1racerdude

If ya had to get the accessories anyway for the LT-1,it would not be but $1-200 more and a screaming set up.
I would get the block that would let me go to close to a 4.150 bore or a tad less,with one more boring left to rebuild.
Those heads will flow ungodly if ya REALLY unshroud the valves.Don't let anybody tell ya .080 is enough,the more ya have the better the air column and more of it into the cyl.

69vette

the dart block can be bored to 4.185 maximum. Is there really much difference in boring it 4.125 or 4.150 for the first round? Seems like by boring it out to 4.150, you are limiting yourself to less rebuilds on the block. With the 4.125 it is a 427.43 cubic inches and with the 4.150 bore, you would have 432.629 cubic inch motor. You owuld gain about 6 cubic inches.

1racerdude

Only for valve unshrouding.Its not the 6CID.

69vette

So you think that unshrouding them that much more will make a huge diff. or is it going to be minimal?

1racerdude

The more ya have the better.I can't say that it would be a huge difference,but one overbore will last 8-10 years if ya don't blow it up.

69vette

Can you put a rough number on the differnce in hp so i can put it in perspective? Or does that all depend on ten million other things?

1racerdude

No
But I will site an example:
A guy had a 598?BB and made it a 640? with a .060 smaller bore and the rest in stroke. He used the same heads,cam,intake. The car was running 8.60's and slowed down .3 tenths.He changed cam's and that didn't help. He talked to other engine builder's and they all scratched their head.
We got to talking and determined it was valve shrouding.He bored it to the other block size and used the same style pistons,except .060 larger,and changed nothing else just to see.
The car went a 8.26 it's first pass after the bore job and has since gone quicker.

So valve shrouding IS important and everybody thought the bore size of that BB wouldn't shroud the valve, but it did. The extra few cubes didn't do it either.

69vette

Alright that def. puts it in perspective then. I didn't realize that the valve shrouding would be bad since the heads were originally set up for a 4.125 bore. I guess the last question in concern tot he block is should i keep it stock deck height or get the taller deck that dart offers? thanks for all the help.

1racerdude

Stock.The tall deck get's REAL expensive to make it do what it's suppose to do HP wise. Automatic new intake and header's and a bunch more.

69vette

www.summitracing.com part number DRT-31121211


so that looks like the block for the application then? wheres the best place to get it so i don't have to weight till august 16?

SStrokerAce

So the heads were cut for the big bore the first time? Make sense that he slowed down. OTOH you can make heads work on a smaller bore, al la LS1... only problem with those things is the heads flow like mad but make power like crap for the cfm. 330cfm should make 700hp if done right, not 550-600hp.

I'm still a fan of bigger bores. Actually a old GM engineer wrote in to Hot Rod about the Bore vs. Stroke story and told the tale of the "mystery motor" development and the shrinking of the 396 bore to use the common crank with the 427 and they lost HP on the motors, once they motored them to find frictional losses TA DA! there was all the HP losses... sometimes it's frictional losses sometimes (especially on BBC's it's bore shrouding issues)

Bret

69vette

so from your point of view bret, would you bore the motor over to 4.150" or just leave it at 4.125 and be able to get more life out of the block in case you need it down the road? Just trying to get everyones point of view. Also if you'll could post up some link for where to get the block and let me know if thats the correct part number. thanks

1racerdude

From looking at his heads the chambers didn't appear to have been laid back to the edge of the bigger bore. IMO it all had to do with the distance between the valve and the bore and I feel that was proven.

Got a first hand idea on what the 330CFM will make.That won't make 700 IF everything else isn't dead nuts.

SStrokerAce

.060 on a bore is a big amount either way.... It would have been interesting to see the flow on the bench with both bores to see if there was a difference as well.

As for the LS1 heads.... they ain't gonna make 700hp out of 330cfm unless you spend lots of money on the R&D of the port... only a few guys out there that can do that too.

Bret

1racerdude

I was speaking my engine .