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Topic Review (Newest First)
09-08-2010 09:53 PM
techinspector1 Last post was 2 1/2 years ago. He probably has it figured out by now.
09-08-2010 05:49 PM

if you do (Google search for Chevy block cast numbers)you will find a lot of places that list a big part of Chevy block numbers. that how i found out i got a 302 for $450. lucky HaHa.
01-30-2008 06:44 AM
302 Z28
Originally Posted by baddbob
If you have a factory 302 crank-sell it!
Exactly, the proceeds from the sale of an original 302 crank could easily pay for the upgrade to a 327.

01-30-2008 05:45 AM
baddbob Yet another option: if that block is a small journal block you could also cut a 350 crank to small journal specs and buy 350 pistons. There's many 350 pistons to choose from.
01-30-2008 05:41 AM
baddbob You need to verify for sure if that is a 283 block and also what crank is in it.
If it is a 283 block there is another option: up untill 1968 the 283 and 327 shared the same main diameter on their crankshafts so you could sell off that little 283 cranks and install a small journal 327 crank. This will open up more options for piston selection and you'll enjoy the extra 25 more cubic inches. Finding a 63-67 327 crankshaft is not that difficult in fact most crank regrind providers will offer a crank kit with bearings for around $150. I wouldn't bore that block any farther if it is a 283 block. Depending on what heads you have you could get the compression you're after easily with flattop 327 pistons. If you have a factory 302 crank-sell it!
01-30-2008 12:56 AM
How to get a Chevy 302 under 10:1 CR

An update on where I got to

I found an SRP Piston with 10.4:1 with a solid dome which can be milled to flat top at

The issue for me is the are 0.30 oversize and my block is 4".

My mechanic has a concern if a 283 block can be taken out to 4.030. He has a book that says it can but he is still concerned that given the age of the block that this might not be a great idea

I would appreciate any thoughts/opinion on this. Is he being over cautious?

Thanks a lot
01-21-2008 07:28 PM
trees I am not sure if you measure your octane rating the same as we do. If you are on the same scale, I don't think you have a big problem with 12.1 to 1 compression ratio on 98 octane gasoline. A couple of questions: Do you add lead to your gasoline or is it unleaded like us? Can you get the casting number on your block to us so we can tell what you have? I suspect you have a 350 block. If the motor is mounted with a bracket attached to the front of the block, then it is probably an older block and it will not live long with a 4 inch bore. If it is mounted on the sides, there is a very good chance it is a 327/350 block. What heads do you have? The cheapest (and better performance) solution would be some good aluminum heads that definitely let you keep your piston set up and increase the size of the combustion chambers.

In the old days, the careful boring of the 283 blocks to 4 inches and using the 351 Ford pistons on specially machined rods produced a screaming 301. I just can not remember the specifics, but there were some after market pistons produced for this conversion (Jans stick in my mind but not sure)

01-21-2008 07:06 PM
Cool 59
too much compression

If 302 cranks are rare, sell it and buy a 327 or 350 crank. The piston selections for these cubic inches are almost endless and reasonably priced.
01-21-2008 02:03 PM
marks914 You can get a set of pistons made for around $600.
I am running SRP 10.4:1 pistons that have been radiused, and a little clean up on the heads. Did it get it below 10:1? I do not know but it should be close.
I have been running 93 with no problems, never tried anything lower. Aluminum heads help too.

Since you have dished pistons, you might be OK. Do the math to find the real CR.

The 302s are really fun! I am running a large journal DZ in my 914! Spins up like a Porsche.
01-21-2008 07:30 AM
Double_v23 PT042H3

The above piston from Wiseco, is for 4.030 but there may be stock diameters available

It is a dome but the lower comp height gives it 10.5 to 1 with 67cc chambers.

You could have the top milled slightly to further decrease compression as well as remove material from the combustion chamber on the head to get it right where you want it.

I think any way you slice it, it will be a lot of work.

I have seen advertisements for a fuel treatment that increases your octane significantly, it is a cannister that you put inline with your fuel system and could bump the 98 to over 104 or something like that. You should check that out as well.
01-21-2008 07:21 AM

So here is a comparison of the two pistons,

The compression height on the Ford piston is almost .300 less than the 302 chevy, this means that the piston would be .300 down in the Cylinder head. This would be very bad.

You could try to compensate with additional rod length but that would get expensive. Have you tried actually calling wiseco or JE and asking if they have a flat top that meets those specs?
01-21-2008 04:55 AM
How to get a Chevy 302 under 10:1 CR

Thanks all for your comments.

I haven't been able to check the crank castings, will probably be tomorrow and I will let you know 302 Z28

Unfortunately my pistons are hollow domes so milling is not an option.

Following up on Double V23 suggestion I have again had a look for some 4 inch pistons and came across some Ford 351 $" pistons
So could someone let me know if these might work and again my apologies for my lack of mechanical knowledge

From Kb Pistons Website

Chevy 302 Spec
Bore 4"
Pin Dia 0.927"
Comp Ht 1.825"

Ford 351
Bore 4"
Pin Dia 0.9.12" maybe could be bored out to 0.927"????
Comp Ht 1.774"

the 351 pistons are flat tops and they quote CR of 10.5:1 with 64cc heads.

the reduced Comp height would reduces the CR some but by how much I have no idea??

Someone told my mechanic Uncle that there was a ford 302 piston available with Chevy pin diameter. Anyone ever heard of this??

01-20-2008 11:31 AM
MI2600 If you can get 98 octane gas then you don't have to lower the CR much. When the 302 was new, the best pump gas we could get was 100 octane.

If it was my engine, I might take a little off the piston tops. Putting thicker head gaskets on is going to mess with your chamber quench.
01-20-2008 11:00 AM
Double_v23 I think you need to find out more about your pistons. Then you can find a piston with the appropriate compression height, wrist pin diameter, and piston diameter and use it. It doesn't have to be for a 302 or 283 or 327 it just has to have the right specs...with all the pistons out there I am sure one will work!!!
01-20-2008 07:48 AM
onebadmerc If your pistons will permit it, mill the domes down as far as they will go. Then install a thicker head gasket. I wouldn't bolt on a set of larger cc heads with domed pistons. Yes, it would lower the compression ratio but it would also increase the surface area being exposed to more heat. Dome pistons are not the best pistons to use on pump gas, they have lots of spots on them that that get hot. A flat top piston will disperse the heat more evenly, being less prone to hot spot and detonation. You can also install aluminum heads which will allow you to run more compression, but keep them at 64cc's. Even if you install aluminum heads you will still need to get the pistons domes down or find some flat tops.
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