heads. Or, with 6x-4 heads, you could have some shaved off the heads, & have some shaved off the piston tops, and still get decent compression.

https://www.jegs.com/i/Sealed-Power/844/L2323F30/10002/-1

If you end up with less than 9:1 CR, a small Voodoo cam will increase cyl pressure & make up for some of the low CR.

https://www.lunatipower.com/voodoo-hydraulic-flat-tappet-cam-pontiac-v8-256-262.html

A 262 will give more top end power. The 256 will have more low rpm power & a smoother idle.

https://www.lunatipower.com/voodoo-hydraulic-flat-tappet-cam-pontiac-v8-262-268.html

Here's another option.

https://www.summitracing.com/parts/hrs-410021-12/overview/make/pontiac

If you have over 9:1 CR, there are other cam options.

https://www.summitracing.com/parts/sum-2801

https://www.lunatipower.com/street-master-hydraulic-flat-tappet-cam-pontiac-v8-276-286.html

The cheapest forged rods are the 5140 Eagle #SIR6625PP-8.

https://www.jegs.com/i/Eagle/356/SIR6625PP/10002/-1?gclid=CjwKCAiArJjvBRACEiwA-Wiqq4w57Jl3iUm6vJgO3KmAkTwXJOFKakzZYYKXANR-vhiRZtFr5fQIAhoCcSgQAvD_BwE

But, the RPM H-beam rods are only a few buck more, $400 shipped, and they are lighter & stronger. I'd recommend these. The part number for the pressed-pin pistons is LG3-6625HP.

http://www.racingpartsmaximum.com/sae4340steelhbeam-2.html

Some chose to keep their cast factory rods. But, most good shops will charge over $200 to resize the cast rods, with new ARP bolts. And you still have 40+ year old CAST rods, that have undergone many heat cycles, and will be very SLIGHTLY shorter than factory length.

« Last Edit: December 03, 2019, 08:54:16 AM by oldskool »

DynoLee

  • Active Forum Member
  • *
  • Posts: 130
      • Lee's website
Re: What pistons should I use for a 400?
« Reply #7 on: December 11, 2019, 11:42:44 AM »
I've been using the Keith Black hypereutectic pistons since the 90's.  I follow the directions on how to gap the top ring, and have NEVER had a problem.  I've used them in 400, 428, 455 Pontiacs and 455 Olds.  The KB's I've seen with damage, have been from insufficient ring gaps - and I've seen OTHER brand pistons that also broke from insufficient gaps.

I HAVE had a TRW/SpeedPro piston break.  Crappy piston design, with two huge voids in the oil ring groove, for oil drainback.  ALL other forged pistons for Pontiacs (and the KB hypereutectics) utilize a few drilled holes for oil drainback.  I had a TRW forged piston break in that area, the entire top (crown) popped off.

Pictures of this at:  http://www.classicalpontiac.com/members/455/2.html

 
« Last Edit: December 11, 2019, 11:45:31 AM by DynoLee »

oldskool

  • Oracle Forum Member
  • *
  • Posts: 2298
Re: What pistons should I use for a 400?
« Reply #8 on: December 11, 2019, 06:48:05 PM »
No way I'd pay $400 for KB Hypercast pistons.

https://www.summitracing.com/parts/uem-kb133-030/

The SP pistons are forged & are cheaper. Me and thousands of other Pontiac guys have used the TRW/SP forged pistons for street & strip use, since way back in the '70's. I raced several 455's with these pistons. Many hundreds of passes, 5000 rpm or higher shift points, at every shift. The piston heads are thick enuff that many have had a dish machined into the top, & used 'em to lower CR. Only bad thing I've read about 'em is that they are heavy. Some buy lighter pins.

As said, if you need a dish, you can use Olds 455 pistons, in either cast or forged.

Auto Tec pistons are a much better value, IMO. For somewhere around $550 shipped, you get lighter, stronger, forged pistons, with thinner rings, and any pin location you need.
« Last Edit: December 11, 2019, 06:51:35 PM by oldskool »

Re: What pistons should I use for a 400?
« Reply #8 on: December 11, 2019, 06:48:05 PM »
You can help support TAC!