jayhawk261

Just a quick question. Is a 427 not as heavy as a 454? I'm not real familiar with the 427 vs a std 396/402/454 block. Is the block that much different that it weighs close to what a small block does?

endeavour32

iTrader: (4)

Same block, same weight. But by the time you replace everything but the block with Aluminum its very close to the same weight as an iron 350. There would have been no difference with a 468 or 496 other than I wanted a shorter stroke. I really don't care about the "no replacement for displacement" deal, I prefer to make more with less when possible.

My opinion is that you run boats much harder than a car. An engine with a shorter stroke has less stress on its internals. I did loose about 50 hp and 50 lbs torque by going this route vs a 496 but I can live with that. Next to the 427, I really like the 502 with its big 4.5" bore and somewhat short 4" stroke. Why GM ever killed that engine for the current gen 8.1 liter is beyond me!

mcollinstn

I say for power to weight ratio, a 540" standard deck BBC is the best bet... unless you go with an internally balanced crank. Then it weighs a million pounds but is smooth as glass..

As far as short stroke "theory" goes, the 502 is a good motor. Bore is big enough to unshroud the valves, and the stroke is short enough to allow it to rev well.

Bottom line is that no BigBlock is going to rev like a smallblock. Bearing journal diameters are too large. You can have a custom forged crank done with SBC bearing diameters, and run spacers in the main caps and get a revvy bigblock, but that's only for kicks and giggles. Boat motors like to be beefy, and we don't really rev them high anyhow. 5,000-5,400 bigblock rpm is your effective ceiling on a normal boater's budget.

The 8.2/502 has a better bore/stroke ratio and rod length to stroke ratio than the 496/8.1, but the 502 was being phased out by GM as far as longblock availability. The 8.1 was much more readily available in mass produced "dress" so there's your answer as to why the 502 black motor was killed.

But the 8.1 is a good motor. Better designed cooling system, and better oil control past the pistons (due to smaller stroke and hypereutectic pressure cast pistons) than a metric ringed forged piston 502.

Nothing wrong with a 427, but if I am starting from zero, I'm going siamese bore and as long of an arm as I can afford. A 540" shorty.

MC

Uncle Dave

Help me understand why anyone would build a 427 BBC in this day and age with so much more displacement available for little to no increase in cost if starting from scratch.

Making "more with less" usually means more money spent on better parts- which is ok.

does RM builder have a dyno sheet we can look at ?

Making an engine scream is no problem.
Making one that screams, idles, and makes a gob of power at 3K is a much harder proposition.

UD

endeavour32

iTrader: (4)

By Aluminum I mean, AFR heads, Aluminum Intake, Stainless Marine Exhaust, crossover instead of cast iron water pump. It all adds up to a lot of weight loss. No aluminum rods, that would be a dumb move, I'm running h beam rods.

UD-
I'm building a 439 because I already had the 427 rotating assembly. I'm at best giving up 20 hp over a 4" crank. So I might be loosing 1 maybe 1 1/2 mph on the top end. I could be all wrong on this I will soon see. There are a lot of forum doubters on this project, but my goal is 70 mph, not 80 or 90 and I think I can hit that goal with this combo.

As for dyno sheet look at the GM ZZ 427 480. That little engine kicks out 480 hp & 490 ft lbs torque out of a factory GM crate engine, with a very flat torque curve from 3300 to 6000. Now take that engine add a marine kenitics cam, afr ovals and a pro systems carb and I think I'll have a very solid engine.

Uncle Dave

If you already have the rotating assembly then it makes complete sense as long as the crank isn't swiss cheesed from being rebalanced over and over. High bob weight hurts acceleration as well.

If starting from scratch I'd do something different, but if you have these parts Id definitely use them.

That zz427 makes almost EXACTLY what my 406 makes for a little less money. (see dyno chart)

You'll kill some HP when you put a wet exhaust on it, but it should flat out rock.

http://www.shopfbparts.com/servlet/Detail?no=434

If you end up with something really close that zz427 youll get to 70.

Uncle Dave

endeavour32

iTrader: (4)

That 406 is an impressive little engine.

As for my crank it was new old stock that was balanced to a set of speed pro pistons and thumb rods which I dumped for h beams and srp pistons. So the crank has only been balanced twice. I'm running the exhaust dry to the tip so I shouldn't loose too much there. Hopefully in a week this thing is on the water. I'm getting sick of talking about it and not using it.

Uncle Dave

Get-r-done and get it wet! Then give me a ride!

Good luck

Uncle Dave

Uncle Dave

Got it ready to roll now.

Hows your project coming?

significant mods make this a potent small block.

I like the new speedway valve covers.
I need to detail out the engine bay this winter, and Id like to go with a single belt kit - but once again hard to find for a small block.




UD

endeavour32

iTrader: (4)

Thats a nice looking engine...... My project is getting closer. Bob has the cam on its way to Dave and Patrick at Pro Systems is working on the carb. I'm hoping I can pick the engine up monday or tuesday. My fingers are crossed. Bob called me friday and said one of his customers with a 502 with the same afr heads I'm using, a milder cam and 1 point lower compression and a std 4 barrel carb made 650 hp. So even if my engine only builds the same hp per c.i. that puts me right around 570 hp. These new afr oval port heads are something else.....