FWIW, the GT35R compressor map indicates it's right around the cusp of the 65% efficiency line at a pressure ratio of 3:1 for a 2.0L engine turning 9000rpm at 90% VE, so a 1.8L engine will fall just inside the efficiency zone at that speed. Is this an area where a larger turbo will make more power by virtue of its better efficiency? Yes. If the turbine housing of a GT35R is a limitation in this area, then it is apparently the real limiting factor (as you asserted).

Your suggestion regarding the longer travel for the fuel/air charge with a stroker motor is interesting, but the charge should be filling the displaced area at least the same rate the piston is moving when the piston nears the end of its travel (as per the inertia effect). What is a proven issue however is the increased velocity of the air charge (due to increased piston acceleration) crosses the threshold of laminar port flow at an earlier point (lower rpm), which makes port efficiency an increasingly greater issue as piston acceleration is increased with a smaller rod/stroke ratio.

Long rod won't do any good if your pressure ratio doesn't permit it, agreed.

Yes, my Ford 2.3L isn't an EVO, but as you mentioned briefly, the reason why porting the head in an EVO won't significantly increase low speed VE is design specific, not displacement specific. FWIW however, if increasing VE at low rpm enables the turbo to spool a bit quicker (as in the case of my 2.3L Ford), than it does increase power nonetheless, albeit indirectly.

 

i don't know anything about the chevy 302, but my guess as to why they chose a bigger bore block with a smaller stroke crank was so they could deshroud the valves for better flow.

but im not sure how good of an example this is when in the situation the displacement is legally limited by a sanctioning body, while we aren't because we are just doing this for fun.

unfortunately, we don't have the option to pick and choose block bores with ease on our EVO's and a simpler way to increase displacement is with going a bigger crank.

 

I'm not confused, and pardon if I don't devote my time to a mental exercise at 7:30am. YOU claimed overboring, and no overboring was done in creating the Chevy 302. I define overboring as deliberately increasing the bore, which didn't happen, period.

I'm not debating any other theoretical issue, of which we probably agree.

 

And not creating an entirely new stroke for the sake of this racing series undoubtedly made the Chevy bean counters happy as well.

 

That probably arose from the fact that

Your comparing a stroked rebuilt car to the same car owned by the average consumer. Of course the stroked engine will more likely be pushed harder and will wear faster.

Your comparing an engine built by the owner to a factory built one, in some cases the personally built motor will be of better quality, but you would think, more often than not, that chance of something going wrong or being out of tolerance would be greater when compared for engines built for the masses.

 

To provide an opinion in response to original question (imagine that!) :

There is no 'yes' or 'no' answer to this question.

Do stroked motors post potentially increased reliability and longevity concerns? Yes. Increasing the stroke increases forces on critical parts of the rotating assembly, which increases heat, influences wear characteristics, and amplifies imbalances.

Can these concerns be largely alleviated through careful building/balancing, upgraded fasteners, and attention to detail? Yes. But you should keep in mind there are no guarantees, especially if one loses track of the fact that a long stroke motor will typically reach its mechanical limits at a slower crank speed, so plan the rest of your setup accordingly if reliability and longevity are important to you.

 

Well I am running a 2.3 with what would generally be considered a smallish turbo (FP White Rabbit) and I am only running it to about 7500 rpm. Why? Bcause the spool up is very fast and I drive my car on the street, I am rarely in the 7000+ range day in and day out. I like having the quick spool up, I have very good torque lower in th rpm range and to me it is just more fun to drive. I was however somewhat concerned with the piston speeds and the balencing of the internals, my engine builder balence the rotating assembly with all drive pullies, the flywheel, and the pressure plate on the crank to within 1/10th of a gram and like I said I have the rpm cutoff set at 7800 but have not even hit the cutoff yet. I would like to think that such a relativly unstreesed combination will last for some time. And I really like the way it responds on the street...

 

Nice discussion, most of the posts are way over my head, but it's enjoyable nontheless.

My long term goal would be one of the "smallish" factory manifold turbos with a stroker motor for a killer street setup. I used to autox regularly, but haven't done so in a few years (babies, houses, and work will take up a lot of your weekend time). I'd like to get back into it, and maybe his the drag strip for giggles and smiles.

I'd like an "11second" 1/4 mile car, just as a benchmark of performance. I think I can achieve this with a stroker, slightly bigger turbo, and supporting mods. I also want to stay flashed and will only ever run pump gas for simplicity. This seems to be reasonable, with people running low 12s on stock turbo. The stroker may be overkill, but I think it's the best/only way to get killer low-end that will be lots of fun for most of my driving. I would keep the revlimit at 7500 or below, which I think would help the reliability, along with a proven engine builder.

Thoughts?

FB

 

It's been demonstrated that one doesn't need to tear into the engine to dip into the 11s, but if torque and street wallop is what you're after, a stroker and a smallish turbo definitely fits the bill.

All you can do is adhere to meticulous prep, assembly practices, and a reasonable rpm limit. I'd suspect the longevity of a properly built setup would be superior to someone using a GT35R on factory internals.

 

If you could, i would really like to see a dyno of your setup as it sounds like a lot of fun.

I think you made a wise choice in having your setup balanced with such precision.

to the contributors of this thread

 

Shiv will be here to tune (in Dallas) not this weekend but next so I will have some numbers then.

As an aside, I went driving with the local Porsche club up in the Arkasas mountains two weeks ago. Right now I have it set pretty rich (10.5-10.7 or so in the upper end) just to make sure it is safe, and I backed off the timing a bit and was only running 20 lbs. None the less I was more then able to keep up with the fastest of the Porsche's on the run (2002 996tt X50 with Moton's) and I found myself running 4000-6500 rpm's just about the whole time exept when passing. I hit 20 lbs at around 2600-2800 rpm so any time I touched the gas pedal I had instant boost. The point is my powerband is VERY flexable, I never found myself having to downshift to pull out of corners and I could more then keep up with not only the other Porsche's, but any road condition which presented itself. Like I said, I have my car set up for the street, as a matter of fact my car has not even been on a track (yet). I can appretiate having a high strung 2.0 with a big turbo, but that would not fit my goals. I know that there are cars out there, even a lot of other Evo's, that would rape me on a highway pull, but if we are just accelerating from a stoplight in a normal fashion and we both get on it I will hand a lot of other cars their as$.

I will have some dyno number to show before long though....

Mods:

2.3 stroker
Light head work (mainly I blended the bowls and removed casting flash in both the ports and chambers with 1mm larger valves in/ex)
HKS 272's in/ex
Works valve spring/retainers
Cam gears
FP White Rabbit
TBE w/resonating test pipe
Upper/Lower piping
Xede/XFlash (boost cut removed and 7800 rpm redline)
Greddy Type S
AEM intake (wanted to stay stock but upper pipe would not allow)
SSautochrome header w/2000 degree JetHot coating. (cracked once and had rewelded after I temporarily put stock mani back on and FELT a loss)
O2 housing

I think that's all of the engine mods.....

 

how is your clutch holding up?

 

I am running an ACT street disk. I have actually used an Exedy twin but I did not like the chattering or the sudden take-up. I sometimes use my wife SUV when hunting or going to our farm and she just could not drive the Exedy, and this is after driving a stick for five plus years. So like I said I went to an ACT.

That being said if I downshift to say third and give it gas while releasing the clutch it will slip sometimes until I let off and give it a chance to catch up, but overall I really like it because it drives like stock (like I have stressed, this is a street driven car and I do not want to put up with anything that makes the car more difficult to drive) but I do believe that with the stroked engine and the tq level that I think I am getting to, it may be a wee bit stressed. I have thought about a sprung six puck to increase the lbs per sq/in on the disk, but I have driven an unsprung six puck and it was BAD. If the sprung six puck does not have the terrible chattering takeup of the unsprung then I may slip it in there next time. I hate doing the clutch on these cars, it will be about the fourth or fifth time I have done one, but what the hell, it is just a good Saturdays work!

I will however wait until the ACT street disk I have in now is done befroe I crack that nut open again....

 

Here you are going into semantics for the sake of arguing. If you read my posts again you will see the concept I am trying to illustrate.

If stock bore is bore limit (whether physical or set by the rules), then that is the bore. Given a raw casting any good development company will push the bore limit which in all probability will exceed stock bore, rules permitting. Fact remains.. destroking is never a target unless there are extremes like weak and unstable bores - and this usually happens only with poorly designed thin wall, short open deck blocks that run large stock strokes and are designed for low RPM, low power. The Evo block does not fit into any of that either.

I think you post well and make sense most of the time but there are several fundamental and critical issues that we do not agree on and this is one of them.

 

Here you are assuming that you will be operating at engine speeds equal to the stock stroke engine. This assumption should not be made. Comparisons should be made with massflow normalized where the stroker is at a large advantage. Engine speed is by far the largest factor since inertial loads increase as a square of it.


Stock 1997cc

Bore---------------------------------------------------- 3.346"
Stroke-------------------------------------------------- 3.464"
Redline------------------------------------------------- 8500 RPM
Volumetric flow at 100% VE*---------------------- 300 CFM

Mean piston speed---------------------------------- 4772 FPM
Peak piston speed----------------------------------- 8035 FPM

Peak piston acceleration [TDC (tension) ]------- 4597 G
Piston acceleration at BDC-------------------------- 2512 G



Stroker 2370cc

Bore---------------------------------------------------- 3.385"
Stroke-------------------------------------------------- 4.016"
Redline------------------------------------------------- 7168 RPM
Volumetric flow at 100% VE*---------------------- 300 CFM

Mean piston speed---------------------------------- 4664 FPM
Peak piston speed----------------------------------- 7996 FPM

Peak piston acceleration [TDC (tension) ]------- 3974 G
Piston acceleration at BDC-------------------------- 1884 G


*100% value for ease of calculation. Flowrate equalized between both examples.

1) Mean piston speed on the 2.0 is higher by 2%
2) Peak piston acceleration on the 2.0 is higher by 16% at TDC, 34% at BDC.
3) Not only is the engine experiencing these higher loads, but it is experiencing them at a rate faster by 18% . Finite cycle life of all components is being used up quicker.

This is true. However, like I have mentioned, there is no need to turn a stroker engine to matching RPM since it has a flow advantage at lower RPM. Equal power, at lower RPM.