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400 Stroker pistons

Meep-Meep said:
I'm building a 451 for a member here and we went with SRP's set at zero deck with a cut down 440 crank and 440 LY rods. You asked about rod length so be prepared for this thread to go to 5 pages! LOL. Some will say short rod and some will say long. I say Chrysler had it figured out pretty well and the result was time tested and it works so I went with the standard ratio of 1.80:1. Thinking back I probably could have gone with the lower ratio 400 rod without any ill effects, or for that matter any drastic improvements. I'd like to know if someone can tell the difference between the 1.696:1 vs. 1.802:1 rod ratio engine by driving it. What does make sense in this build, and something that might actually be measurable, is the drastic weight reduction to the reciprocating assembly.

Now to cram 470 cubes into that short package would require a short rod and result in a very low R/S ratio. Too low of a ratio might play hell on the thrust side of the piston and scrub off power due to friction. It is also said that low R/S engines don't rev well and tend to "vibrate" at high RPM. Mechanically speaking I think there is a point of ideal R/S ratio to balance torque and component wear. Again, the engineers knew something back in 1958 when these things were designed. The R/S ratio changes the torque of the motor and can be very beneficial to be on the low side if you want a tractor. A lot of newer engines run low R/S ratios probably for the torque reason but they are not of a 1958 design either. Note: The engine in the Honda S2000 has a R/S ratio of 1.82:1. It also has a red line of 9000 RPM!
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PM sent to you MeepMeep
 
Good point, Meep Meep, the shorter rod is going to be lighter, of course. And the higher C/H of the piston will make it a little heavier. But Prob not enough to off set the weight savings of the lighter rod. With a 3.9 to 4 inch stroke, short 6.358 rod, you could get the weight savings on the piston AND the rod. Plus still get the lower Rod length to stroke ratio.

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I noticed on the Ross piston web site, they have a piston for use with a 3.91" stroke, C/H of 1.47", and weight of 550 grams. Uses a rod length of 6.535". This looks like a good way to go at first glance.
 
I was actually thinking of using some late model pistons I had that are .1" in the hole but making them zero deck by adding a 3.9" stroke crank. You would end up with 455 inches, a flat top piston and more compression without a pesky dome in the way. I'm pretty sure to get the 3.9" stroke all you would need to do is offset grind the rod journal to 2.2" and run an H beam 440 length rod.

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PM replied Grabber.
 
HT413 said:
Mopar 400 rod length is 6.358", so w a 3.75" stroke, RR is 1.624. With a 3.915 stroke, RR is 1.599.
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Now keep this in mind, both of those will want air, lots of it, so big heads, big ports, larger cams...what is big, aggressive, not street friendly in a 440 is lame or docile even in a motor which it's STROKE was changed and HAS effected the RR. A 451 that is USING everything from the 440 IS NOT a stroker, it is a 440 in a lighter, shorter block, with a lighter shorter piston, that isn't a stroker, a stroker is when the motor has changed completely because the stroke has greatly effected the RR and made it not anything like it was when originally design from the factory.

Like the sb issue, how many guys that you know are running stroked sb's ??? everyone with a 408 is running a 1.5 RR, and then the mistakes are made with using the same cams they would use in a 340 and any factory head without and with lots of porting is killing/hampering it.

Ever looked at a gm 396, look at the heads they used on them, the oval port heads on a 396 (forget the RP 427) it has a large port on the oval port heads, like 250 or more cc's... BUT 396" ....now lets look at our sb's, put in a 4" crank, that's more crank then the 396, more than the 427... WHY would anyone even contemplate ANYTHING from the mag design here... contemplating anything mag design here makes me want to reach thru computers and choke people. . . . You're building a HUGE BREATHING sb, a SB which it's bottom end is capable of the same breathing of a 454, not a stupid mag design for which mopar used for both it's sb's to share the same head and both make good performance.
You do not use factory heads, you want to skip to big heads, ports in the 250 area and actually better...

Same with ANY stroker bb, and stroker bb, and by STROKER i mean it has changed the parameters of the motor completely...

You're building a 500" bb, you want big heads, you want the larger Indy, YOU WANT to PORT that larger INDY, you want cams starting in the 260@50 area, YOU are not building a 440 ANY LONGER, you are now building a heavy breathing motor that wants nothing a 440 wants.

.
 
Super is right, but I told you he was a Chevy guy - and wants to turn BB and SB MoPars into Chevys. Truth is both architectures have make it down the track and got there at the same time. There are recipes to deal with whatever you are working on so unless you totally F$#@ up the build you will do OK. Ramchargers and Dick Landy seemed to do well with old out dated junk, as well as Sox and Martin, Leal, etc.. So unless a 10 second 1/4 mile from the 60's and 70's is not the same 10 seconds as it is today then I don't see a problem using whatever works.

To me the advent of the big inch motor means you can do more with less, and for a street car, which is where I'm coming from 90% of the time, this is great news. You can run lower compression, less overlap cams and have equal or better performance on junk gas. It's like putting a 500 Cad in everything.
 
Dick landy's 60's stuff is different and no where near competing with now, im not a gm guy, i understand motors wants, short RR wants huge ports, building a stroked motor doesn't want what a 440 does. Short RR wants big ports, so using a gm head as an example is easy to see the issue.

Big difference Then and Now

You can build a stroker, but building it wrong leaves power lost
 
Quick question - so how does the choice of 1.5 vs 1.6 rocker arms affect things, regardless of the rod ratio? Can a 1.5 rocker setup be used with both the short 400 rod or long 440 rod in a 451 build and why do you choose one over the other?
 
HT413 said:
Mopar 400 rod length is 6.358", so w a 3.75" stroke, RR is 1.624. With a 3.915 stroke, RR is 1.599.
Click to expand...

You're going down the right train of thought here and I hate seeing all this rod ratio crap being spewed. The stroke in relation to port size, flow capacity and all the other variables will have a much larger effect on the torque curve and the engine performance than the actual rod length.
 
68 Sport Satellite said:
Quick question - so how does the choice of 1.5 vs 1.6 rocker arms affect things, regardless of the rod ratio? Can a 1.5 rocker setup be used with both the short 400 rod or long 440 rod in a 451 build and why do you choose one over the other?
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Forget about the difference in rod ratio of the 400 rod vs. the 440 rod.

The rocker ratio will increase valve lift and slightly alter the opening and closing rate of the valve. Either your engine likes it or it doesn't care and there is only one way to find out. A higher rocker ratio will also put more stress on the shaft, but the MoPar stuff is pretty tough so probably not a concern. Even a cam with a fast opening rate will cause more stress and that's why I'm a proponent of a good solid valve train in even a mildly over stock street engine.
 
m79ded said:
Hi

I am planning on putting together a 400 stroker motor. I was looking at piston choices and realized that 1.32 comp height pistons are appropriate for what I am planning to do. I was told to be careful about piston wobble in the bore because of the short comp height and the smaller piston. Is that true? I am planning a street motor and aiming for about 500HP so reliability and drivability is a must.If I have a choice of short or long rod which would be recomended? for a more reliable engine. I will be doinf either a 451 or 470 ci

Thanks
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I have the 440 source 500" stroker kit for the 400 block, 4.15" stroke, 6.760" rods with the flat top pistons, 74cc Victor max wedge heads,so compression is a bit over 12:1, and running a decent sized 0.714" lift (with 1.6:1 T&D rocker arms) solid roller cam. The piston pin does go through the lower part of the oil ring, so it uses a oil ring support. It's not a big deal. The pistons are sort of short, but compression distance does not determine the overall length of the piston, just the distance from the piston pin center to the top of the piston. The length of the piston skirt is limited to what sticks out the bottom of the cylinder bore and clears the crank and rods. A short rod piston with a larger compression distance could end up with shorter piston skirts because at BDC, the pin end of the rod will be closer to the bottom of the cylinder bore than a longer rod.
The whole rod ratio issue is not that big a deal in the limited range of either stroker kit.
I chose the 500" kit over the 512 kit because I was planning on running high RPMs with the engine.
For a street car that won't see 7,000+ RPM, the 512" kit would be my choice.
 
That being SAID above, the 1.6 ratio that is in 451mopars motor is a FAR cry from the 1.8 ratio.

Rod ratio is very important, unfortunately not understanding it is what makes power differences.

I don't get how no one understands the effect rod ratio has on the tq being made and where, how that effect can make larger power by the RR effect on using larger ports and cams you normally couldn't without having a high pk area, then they say it makes no difference.

.
 
More like 1.69 (or round to 1.7:1) vs. 1.80:1. You are going to sit here and tell us that a ratio difference of .1 is going to be something notable??
 
Supershafts said:
That being SAID above, the 1.6 ratio that is in 451mopars motor is a FAR cry from the 1.8 ratio.

Rod ratio is very important, unfortunately not understanding it is what makes power differences.

I don't get how no one understands the effect rod ratio has on the tq being made and where, how that effect can make larger power by the RR effect on using larger ports and cams you normally couldn't without having a high pk area, then they say it makes no difference.

.
Click to expand...
j
What you're attributing to rod ratio is a function of stroke for a given combo. I've dyno'd short rod strokers and long rod strokers of the same cubic inch and stroke and the torque curves and power outputs were very close. Too close to attribute anything to the rod ratio. It's the stroke variation that's producing the results.
 
You're saying you built 2 motors IDENTICAL in every way and the SRR was the same as the LRR.

Here's the problem with that, put the specfics of those 2 identical motors and then i'll put where and why they were close.

If you build a LRR motor with my heads it's gonna peak high and be kinda shitty low and kinda ok mid, but great high.

If i put heads most are running on my SRR motor it would be shitty too since now the motors ability to pull in all that air early has been choked, this is the problem with ALL the SB strokers, not nearly enough port for what they can breath.

The little difference in RR makes up in early power and they both need other differences to make the power.

Now having said that, EVERYTIME you take a 440 recip and put it in a 400 block you built a 440 .060 over and all it really is happens to be is a LIGHT overall packaged 440.

Building a 500" 1.8 RR motor identical to a 500" 1.6 RR motor and not increasing cam and heads that WOULD hurt the perf of the 1.8 RR motor is where the mistakes are made and why YOU don't see the benefit.
The 1.8 RR motor with 270@50 isn't going to be all that great at 2000 thru 4000 or with the big 300+cc intake heads, whereas the 1.6 RR motor will kill that 1.8 motor with the larger 300+cc intake and large cam, and will make more power sooner than the 1.8

Yes that .1 is very substantial in the effects of how early things start working, LRR starts making power later than SRR, so the SRR is making the power early and holding it longer.

So if you believe in low end, then you want SRR not LRR

If you want the low end and more power thru out you want to stay away from 1.7 and anything larger, ultimately 1.5 and 1.6
 
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