KJL

I am having my Dart Little M Sportsman block freshened up by a very reputable local engine builder. One of the things I am considering is over-boring to a 434 displacement to maximize its potential. It is a standard deck height block. He recommended leaving it at 427 because of rod ratio issues which result in high piston skirt pressures, overheating and potential issues with head gaskets. The block is designed to be over-bored 0.06" max. Not sure if the cost for an extra 7 cubic inches is worth the risk and the power gain. I am currently running a 1.5 rod ratio (6" rods and 4" stroke). This builder has been building performance engines for 40 years and I respect his opinion but thought I would float this out to the forum experts as well. Cost is not the main issue but I want a reliable engine that will last and I don't want to wish a few years from now that I went ahead and over-bored to a 434. This is the last hurrah for this engine...of course I though so 10 years ago too...

StraubTech

A good pump gas engine makes 1.4hp per cube. 7cid x 1.4 = 9.8HP. I would leave it also.

bluedawg

Rebuild the 427" even meaner.

OzzyTom

And the numbers 427 just sound right for a Corvette!

OzzyTom

Oh! I just checked your profile.......
Your 427 specs are already very good.... 450 rwhp!
And the car appears well matched with TKO-600 and 3.73 rear end.

How much more power do you want?

gkull

As a proud owner of a 434 it was worth it to me. My block can take a 4.200 overbore. I thought that the little M's were 4.180 max bore, but anyway I'm not going to look it up.

Anyway have the bores measured and if your pistons are okay just cheap out on the rebuild.

The builder probably does very few Dart blocks. They are so much thicker than a stock that over heating with even a 0.60 overbore is not an issue.

Rod ratio is rod to stroke length. A bigger bore is less cylinder wall loading because the piston is physically bigger.

To anybody just going to a new 427 it is stupid. it is only something like $100 more to order the .030 overbore blocks. 100 bucks for 9.8 more hp is very cheap

KJL

Thanks for the input, not sure where you came up with 4.20 in my thread. The bore is actually 4.120. The published max is as you stated 0.06" over 4.125 for 4.185 maximum.

C3 Stroker

I would definitely go 434".....more potential.......no gasket problems.....it has already been done for you......check this this out:

http://www.ultrastreet.net/engines/434_bigdawg.php

KJL

That is pretty much where I am heading with this. Very interesting.

76CSRvette

434

gkull

I guess that i was not clear. My Motown block can be bored to 4.200

The Dart block must be slightly thinner and a max over bore of 4.185.

So doing a 4.155 bore 434 still has enough room for future boring. Pistons are made in all bore sizes. Like a .040 over or a .020. Paul went for the max over bore and a 3.875 stroke to get 427.

In the past I bought a used racing block that had steel cylinder sleeves and a custom bore size to use a 3.200 stoke and end up with 359.5 ci. it was a 360 max ci class motor

StraubTech

I would highly recommend a 2" kickout on the pan rail.

KJL

Seems like that was smart thing to do. Looking at the 434 in the above post, it may have been smarter to buy the crate engine and sell my current setup. I would have saved some $$. I am going to ask my builder for a quote to go 434. My guess it will be high because I don't think he thinks it is a good idea.

KJL

I am going to call Milodon to see if they have one that fits a 72.

gkull

This is the idea for big stroker small blocks. Maybe they have a 4 inch stroker version, but 9 inches is too deep. I have a morroso 8.5 inches deep 8 quart with filter and my header collector flanges and the blow proof bell housing are lower

KJL

When you say lower, I am not sure what you mean? Are you saying this pan should fit a stock height components?

BTW, nice pan.

L88Plus

Because of the metallurgy of the cast iron used in aftermarket blocks, they wear very little. Most of those that have to replace blocks do so due to catastrophic damage, not wear. There's nothing wrong with going a little bigger, leave yourself .030 short of Dart's recommended max.
I have a couple of BBC Darts that would have been discarded at 4.600 bore had I not shown up when I did to rescue them Gonna be some wicked mills when I can afford heads for 'em!

claysmoker

He means lower to the ground.

KJL

OK... but what does that have to do with whether the pan will fit or not? Just trying to make the connection.

KJL

As a follow up, I spoke with my builder today and apparently we got our communication a little crossed. He assumed I was asking to go 0.03 over with the same pistons which he strongly recommended against. I told him no, I was just assuming we would need new pistons. He is going to work up a price for me now.