BIGCAT7274

It's been done before. I have a article from the late 70's about how they did it.

Catmaigne

iTrader: (6)

build it because reasons

great421

iTrader: (1)

Yes, but you cannot break the laws of physics.

A 4.125 x 4 = 427

and, 4.125 x 3.875 = 414

and, 4.125 bore x 3.75 = 401

However, an LT1 with a 4 inch stroke and a stock length (5.7 inch) rod makes an engine with a R/S ratio of 1.425, which is almost as bad as Chevy's original 400.

FYI - The low-revving SBC 400 had "special" (i.e. - short) 5.565 inch connecting rods, because GM knew that if they made the ring land height too short, the pistons would prematurely fail; so, using this shorter / special rod, the Chevy 400 had a very poor R/S ratio of 1.39125, but this allowed for a thicker piston that used up almost all of the available 1.585 inches of available space above the rod.

Now, getting back to your sleeved and stroked 427 example, at a milled 9 inch deck height (vs. 9.025 unmilled) with a standard SBC rod, the piston crown could only be 1.3 inches (9 - 5.7 - 2 = 1.3) above the top of the connecting rod, which is 'almost' too short to be safe.

Please note - I said "almost" - because newer pistons are (like Steve Austin): Better, Stronger, Faster!

Additionally I know that a couple companies make pistons at the required 1.3 inches, and at least one makes a "super short" 1 inch ring land piston (for 6 inch rods), but - if you wanted to get an "ideal" Rod to Stroke ratio of 1.7 in your theoretical 7 Litre small block chevy, you'd need a 6.8 inch rod (Longer than stock Pontiac connecting rods!) , which means you'd only have 0.2 inches for the piston's ring land height.

FYI - The legendary and fabled Chevy 302 had a R/S ratio of almost 1.9 and the highly touted over-square 350 HP 327 had a R/S ratio of an almost perfect 1.75.

So, it's not that it can't be done, it's that even if it were done with the best materials available, there would be at least one required trade off that would cause problems.

joelster

Show me one that has failed.

Who said you have to run a 5.7" rod with a 4" stroke. I don't. Pistons are incredibly stout nowadays. Don't believe all of the voodoo hype about rod ratios and power. There is no magic there. Go look back through EMC competition engines and you'll see what I mean. Kaase and Bischoff go back and forth with massive stroke/small bore, to massive bore/small stroke engines with rod ratios from one extreme to the other. They always end up at the top of the competition. For every con to having a high r/s ratio there are pluses too.

Here's a nice 427 sbc that runs a 6" rod and short pistons, 4.125" bore / 4.00" stroke.

http://test.shafiroff.com/engines/427_realstreet.php

and another............

http://www.shafiroff.com/econo/427_econo.php

They actually have several other variations of 427's available. You'd think they'd have all sorts of "problems" according to your post.

BIGCAT7274

one big part of the r/s ratio equation that your overlooking is piston dwell time.

Stefan D.

Was the block damaged? Is that why you wanted it sleeved?

SS RRR

iTrader: (2)

Yours?

great421

iTrader: (1)

BIGCAT7274 -

Nope - I did not overlook it, I just didn't address dwell time, or the issues associated with rod angles either; I simply thought my post dealing with R/S ratios was long enough (no pun intended).


Joelster -

Our OP (nitrous2fast) took issue at paying $2,000 to get his block sleeved, but you point to two $10,000 first generation SBC engines as proof that LT-based 427's are indeed possible.

Please understand, and let me be as respectful as possible, I never stated that a 427 cubic inch LT1 was not possible, I simply stated it was not practical. I apologize if I seemed to imply anything to the contrary.

However, the math is sound. If a 427 LT1 was indeed practical, then many more people (including myself!) would upgrade to a 427 vs staying with a 383 or a 396.

(I kinda' actually prefer 421 cubic inches, but that's just me with my Pontiac bias...)

Now, at the risk of causing even more interbox fury with my own bit of anecdotal information as "proof", I will simply point to Golen Engines and respectfully submit the fact that they only offer two sizes to their LT-based strokers, 383 (3.75" stroke) and 396 (3.875" stroke).


Nitrous2fast -

Talk to a few different machinists and engine builders who have actual experience building LT / Gen II SBC engines - don't listen to me. However, understand that if a 3.75 inch stroke requires an LT block to be clearanced slightly, then anything greater with require even greater clearancing. This may result in issues at the bottom end (requiring block fill) or issues at the top (requiring very short pistons that may rock in their bores and cause excessive wear).

Having said all that negative stuff, maybe there are new alloys or new machining techniques, that I am completely unaware of, that will resolve all these (and any other) issues resulting in an engine that you can build once and use for many years, without replacing internal wear items every season.

Good luck and have fun!

joelster

That's a complete engine price. My point is that they offer that EXACT bore/stroke combo, and offer it in many different power levels. Surely if Shaiffiroff thought there would be problems with poor rod ratio, or too short of a piston that they would pick a different displacement level. You talk about 427's with 4.125/4.000 as though they are ticking time bombs waiting to go off. Clearly they are not.

Of course it's not practical. Once you go beyond the 383 norm, everything gets expensive.

The only math is counting how much money you want to spend. It has nothing at all to do with the geometry of the block, pistons, rods, etc. To use those cubes properly you'll need heads that can support a ton of power (220cc +), and everything else associated with making big power (big fuel system, big intake), not to mention a small base circle camshaft. That's primarily why you don't see them. Any LT1 based engine over 400 cubes will most likely run you over $8k. Who wants to put $8k into an LT1 engine, when you could buy an LSx f-body car for cheaper?

Golen? Really? You point out that tidbit as the reasoning behind not making a bigger cube LT1. Probably because they can bang out 383's and 396's much cheaper. Ask them if they could do it. They'll tell you there is no market for it. Go and price a 4" crank, they run around $895.


You don't know what you are talking about here. Not at all. You think that because a crankshaft has a slightly larger stroke that the block has to be clearanced slightly more. The interference comes from the rods and bolts that you choose. Everyone loves to run a big ol' H-beam for some reason. My block is not clearanced any more than a typical 383 is. It has a very specific I-beam rod and tiny cap ARP rod bolts. There is plenty of room, probably more than most 383's that run H-beams. The shop that built my shortblock has plenty of experience stuffing 4" cranks into sbc's. They know what works and what doesn't.

I'm here to learn and share just like you. Posting up the geometry of an sbc 400 engine that was designed in the mid 60's as proof of bad internals has no merit in 2014. That's almost 50 years ago.

nitrous2fast

iTrader: (2)

When I first posted I was trolling a little bit. Lol I've known for a long time What is necessary for the block to be sleeved with 4.125 bores. This section was being a little dead so I figured I'd throw out a bone and see who the idiots are and the ones who know Wtf they are talking about. There aren't many machine shops who like to deal with small money stuff so I was gauging the interest and thought about getting a few good blocks and having this done to sell. Seems like there isn't much interest and a few morons talking about poor r/s ratios thinking they know **** about building big inch sbc's. Lol there are compromises to everything in the modification world. The key is to know when to push further and when to stop. There is a lot of old school thinking that just isn't correct. Hell its funny my machinist has been doing this since they put shims in rod bearings. Even he will tell you some of that knowledge is a bunch of crap from the old days.

Puck

iTrader: (17)

Plenty of people - You, me, Mike, Taner, Shepard, Ellis, and...ummm......dammit .

Seriously guys, if you want a big cube motor build an SBC or LSx. LT1s are at a handicap, and the people that spend big money on them do them for nostalgia or just because they like the engine - not because it is practical. I could have made a NASTY pump gas BBC what I have into my turd, and I'm not even using it - its been sitting on an engine stand in my porch just waiting for a computer for ages but I haven't had enough drive to finish it yet.

IF you like it, stick to it, but don't hunt for huge numbers or exotic builds and then try to be thrifty or practical.

Shownomercy

iTrader: (1)

Turbos, the replacement for displacement.

Pushing the block displacement wise to the limit seems silly when you can just add more boost.

stevo9389

so you were just pulling a "Dart" on us?

Puck

iTrader: (17)

Ouch, too soon . I had a nice fat tax return waiting for that!

.

nitrous2fast

iTrader: (2)

Dart is a business just like any other business and makes decisions based on a certain set of rules. Yes I Could get a couple done for a few people if they were truly interested.

Chopstix

iTrader: (1)

there were quite a few of us with the $$$ ready to place orders with Dart

OutlawZ

iTrader: (4)

Just buy my motor throttle body to Oil pan for 6,000 complete......

one of the fastest in the world on spray....... the best of everything.... cost me bout 15k...

Puck

iTrader: (17)

Wow thats ridiculously cheap. I would at least sell the top end separate from the shortblock, you'll make more.

What would you be going to?

moehorsepower

iTrader: (3)

Is that all, Heck for what I have into my LT I could of had a 632 inch BBC and a 427 as a back up while towing an LS car! Lol...

OutlawZ

iTrader: (4)

probably a wakeboard boat..... i'm taking a step back from all things automotive...too much money invested..... too much time.... i'm getting divorced so that doesn't help....

You are right. I might separate the top and bottom end cause nowadays ppl still trip about spending 6k on a 15k motor.....

single plane, heads, and throttle body WITH the shaft rockers i'd probably ask 4k...

short block...ummmmmm 3000-3500