3.58 stroke x 340 main (rods/pistons?)

[go-fish]

Saw this. SCAT Engine Components 9-340-3580-6123 Scat Cast Crankshafts | Summit Racing
Thinking about a rebuild to up compression in a '73 340. Hmm.

Objective: Hot Street driver/cruiser Iron stroker that leans toward an all shelf parts list (ie. ductile iron rockers like 273's, 6.123 rod, shelf piston). Daily driver! Old school vibes, ala vintage anodized blue Direct Connection valve covers, vintage DC air cleaner, LD340. Think F.A.S.T. for a Day 2 build. No high lift, tall valve cover, tunnel ram, .... This hypothetical build would be sneaky fast car played off as "just" a relatively, unassuming, stock appearing 340 4-speed. Also, this hypothetical "fun" having wouldn't be from racing other cars. The fun for this car would be personal enjoyment driving. This is for corner ripping, down shifting, fast acceleration, and twisty roads.

Scope of conversation: Identify parts compatibility using stock or, at least, OE spec parts using a 3.58 stroke in a 340. Discuss characteristics, benefits, disadvantages of the stokers that allow for shelf pistons and rods. Not trying to get into building particular combo but the parameters of this hypothetical build is an iron head that is ported to achieve the air flow that the extra stroke wants. Intake would be worked as well. Regardless of cam, other than to say this is a hypothetical street car built for everyday driving.

Off Limits:
"Just get a 360". Re: 340 in hand. Numbers to the car.
4" + stroke. Re: Not against them just gaming out the 3.58 340 crank that is currently offered by several vendors. Another reason MAY be because if you go 4" then that pushes the whole program to outgrow the restrictions/limit of an iron head.

Some of my starter questions:
When using a 3.58 stroke crank in a 340 do you use a oversize 360 piston and a 6.123 rod? I'm thinking this is a stupid question. Or, at least a simple answer. Compression height would be what a stock 360 compression height is? Would the air flow needs this stroker be the same as an over-bored 360?

Alternatively, I see 3.51" strokes on 340 mains too. I have read that you can use a 6.123 rod and a factory low compression piston to achieve +.100 above deck and can machine to suit. Wouldn't a stock piston be a really heavy choice? The hypothetical engine is a 73 340 and could theoretically just change the crank?

This is what my machinist buddy did on a set of X-heads. Could have kept going but for that particular engine that's what funding, time, and needs allowed for. I'd look for similar or better on a set of J's, Z's, or O's too.

Lift----------Intake-----------Exhaust

.100 _______80________ 63.81
.200 ______134.4_______115.15
.300 ______187.7 ______161.42
.400 _______224 _______179.3
.500 ______236.8 _______190.7
.600 ______256.7 _______193.7


@AJ/FormS This pair with the Commando A833 discussion. You were calling for the engine to be rebuilt. This is a thought into how I should approach that build.

3.58 340 crank = $364 ;Cheaper than an internal balance 3.31 replacement crank
Eagle SIR 6.123 rod = $385
Pistons: Open chamber and 92 octane. Streetable compression.

 

[crackedback]

You are building a .040 over 360 if using the 3.58 crank as a starting point in a 340 block.

 

[go-fish]

You are building a .040 over 360 if using the 3.58 crank as a starting point in a 340 block.

That's what I'm thinking but I'm trying to see the virtues. For one, the 340 is in hand and for $364 and a set of 360 pistons you could pick up 27 cubes. So, air flow requirements aren't any different than a LA 360.

 

[crackedback]

Probably 368 ci to start , make .060 over 360 370-2ish

For all the considerations, it's a overbored 360 from an air flow requirement standpoint.

That crank and KB107's for the lower buck build

 

[NC Engine Builder]

If you use the cheaper cast crank, the cost to internally ballance the rotating assembly with heavy metal, will end up costing as much as the better steel crank.

 

[go-fish]

If you use the cheaper cast crank, the cost to internally ballance the rotating assembly with heavy metal, will end up costing as much as the better steel crank.

The crank in the link is cast and it also says it's for internal balance. Does that mean it is for internal but still has to have mallory? I'm not an engine builder so forgive me.
This is all just possibilities and anything that came to reality would be if the cost was negligible, say just couple hundred bucks over a performance re-build. Previous owner had the 340 rebuilt using the low compression pistons. I was going to do a simple rebuild with the same combo but just higher compression pistons and have the heads worked to similar numbers as above.
I've always thought the same as many when the 3.58 340/318 crank comes up. Just build a 360. I saw the crank on Summit and thought for $364 and not much any cost above a basic rebuild you get more more cubes! Didn't know internal balance cast cranks still need to be balanced.

 

[NC Engine Builder]

Yes, it "can" be internal balance is what they mean. But it takes heavy metal to get there normally. That zeros out the cost benefit of the cheaper cast crank

 

[Professor Fate]

So, just basically a Hoover motor? Tom Hoover did it in the mid '70s, he basically used a 360 crank with cut down mains, and heavily re-machined '73 340 low compression cast pistons (crank clearancing the skirts, shave a bunch off the tops). Pop Rod did a writeup on it, as well as other sources- Google "Hoover 360" or "Hoover's Mover". Went like stink (Of course it did- this was Tom Hoover, man) at a time before strokers were common and there were no 360 pistons available.

 

[Locomotion]

A few tidbits that may or may not be worth considering:

When mixing parts, watch the crank counterweight clearance to the underside of the pistons.

If it's within the budget, Eagle SIR rods are forged from 5140 steel. Scat I-beams are stronger being forged from 4340 steel, but more expensive. However, the Summit brand I-beam may be relabeled Scat I-beam and only slightly more expensive.

Stock type pistons are on the heavy side and I personally wouldn't feel comfortable using SIR rods with them.

The lightest piston & rod you can afford would provide extra durability & performance benefits. Not sure if it would be more affordable to balance externally and probably remove weight from the crank or balance internally and add probably add Mallory metal. It depends how the crank counterweights are made/weighted. Internal balancing would be helpful especially when using a flywheel.

I ran a Scat 360 cast crank, SIR rods and light SRP piston combo. (Not sure if there is a lighter "shelf" piston available.) Crank was neutral balanced or may have needed very little Mallory Metal. Scat I-beam rods are slightly heavier than SIR.

Using more common & less expensive 915, 587, 596 heads and enlarging original 1.88" seats to accept 2.02" intake valves with "fresh, high" seats will likely provide a performance gain over trying to optimize original 2.02 seats in X-heads that may have had multiple valve jobs over the decades and may be "sunk".

I ran a bracket combo many years ago using a stock 360 crank, bushed OEM 340/360 rods and Direct Connection pistons for a 3.454" stroke crank. (Used for 355 Nascar engines.) Piston tops had to be milled to get around "0" deck without the need for extra decking of the block, which reduces the need to mill the heads and/or intake to get the intake bolts to line up. The underside of the pistons also had to be milled underneath the wrist pin bosses & skirts for counterweight clearance. I don't know the final weights & measurements but it made the pistons a good bit lighter. (I recently saw some of those pistons for sale somewhere.) At "0" deck, compression may end up too high for the street and I don't know what the piston top thickness limits are.

The Direct Connection 3.454" crank pistons & SRP pistons have generous valve pockets.

 

[go-fish]

So, just basically a Hoover motor? Tom Hoover did it in the mid '70s, he basically used a 360 crank with cut down mains, and heavily re-machined '73 340 low compression cast pistons (crank clearancing the skirts, shave a bunch off the tops). Pop Rod did a writeup on it, as well as other sources- Google "Hoover 360" or "Hoover's Mover". Went like stink (Of course it did- this was Tom Hoover, man) at a time before strokers were common and there were no 360 pistons available.

This is what I'm after! I read about that too long ago. I thought it was a 3.51 crank they used '73 340 pistons on. Even though I have eight of those pistons in the engine I don't think I'd do this but what I'm after is possibly doing it with aftermarket shelf parts. Maybe. Just gaming it out.

 

[go-fish]

I ran a Scat 360 cast crank, SIR rods and light SRP piston combo. (Not sure if there is a lighter "shelf" piston available.) Crank was neutral balanced or may have needed very little Mallory Metal. Scat I-beam rods are slightly heavier than SIR.

Yes, definitely. Comparing both Scat and SIR I would be happy with either with this so I would go for the cheaper Eagle if piecing it together.

Here's a kit from Hughes that that is priced as balanced minus cost of heavy metal.

And Scat kits: Balanced and Non-balanced

I was going to buy pistons and rods for my rebuild anyway so to go this much further would be a few hundred dollars. But how much is Mallory? Is this a point where I say I might as well get the forged 3.58 crank to save cost? Forged rotating assembly, balanced, discounted $113 to $2131. SCAT Engine Components 1-48005BI Scat Engine Rotating Assemblies | Summit Racing

 

[NC Engine Builder]

This is what I'm after! I read about that too long ago. I thought it was a 3.51 crank they used '73 340 pistons on. Even though I have eight of those pistons in the engine I don't think I'd do this but what I'm after is possibly doing it with aftermarket shelf parts. Maybe. Just gaming it out.

Just buy a set of higher compression pistons for your current combo. Otherwise, your heading down a rabbit hole of custom machining, balancing, for a minimal return.

 

[go-fish]

Just buy a set of higher compression pistons for your current combo. Otherwise, your heading down a rabbit hole of custom machining, balancing, for a minimal return.

LOL, yep. My last post with the screenshots I'm starting to justify spending more and more! You're so right.

 

[AJ/FormS]

Have you measured the current cylinder pressure? or
Do you know the exact Scr?
And do you know the camspecs? and
what specifically is the complaint with the current combo?
----------------------------------------

Having been running my 367 on the street since 1999, in my 68 Barracuda at 3650 pounds with me in it, I can tell you that, IMO, it makes way more power than the chassis can ever use. Don't get me wrong, it's a lotta fun, but if I was to do it again, I probably wouldn't go with a 360.
Except for two reasons;
1) Lightweight Kb 107s fell in at .012 below deck. So with a quick clean up, and closed-chamber heads, I had a tight quench engine for cheap.
That's NOT gonna happen with a 318.
And with a 340, you'll likely have to mill the crowns off the hi-compression pistons to use a closed chamber head. which ain't happening for free. and
2) the 360 makes a good bunch of low-rpm torque, which if you exploit that inherent capability, you can drive your hiway fuel-economy into the realm of fantasy. And for a DD that is a really big deal.
That's not gonna happen with a similarly powered 340, much less a 318.
So, if that kind of thing interests you, sell the lo-po 340 and grab a good core 360. If you reel in your dreams of big power numbers, you can build yourself a well matched, hi-torque, infinitely better, street engine, to pull 65= 2200rpm, a 12 second car, that still roasts the tires, and if yur fastideous, she might get you mid to high 20s mpgs on the hiway.
That's what a 360 can do for you.
and you don't need a stroker to do it.

 

[RustyRatRod]

If you're gonna buy a crank, get a 4" arm.

 

[273]

I'd just keep the stock stroke especially if your using ported stock heads but you really want to go stroker might as well go with a 4", Makes the most $$$ sense.

 

[4eighteener]

I built a stroker 340 with a 4" scat cast crank.
I used the light kb416 .040.
hypereutectic pistons and the summit (scat) rods.
I paid $400 for balancing and $350 for the heavy metal.
If I was to do it again, or advise, I would have bought a balanced kit with the forged crankshaft

 

[Newbomb Turk]

I built a stroker 340 with a 4" scat cast crank.
I used the light kb416 .040.
hypereutectic pistons and the summit (scat) rods.
I paid $400 for balancing and $350 for the heavy metal.
If I was to do it again, or advise, I would have bought a balanced kit with the forged crankshaft

I never tell anyone who isn’t living in a cardboard box to buy steel cranks.

Of course all the cheap bastards jump in a day that guys are burning fuel on cast cranks.

I had a guy try and tell me Pro Stockers using cast cranks and everyone in the top half of the field was doing it.

So I spent some time to verify the claim and he was as full of **** as a Christmas goose.

Cast cranks for over a 3.58 stroke stock build is just silly.

But the cheap bastards in full gang force rally to the scotch guy asking the question and convince him that cast is the best deal for him.

Back in 2000 I did a stroker for a guy. I don’t know about forums back then. At virtually every point I was getting kickback from the guy. It started with me getting a steel crank for it.

The forum gurus fought the HR roller used, the compression ratio, how much power it would make. Oh yeah, the internet hates the headers, intake and ignition.

The upshot is I knew it would make 500 hp falling off a log. The gurus said no it won’t.

We get to the dyno and it did 540 something power and I’m so tired right now I can’t remember the TQ. The owner took video on the dyno.

And it did that at 5k rpm.

I sent the dyno sheets to the cam grinder because they wanted to see the numbers. He called me back right after the fax showed up and BEGGED the owner to change cams.

He said if we moved the power curve up to 6k it would make another 20-30 hp. If we moved it to solid lifters it would be in the 570ish range. If we went to 7k it would go over 600 pretty easily.

The owner wouldn’t budge so it was what it was.

The upshot is there is no way on earth I was using a cast crank for 500 hp. Ever.

That’s insanity but some guys will step over a donut to grab a turd every time.

 

[AJ/FormS]

to continue post 14; You said;

Objective: Hot Street driver/cruiser

Thinking about a rebuild to up compression in a '73 340. Hmm.

Also, this hypothetical "fun" having wouldn't be from racing other cars. The fun for this car would be personal enjoyment driving. This is for corner ripping, down shifting, fast acceleration, and twisty roads.

Knowing what I now know;
and for your application, as detailed above;
Firstly; If you want to row gears, I'm sorry, but yur gonna need a much smaller engine and at least a 5 speed. So;
If I was gonna upgrade as you are thinking about doing, to go with a 4-speed, then, here would be my plan;
1) I'd get rid of that 114Lsa pressure busting cam.
2) I would install alloy heads pretty much just so I could run 190 or so psi cylinder pressure.
3) I would analyze at what roadspeed you are doing most of your driving, then gear the car to cover that window. Yur likely gonna find Second gear is gonna cover it.
4) From that information, I would cam it for torque at the bottom of the speed window, and spring it to keep the valve train together at the top of the window. and I would install whatever cam I need, on a 108 or tighter LSA.
5) and then I would build the Scr, up to whatever it takes to get close to at least 190psi.

What I mean is this,
my car has 3.55s, and in 1.92 Second gear;
3000 rpm in is 35mph, and 6000 is 70. So that is my window/that's where all my hot-dogging occurs.
so I stuck a lil cam in it ; 270/276/110 (223/230 @050), at 11.3 Scr.
This cam made gobs of torque at 3000 (in a 367 mind you), and peak power was around 5100, so the springs held it together (actually to 7200, or more) and so, I rarely need to up/down shift. And those 3.55s still got me 65@2870rpm.
Your manual shifter costs you time to shift. By gearing it right, using just one gear, you never lose that time.
Ok I get it, in competition, you want to keep the engine on the cam and if that takes a shift, or two, that is just how it goes; staying on the cam, trumps the time to shift.
But not for a country-road ripper. On gravel, you're gonna have your hands full just trying to keep it on the road.

As for the Factory 340 cam here's what the factory 114LSA cam looks like in at 110, to your engine; Followed by same cam on 108, in at 106.
268 intake-116 compression-103 power-276 exhaust-Ica of 64*-44* overlap
268 intake-120 compression-112 power-276 exhaust-Ica of 60*-56* overlap
Notice 120* of compression, versus 116. That by itself is worth about 8 or more psi
Notice 56* overlap versus 44*, that will put more hp on the table over the peak.
Notice 112* of power extraction, versus 104*. 340s with stock cams suck gas principally because of that short power extraction cycle. Those extra 8* are a game changer.
But, in your case, I wouldn't use either of those cams.
I would likely choose
Firstly; a SOLID-lifter cam, that has a faster rate-of-lift than what the hydro has,
Secondly; has more lift, and
Thirdly ............... something that works in your window of operation, and
Fourthly; never mind about the actual power numbers. Yur almost never gonna be at 5000, and never for any length of time, so then there is no good reason to sacrifice the bottom of the torque curve for a few power numbers on top that are nothing mostly just bragging rights.
I mean, IMO, lol.
To that end, here's a cam possibility, measured at zero lash, which could have the very same 050 numbers as the factory cam;
262 intake-124 compression-118 power-270 exhaust-Ica of 56*-54*overlap.
Notice 4* more compression, and 6* more power with a loss of only 2* overlap.
Again, more pressure, and more mpgs, with what could be the same 050 numbers.
In an 8/1 engine, the Wallace predicts a 10psi pressure rise. over the stocker. Not much, and not enough to be able to keep those 8/1 pistons, but it's a start.

For chits and giggles here's the hi-torque hydro cam I once ran. In at 106*
270 intake-119 compression-108 power-276 exhaust-Ica of 61*- 53* overlap
This made over 190 psi @11.3Scr, at my elevation of 930 feet. and it pulled fantastic mpgs in double-overdrive geared for 65=1650rpm.
This cam was 223/230@050. Engine was happy with 87E10 full time. It was a crazy-much fun combo. That cam would happily pull every starter gear I tried.
And it would easily roast 245s thru two gears and more. Even 275s burned a good part of Second gear.

Do you need 190 psi?
No that's just overkill, When that 270cam dropped lobes, I installed the next bigger cam, and dropped the compression down to 11/1 and the new pressure is just around 180psi, which is still plenty of fun.............. but as you know, I got a 3.58 stroke, which I'm not supposed to mention, lol.
At 180 psi, she is easier to drive real slow. I just retard the timing to 5* and idle along at a tic under 4mph. She runs much smoother. That 270 cam would idle at 3.5mph.

 

[4eighteener]

I never tell anyone who isn’t living in a cardboard box to buy steel cranks.

Of course all the cheap bastards jump in a day that guys are burning fuel on cast cranks.

I had a guy try and tell me Pro Stockers using cast cranks and everyone in the top half of the field was doing it.

So I spent some time to verify the claim and he was as full of **** as a Christmas goose.

Cast cranks for over a 3.58 stroke stock build is just silly.

But the cheap bastards in full gang force rally to the scotch guy asking the question and convince him that cast is the best deal for him.

Back in 2000 I did a stroker for a guy. I don’t know about forums back then. At virtually every point I was getting kickback from the guy. It started with me getting a steel crank for it.

The forum gurus fought the HR roller used, the compression ratio, how much power it would make. Oh yeah, the internet hates the headers, intake and ignition.

The upshot is I knew it would make 500 hp falling off a log. The gurus said no it won’t.

We get to the dyno and it did 540 something power and I’m so tired right now I can’t remember the TQ. The owner took video on the dyno.

And it did that at 5k rpm.

I sent the dyno sheets to the cam grinder because they wanted to see the numbers. He called me back right after the fax showed up and BEGGED the owner to change cams.

He said if we moved the power curve up to 6k it would make another 20-30 hp. If we moved it to solid lifters it would be in the 570ish range. If we went to 7k it would go over 600 pretty easily.

The owner wouldn’t budge so it was what it was.

The upshot is there is no way on earth I was using a cast crank for 500 hp. Ever.

That’s insanity but some guys will step over a donut to grab a turd every time.

Yeah, I originally bought the cast crank for a 318 stroker that was to go into a truck.It was for a truck that would probably never see the high side of 4500, and i just wanted more grunt to pull a camper, and i wanted to fo it on the cheap. The crank I got on sale. I thought building a stroker with the smaller 318 pistons it wouldn't need any metal to balance it. At the same time as I was accumulating parts for the build, a 340 block dropped into my lap, so I put it in there instead. This has become my regret build.