Progress Report - 3.1L Running On The Dyno
The Purpose of this page is to provide a progress report related to my "3.1L Stroker Motor" Project. So here is some early feedback, now that the engine is assembled and running - [at least on the engine dyno.]
As of 21 Aug., 1998
My 3.1L engine is assembled and running [at least on the Chassis Dyno}. I am hopefull that I will have the engine operational in the car within the next two weeks. I know that a few of you have been waiting to hear how the engine worked out.
To say I am VERY happy with the engine is a huge understatement. While
it's power is not astronomical, it is however, spread over a LARGE power
band, like 4k-7k, and almost flat as a table,(more on that later).
For those who have joined this discussion late, here is the engine combo:
- F54 block,(turbo block, extra reinforcing between cylinders, in water jackets, best for the 3mm overbore)
- P-90A head,(this is the hydraulic one)
- triple SK's,(basically the same as webers, but a japanese version)
- LD28 crank w/240 rods, 240SX 89mm pistons
- Nissan Motorsports big header - 1 3/4 inch
- other mixed and matched parts to make a whole engine.
So net result? 3.1L motor. As I said in the response to the question about jetting, we had a heck of a time getting it right. I ended up paying about $550.00 for the dyno time, and it was no question worth every penny. I would have paid at least that for tuning the carbs with how bad off they were. We couldn't get an idle, the idle screws didn't even make a difference, the runs were very inconsistent, and the exhaust temps were sky high.
We were seriously concerned that we might burn a piston before it was done. Temps at half throttle and about 3-3.5k RPM, were over 1600 degrees in most cylinders. FYI, the temp sensors were mounted about 1.5 inchs after the header flange on the top side. For those of you who know nothing about temps, like I did just a week ago, they shoot for 900-1100 or so at 3000RPM and half throttle. For those of you engine experts, 1480 degrees is the optimum combustion temp, but if you set it for that, if you go lean for any reason, one quick hole in a piston, no charge. So the idea is to set it a little below that, and then it hovers in the 1300-1500 range at full throttle, max rpm, right where you want it.
Anyways, enough on temps, needless to say, we got it right. And to say the power was there, yes it was. Most of the runs were started about 3500 and run over 7000. And while theoretically, we weren't supposed to encounter any problems with the hydraulics, they seemed to be bleeding down at about 6900RPM.
The power would go from about 200-210hp, and drop 20-50hp in 200 rpm. So we thought that was what was happening,(bleeding down). Well, as the fuel curve got dialed in, the power kept coming. It turns out it was leaning way out at about 6900, not bleeding down.
The highest run we made went to about 7300RPM with the correct jets, and the power was still about 185-190, and clearly no bleeding. So the best runs produced about this power,(I don't have the sheets, so this is memory). run from 3500-7100 avg power: 208hp, peak power:224hp.
As you can see, the peak is just a little more than the average. at 3700, it was just under 200hp, at 6900RPM, it was still over 200hp. This is going to be an incredible car to drive when I finish hooking it up in the car.
Yes, dynos can be off, but he didn't put in a correction factor, and it was hot as all else in the dyno room,(~100 degrees). I can already hear some people saying, Hey, that is too little power for that motor. No, it should be just about right for the combo I have. I am just surprised that the power curve is so flat. Oh, and I just talked to a guy yesterday that told me that he had a 2.8L built and producing "just over" 500 hp with webers. I just laughed.
The cam, incidentally, is not for a hydraulic motor, so we are getting a little different profile than the specs, which are 270/280 duration, (exhaust/intake), and .460 lift,(the motorsport auto 2003 cam, made by schneider).
I fully expected,(as did the builder), that the motor would peak and drop off somewhere in the 5k range. I have heard many people say the stroker motor has a redline,(useful that is), of about 5500RPM. That clearly is not true with mine. I don't know if it is the combo I am using, or what. We did a through job of the balancing, building, and jetting, so I think that is a factor.
I feel that the head may play a small role as well, most people who have built a stroker, use an E-88, N-42 or similar. My personal feeling is the swirl chamber makes a large difference, (as well as an excellent balance job). I think the peak was about 5800, but as I said above, it was more like a small bump, not a peak.
Of course, there are a million factors that play into how well an engine runs, so I don't think I could say that X thing I did made it work as well as it did, it was a combo of everything.
I still intend to run the car on a chassis dyno when it is all set up, but that may be early next year before I have access to one of those. I expect that I will get 160-180hp at the wheels. Maybe 190hp if I am lucky.
So, P-90A not good for performance? I have to strongly disagree. I would say, however, that you need to insure you have good lifters. Bad ones will bleed down with even a stock cam. They are not cheap either, $42 each through Courtesy Nissan. That is a hefty price for all 12. Get the head off a good, clean, low mileage motor if you can. And of course, make sure you have the correct spring pressures.
For an aftermarket cam, seat pressure of ~100-110, and max lift of ~210-240, maybe 250, but that is pushing it. Always talk with the cam manufacturer, and work with them. I talked with Schneider extensively about my combo.
Lastly, use at least a turbo oil pump. If you are running an oil cooler as well,(I have adapted the stock one), use the automatic oil pump, it has a slightly higher output volume to make up for the oil cooler.
I know I didn't cover everything, because there is so much to say about
it, (the motor that is). If you have questions on anything, let 'er rip!
- Bob Hanvey
240 3.1 FINALLY