Secondaries? Pros and cons?

[KILLSHOTS]

Originally Posted by Paul Workman

On a 90 the "valet" key function is lost, i.e, must always be in FULL setting ALWAYS!** in that with the secondaries removed, the fuel delivery is split between both injectors, and should one injector be turned off, the calibration doesn't have a way to revert and a very lean situation results (according to Marc, when he sold me his chip).

From 91 on the calibration can be programmed to keep the system in FULL POWER. However, the 90s depend on that mechanical switch to remain in FULL 100% of the time. Those switch contacts in the 90s have been known to become tarnished over time, and electrical connections become sketchy. SO! I simply soldered a bridge (wire) across the two wires leading to/from the switch contacts, thus removing the possibility of the switch contacts becoming sketchy - or someone switching it to NORMAL w/o me noticing.

PROS (for keeping the system stock):

• At low throttle, as in city traffic, Graham produced some dyno graphs that show slightly higher torque is produced in the stock motor with the secondaries not activated.
  
• Although meeting emissions, even in some severe States, has been demonstrated - WITH the proper calibration - keeping them AND having the stock calibration chip handy, might make keeping the system intact.
  
• NCRS cars might benefit by keeping the system intact.
  
• It IS possible to pin (tie-wrap) the secondaries open to give one the option of running w/o secondaries and retuning to stock setup relatively easily by clipping the ties, re-plumbing the MAP, and installing the stock chip.

CONS (to keeping the secondaries)

• Throttle response lag when snapping to WOT, and between gears too, unless the throttle is held above a certain % during the shifts.
  
• The secondary intake valve becomes caked with carbon to the point of impeding WOT performance. This can be minimized when on a long cruise by going WOT to open the secondaries and then maintaining something like 10-15% throttle after WOT will keep the secondaries turned ON. However, this gets to be a nag real quick in traffic or when on hilly terrain.
  
• It is difficult to quantify due to practical matters e.g., removing the plenum to remove the secondaries, but the throttle plate rods run through the center of the laminar flowing air stream in the runner. This is never a "good thing", far as theory goes. For an all-out effort to gain hp, certain things are based on good engineering practice, if they can't be practically proven, and removing those plates/rods falls into this category. I'm skeptical of absolute numbers "before and after" removing the secondaries, due to difficulties in controlling all the variables that affect dyno results in the interim of removing them to re-test. But, the principles of laminar flow convinces me there is some advantage, maybe 5-10 hp would be about what I would guess.
  
• "What parts don't exist seldom break, and they don't cost anything!" If for any reason one has to go plenum diving more than once to chase a secondary problem, one might consider deleting it entirely...is what I did.
  
• If one ports the intake runners beyond 36mm, then the throttle plates no longer function as designed anyway. So, keeping them becomes moot and a detriment to performance.

Getting back to the loss of low speed torque resulting from removing the secondary port throttles (SPT):

From my personal experience, if there was some torque loss, I didn't notice it at all. But, mitigating circumstances includes the fact that I switched from the stock 46# dual mass flywheel to a 13# single mass aluminum flywheel at the same time. I don't know to the extent the FW mitigated some of the low end torque "loss" due to pulling the SPTs, but theoretically it would have resulted in more engine torque passing through to the drive train instead of being absorbed by the heavy dual mass FW. (Marc Haibecks inertia dyno sheets substantiate an effective 15 hp gain at the rear wheels by switching to a light aluminum FW.

In my case, the difference in FW mass calculates to a 11.9 ft# increase in rwt at peak power rpm (note: 4th gear). HOWEVER, the effective torque throughput resulting from the lighter FW increases with the rpm rate of change. The rate of rpm change is much higher in the lower gears, and so the mitigating effect of a lighter FW would also be significantly more than that 11.9 (effective torque) in 4th gear - perhaps exceeding the torque advantage of keeping the SPTs. (I believe that to be the case.)

AND, as part of my top-end porting mods, I realize a significant increase rwt across the full rpm range, compared to my baseline dyno results for my stock LT5.

This is awesome, Paul. Can't imagine a more complete explanation, answers my questions fully. The idea of going to the lightweight flywheel does intrigue me but I don't want "gear rattle." Or at least I don't think I do...what does it sound like exactly, and do guys have a problem with it after this switch?

Thanks so much for taking the time!!

[KILLSHOTS]

Originally Posted by tf95ZR1

To REHASH:

#56
http://www.zr1.net/forum/showthread.php?t=19823&page=6

But read the entire post for (+) and (-)

If I'm reading this correctly, it looks like there is a difference of less than half a point in both HP and torque at peak. That probably falls within "variances between runs" anyway. Unless there's something else that I'm missing? Thanks!

[XfireZ51]

I call this my "Stairway to LT-5 Heaven" dyno graph. It shows the progression of power and torque through stages of modification and tune. The bottom one demonstrates a ported top end with secondaries tied open. The throttle plates had been removed however but the shafts remained albeit w the least surface facing airflow. The calibration has an injector "turn-on" delay which is eliminated when the secondaries are deleted or at least it should be.

[Paul Workman]

Originally Posted by KILLSHOTS

This is awesome, Paul. Can't imagine a more complete explanation, answers my questions fully. The idea of going to the lightweight flywheel does intrigue me but I don't want "gear rattle." Or at least I don't think I do...what does it sound like exactly, and do guys have a problem with it after this switch?

Thanks so much for taking the time!!

With stock cams, and even with some custom phasing, there is very slight rattle, especially at the first start-up of the day when the engine is dead cold.

However, Marc increased my idle to about 850 to help with smoothing the idle, and that all but eliminated it.

As far as the rattle itself goes, it sounds like marbles rolling around in the transmission. It is noticeable? Yes. But, is it annoying? Well, that is subjective, and except for a cammed LT5 it is very subtle with good injectors and 850 rpm idle, IMO. (Note: My NOS injectors succumbed to alcohol in an insidious manner over a couple years. After replacing them, one of the unexpected bonuses was the near disappearance of the trans rattle.)

[Hog]

Originally Posted by KILLSHOTS

If I'm reading this correctly, it looks like there is a difference of less than half a point in both HP and torque at peak. That probably falls within "variances between runs" anyway. Unless there's something else that I'm missing? Thanks!

Lets make that a bit bigger.


From one of my previous posts, much more than 1/2 a point at the power torque peaks. Make sure you are NOT comparing teh numbers noted on teh actual graph, as they are giving power/torque numbers at 3900rpm which is NOT a peak for any of the curves. For peak outputs compare teh actual numbers at the top of the graph labelled MAX POWER/MAX TORQUE.


"You can see the torque advantage of 30 lb/ft at 2600rpm for the closed Port throttles, but at just 4500rpm, the Closed Port Throttles give up roughly 45hp at 4500rpm to the open Port Throttles. At this same 4500rpm, the CLosed Port Throttles are all done and power falls off abruptly after than as airflow is choked off It should be noted that the low rpm torque difference between the Open vs. Closed Port throttles would increase if the dyno run was started at a lower rpm.
It appears to be a significant low rpm difference between Open and Closed Port Throttles.

The Open Port throttles continue to build another roughly 125hp from 4500rpm to their peak of 469hp at 6600rpm or so.
All totalled the Open Port Throttles are worth an extra 160hp vs the Closed Port Throttles.(469 vs 309hp) and an extra 428 lb/ft of torque (417 lb/ft vs 389 lb/ft) when the entire vastness of the LT5 rpm range is considered."

To keep or remove the Port Throttles, THAT is the question. And the true answer for you personally is exactly at what rpm you drive.launch/cruise. Get under 2000rpm and the torque difference gets larger, at least on the graphs.

Basic answer to one of your questions, no, you cant retain your "power key" function once you delete your Port Throttles.

[Paul Workman]

The graph below is veering OT, but with regard to PORTING in conjunction with removing the SPTs, one of the myths so often bantered is how opening up the runners will slow velocity and thus "kill" low rpm torque. Bullshiet!

Apparently, the LT5s (especially the 90-92s) were starving for air (something addressed, perhaps, with the Gen II LT5 that was destined for the 95 ZR-1).




This graph depicts the torque plotted for my stock LT5, and after being fully ported. The motor retains the stock cams AND throttle body (see my signature for more details).



For planning purposes, removing the SPTs in conjunction with porting appears to buy back the 25+ pounds of torque advantage through 4000 rpm when in NORMAL power mode. And, of course, above 4000 rpm torque comparisons for the ported LT5 simply runs away from the stock performance. What a shame Graham's new GEN II LT5 baby never saw the light of day. To use a phrase borrowed from Mike 100, there's a lot of "low hanging fruit" available with the LT5 - and 500+ hp is possible w/o compromising the nikasil liners or stock cams; i.e., the reliability.

[Hog]

Was the OBD2 LT5 engineered for roller cam followers, I cant remember?
EDIT-The mods I was referring to were part of the planned 1995MY upgrades to 475 bhp, that ended up being as tillborn project, unfortunately. It was incorrect for me to refer to the 1995MY upgrade engine as the "OBD2" engine although the upgraded engine would have required OBD2 qualification for MY1996.

[A26B]

Originally Posted by KILLSHOTS

........... The idea of going to the lightweight flywheel does intrigue me but I don't want "gear rattle." Or at least I don't think I do...what does it sound like exactly, and do guys have a problem with it after this switch?

Thanks so much for taking the time!!

I also have the 13# Fidanza Flywheel in my 94 ZR-1 with a 415 LT5. Cams are moderately "lumpy." I don't have any trans gear rattle as long as the clutch is depressed. I do have gear rattle when it's in neutral and the clutch is engaged.

The gear rattle is of no consequence to me because I am seldom ever in the car with the clutch engaged, in neutral. Some folks do that at stop lights, I don't.

The lighter flywheel takes a little street driving adjustment because of the lighter rotating mass & faster spin-up. Likewise, if you are drag racing, the correct launch rpm & clutch release is more critical, walking a fine line between bog & excessive wheel spin.

Doug Rippie used to offer a 24# iron LT1 flywheel for the LT5 that was popular. It helped mitigate the street driving & drag racing issues while shedding several pounds from the D/M flywheel.

I would expect the heavier flywheels would also help reduce the transmission rattle.

Fidanza 13# (alum billet)
Jerrys Gaskets 18# (alum billet)
Jerrys Gaskets 22# (alum billet)
Stock D/M 33#
McLeod (I don't know the weight, guessing around 16~18#)

[A26B]

Originally Posted by Hog

Was the OBD2 LT5 engineered for roller cam followers, I cant remember?

I don't know if the OBD2 is the same as the 95 MY 475Hp LT5 that never made it to production, or not. If it is, the answer is no.

[WARP TEN]

Originally Posted by A26B

I also have the 13# Fidanza Flywheel in my 94 ZR-1 with a 415 LT5. Cams are moderately "lumpy." I don't have any trans gear rattle as long as the clutch is depressed. I do have gear rattle when it's in neutral and the clutch is engaged.

The gear rattle is of no consequence to me because I am seldom ever in the car with the clutch engaged, in neutral. Some folks do that at stop lights, I don't.

The lighter flywheel takes a little street driving adjustment because of the lighter rotating mass & faster spin-up. Likewise, if you are drag racing, the correct launch rpm & clutch release is more critical, walking a fine line between bog & excessive wheel spin.

Doug Rippie used to offer a 24# iron LT1 flywheel for the LT5 that was popular. It helped mitigate the street driving & drag racing issues while shedding several pounds from the D/M flywheel.

I would expect the heavier flywheels would also help reduce the transmission rattle.

Fidanza 13# (alum billet)
Jerrys Gaskets 18# (alum billet)
Jerrys Gaskets 22# (alum billet)
Stock D/M 33#
McLeod (I don't know the weight, guessing around 16~18#)

I took the opposite approach with regard to the flywheel when Marc did his 510 package. I stayed with the dual mass flywheel because unlike Jerry and others, I do put the car into neutral every time when I come to a stop. It is easier on both my leg and the throw out bearing. I have heard the gear rattle on other cars and I do not like it. As a result, my 510 package is technically about a 500 package but anyone who wanted it all could install a Fidanza. I have also heard some people complain that the lack of mass in the Fidanza sometimes makes getting off the line more difficult. As I recall Marc said a stock dual mass flywheel will handle up to about 550 hp.

I also had the secondaries removed when Marc did his work and I notice no issues without them. The car runs strong and although Marc and others say you do lose a little low end torque, I certainly don't notice it.--Bob