Stroker Kits

[CJ]

You can say that again Nic

[CJ]

OK, enough of this charade, let's all really be ourselves, eh?

John, you are always yourself

[JohnA]

You are what you is (Frank Zappa's distilled wisdom....)

[Nic]

You can say that again Nic

 

CJ's technical car knowledge

 

stupid site hanging in middle of reply

[arnout]

Hi CJ,

You asked me if I can do some contribution in this thread so lets answer everything and do a slight sum-up of the other answers.

 

So, that means you will still need to use your existing block and head?

Yups on all kits you install the stroker kit on your own block or if you are fortunate enough on your spare block. I really advice to get a spare block and install it there cause the downtime is greatly reduced and you can take your time so that will result in better numbers normally.

1. Would you need to bore out the block for the new piston size or is 87.00mm standard size?

On the HKS kit yes, but you can buy stroker kits with stock bore as well. If you would like that is another question. 1mm O/S is really the biggest I would advice on a 2jz, you might be better off getting a +0.5mm O/S cause it keeps the block stronger. I have rebuild a few RB26 engines and there you can overbore a lot, although JE pistons only has +1mm O/S off the shelf.

DO keep in mind you must ALWAYS bore with torqueplate. A torqueplate is bolted to the shortblock so that the block is bored in it's shape as it was in the car with the head bolted to it. If you bore a block without a torqueplate you are just stupid. Blocks do deform about 40% of the regular wall to piston distance (I measured this).

2. What else would need to be done to the block?

3. Would the head or head set need any changes?

I advise to do a certain investment in the valve train as well, especially cams and optionally bigger valves. It all depends on what your goal is. A head can be replaced in the future as well ofcourse. Do realise you have at least 10% more volume so you need to feed that of course.

OK, so now down to the nitty gritty. What is the advantage of running a stroker kit over a standard car (assuming one with a single turbo conversion). What differences in performance and torque (not exact figures just generalisation) would one see?

You will have more torque down low and the added volume from the engine makes your turbo spool quicker. You can also install a bigger turbo ofcourse.

The downside is that you cannot rev to 10.000 rpm.

just rev higher mate.

Sorry Terry, but this is a no contribution at all. Revving your car higher is completely something different than stroking. Torque down low what is given by a stroker kit will not be given by a higher rev limit. The driving experience from a car with stroker compared to one with a rev limit of say 8700 RPM is something completely different.

Exactly. You will not be able to rev a stroker like you can/do a stoke displacement engine. Also, what happens if god forbid, you spin a bearing. If its bad the lot is just junk as HKS AFAIK dont sell cranks seperately.

Your statement that you cannot rev a stroker like you can on a stock displacement is not entirely true, or complete. You can rev a stroker higher than a stocker if the crank and rods are stronger and if the pistons are lighter. Normally this is the case. Obviously it depends on how much higher you want to rev it as well. Furthermore I've seen in developing stroker cranks for the RB26 and the 2JZ that the shape of the counterweights also helps in the stability of the whole stroker assembly. Spinning a bearing can happen on any car. If you spin a bearing on a freshly built engine you have a bad machine shop. Always use the correct bearings and check the bearing clearances. Always line hone the block. You might consider installing the Pro-gram main bearing caps, in that case you have to line bore the block as well. Do think of a girdle assembly on top of the caps. It all helps making the block stronger. But again, oil clearances on the bearings is the most important issue. Bearings don't go because they are of bad quality or something. The only situations a bearing will go is when you assembled the block wrongly or when you don't have enough lubrication and cooling from the oil. So enough oil clearance and also DO install a fresh (new) oil pump of course!

The bearings for the 2JZ are so called wedge-bearings. They have less clearance on the vertical / horizontal lines while they have more clearance diagonally. This will result in a very high oil pressure very locally, just there where the bearings gets it biggest bang.

 

To complete the story on the rev limit people have already suggested the rev limit is determined by the piston speed, the weight of the piston, and the strength of the rod and more or less the quality of crank. All true. But there is one factor you cannot influence with better metallurgy or material: the rod / stroke ratio. This ratio determines how much of the force goes up-down and how much sideways (as you have a rotating assembly). If you were to design a stroker kit how would you compensate the combustion chamber size linearly to the added stroke? The best solution is welding a plate on the deck so that the pistons can go higher than the stock deck. Obviously your piston rings would hit the welds or the crack, so you should install sleeves in the block as well. I would say: very costly

Making the combustion chambre bigger can also be done by making the rods shorter. The downside of this is your rod/stroke ratio will be even worse! The longer the stroke, the longer your rod needs to be. You're not increasing the stroke and decrease the length of the rod.. that's insane!

Ok.. so how do we compensate then? Thicker headgasket? Might be an option. I choose for a deeper dish piston. In my kit, and I think in the kit from HKS as well, we choose for a stock dimension rod, so you can choose from every rod company in the world offering 2jz rods. The pistons are a custom JE job. They are 87mm (yeah, 86.5mm might be better, but +1mm oversize is very good doable on the 2jz as well) and they have a deeper dish so all compensation for the stroke is there.

 

Then about my projects: The vvti engine with turbo and supercharger will go in my mk3 supra. The engine will remain stock stroke, as with the stroker kit I must overclock the charger and that's currently too much work cause we have made the pulley for it already.

For my mk2 dragrace supra with the TH-350 transmission and solid axle conversion I will build a stroker engine most likely. It all depends on time, money and beer

[Ian C]

Thanks for all that Arnout How much would you charge people to ship a stoked-out exchange-basis short block d'ya think?

 

Also I think Terry was saying on a bangs-per-buck basis it's cheaper and easier to raise the rev limit than to go for a stroker kit, but he didn't say it was an exact replacement for strokers

 

-Ian

[CJ]

Good stuff Arnout - God I love this forum. What great VFM the £10 is

[Nic]

Very interesting post Arnout, thanks for sharing your views/knowledge

 

I'd also be very interested in CW's thoughts on the subject if possible.

[arnout]

What great VFM the £10 is

 

That's why I didn't pay for access. Normally I get paid for providing information

[Guest Terry S]

Thanks for all that Arnout How much would you charge people to ship a stoked-out exchange-basis short block d'ya think?

 

Also I think Terry was saying on a bangs-per-buck basis it's cheaper and easier to raise the rev limit than to go for a stroker kit, but he didn't say it was an exact replacement for strokers

 

-Ian

 

Thanks Ian, thats exactly what I was saying, I also dont sell them...

[Chris Wilson]

Nice post Arnout, if you don't mind me saying so?

[Dragonball]

Nice post mate...thanks for taking time out

[Digsy]

Just a few notes from me (sorry Tel, no 35000 word writeup on this one )

 

DO keep in mind you must ALWAYS bore with torqueplate. A torqueplate is bolted to the shortblock so that the block is bored in it's shape as it was in the car with the head bolted to it. If you bore a block without a torqueplate you are just stupid. Blocks do deform about 40% of the regular wall to piston distance (I measured this).

Sounds like a reasonable preventative measure to take - especially if you are taking a lot of material out of the block. However, OEMs don't do this when they initially machine the block (and the roughing operations will take out a lot more material than any re-boring). If Arnout has measured a significant distortion, then so be it, and repsect to him for even going looking for it. It's interesting that taking out a small amount of material produces a so large a distortion, though.

 

You can rev a stroker higher than a stocker if the crank and rods are stronger and if the pistons are lighter. Normally this is the case. Obviously it depends on how much higher you want to rev it as well. Furthermore I've seen in developing stroker cranks for the RB26 and the 2JZ that the shape of the counterweights also helps in the stability of the whole stroker assembly. Spinning a bearing can happen on any car.

Being picky, assuming that any mass reduction or strength increase you apply to a stroked engine you could also apply to a stocker, then all things being equal you will be able to rev the stocker higher than the stroked engine because the tensile loads for any given RPM will be lower.

 

If you spin a bearing on a freshly built engine you have a bad machine shop. Always use the correct bearings and check the bearing clearances. Always line hone the block. You might consider installing the Pro-gram main bearing caps, in that case you have to line bore the block as well. Do think of a girdle assembly on top of the caps. It all helps making the block stronger. But again, oil clearances on the bearings is the most important issue. Bearings don't go because they are of bad quality or something. The only situations a bearing will go is when you assembled the block wrongly or when you don't have enough lubrication and cooling from the oil. So enough oil clearance and also DO install a fresh (new) oil pump of course!

Almost all of the above is equally applicable to bored or stroked or high revving or increased boost or any mod that significantly increases the performance of the engine. Especially the bearing clearance stuff. Engines with high boost and engines with increased bore and/or stroke will put increased gas loads on the bottom end, which means that the block will benefit from being stiffer and uprated caps and ladder frames will help this. As an additional note, the pure compressive force on the power stroke will be trying to separate the main cap from the block and uprated caps will not help to deal with this. A ladder frame will help to distribute the load amongst all the bolts but main bearing bolts with a higher preload (not just stronger ones done up to the same torque as stock) could also be considered.

 

Incidentally, the same thing goes for the rod bolts if you are increasing the rev limit. In this case the inertia loads caused by the mass of the piston assembly and the top half of the rod are trying to separate the big end, which could cause loss of compression in the bearing shell, and a spun big end bearing.

 

To complete the story on the rev limit people have already suggested the rev limit is determined by the piston speed, the weight of the piston, and the strength of the rod and more or less the quality of crank. All true. But there is one factor you cannot influence with better metallurgy or material: the rod / stroke ratio. This ratio determines how much of the force goes up-down and how much sideways (as you have a rotating assembly).

True, but even though it affects piston side loads I don't think that this puts as much of a direct physical limit on max revs like reciprocating mass does. AFAIK, in practise the r/l ratio just determines the second-order out of balance forces (meaning that twice per engine revolution the cylinder tries to jump up and down). In OEM-world this is primarily an NVH/refinemnt issue and in an I4 is countered by using balance shafts. In the race world where you run stiffer (or even solid) engine mounts, no one is going to notice a slight additonal second order shudder from the engine. Anyways, the beauty of an I6 is that all the second order forces (in fact all the forces) cancel each other out anyway, so providing that you don't go daft it doesn't matter what r/l ratio you run.

 

Making the combustion chambre bigger can also be done by making the rods shorter. The downside of this is your rod/stroke ratio will be even worse! The longer the stroke, the longer your rod needs to be. You're not increasing the stroke and decrease the length of the rod.. that's insane! Ok.. so how do we compensate then? Thicker headgasket? Might be an option. I choose for a deeper dish piston. In my kit, and I think in the kit from HKS as well, we choose for a stock dimension rod, so you can choose from every rod company in the world offering 2jz rods. The pistons are a custom JE job. They are 87mm (yeah, 86.5mm might be better, but +1mm oversize is very good doable on the 2jz as well) and they have a deeper dish so all compensation for the stroke is there.

I think Arnout and I disagree on this one. If you want to take a 3.0, 6 cylinder engine up to, say, 3.2 litres by a combination of boring and stroking, then for an 87mm piston you would need an additional 4mm of stroke, which is 2mm of crank throw.

 

If you take the "insane" scenario and keep the stock compression height (piston pin to crown height), then the rod will need to shorten by the same 2mm. This will take the r/l ratio from something like 0.307 to about 3.26 (I've assumed a 140mm rod - not sure what the Supra's actually is). Now, if you want to keep the same r/l ratio as stock you would have to increase the rod length not by 2mm but by more like 6.5mm (the increase in crank throw divided by the desired r/l ratio). This will probably put you outside of what you can do within the confines of the stock crankcase.

 

Taking the stock rod length (while it does give you more options for what rods to fit) does next to nothing for the r/l ratio in this case. For a 45mm crank throw, an 140mm rod gives an r/l of 0.321

 

From OEM perspective, an r/l ratio of anything around 3.1 is OK but there are engines running around with r/l s up to 0.333. As long as you are below that figure you should be fine.

 

To keep an 8.5:1 compression ratio you would need to increase the head gasket thickness by 0.8 of a mm (or find the equivalent volume somewhere else in the piston, or knock yet another 0.8mm off your rod length).

 

FWIW I think the biggest killer for revving or stroking or boosting an engine is the oil film on the big bearings - simply because its the one thing you can do the least about. As Arnout says above the rest can be fixed in metallurgy and design. However, the oil film thickness is defined largely by the diameter and length of the bearings, and once you exceed the limit of what will squeeze the oil out of that clearance then you are going to be grinding metal. Good quality, cool oil is about all you can do unless you want to uprate the oil pump somehow.

 

Just my tu'penn'th, anyhoo.