Best way to build a 350 hp 348

[jim_ss409]

I had someone ask me about building a 350 hp 348.
The starting point is a 1960 250 hp 348.

I don't know much about those engines but I'm guessing 350 hp should be a reasonable target.
I could see a lot of guys aiming for that horsepower level, so I think a tread like this could be very helpful to several people thinking of building an engine in that power range.

So, I'm completely open to any suggestions about compression, cams, head modifications etc.
I'm hoping some members will have some ideas on what's needed to hit that target.

 

[yellow wagon]

Worked over 333 heads

 

[Don Jacks]

Worked 1147,817,or 333 heads,10.5 compression,a small hyd.roller cam[225@.050,.510 lift],an Edelbrock single 4 barrel intake,650 carb.and small tube headers will get you there.The smallest Howards hyd.roller lifter cam they list would be very good for this package.On the 333's,I'd suggest 2.065-1.725 valves,pocket port and gasket match,stock valve size,pocket port and gasket match on 1147's or 817's.This power limit could be reached with a max.rpm limit of between 5500 and 6,000 rpm,and would be perfectly happy in front of an automatic with a 2,200-2,500 converter,and tall gears.

 

[1961BelAir427]

Never done it, but as that's a rough target of 1 HP/CI it shouldn't be too hard.

HP 348 heads, 340 horse 409 heads, or worked 333's, 10.5:1 compression, Hydraulic camshaft with somewhere around 224 degrees at .050" lift, headers or 2.5" exhaust manifolds.

I think that should do it just fine.

Edit: I got busy at work and didn't post quick enough.......Don Jacks said it better anyway.

 

[hanke]

Can/does it make cents to rework 379 heads (1.94 1.66)? What about the Edelbrock heads?

 

[Don Jacks]

You can't port the 379's to the size of the stock 333,1147, or 817 .That having been said,some fairly heavy porting work and 2.065 -1.72 valves can be done,and will help a bunch,just not as much.The cheapest head package would be 333's with bigger valves. I would think that the Eddie head would be too big,and too expensive for an engine of this level.

 

[buildit]

I did put together a 3x2, .030 0ver, 9.5-1 comp 348 that dyno tested at 360 hp with stock #379 heads. It had a mild cam upgrade (regrind from Delta Cams) and 1 3/4" dyno headers. Any of the other above mentioned heads are already better than ported 379's, and I wouldn't put any time or money into them.

 

[Rickys61]

Best money spent on a 348 is add a 409 crank...

 

[wally72974]

I've got one if you need one Jim. (it's a truck 09 crank) like to get a $100 for it.

 

[jim_ss409]

OK, so the #379 or #738 heads will be a problem unless someone was willing to do a fair bit of porting, and install bigger valves.
I'm guessing they'd be better suited to a 300 hp build in most cases.

As we know, the #333 truck heads are available for very low prices. I think the #333 heads come with small 1.94" valves but it's not hard to upgrade them to the 2.065 / 1.72 valves Jack mentioned.
The Edelbrock single quad intake with a 650 cfm carb like Jack mentioned should also work well. I think maybe the Edelbrock heads could work but they're really a bit too big even with a smallish cam. If a guy was going to use a crank from a 409 or even better, a 4" Eagle or Scat crank, then the Edelbrock heads start to look like a reasonable way to go.

All things considered, the #333 truck heads look like the best fit and best value for a 350 hp build.

Headers are always nice but often where you find a set of truck heads you might also find a set of truck exhaust manifolds with 2 1/2" outlets. They would give up a little power compared to the headers, but they would be OK. Shorty, block hugger headers are also a good fit for a 350 hp engine.

What do you guys think about pistons and rods?
Will stock rods and cast pistons hold up or should a guy go with forged pistons and better rods?

I notice that cast pistons cost $359 and the Icon brand forged pistons cost $579
I'm guessing the extra $220 might be money well spent if a guy wanted to rev this engine with confidence, but I'm also interested in what others think.
I'm also thinking that BBC rods would be a nice upgrade too.

I appreciate all the input we're getting here.

 

[1961BelAir427]

I personally wouldn't use cast pistons in a 348 or 409 just because of the build and core cost of these engines. The extra couple hundred would just be for peace of mind, but the cast should be fine at the 350 hp level.
I'm with you on the bbc rods being a nice upgrade that shouldn't cost much or any more than rebuilding the stock rods. Or spend just a little more on the Scat I-beams that a lot of us run. Those are under $300 a set and both sets of mine were perfect out of the box. When you add up the cost of resizing, ARP bolts, and bushing the small ends if using forged pistons.....sounds like a good idea to me.

Since the lowest rated 348 was 250 horse, cast 4 barrel intake, tiny cam, and low compression.......I would imagine that any rebuilt 348 with a slightly larger than stock camshaft, 10.5:1 compression, and 3x2 or Edelbrock intake would make over 300 HP with even the lowest power stock heads.

 

[Last 60]

Best money spent on a 348 is add a 409 crank...

Yeh, but they break rear ends!!!

Lonnie

 

[Fathead Racing]

Years ago I built a 9.5 cast piston 348. Engine had a flat tappet hydraulic cam with three two's. Ran 14.60 all day long shifting at 5500 rpm. Had the 379 heads with bigger valves and a little grinding on my bench. Must have been at least the advertised 305 hp. That GM said.

 

[Tom Kochtanek]

Funny that you bring this particular combination up. I recently acquired a 1960 250 horse short block that originally had the 379 heads. The crank, rods and pistons are in good condition.

I was thinking of slapping a set of highly modified 333s on top and bolting on a single 4 barrel intake and carb and just making a runner out of it.

Another approach would be to slip a 409 crank in, use different rods and spring for new pistons to make a sort of "cheap stroker" out of a 348 .

I look forward to reading what others might think!

TomK

 

[Don Jacks]

The only I con piston you could use would be the one for the 4 inch stroke,6.135 rod[or the 3.5 stroke,6.385 rod].KB did make a stock stroke/rod 11-1 Icon pistons 2-3 years ago,but the last I heard was that Show Cars[who had the best price by far] would have to order 10 or more sets of pistons for the factory to set up a run.This a shame in that piston would be a reasonably priced,far better stronger part,at an affordable price.I guess the market's not there to stock these items,as they are a slow mover.These pistons ,in an engine with reworked 333's would put your compression in the 10.5 range,perfect for street performance,for long term durability,as well as power,go with a hyd.roller cam,and you'll see closer to 400hp,with the 409 crank,insane low-mid range torque for moving that big,heavy car around.Keep the revs down to 5,500-6,000 rpm,and it'll never wear out.Tom,there's no replacement for displacement-go stroker.With your STASH of parts,the only question would be which 409 crank to use!With the KB piston and 6.385 rod,you can build an affordable,stout little engine.

 

[hanke]

I am leaning towards the 333 heads 2.065-1.725 valves port and gasket match,

hyd roller cam [225@.050,510 lift], need to look into the Howards hyd. Roller cam

10.5 forged pistons, big block rods or Scat I-beams (want to make sure it stays together)

Edelbrock 4 barrel intake 650 carb. "My concern with the 3x2's is tuning."


Measured the cylinder bores with bore gauge resting on piston rotating crank. Looks like the bore was standard @ 4.125”. one cyl. was +.008 one +.007 the rest were +.005-+.006 measured at top; the rest of the cyl. Bore was +.0015-.002. What type of machine work should I have done? Bore 0.010” standard size pistons and size rings to fit? I hate to open the cylinders any more then necessary.

The motor is going in to a 31 roadster I’m building (my 2nd build) my heart wants to put a newer manual trans in it, my common sense side says I should put and automatic in her. What are your thoughts?

Thanks for everyone’s input I was getting a little overwhelmed with how to build this motor.

 

[Don Jacks]

Are you staying stock stroke,or building a 409 crank based stroker??

 

[hanke]

Stock

 

[Don Jacks]

Okay,you're gonna need the Ross forged piston.They make both a 10-1,and an 11-1 [same price] piston,with your 333's.the compression will come in around 10.5.I cannot recommend a cast piston,failure here can cost you an expensive engine,just to save a few bucks.Penny wise and pound foolish.As to the bore,the smallest oversize is .020,and with that much wear,it's gonna have a lot of taper in the cylinders.so a 20 overbore is needed.As to the piston rings,Show Cars has them availeable with the standard width ring,or the thinner ,more modern ring,same money.I prefer the thinner ring for less friction,but others will differ.As to machine work,check main bearing bores,align hone if necessary,or if your replacing the stock main bolts with aftermarket[arp] main studs.Make certian that the deck surface is parallel to the crank centerline on both sides.Your machinest may want the piston that you're going to use[go big block sized 6.135 rods],and crank to do a mock up in order to do the decking in one step.

 

[buildit]

The stock 348 rod is really skinny, and risky to use if you're going to run the engine hard. But if you use BBC or aftermarket rods, the 348 crank counterweights will likely be too light and require Mallory metal to balance (read expensive). It might be cost effective to plan the build using a truck 409 crank (that has heavier counterweights to achieve balance), Scat I-beam 6.135's, and forged pistons to suit. Just need to weigh truck 409 piston, pin, rings, and rod to compare w/aftermarket parts to see if it is feasible.