[ponjohn]

Are special pistons needed because of the cylinder chamfer in the 67 400 blocks?

I recently read this and had no idea the 67 400 was different.

[25stevem]

All the 67 400 blocks and the early 67 428 blocks all had the top of the Bore chamfered for earlier 17 degree inclination angle of those 326,389 and 421 heads heads.

If you want the best Intake breathing when running any head with a 2.11" valve then the chamfer should be added to the top of the Bore as was done for the latter 14 degree heads.
Doing such depends on the chamber your working with and the compression you want/ need for the Cam your running.

Adding the needed chamfer will add near 4 CCs to your calculations for compression.

On most common Pontiac Bore sizes 4 CCs will change your ratio by a 1/4 of a compression point, so if that's a problem you can easily mill the heads or deck the block to retrieve those 4 CCs .

If your getting custom Pistons made then increasing the compression height by .018" will make up for the 4 CCs you put in from getting the valve Bore notch in the right place

Note that boring the block .045" over will remove about one half of that unneeded valve notch that was held over from the 17 degree heads.

[PAUL K]

The chamber depths will vary. I've only had one issue with the ring being too high and getting into the chamfer, this block had abnormally large chamfers. It's okay for the ring to come right up to the chamfer but you don't want any part of it to go past the cylinder.

[chiphead]

I've built a 67 400 block. On my motor, the top ring needs to be .300" down from the top of the deck at TDC. Measure the chamfers and go .015"-.020" below that for top ring placement. Otherwise, use whatever piston works with your bore size and the valve angle of the heads you're using.

[ponjohn]

Originally Posted by chiphead

I've built a 67 400 block. On my motor, the top ring needs to be .300" down from the top of the deck at TDC. Measure the chamfers and go .015"-.020" below that for top ring placement. Otherwise, use whatever piston works with your bore size and the valve angle of the heads you're using.

Did you specify the year of the block when ordering the rotating assembly.

The heads will be SM or Ehead round ports.

Is zero deck out of the question with this block?

Thanks.

[chiphead]

I specified the top ring placement when I spec'd the autotec pistons from Paul K. The top ring will sit lower on the piston, but the piston crown can still reach 0 deck. Like I said, you or your machinist need to verify the dimension of the deepest chamfer and specify the top ring placement based on that.

Deck it, bore it, stroke it, do whatever you want. Just verify you've got enough valve to block clearance at max lift. Unless you're running very high lifts (590+ where you might hit the block) the only issue is the shrouding of airflow like Steve mentioned. In either case, just have the (competent) shop add the later valve reliefs to the block.

[77 TRASHCAN]

Originally Posted by ponjohn

Did you specify the year of the block when ordering the rotating assembly.

The heads will be SM or Ehead round ports.

Is zero deck out of the question with this block?

Thanks.

You going standard bore?

Boring will remove some of the chamfer.

[PAUL K]

Originally Posted by 77 TRASHCAN

You going standard bore?

Boring will remove some of the chamfer.

Correct, so will decking.

[25stevem]

But let me say this for the sake of other people that may be using whatever chamfer they have in there block,.

1) boring removes some of the chamfer but does not reduce the effectiveness of the chamfer in aiding Intake flow.

2) decking reduces the effectiveness of the chamfer in aiding Intake flow due to that machining process making the chamfer more shallow, as in more lip like.

[Lee]

RaceTec made me a set of pistons for such a combo. They used thinner "metric" rings which allowed a tightened ring package. No problems.

[lust4speed]

Some over-thinking going on here. The stock '67 GTO block had chamfers in the wrong place and survived nicely for 55+ years. By the time you bore and deck the block those old chamfers are pretty small, and while they are still there they don't cause a problem.

You get to add new chamfers if you want and the end result will be the same chamfer as a late production '67. As Steve said the most important part of the new chamfer is the top going out to match the head and gasket. And as Chiphead said, the bottom of the chamfer probably not exceeding .200" down in the bore.

[Tandyman]

I run a 67 400 YT block with a 495 Eagle stroker kit (4.5 stroke , .065 over Mahle pistons and 6.8 rods ) . Like Mick said , after a bore and deck there is not much chamfer left and
they were not an issue with my build. Currently have over 900 1/8 miles passes on it and its still running strong .

Glenn

[ponjohn]

How this came up was, a person was shopping for a stroker kit on Jegs. Jegs website said a different piston was needed for 67 blocks.