ZX-Tex

iTrader: (15)

I think Sav summed it up nicely here.

In my humble opinion I would not get the stroker. I would spend the money instead on a good intercooler, a higher RPM limit, an efficient turbo, and maybe some port WI for good measure for more detonation margin. You should still come out way ahead.

If I was going to spend that kind of money on a stroker, I would start thinking about the LSx V8 conversion. By the time you add it all up, I'll bet you are pretty close, and the V8 is going to be much simpler (once installed) and more durable. Hell as it is I am tempted to sell off my fresh built 1.8L motor, S4 mani, 6-speed, XT clutch, 3.63 torsen, etc. etc. and use the funds to put an LS1 in my street car. The only thing stopping me is I think I would end up spending more money in the end. In other words, the parts sell off would not completely offset the cost of the V8 conversion. Plus I have so much fab time in my current setup, and I would 'lose' all that going over to the LS1. But if I HAD to spend that much money on the stroker to meet my power goals I would probably go with the LS1.

But, I digress. To get to the point, I would not spend the money on the stroker. I would either stick to a well built 1.8L or go with the V8 conversion.

bbundy

I agree and I have done a 2L.

Having said that back when I first went turbo like in 1999 I didn’t see the need to go to 1.8l from 1.6. As time passed that assessment became wrong. I didn’t want to make that mistake again so when the opportunity came up again I went for the most displacement possible short of some bastardized motor swap this time. I wonder if eventually the same thing will be true for the 2.0L as what has happened to the 1.6 to 1.8 swap decision logic.

Bob

DOHCPanther

So to summarize what I learned. The stroker engine will allow more power but will increase piston speed, increase crankshaft weight, and make the camshaft feel smaller. The stroker kit is about 2500 more than just rods and pistons and only increases the displacement 156 cc.

Bore Stroke Displacement
Stock 83 85 1839
Overbore 84 85 1884
Overbore 85.5 85 1952
Fm Stroker 84.5 89 1995
FM Stroker and large bore 85.5 89 2040

**** kicked off again.

sn95

iTrader: (2)

Yup, spend your $2,500 on any of the following and you will be happier:

1. Driving school; the nut behind the wheel is always car's slowest part!
2. Better suspension
3. Lighter wheels, stickier tires and bigger brakes
4. Dyno tuning
5. Multi angle valve job and pocket porting of your head
6. Custom cams matched to the airflow of your intake, head, exhaust & turbo along with an adjustable cam gear for your exhaust cam

FWIW, 1-3 are probably the most important; more power isn't much use if you can't safely harness it. YMMV

gospeed81

iTrader: (51)

+1

I'd go with a good overbore...but I'd put that kind of money (or half that much) into the head before I put it in the crank.

Call Integral, and start talking to them about a Stage2/Stage1 setup with a valve spring set....I'd imagine the gains are on par if not better than a stroker kit.



If I was convinced I needed 2 liters...I would've done the FE3 swap.

MartinezA92

iTrader: (4)

Maybe I'm overlooking something really obvious here but...care to explain?

Savington

iTrader: (31)

Less material in the cylinder walls, more heat transfer to the coolant passages, less material to absorb heat in general. 85.5 is all good and fine for a 190whp NA build, but for a 400whp FI build you're gonna want some cylinder wall thickness. 84.5 is about as far as I'd go.

MartinezA92

iTrader: (4)

The way I see it, a bigger piston may hold more heat, but it still transfers X amount of heat through the cylinder wall into the coolant. I'm assuming all cooling is done through the coolant, I don't see why the cylinder wall would just hold heat when there is cooler liquid surrounding it, regardless of the thickness.

So you're saying that a 400whp BP with 84 mm pistons runs cooler then a 400whp BP with 85.5 mm pistons?

Now if you're talking cylinder wall thickness for the sake of more material holding in all that cylinder pressure from 400 whp, then forget everything I just said. I'm sure you're not spewing BS, I'm just not really understanding the logic behind it.

triple88a

iTrader: (2)

Thicker wall would hold more heat than a thinner wall however thicker wall would take more heat to heat up while a thinner wall would heat up real quick and then cool off real quick.

gospeed81

iTrader: (51)

In a steady-state situation Martinez has a point.

It's really just about heat flux. In his example the same horsepower is being developed, and the same waste heat is being produced. That heat is carried away by the coolant, and if anything meets with less resistance through a smaller cylinder wall. The surface resistances are greater anyhow, and stay the same, although the inside of the cylinder now has more area with which to conduct heat transfer.

If an overbored motor runs hotter, it's simply due to the fact that it's making more power. This could be a result of higher compression, more mass transfer (larger volume), or whatever, but all of those increase power output as well as adding more load to the cooling system.

But real life is not steady state...

Sav has a point in dynamic situations where under load the cylinder walls are going to absorb a tremendous amount of heat, and the thicker walls will have more capacity. They can then unload that heat into the cooling system over a longer period of time when the motor is not under load.

I could see how this would cause higher peaks in your local coolant temperature, and raise the average coolant temp. Automotive cooling systems are designed to handle a certain heat transfer rate, and their capacity, routing and flow rate are optimized for that purpose. It is very easy to overload a cooling system with intense dynamic loads, like what a 400hp turbo car would see on the track.

MartinezA92

iTrader: (4)

Why would you want the cylinder wall to hold a bunch of excess heat for a longer period of time? My thinking is, if heat rises and falls quickly and you have a cooling system to handle it, wouldn't it be better then just saving a bunch of heat in the cylinder wall and not letting it escape into the coolant?

gospeed81

iTrader: (51)

Because you want a stable rate of heat transfer into the coolant. There is a limit to how much heat can efficiently be transferred into the coolant over a given period of time. If the delta T between the cylinder walls and the coolant is too little, and the cylinder wall is too thin to serve as a capacitor in the interim (until more fresh coolant is circulated) then the resistance to heat flux spikes, and this heat is essentially rejected, and dumped back into the cylinder. This could cause detonation, loss of power, and will only serve to produce more heat in the cylinders.

I'm sure that in practice this is what makes thin-walled cylinder motors run hotter. Try thinking of the cylinder wall material as a medium for maintaining a reasonable surface temperature for the coolant to interact with. You're not letting the hot combustion gases directly contact the coolant of course, but the cylinder wall DOES see both sides. If this wall is too thin, it will see more temperature fluctuation than it should, and therefore be less efficient at heat transfer. When transfer efficiency goes down, overall system temperatures go up.


EDIT: Imagine you are 4 ft away from a torch that fires every 30sec, and you have have to hold your hand up in the direction of the flame, against a steel plate. You have your choice of a 1/2" plate, and a 1/16th" plate. Which one do you choose?

It's intuitive right...your hand can withstand, without pain, the constant 125* or so the thicker plate will stay at, even if it's always that hot. The thinner plate may be cooler in between blasts, but for a few seconds after each one you're going to burn your hand at the temperature of the plate jumps up to 200* or so.

To your motor this is the equivalent of localized boiling during loaded runs, where the heat capacity of water is nil, and hardly any good heat transfer is going on.

MartinezA92

iTrader: (4)

Ah, if its getting hot enough to boil the coolant around the cylinders during high load I see how this makes sense.

ZX-Tex

iTrader: (15)

Excellent description. Well done. I totally agree.

DOHCPanther

So, after searching the net on the subject of bore vs. stroke I found a article from engine masters challenge. The short of it is on paper bore looks good for unshrouding the valves, giving dispacement, and increasing compression. But taking detonation into consideration it dosent work out o well. Of course the engine they tested on has a much larger bore than the BP but it still may be an issue. also the subject of cylinder wall thickness becomes a concern.

Another thing I read was to put your money in the big three; head, compression, and camshaft. If I save the 2500 from the crankshaft I could use that cash toward head porting work. The FM head is 2100 a little less than the stroker. The cam is not such an issue with the VVT and adjustable cam gear and the compression is basicly adjustable with the boost.

Also I read that valve shrouding could be reduced by milling the head.

Arggggg got to go.

sn95

iTrader: (2)

OMG, quit fixating on **** you can't change! Focus on moving forward with a positive and cost effective build. Stock 1.8 with mild overbore, multi-angle valve job + pocket porting on 99+ head with ported intake. Add 10-18psi boost from your turbo of choice and you are done!

rharris19

iTrader: (41)

So the 85.5 would be fine for an N/A car correct? Everyone keeps saying the walls would be too thin.

gospeed81

iTrader: (51)

You know how valuable my opinion in this matter is (building first motor in garage with HF tools ) ...but I would say yes, with a beefy radiator and good coolant reroute.

sn95

iTrader: (2)

If you are worried about the cylinder wall thickness, have a shop sonic check the bores before you have it bored. It will cost more, but at least you'll know for sure that the walls are thick enough.