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

[tomtom72]

Hey Gordon welcome to our asylum and I do hope that you find a ZR-1 that meets your approval. These are unique cars and our Brotherhood is unique in the corvette world.

I have to say that I'm out of my depth in trying to have a discussion about engine design with people that have already done it. I do hope that you find a car to buy because you seem likely to bring a good deal of knowledge to our community.


Tom

[gmonsen]

Thanks, Tom, I'm really close on getting one. Also, I have found the guys here to be just great. I'm going to Carlisle and hope to meet a lot of you guys personally there.

Gordon

[QB93Z]

Hi Gordon, I enjoyed talking with you and I am interested in your ideas about the LT5. I look forward to meeting you at Carlisle.

There will be a Westminster Maintenance Day on the weekend before Carlisle (20-21 Aug). Please stop by if you can and we will let you test drive some ZR-1's.

Good luck with your search and aquisition.

Jim

[Kevin]

Originally Posted by gmonsen

Thanks, Tom, I'm really close on getting one. Also, I have found the guys here to be just great. I'm going to Carlisle and hope to meet a lot of you guys personally there.

Gordon

gordon,
What part of pa are you from? I'm heading up to carlise mid day friday and would love to have another zr-1 to cruise up with

[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.

[sammy]

Originally Posted by 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

one would think that you would lose low end tq when going to the pinned open secondasries .but funny as it may sound the opposite is true . i did a conversion to as low mile 90 (10)k miles . and when we got done wiring them open with air craft wire and installing marks wonder full prom , the car had more grunt all the way through the rpm range and this car had the stk 345 gears .how it comes out i believe is how the prom is redone. knowing mark he really did his homework on this . to me it is a no brainier and a great mod to do . my buddy also says he hasnt noticed any loss in fuel mileage in about 1000 miles of driving since the change . i plan on doing this to both my cars asap