What is the difference between a darton sleeved 3.8L and a 3.8L GTM stroker?

Is it that the Darton has a larger bore to achieve 3.8L while the GTM stroker uses a longer stroke?

If that is so, would it be possible to combine the 2? Larger bore plus longer stroke? What if it was combined with the 4.2L stroker kit? What would be the final displacement?

I may be on the wrong track here...please correct me if I am.

Thanks

 

The GTM 4.2L stroker kit uses Darton sleeves. The sleeves are bored to 100mm and the stroke is increased to 90mm with the custom stroker crankshaft. The Darton 3.8L is also bored to 100mm but with the stock crankshaft. So they are already combined for maximum displacement.

 

So a stock bore plus the GTM modified crankshaft gives 3.8L?

Thanks for the explanation

 

Yes, the stock bore plus the GTM 90mm stroker crank gives about 3.8L (3.87L to be exact).

 

problem with a stroker, is that higher revs won't be possible as easily as simply sleeving and boring to 100mm. With a longer stroke, the piston speeds get faster sooner...which is dangerous!

I plan on doing the 100mm bore sleeved, stock stroke. So I'll rev to 8k, and that'll be a good bit of additional powerband to use!

 

yea but didnt sam say that it was capable of reving to 8k with the 4.2L or am i

 

What cams/intake manifold do you plan to use for power above 7500rpm's? I doubt you could even make power to 7500 even on race gas...fwiw I didnt go with the 100mm bore as it reduces headgasket surface area by about 30%, not worth it to me, just crank up the boost.

 

Interesting so Stroker kit makes a longer stroke, and the piston speed gets faster making it more dangerous?

And a 100mm Bore decreases surfarce area....

If all that is true then I would use a stock bore engine like mentioned and crank up the boost

Will a VQ35HR motor be a better swap when building it up for boost?

 

The effects of fast piston speed can be offset by using lighter and stronger components. GTM rods are even a little bit lighter than stock. Sam's engineers did all the math, to insure piston speeds remain safe at 7500-8000rpm. It's really not that bad at all.

The question, as Alberto mentioned, is who will be the first to crack the nut, in creating a powerband that rises to 8000rpm (without nitrous). There are other restrictions that we are dealing with here.

 

I don't know why everyone is on this rod/stroke ratio binge lately. At least it seems to me to come up a lot, but really it's not that important in the scheme of things. Vurtually everything else needs to be considered more important over the piston speeds in the VQ. Consider this, even with the stroker kit, the piston will have a max velocity of around 40 meters per second at 8000 rpm. Factory stroke would be 35.5 m/s max velocity. Honda's F20 hits a max piston speed of 41 m/s and it revs to 9000rpm all day long.
Building the engine up for high revs, its nice to know the speeds your pushing your pistons, but it's by no means a limiting factor. Building the head and reciprocating assembly to withstand the abuse and actually make power at that rpm is the limiting factor. If you have the parts and tuning to do that, then by all means rev away. And like Sharif said, the lighter the components, the better they behave at such high rpm.
Will

 

The rod/stroke ratio is what determines how much force is being applied to the walls of the cylinder. Its pretty important for determining structural integrity (as well as when power is made). Also, it greatly decreased stability of the crank. An improper stroke/rod ratio to the size of the engine block can lead to a very ****ty and unbalanced engine.

Also, a proper rod/stroke ratio determines the velocity of the piston. While this isn't that important w/ FI (actually it is, if you're talking about structural integrity of just the piston), in N/A its probably far more important than any thing else. The velocity of the piston is what creates the vacuum for the air charge on the intake port. Without a high speed piston, the power range of an engine is usualy on the lower end of the RPM band. A larger rod/stroke ratio would mean more power at the latter part of the RPM band (i think)

 

A higher rod:stroke ratio is always desireable since it allow for more piston dwell time at TDC (more complete combustion) and BDC (higher dwell leads to better cylinder filling at high RPM) and because of the lower rod angle and subsequent lower thrust loads on the cylinder wall. I wouldn't lengthen the stroke of the VQ35 for this reason. If you want a longer stroke VQ, find a way to retro the VQ40 in.

 

First, the amount of side loading on the piston is not very important. Period. If you think it is, so be it, but no one is ever going to damage their engine from side loads before EVERYTHING else goes in the engine. Rather, it's the acceleration the piston must achieve that the rod/stroke ratio determines- and that is important.
The rod stroke ratio determines the amount of acceleration the piston has to go through from TDC and from BDC after the intake stroke. The piston acceleration will place an inertial loading on the conrod far more abusive than the compression loading does, simply because tenion leads to fatigue and compression does not. In any engine, if the piston speeds are too high the tension forces from the inertial loading can easily become greater than the compression from combustion.
The integrity of the crank will also be affected under the same tension forces.
The comment on an unbalanced engine if the rod/stroke is not the right size to the block is incorrect. The balance of the crank is not in any way affected by the rod/stroke ratio. If the crank is balanced for a given rpm then it doesn't matter how long a conrod you use or how long the stroke is. The dynamics of the reciprocating assembly are affected by cycle and cylinder number/arrangement.
Yes the rod/stroke ratio determines the velocity of the piston, but at a given rpm. It's the acceleration that actually does damage and is a more direct result of the ratio, not the speed- but I see where you're going with it.
As far as cylinder filling and VE, then that's a compilation of a lot of things. All of which are more important than the rod/stroke ratio. The cam timing, overlap, and lift will have more to do with the rpm at which max VE, and therefore torque, is made.
A higher piston speed is dictated by the rpm, and the rod/stroke ratio will dictate how quickly it must accelerate from the bottom to the top of the cylinder and back again. A high rpm engine will benefit from a longer rod to minimize that accepeleration, and therefore have a higher dwell at the top and bottom of the cylinder.
Now, what I'm saying is this: For a high rpm, the longer rod and consequent dwell will aid in cylinder filling, sure. But minimally so. The cams will do more to aid in VE than anything. Of course altering the rod/stroke will help, but it is not needed to make power. And it can't really be changed.
If this thread was about designing an engine from scratch, then it would be worth considering. But its not. There's very little we can do to change the rod/stroke. And if we did, what would we gain? The piston speeds are safe as it is even stroked. If someone wants to rev higher and is worried about the inertial loads, then lighter components are going to do more for reliability and power than just changing the rod/stroke ratio. If more power is wanted at the high end of the rpm scale, then getting some custom cams will do more than customizing the rod/stroke ratio. This is all I'm saying, that virtually everything else is more important since there's very little that can be done to change it. And it is not limiting the rpm band in any way. Hell, SR20's can rev to 10,000 rpm and they have a worse rod/stroke than the VQ. But they built everything else that is important. Same with 2JZ, they pull almost 38 meters per second at 8000rpm, more than the VQ at the same rpm, and can be built to run 10,000rpm as well. Do you think they figured the rod/stroke isn't very good on this motor (it's not with a 142mm rod and 86mm stroke) and thought it can't be done? No, they simply realized the same thing I said, that virtually everything else is more important to make power and then they did everything needed.
Will

 

Yes, you are correct about the side loading and piston accel and dwell. These are great things to consider, for sure. But in no way are they a big deal in limiting what can be done because as I said in the last response, there are a number of things way more important to consider for longevity and power. Look at it this way, if the guy strokes the VQ he has and then boosts it and revs it to 8k rpm he'll make xxx amount of power. Then if he waits because he's all scared about the recent rash of rod/stroke ratio talk goig on, and so he just swaps the new HR engine with a longer rod and taller deck. He then boosts it the same and revs to 8k rpm, he'll make less power than if he had just stroked his original VQ. Both engines revving the same, the new HR will have a lower piston speed and higher dwell at TDC, but it won't have any extra power to show for it. The reliability of each will be identical under the same circumstances because neither will be running on the high end of piston speeds. It would be like a SR20 guy dropping in a SR16 crank for the longer rod, and then thinking this was a good move. He'll never make up the discplacement, and the cams/springs/retainers/conrods/etc.. needed to rev over 8k would be the same in either case.
Will

 

The velocity of the piston is what creates the vacuum for the air charge on the intake port

The earth's atmospheric boost 14.7 psi is what rushes in to fill the lower pressure created from the heat expansion out the exhaust port......what vacuum?

At WOT there is little pressure differential in the intake tract..... 1psi max.

 

I'm sorry if I missed something, but is this directed at me?

I don't want to get on a tangent on what contributes to cylinder filling and volumetric efficiency, so I'll leave all that alone. My point to the OP is that stroking the motor will affect the rod/stroke ratio as people have said. However, it's not a major limiting factor in reliability or power production. There are a number of other issues you'll have to deal with that are far more important. Unless you're building an all new engine from scratch, in which case we wouldn't be dicking around with the thought of a 4.xx L V6 to begin with, then considering the rod/stroke ratio is all well and good but not very important as there's little you can do to change it.
Will

 

And FYI...when we figure out how to cram 900whp+ worth of air through the piping, TB, and intake plenum, I will be sure to let everyone know.

There are plenty of roadblocks ahead, and many will have to be engineered from scratch, for those pushing for the magical 1000whp mark.

I have no doubt whatsoever, that the reliability of these stroker motors will be outstanding.

 

Good questions; but why, might I ask, should we be concerned with high rpm (as in 9000), wider bore plus longer stroke on the current VQ35DE…is beyond me. First off, is anyone even considering the integrity of the block based upon its geometric design? And, it’ll take more than lighter and stronger components to compensate for the laws of physics on a wider surface area, a longer stroke at 9,000 rpm; as the longer the stroke, the more difficult it becomes to achieve internal balance.

Right off the bat, forget the stock heads, as one would need well ported heads and equivalent valvetrain to meet the necessary fill rate and to avoid the valvetrain from being blown to smithereens. And, are we expected to do all this based upon stock variable timing?

And, what is the fuss now about, 900 rwhp when 800 rwhp to 1,200 rwhp have already been achieved on the VQ35DE, without the longer stroke and wider bore?

G

PS: Thanks thawk408
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and the rpm extremes

 

who has 12,000 rwhp?!?

 

I think he meant 1200.