How Much to Mill Heads? 73 Heads on 71 Block?

Making a rough assumption on my part, if the first .020 of the head is the largest volume and possibly close to the same volume as .020 off the deck, it would raise my compression to almost exactly 9:1. The cam I have is a TA 290-94. Probably more cam than I need but with a low first gear stick, I'm hoping it will be fine.

 

how far are your pistons down in the cylinder? Mine were around .050 to .060 but some guys report as much as .10 which is crazy. I think my engine was pretty close to the stock 9:01 before I shaved the heads. My pistons also didnt seem to be dished as much as some of the other 70 pistons I've seen.
One thing I didn't do was mill the intake side of the head. Some guys do this for better intake manifold alignment. Instead I used the thicker composite gaskets from ta performance. I'm not sure I would go this route again. It held my intake off the end seals quite a bit. A larger than normal Gap. It took lots of sealant to fill it. You'll Definitely want to wait a couple days before starting the engine so the sealant can cure. So far no leaks for me but made me nervous.

 

I've got stock 71 pistons and assume 24cc dishes. I measured mine at about .051 in the hole when I was tearing it down. I'm getting the block milled .010 so I should be .041 down in the hole.

With .041 down in the hole, .020 steel shim head gaskets and shaving .020 off the heads, I'm expecting 9.0:1 compression. I calculated 8.2:1 as assembled. I will mill the heads on the intake side as necessary to make everything fit.

 

You will find the idle to 3000 rpm torque and performance to lacking unless you get over 9.5:1 static compression it will be a mismatch to that cam.

 

I really need a smaller cam. Probably should sell this one and go with the next smaller. I was even thinking the TA212 like in my Stage 1. A hint of a lope but awesome off-idle power.

 

I have the 284-88h which is one step above the ta212. Not sure I'd recommend it. Obviously my mismatched build combo has had all kinds of issues BUT my cam was supposed to be a good match to my compression.

 

Yes the 212 will work with 8:1 even, the larger cams really need 9.5:1+

 

Without a cam card and just using a Summit calculator to find the cam timings, this is what I get.

With that cam, I get 7.61:1 if it is advanced 4°. 7.43 straight up.

With a TA 212 I get 7.79:1 4° advanced. 7.61 straight up.
The TA 284-88H gives 7.68 4° advanced. 7.5 straight up.

Hmm, I can include this in my engine calculations spreadsheet.

 

Greg, try the calculator at zero advance. Try it at 10 to 1.

 

That calculator was way off some how. That's too high and I found another one that is much more inline. I'll update the numbers in my original post DCR post.

 

My 284-88h cam card. My cam was installed by the machinist to the exact specs on the card. My receipt said 2 degrees advanced. I don't totally understand how all of this works still but based off your calculations. The 284 installed straight up gives you that 7.5 dcr. The guys on here convinced me to mill the heads to get closer to that target. Glad I did. I'm still learning all of the time. Hopefully my cam card can help you a little.

 

You will find that you would want 10:1 or better with that 290 cam. Ta suggests 9:1 or more but 9:1 with that cam would be a dog. You would find it to idle very high and have low vacuum. Poor manners off idle till 2800 rpm.

http://www.taperformance.com/proddetail.asp?prod=TA_290-94H-350

 

Last I heard Scotty brown has 350 cam
Cores, and his custom grinds are no more $ vs an off the shelf cam. That was a few months ago that he had cores, I just had him grind me a new turbo cam.

 

At 2° advanced for your cam, I come up with 7.66:1 DCR using my theoretical engine with an 8.84:1 SCR.

With my current cam straight up, I come up with 7.43:1 DCR for the same 8.84:1 SCR. I think I need to go smaller.

I don't think I need to use this cam after all. I don't want anything this radical. The 284 seems less and the TA 212 would be even better from the specs with my current build netting around 8.8:1 SCR

I may do that. Something between a TA 212 and the TA 284?

 

This chart is from Comp cams:

 

Yes close to the 212 would be best, I think they are currently sold out though that’s why I suggested Scotty. Even the 284 is a bit much for 8.8:1.

 

If I take .020 off the heads, I think it will be just about 9:1.

 

the only way I would suggest that cam you have is if you get over 9.5:1 but then it’s a high octane engine. 10:1 would be ideal. I though you said you wanted to stay low octane? Honestly you would likely be more happy with a stock cam and 8.8:1 compression vs 9:1 with that big cam.