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377 sbc build questions

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377 sbc build questions

Postby jeepracer » Fri Dec 16, 2011 6:44 pm

Im looking for information on 377 sbc's. ive searched the web all over and cant find any info on these motors. eventually i want to build this and i was wondering what kind of horsepower they are capable of with world sportsman 2 heads. they seem to be a good race head but i cant find any info on a 377 with them
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Re: 377 sbc build questions

Postby 6sally6 » Fri Dec 16, 2011 6:59 pm

You talk'in bout a 400 with a 3.48 crank?...OR a 350 with a 400 crank?
I would think....using the 400 block and de-stroking to 377 would make a heckuva high RPM engine.(Like a lightswitch...all on..all off!) Get the advantage of high reving short stroke with the big bore of the 400. Upper 7's to 8000 range. Sure sounds sweeet to me! Make sure its well balanced and maybe part-fill the block to stiffen it up.
Pardon me.....I'm just jabbering
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Re: 377 sbc build questions

Postby jeepracer » Fri Dec 16, 2011 7:07 pm

i am looking to do the 400 with the 3.48 crank. how much can the 400 blocks handle hp wise and rpm?
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Re: 377 sbc build questions

Postby DaveMcLain » Fri Dec 16, 2011 7:11 pm

Why not just run a 3.75 stroke crank and build a 400? Is there a reason to run a smaller engine?
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Re: 377 sbc build questions

Postby bigjoe1 » Fri Dec 16, 2011 7:11 pm

The 377 is one of the bore and stoke things that just dont make any sence.. If you use the 3.75 crank the engine will make 45 pounds more torque automatically, plus , with the correct cam, it can make 25 to 40 more horsepower. The only time the 377 thing looks good is if you are building an engine to fit a cubic inch class Why give away all that extra power that comes with a real 406.


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Re: 377 sbc build questions

Postby jeepracer » Fri Dec 16, 2011 7:36 pm

there are cubic inch rules limiting me to 377
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Re: 377 sbc build questions

Postby DaveMcLain » Fri Dec 16, 2011 7:56 pm

Compression height is the same as with a 350 so if you use a 400 piston, 5.7 rod and a 3.480 stroke crank you'll have something that will work. The 4.125 bore piston will probably weight a little more than a similar piston made for a 4 inch bore but not by a whole lot so balancing shouldn't be difficult. Compression ratios will of course be lower than what's advertised for the 400 piston of choice so keep that in mind when selecting parts.

The 400 block has a larger main bearing bore and there are two ways to go in this area. You either have to run a specially made spacer and a bearing made for a large journal crank or use special thick bearings which are made for this application. 400 blocks have 6 steam holes but I've always only drilled the bottom 3 of those when using heads without them to begin with. The 400 block also requires the use of a different oil pump drive shaft that's necked down for clearance where it goes up through the block. Those are the only real differences that I can think of really. Some 400 blocks don't have all the holes drilled for the clutch and especially the 4 low ones on the front of the block that have been used for motor mounts and other things over the years with the small block engine.
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Re: 377 sbc build questions

Postby emmarinc » Fri Dec 16, 2011 8:46 pm

I've been running a 377 for 15 years in a drag/street car. 1973 2 bolt block,3.48 GM steel crank, main bearing spacers{not pinned} 5.7 stock rods ,KB flat top pistons , Brodix Track 1 heads,Lunati 50121solid roller cam,Victor Jr.,750 holley.560HP@6800,495 lb. ft.@4500. I was told it would be a peaky /high revving engine, this isn't true.However if i didn't have the parts laying around to build a 377 i would 've probably went 406.
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Re: 377 sbc build questions

Postby Keith Morganstein » Fri Dec 16, 2011 8:56 pm

jeepracer wrote:Im looking for information on 377 sbc's. ive searched the web all over and cant find any info on these motors. eventually i want to build this and i was wondering what kind of horsepower they are capable of with world sportsman 2 heads. they seem to be a good race head but i cant find any info on a 377 with them


What info are you looking for? there's no mystery, it's just another SBC. You will need to use bearing spacers or special bearings to fit the crank. It's a good combo if you're limited to 377 inches or so.

The Sportsman II is a very old head. They can make some power in the right hands, but an Dart iron eagle platinum, RHS iron, EQ Iron, or a GMPP Bowtie Vortec are way ahead. Any of those are the better choice for iron head classes.

Old used 400 blocks are fragile. Anything over 600HP drag race or 500 HP endurance is really asking for trouble.
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Re: 377 sbc build questions

Postby jeepracer » Fri Dec 16, 2011 10:13 pm

how much can the main spacers take? are they good or bad? is it worth the money to just get a new crank? i know you have to pay for the good stuff but if the oem crank can handle it, then i wont worry.

sorry i ment more like, has anyone built these as high performance race engines that wouldnt mind sharing, when i said info. i know the basics of what it is but its the more high performance stuff that is hard to research.
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Re: 377 sbc build questions

Postby bigjoe1 » Fri Dec 16, 2011 11:46 pm

Many years ago I built a 377 combo for my kids Nova== It made 700-710 HP, and with a two carb , tunnel ram set up, ran 9.70 at 139 MPH back in the 1990 years. It lasted about four years, then one day, he stuck all the rods out of the pan- I ran alu rods, and we reved it up to 8800 RPM every run. I used splayed caps, with the main bearing spacers on a stock 350 GM block-Also a stock GM 350 steel crankshaft


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Re: 377 sbc build questions

Postby kirkwoodken » Sat Dec 17, 2011 12:22 am

Why would a 3.480 stroke in a 400 block rev faster than the same stroke in a 350 block? Why would a 350 with a 1/8" overbore rev any differently than a standard bore? Yes, the shorter stroke MAY be easier on the block, but I see it as a waste of a 400 block. Why throw away 40 Ft Lbs torque for more money? Anything you can do with a 377, you can do better with a 406. Revability depends on valve timing and valve springs; not much else.
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Re: 377 sbc build questions

Postby clueless » Sat Dec 17, 2011 5:47 am

Years ago I threw together a 377 for street/drag duty. It was a result of my 355 having excessive piston to bore clearance. I was up for a set of pistons and a bore/hone anyway so threw the factory steel crank and SIR rods into an old 400 block I was given with some KB's that weighed the same as the old TRW's I ran in the small bore block. I used the bearing spacers unpinned, home ported Sportsman II heads and a 249/254 @ 050 FT cam. It made an honest 500HP and pushed my 3300 lb junk to a best of 11.0 @ 121 for years before I starved it for oil in a burnout comp and kicked the rods out. At dissection time the unpinned spacer bearings were still in position and unscathed.

I have now built a 400 for it but at the time the 377 served me well.

Hope this helps.
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Re: 377 sbc build questions

Postby FastBuick » Sat Dec 17, 2011 6:23 am

I ran a 377 (4.155 bore x 3.480 stroke) for a couple years in a drag car. I loved it. It made great power and would rev easily and efficiently. I have never run it with sportsman 2 heads however. I ran a best of 9.49 @ 140 mph in a 3150# car. It still had more in it with a bigger intake and heads. I turned mine 8800-9000 RPM every pass and was very reliable.
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Re: 377 sbc build questions

Postby ZIGGY » Sat Dec 17, 2011 8:40 am

In a circle track application, many drivers think a 377 "feels good" for a slick track. May be just imagination or ???
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