cutting the deck

timmyw28 · Post by **timmyw28** » Wed Feb 11, 2015 1:28 am

I currently have my 2.0 block at the machine shop. Having it bored .040 for the dohc pistons I got. And I was also going to get him to cut the deck. Just wondering how much could he cut off the deck before I run into piston to valve clearance.and about how much would he have to cut off to get it to 11 to 1 compression . I'm going to clay it before the final assembly just to make sure it has the right clearance.

Dranz · Post by **Dranz** » Wed Feb 11, 2015 7:28 am

Running a cam?
When I had my block decked, I just had them clean it up. I think .015"? Don't do a lot with the block. You can't un-deck it if you end up with interference... Shave the head, do the head gasket mod, and be happy with darn near 11.

Post by **occasional demons** » Wed Feb 11, 2015 7:37 am

What head are you using? SOHC or DOHC?

Just asking, but assuming you are SOHC/stock spec DOHC pistons, then Dranz's advice is pretty well on the mark.

The added bore will raise the CR a little too. If they are 10.5:1 for a DOHC head, and you are using a SOHC head, then you will be nearly at 11:1 without shaving anything.

I may be wrong, but I can't see a major gain between 10.5+ and 11:1.

Stock DOHC pistons with a SOHC head will net you ~10.3. You will need to massage the head chamber, or the pistons to keep contact from happening, especially with the larger bore. The head is the preferred method. The larger bore may automatically get you close to 10.5, assuming stock type replacements.

timmyw28 · Post by **timmyw28** » Wed Feb 11, 2015 8:30 am

I'm running the the sohc and plan on getting the comp 400 can

Post by **occasional demons** » Wed Feb 11, 2015 9:36 am

10.3 - 10.5 will be plenty for that cam. There is no valve overlap, so going higher than that will only create issues. You should be able to use the stock PCM or a reprogrammed unit and still pass emissions.

timmyw28 · Post by **timmyw28** » Wed Feb 11, 2015 10:15 am

I don't have to worry bout emissions around here so 10.5 would be good with that can and run 93

Post by **occasional demons** » Wed Feb 11, 2015 12:38 pm

Should be good. Possibly even with 87, the PCM will just pull the timing back.

Our '96 runs fine on 87, stock cam, ported head, 10.3:1. You can always try it with a few gallons, if it pings, fill the rest with 93, or add some E85.

timmyw28 · Post by **timmyw28** » Wed Feb 11, 2015 1:35 pm

Sounds good I may try to push it a litter higher but not sure yet

Post by **occasional demons** » Wed Feb 11, 2015 5:14 pm

What you need to consider is dynamic compression. With a zero overlap cam, there is nothing bleeding off pressure. Once you get some rpm up, the cylinder pressures might be too high for even the base lowest spark map to keep it from pinging.

Even back in the sixties when there was real gasoline, Pontiac had a factory ~11:1 engine. But they cammed it very big so it could still run on street gas. It didn't make real cylinder pressure until it was up there in RPM.

To run over 10.5:1, you are going to need a bigger cam than a 400. And anything bigger than a 400 needs at minimum, a piggy back control for fuel, etc. You are now beginning to add probably more cost than you want, for the power gained.

IMHO, if you are getting into the need for engine management to make power, you may as well spend for boost. Because there, you are going to get a better return on your investment.

It will be a substantially higher investment, but so will the power gains. And driveability.

timmyw28 · Post by **timmyw28** » Wed Feb 11, 2015 10:50 pm

I under stand exactly what u are saying. If I go up any more than 10.5 I will need a cam with some overlap to bleed some of the compression off. But if I get a cam bigger then 400 then is not going to work with the stock ecm too well. Thanks for the advise