1973 Rebuild

[Matthew Abate]

Update:

[Patcon]

Pretty pistons, forged?

[Zed Head]

Exotic.  The top ring land is way down the bore.  Are they for a turbo application?  Race motor?  Can't imagine they'd fit under a stock combustion chamber design.

Or will they?

[Matthew Abate]

Forged. Carbs, not turbo.

Trial fit looks right on so far.

[Zed Head]

Do you have target specs?  Like CR, cam lift, duration, etc.  Just curious.  With that dome it seems like you'd be running high CR and with the valve cutouts, high lift and duration.  It's definitely not a factory spec. 8.8 CR engine, I'd guess.

Curious.  The specs. make the power.  It's an odd looking piston shape, but not clear what it's supposed to be doing.

[Matthew Abate]

Do you have target specs?  Like CR, cam lift, duration, etc.  Just curious.  With that dome it seems like you'd be running high CR and with the valve cutouts, high lift and duration.  It's definitely not a factory spec. 8.8 CR engine, I'd guess.

Curious.  The specs. make the power.  It's an odd looking piston shape, but not clear what it's supposed to be doing.

The Pistons were designed to fit into a p90 head combustion chamber so that it will yield a compression ratio between 9.8:1 and 9.9:1.

I don't have the cam specs readily available, but will share them later. We were going to go with Isky, but after 13 weeks of communication headaches we are going (I think) with Comp Cams.

[Matthew Abate]

Update:

[sweatybetty]

thats almost pretty enough to post in the boobs thread

[Takhli]

Okay, guys...

I'm building Matt's engine and, although a response may not come at light speed, I can answer almost any question you may have about his engine's build.

Right now, the block and rotating assembly are as Matt has posted in the photos...  Bearings were ordered today and I expect them by Saturday, so the buildup should begin soon there after.

What's left before we start? First, we take a highspeed grinder to the casting flash in the crankcase. Tape and plugs will cover all the oil passages in the mains and up to the top end; then, the main oil gallery expansion plugs come out so I can tap the gallery for plugs. I have to do this because, as you may have seen in the photos, our machinist fabricated and installed a plug in the oil bypass: I want to make certain the gallery is absolutely clean so the plugs come out to provide access to the rifle cleaning rod and bristle brushes I use to clean the passage with. Every bolt hole on the block will recieve a chamfer as well, so that threads aren't pulled.

When all the grinding, cutting, and tapping is finished the Block gets a major bath with high pressure soap and hot water, followed by a good coating of WD40 to prevent flash rust. I haven't decided to seal the casting with Glyptal,  but probably will not.

Assembly documentation and photos will go to Matt for posting so he's first in the loop of information.

Cheers.

 

[Zed Head]

Just curious about who picked the parts and how they decided.  What the goal is.  Sounds like you're using the basic "How To Rebuild" and "How To Modify" recommendations.  Looks like fun.  Good luck.

[Takhli]

Choice of Block and Cylinder Head were Matt's. The choice of rods - the longer factory stock 240Z variety - was a colaboration between the two of us. Pistons were custom designed due to the combination of parts chosen, with the dome volume prescribed by the gasket and head, for approximately 9.85:1 compression ratio. Once I've done a preliminary buildup of one piston, I'll be able to provide absolute dimensions.

BTW: For anyone thinking that all P90/P90a cylinder heads have chamber volumes of approximately 53.6 cc, they should think again. Our machinist and I cc'd three different P90 series heads and found a variation of 4cc's or more between them. The P90 we have has been milled and still holds about 55cc's, while each of our stock P90a's have chambers between 55.8 and 57.6 cc's. On Matt's engine, I will use a P90a's with about 56cc's and equalize each chamber after I accomplish pocket porting and port matching. I'll install a cam, do a valve clearance/dome height clay check, and then the head gets sent to the machinist for minimum material surfacing - about 0.003-inch - to clean up areas that needed weld repairs. I expect this head to have about 55cc's volume when done.

[madkaw]

Longer factory stock rod ?


Sent from my iPhone using Classic Zcar Club mobile