[Mk2] [Turbo] Which is best block/head marriage?

[paulharry]

Hi
What is the best block and head to have when building a new engine
I've heard that a rev2 block and rev 3 head is the best way to go
Is this right? Or is the rev3 block and head better?
I was also told the rev 2 block is stronger then the rev3
And the rev3 turbo is better suited to a rev2 because the block has lower compression and the rev3 turbo Runs better with the lower compression of the rev2 block
Is any of this right?
Thanks

[jimGTS]

5s block.


It's the pistons and HG thickness that give you high/low compression.
Not the block itself. Least that's my understanding.

A rev2 is maybe marginally better than an early rev3 block.

But there were better mr2 blocks, more meat in the water pump area I believe with the rev4/5 block which is where many earlier ones crack.

So

5s
St215 (caldina)
Rev4/5 block
Rev2
Rev3

Not stating this as fact but going on what ive picked up and read between the lines, I could be wrong.

[paulharry]

Thanks Jim
I was thinking that after the rev2 all the other revs where the same block
So it's a 5s strongest and going down the list a rev3 is the weakest?
And am I right in thinking the rev 3 onwards head for the best airflow?

[ashley]

Late 5S block is the one to go for if you want to give it some serious stick, the whole block is far meatier when put side by side with any 3S block, and the increase in bore size is nice as well- even if you use a 3S crank and keep it at ~2l.

There are supposed to be later 3S blocks, rev5 and possibly some rev4, that have more material around the bores...I've not seen one in the flesh, so can't comment.

The early rev3 blocks are probably the worst, having dissected a couple of them- the cylinder wall thicknesses vary all over the place, and potentially get a bit too thin in places- which increases the potential for cylinder wall cracking when you get localised super heating of the coolant (through over retarded timing, too much boost, hot intake temps, etc).

The rev 1/2 block cylinder walls are more consistent, and thicker than the rev3/4/5 blocks I've seen, but there seems to be an inherent weakness around the water pump area- and this can lead to cracking on the outside of the block. My pet theory is this is exacerbated by deleting the aircon, and not using the bolt hole through the outside edge of the water pump that would have supported the pump bracket anymore.

So...all blocks have their own potential areas that can go wrong, it's just a case of how much abuse you give them, and what lets go first. The best bet is to concentrate on rock solid cooling and fueling (oil, coolant and charge temps), and a safe tune...don't go crazy with timing retardation as this will stress the block as peak combustion temperatures occur further and further down the cylinders instead of in the head (which causes localised pockets of steam in the coolant system on the outside of the bores, and potential cracking).

As for cylinder heads...supposedly rev 1/2 heads actually flow more gas in their stock form than the rev3/4/5 heads...but the rev3+ MAP sensor system is superior. The ultimate would be the 3S beams heads, where the port angle into the intake valves is superior. That said, the rev3+ is a good head for most power levels in these cars, and can be improved with proper porting and larger valves...just make sure this is done by someone who has actually bench tested these heads, they are easy to f**k up if just done "by eye". The main area of improvement to look for is on the exhaust side, and trying to get gas out of the head.

All in my opinion of course

[C35Rob]

Did you cut open any of the later "96+" 3s blocks with the extra meat around the water pump area Ashley? I wonder if there's any relationship between the 'revised' block casting and (potentially?) thicker/more consistent cylinder walls (this interests me as my car is a Jun 96 Rev 3 and does have the 'revised' block casting)

Do you have any pics/measurements of the ones you did cut up? Was the inconsistency in thickness due to core shift?

[ashley]

We sectioned two rev3 blocks, and a rev1 block (and a rev 3 NA head)...I've probably still got them stashed away somewhere in Dad's workshop- next time I'm there I'll have a look. I don't think I had one with any extra material around the water pump though...

The inconsistency in the cylinder walls (from memory) looked to be a function of the casting process- the rev3 blocks had not been rebored, so assuming the bores were originally cut straight, it was the amount of material on the coolant side that varied.

[C35Rob]

We sectioned two rev3 blocks, and a rev1 block (and a rev 3 NA head)...I've probably still got them stashed away somewhere in Dad's workshop- next time I'm there I'll have a look. I don't think I had one with any extra material around the water pump though...

The inconsistency in the cylinder walls (from memory) looked to be a function of the casting process- the rev3 blocks had not been rebored, so assuming the bores were originally cut straight, it was the amount of material on the coolant side that varied.

Awesome, thanks