340 Stroker Rotating Assembly

[JedIEG]

Looking for feedback on my rotating assembly.
Application: This is a primarily street engine with some eye towards autocross/road race use.
My goal is to match a 392 G3 Hemi for power and tq with good driveabilty and reliability.
~500HP/500TQ

394-396cid
340 Block 4.070-4.080 bore
Molnar 3.79 crank
Molnar 6.400 SBC rods
Autotech 4032 12-18cc dish pistons. (10-10.5 cr target)
1.2/1.2/3.0 summit GXP gas ported piston rings
Clevite p-series main and rod berings

Heads- edelbrock rpm, mild clean up and porting
Cam- TBD- looking in the 230-240 @.050 range

Would like to protect for an upgrade to W5 heads and 2.05 vavle if I scrounge up a set and ability to move to a 240-250 cam if power goals increase.

 

[mygasser]

you'll be ok with the hp and torque goals, as for matching the gen 3 hemi for driveability and reliability? doubtful. not saying it can't be driveable and reliable, it just won't match a new car for those.
neil.

 

[mbaird]

IMO 500 will be stretch with mildly ported Eddies and a 230-240 cam . My 408 dynoed just under 500 with a 246/250 cam and ported W2s flowing 297cfm. Now I’m sure I left some power on the table somewhere but the difference between the heads will be substantial.

 

[pittsburghracer]

Looking for feedback on my rotating assembly.
Application: This is a primarily street engine with some eye towards autocross/road race use.
My goal is to match a 392 G3 Hemi for power and tq with good driveabilty and reliability.
~500HP/500TQ

394-396cid
340 Block 4.070-4.080 bore
Molnar 3.79 crank
Molnar 6.400 SBC rods
Autotech 4032 12-18cc dish pistons. (10-10.5 cr target)
1.2/1.2/3.0 summit GXP gas ported piston rings
Clevite p-series main and rod berings

Heads- edelbrock rpm, mild clean up and porting
Cam- TBD- looking in the 230-240 @.050 range

Would like to protect for an upgrade to W5 heads and 2.05 vavle if I scrounge up a set and ability to move to a 240-250 cam if power goals increase.

I really question your desire for W5 heads when there are way better more reliable options out there.

 

[Brian Hafliger]

Looking for feedback on my rotating assembly.
Application: This is a primarily street engine with some eye towards autocross/road race use.
My goal is to match a 392 G3 Hemi for power and tq with good driveabilty and reliability.
~500HP/500TQ

394-396cid
340 Block 4.070-4.080 bore
Molnar 3.79 crank
Molnar 6.400 SBC rods
Autotech 4032 12-18cc dish pistons. (10-10.5 cr target)
1.2/1.2/3.0 summit GXP gas ported piston rings
Clevite p-series main and rod berings

Heads- edelbrock rpm, mild clean up and porting
Cam- TBD- looking in the 230-240 @.050 range

Would like to protect for an upgrade to W5 heads and 2.05 vavle if I scrounge up a set and ability to move to a 240-250 cam if power goals increase.

Better combo would be a 4" crank and 6.125 rod...more porting on the heads, and cam it 236-248 @.050 on a 108lca.

 

[B3422w5]

I really question your desire for W5 heads when there are way better more reliable options out there.

Exactly. No shelf headers anymore. The castings themself are of poor quality. Other options available that make similar power with more integrity

 

[JedIEG]

Better combo would be a 4" crank and 6.125 rod...

I'm curious what benifit a 6.125 rod brings to a 4" crank other than a shelf piston? Looking at moving up to a 4" stroke, I was still looking to run a 6.200- 6.300 rod to get a shorter piston, less wight and less friction.

 

[B3422w5]

I'm curious what benifit a 6.125 rod brings to a 4" crank other than a shelf piston? Looking at moving up to a 4" stroke, I was still looking to run a 6.200- 6.300 rod to get a shorter piston, less wight and less friction.

Very little downside to a longer rod in a performance/ race build. I ran a 6.300 Compstar rod in a W5 motor.
Less sideloading, lighter piston, better rod ratio, in a race motor perhaps better power where the engine lives at going down the track compared to a short rod.
For a strictly street deal, I probably wouldn’t bother

 

[Brian Hafliger]

I'm curious what benifit a 6.125 rod brings to a 4" crank other than a shelf piston? Looking at moving up to a 4" stroke, I was still looking to run a 6.200- 6.300 rod to get a shorter piston, less wight and less friction.

For the intended application you won't see anything really from a longer rod...less piston weight but heavier rod...short rod works well with pump gas and tends to be peppier throttle response. Just how I would do it from experience.

 

[autoxcuda]

I bought a Scat cast rotating 4" assy from Brian at IMM 13 years ago. A pre-balanced one even.
Run a 236/242 solid with mild port heads. Even with a single plane intake the power and torque is plenty for autocross. On road course a SRT 392 Challenger was behind me along the big straight at Willow Springs big track, he said he could not pull around.

 

[autoxcuda]

BTW a 392 Hemi Challenger's weighs ~4300 lbs.

My Barracuda weighs 3209 lbs on computer scales.

 

[Bewy]

Longer rod means shorter piston......
See the Salter Racing you tube video on rod lengths.

 

[Newbomb Turk]

I'm curious what benifit a 6.125 rod brings to a 4" crank other than a shelf piston? Looking at moving up to a 4" stroke, I was still looking to run a 6.200- 6.300 rod to get a shorter piston, less wight and less friction.

The thing is guys get wound up in this. And what Smokey said 50 years ago is still true.

Use the longest rod you can fit. Is that a hard and fast rule? Nope. We live in a Chevy world and engine building has been infected by that.

If you were building a 340 stroke engine I’d tell you don’t make the rods any longer. It’s already at 1.8x ratio.
when going to these long stroke cranks you can’t get the rod too long. Even with a 6.4 rod you are still a 1.69 ratio.

Regardless of what the web and YouTube says, rod to stroke ratio matters.

Is there a perfect ratio? Nope. But that ratio affects cam timing. A bit more than most might think.

As an example, as the rod to stroke ratio gets lower, the spread between intake and exhaust lobe duration gets bigger. As stroke length goes up compared to bore diameter, that spread goes up.

Cam timing SHOULD reflect those changes.

As an example, if someone thinks a 340 Chrysler takes the same lobes as a 350 Chevy I’d say they need to look at the math they are using.

I have a 3.79 crank in the shop. Two of them. I looked at the 6.4 inch rods. That’s a 1.6887 ratio. That’s pretty close to what Pro Stock currently runs. I know none of us have that much induction. IMO that’s a pretty low ratio.

A 6.125/4 inch crank is 1.53 so not only is the cam timing requirement different due to displacement but also due to rod ratio.

It all matters to varying degrees but it all matters. I don’t know what you have for induction but on cylinder head limited stuff I don’t like a 4 inch stroke. That’s .240 longer than a 427 Chevy with a significantly smaller bore.

If you like inverted power and torque curves (I don’t like it) then run a longer stroke. And by that I mean it makes the same or more torque than power. I know some guys love to touch the throttle and blow the tires off. I’m not into that. It makes people think they make more power than they do.

 

[JedIEG]

See the Salter Racing you tube video on rod lengths.

This pretty much lines up with what I have heard. Make the piston as short as you can without jeopardizing stability. I also don't want a piston with oil rail supports so I won't push the compression height down to 1.150 like he suggests as optimal. I think Autotech starts including rail supports around 1.200 CD on their shelf pistons and my combination of 6.400/3.79 gives me a bit of margin around 1.275 +/- a few tenths depending on the decking.

 

[Nat]

Looking for feedback on my rotating assembly.
Application: This is a primarily street engine with some eye towards autocross/road race use.
My goal is to match a 392 G3 Hemi for power and tq with good driveabilty and reliability.
~500HP/500TQ

394-396cid
340 Block 4.070-4.080 bore
Molnar 3.79 crank
Molnar 6.400 SBC rods
Autotech 4032 12-18cc dish pistons. (10-10.5 cr target)
1.2/1.2/3.0 summit GXP gas ported piston rings
Clevite p-series main and rod berings

Heads- edelbrock rpm, mild clean up and porting
Cam- TBD- looking in the 230-240 @.050 range

Would like to protect for an upgrade to W5 heads and 2.05 vavle if I scrounge up a set and ability to move to a 240-250 cam if power goals increase.

looks good only thing is heads and intake is where the power is , had that with my stroker limited to 536 hp 547tq because heads and intake could not handle it . Ede heads ported with pushrods moved 2.08 valves and a victor intake , with a ported airgap it made 527hp 560 tq

 

[JedIEG]

Ede heads ported with pushrods moved 2.08 valves and a victor intake , with a ported airgap it made 527hp 560 tq

I am considering this modification. I found a set of econo W2 rockers that could allow me to fully relocate the pushrods in the heads. A bigger valve is also tempting especially if I can get a lot of benefit in the lift range for the cams I am looking at.
What made you go with a 2.08 vs a 2.055?

 

[pittsburghracer]

I am considering this modification. I found a set of econo W2 rockers that could allow me to fully relocate the pushrods in the heads. A bigger valve is also tempting especially if I can get a lot of benefit in the lift range for the cams I am looking at.
What made you go with a 2.08 vs a 2.055?

Coming from someone that has done this mod you can get over 330cfm without moving the pushrod