Common block and Tall Deck block.

[Koreth]

I have been thinking again My mother alwayas told not do do that, as it would eventually make my brain melt, but I never did listen.

So the argument is that the common block is the best block to be had for high output builds, because of its strength with beefy mains, and webbing on the back of the block. I really don't know what people are talking about when they mention these things, having not seen the internals of a pre-common block engine to compare against (pics would be nice, hint). But I have also heard about the 88 tall-deck blocks having the same features. Can anyone confirm this?

What it comes down to is I am brewing up ideas for a nice, reliable, sceamin' high output hybrid turbo setup. I want to use the strongest block available for this, but I also want to be able to make use of the 2.5s additional torque. The problem is, the 2.5s rod ratio in a common block sucks, and they don't rev well as a result. It ocurred to me that if you took 2.5 common block pistons, a 2.5 crank in a tall deck motor, you'd have the space needed for extra long custom rods and have a good rod ratio and the 2.5 should then be able to rev easier. My understanding is that the main things preventing our engines from reving is a) airflow thought the stock head sucks b)being engines with long strokes, the stock rod ratios suck, with B being the bigger issue.

I cannot find any numbers for tall deck motors save for the lenth of the rod on The Dodge Garage. A lack of pictures doesn't help either. Does anybody have either of these, especially pics, so I could compare to a common block. I want to have block that be able to take the kind of power that Stephane (did I spell that right?) was making when he was cracking common blocks when still using equal length halfshafts. I am wondering if the tall deck bock is my ticket or if I should have the deck welded up on a common block ($$$!)

Can anyone help me out with this?

[DirectConnection]

What are your goals?
You don't need the tall deck block with special rods and pistons to make 400whp.
If you're shooting for the sky.... then I believe the tall deck block would be the way to go. Sucks that I have stockpiled a bunch of turbo common blocks when sometime down the road, I may try the tall deck idea. BTW... it's not just about a poor rod ratio that hurts HP (this claim only been proven by a few HP in Hot Rod I believe) but more about piston speed/velocity. The poorer rod ratio, such in our case with the 2.5, really whips that piston up and down. As you know, the piston doesn't stay at a certain speed throughout the stroke. It slows down when approaching TDC and at BDC, but really gets whipped leaving after. It's that acceleration of the piston that robs HP if the ratio is poor and makes the piston act like a big anvil.

[Koreth]

This whole thing is still in the realm of "Wouldn't it be cool if..." I'm hoping to get enough hard facts about the tall deck block to bring the idea into the realm of "Won't be cheap, but can be done." Kind of like the hybrid motors. First it was a "hey, the 2.0 and 2.2/2.5 have the same bore, bore centers and bolt patter for the head. Hmmm...." now it can be done if you have the extra money needed.


The idea would be to take the hybrid as high as it can go. My understanding is that the poor rod ratio of the 2.5 it what kills its torque curve at around 5500 rpm. That because of the pistons severe acceleration (the side loading witht that rod ratio a those speeds probably isn't good either), none of the power from the power stroke is left after starting and stopping the piston on its strokes to go out the flywheel to the trans and ultimately to the wheels. So an improved rod ratio should adress this, I would think.

Now, a wrench in the works for this idea is that longer rods have more mass, and the increased reciprocating mass will eliminate any gains to be had from the improved rod ratio, in terms of power output.

Back to my original train of thought though, can anyone confirm with pictures that the tall-dek block has the webbing and beefy mains of a common block, in comparison to the pre-commonblock? I've never seen the inside of a pre-commonblock. And does anybody have dimensions of deck-height, stroke, piston heights, etc. that would pertain to this idea of a long rod 2.5?

[jammerz63]

i think donavans might, if not it might be in allpar. also as far as rods go, look for
198 slant six rods. at 7 inches long i think they would work beautifully in your engine
combo. also, if you don't have the pistons putting stess on the cylinder walls with the
lousy rod angles,would you really that much more strength in block? basically, about the only week point i remember in the 86-88 blocks at the main caps. another area was cooling, but then i believe a cool motor is a fast one.