anyone have a near stock zr-1 with the secondaries removed?

[gmonsen]

Another note. I don't know what the cubic volume of the plenum is or how much room there is under the hood between it and the hood, but, if the plenum is less volume than the engine displacement, you can add quite a bit of power at the top end by increasing the size of the plenum. Given the complexity of it mechanically, you would probably have to just add to the height of it in the middle and back side closest to the firewall, but that would add a fair amount of top end power.

If someone actually designed an entirely new plenum and runners setup, you could gain more than all the porting usually done to the heads. PITA, given the design, but some real gains. I built a custom 3 rotor rotary engine that displaces 4 liters in like metrics to piston engines and tripled the size of my plenum to equal the displacement of the motor and added 35 rwhp. Lotus probably sized the plenum to fit the engine bay and between the size and the length of the runners achieve what they thought was the best balance of low torque and high power. A bigger plenum and shorter, stubbier runners would seriously add to the top end power and should fit. Just a pain to transfer the throttle butterfly setup.

Gordon

[tomtom72]

Gordon, yes and no......both injectors are mechanically the same, flow wise. The necessary pulse with for each injector is halved when the conditions for secondary operation are met. In that circumstance each of the 16 injectors are actually only provided with 1/2 the pulse width needed to release the necessary amount of fuel vs load vs throttle position. The recalibration of the fuel map to delete the secondary control mechanical parts takes advantage of the fact that at some very low TPS % you can have all the injectors firing accurately and not loose enough ( I'm told by people that have this mod ) low end to notice. Now I will allow that most of the people that have this mod also have other major top end work.

At a seminar this year at our Gathering, Dave, Graham, & Jim Ingles spoke about the two injector set up and some of the reasoning. A lot of the reasoning was for stupid EPA and Federal noise standards and CAFE numbers. They knew that they could absolutely meet all those stupid rules if they did the primary./secondary thing with a power switch. They could argue, successfully that all the testing should be done in the "Normal" power mode vs the "Full" power mode as the car is intended to be driven in "Normal" until the situation demands extra power......I know there were proly some raised eyebrows at the EPA but Dave & Company got it past them. Dave & Co also said that they were knew that they could meet CAFE & Emissions without the secondary system being a commanded system, but they were not sure about the drive-by noise level test mostly.


Tom

[tomtom72]

I type too slowly to keep up!

There has been experimentation in the area of adding plenum volume. The under hood clearance is an issue so the people that added plenum volume did so by dropping the floor as there is some room to allow this and not have clearance issues to the coil packs. I'm just not sure if this has benefit on a stock displacement motor or if you need more cubic inches to take full advantage. Also, although not specific to your point about plenum volume, it is common when porting aggressively to remove the dividers in the legs and the head ports to some degree or even eliminate the dividers in the legs entirely.

There is a thread here where a member did some re-engineering of an LT5 to make it a 427 cu. in. motor. If you can find that thread it has some interesting photos. We also have some pictures of the second design LT5 in the proto-type section. There was also a very interesting seminar given by Dave & Graham at our 20th anniversary Gathering last year about the second generation LT5.


Tom

This is the link to the 427 thread: http://www.zr1.net/forum/showthread.php?t=10268

[gmonsen]

TomTom... I hear you, but still feel that there is a better way to accomplish the added power without losing low end torque. The thing is that the secondary cam lobes have much longer duration compared to the primaries... for good reason. The shorter duration will generate more torque at low rpm faster. The idea of just opening everything up and shoving as much air fuel into the motor as that allows seems fairly crude, given what you could do by changing where the secondaries come on, increasing plenum size, maybe changing the runners, and perhaps even adding bigger secondary injectors.

Plenum size is just relative to any engine size. The general rule of thumb is that plenum volumes smaller than the engine's displacement emphasize torque in the lower ranges and plenum sizes equal to or larger than engine displacement emphasize power at the top of the rpm range.

I would add that I don't own a ZR1 yet, though I hope to have one in the garage next month. I have a few cars right now where I have reworked the engines a lot (too much) and am worried I might do the same thing with the LT5. I think this motor could make 500-550 whp without changing the displacement. I think you could add 50-75 whp just with the plenum and injector changes, depending on how much room there is to increase the size of the plenum.

Gordon

[Paul Workman]

Originally Posted by gmonsen

I don't know what types of injectors are used and what their flow rates are, but there could well be problems with this approach, because the secondary injectors should have more flow than the primaries and some injectors don't work well when the duty cycles are very low, which they would need to be down low in the rpm range. The whole premise of the motor was to make a lot of torque down low and yet have the air flow and fuel to make max power at the high end of the rev band. The approach you are thinking about will probably reduce torque at the bottom end and might add some to the mid-range. The top won't change at all. I would think trying to open up the secondaries a little sooner and retune would be a better approach.

Gordon

Hello and welcome!

Moving from hypothetical to empirical LT5 (secondary facts and characteristics), I found these departures from the "textbook" as you may soon discover (hopefully):

1. Both injectors are 21# ers.
2. Short PW issues (apparently) become more prevalent with higher flowing injectors and or fuel pressures. I, and many others running sans secondaries can put to rest any concerns about these injectors able to operate at low PW under low throttle demands.
3. In short, the secondaries open along an inverse, exponential curve (not a straight line) according to rpm and throttle position, e.g, just off idle (1500ish) at 70% throttle will trigger the secondaries, but as rpm increases, the amount of throttle demand resulting in the secondaries opening drops dramatically. Furthermore, once opened, they are programmed to remain open over a wide range of operating conditions until throttle and rpm levels drop below a much lower threshold curve than was required to open them.
4. Practically speaking, unless the power switch is turned off, mid range power comparisons with or without the secondaries installed is somewhat moot due to the fact that under loads where mid range torque was needed, the secondaries are already open!
5. Ah, the plenum...AND runner length, & the velocity vs. volume thing; bring Helmholtz into the picture, and things get really interesting, huh? To each his own, but build me a system that will give me a flat torque curve from just off idle all the way to the rpm limit of the motor...and the more (torque) the better, of course, and you have my attention. But, if peak torque or hp is of ultimate necessity, then usually one or the other has to suffer somewhere. I hope you are willing to share the "Holy Grail", should you find it.

I'm gonna guess and say that most that have eliminated the secondary throttle plates for one reason or another probably have other flow mods in place. Such is the case w/ me. So, the two graphs below are "apples to oranges", far as comparing goes, but one is with my stock engine, and the other is after being fully ported, optimized exhaust, and tune.

I don't know what significant information can be gleaned from the results of these drastically different motors, but in the context of the general discussion, I thought they'd be interesting in their respective right, no?

My stock LT5 (note the leaning was due to the secondary fuel pump failing)



This is the same motor after being fully ported according to "FBI" models that demonstrate proven characteristics I particularly like.



And, rules and theories and empirical data that apply to 2-valve motors struggle to apply absolutely to 4-valve, dual intake runner motors - or at least to the LT5's design. For comparison, look at the characteristics of a stock(?) LS7, the torque and power curves in particular, compared to the (350 ci) LT5.



For a comparison of an LT5 a bit closer to the LS7's cid, there is this: a 415 cid (stroked and sleeved) LT5:



I've rambled too much (as I tend to do..)

P.

[gmonsen]

Paul... Thanks much for the data. Haven't really done the math, but my gut take is that its pretty much as I expected, though the scaling of the first 2 graphs is a bit different. From looking at the shape of the curves, the modified motor has a lot more midrange torque and relatively less torque at the bottom end. The base motor seems to make about 280 ft lbs at 2000 and peaks at 330 or so, which is 16% higher. The modified motor starts at about 300 ft lbs and peaks at 377, which is 26% higher.

As to the injectors, I have to look up the model number you mentioned. I am used to thinking of injectors in terms of how many cc's they flow, like 850cc Bosch's or 1600 cc Bosch's or whatever. When I use a larger flowing injector that I want to work down low at lower pulse widths, I like Injector Dynamics modified Bosch's, because the take the pinhole and run it out through 6 channels, like the spokes of an umbrella, so the fuel is better atomized, which helps at low rpm and low duty cycles.

I'm not an engineer, but read a lot and talk to motor builders a lot over time, so I can't quote Helmhotz. But, I have empirically tried differing sized plenums, different length runners, tappered versus non-tappered, and a lot of work on header diameters and lengths, as well as trying exhausts with multiple pipes controlled by cutouts to increase flow velocity. For instance, I found that cylinder temperatures varied from front to back on some motors and that differences of an inch in header lengths would improve flow and pulsing because of better equalized velocities, since heat changes velocity.

Most of my better experiments have been done with an E30 M3 piston engine and 2 and 3 rotor rotaries, all NA motors. Definitely spent more than a college engineering degree on my learning process! I agree about getting a flat torque curve, though I'll say that my old Ferrari 512 had more torque up high than down low and it really gave it a bike-like kick!

Sorry for all this talk, since I don't even have a car yet, but, honestly, this motor is just such an exciting design that I can't help thinking about it.

Gordon

Gordon

[XfireZ51]

Gordon,

What the hell are you waiting for?

[Paul Workman]

Originally Posted by gmonsen

Sorry for all this talk, since I don't even have a car yet, but, honestly, this motor is just such an exciting design that I can't help thinking about it.

Gordon

Gordon

Well, join the club. We love to hear about experiments and to compare notes. I'm still on the steep side of the learning curve of this motor, with no leveling in site. There are sooo many nuances and epiphanies associated with this motor that pushrod motors, for me, seem almost boring!

Ya might as well get off the sidelines and get your feet wet. Oh, and bring some cream for that permagrin you're gonna get!

P.

[Kevin]

as for why I started this thread, I've decided I'm going to pin the secondary plates open and get a new chip for it. if I don't like it i'm out $200 and if I do then I finally get rid of this stupid secondary system.