Secondaries? Pros and cons?

[Hog]

Originally Posted by A26B

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.

I just wanted to add a correction.
This engine should have been referred to as the MY1995 "upgrade" engine. It never made it to production as MY1995 was the last year of ZR-1 to be built, not the OBD2 engine as I did. The 1995MY upgrade engine would have had to qualify for OBD2, just like the LT1's did. Chev. was preparing for OBD2 in for MY94/95 with the introduction of the flashable ECM/PCM's.
To certify the 95MY uprgrade engine would have required a substantial effort, probably including a new ECM to include the missfire detection the OBD2 requires.

The lifters/followers were not rollers, 2 test mule engines were built either with a special Lotus lifter, or using camshafts that were developed FROM the info supplied from the Lotus piece.
The Lotus hydraulically variable device that fit into the space of the OEM lifters and would switch profiles to boost low rpm torque(the lack of was often criticized) and an upper rpm breathing to 475 bhp profile. But again my interpretation of Mr Behans report of the 2 1995MY upgrade engines isnt clear, the engines either used the Lotus variable lifter device as part of the 95MY upgrades, or used cam profiles with conventional LT5 valve actuation equipement, that were derived from testing with the Lotus device installed.

[Billy Mild]

Was that dyno of a stock car with the secondaries removed? If so I need to rip that out ASAP on my 1991. 469 WHP at the wheels is impressive.

[Hog]

Originally Posted by Billy Mild

Was that dyno of a stock car with the secondaries removed? If so I need to rip that out ASAP on my 1991. 469 WHP at the wheels is impressive.

I doubt these were chassis dyno numbers, but engine dyno numbers. I really wish there was a date on this graph

No that was the same engine, and same configuration. One pull with the port throttles closed for the whole pull overlayed by a pull with the port throttles open. As you can see, port throttles open allows excellent upper rpm breathing, PT's closed, no upper rpm power, but more torque(30 lb/ft)and growing) at 2500rpm.

This was a full open vs closed port throttle exercise. You gain 160hp and 30 lb/ft torque by having the port throttles OPEN vs. CLOSED.
The graph is really showing what happens when you turn that "Power Key". Obviously you want them opening if you are driving, maybe not if you are letting Junior take a date out in your car.

.

[Billy Mild]

How hard is it to eliminate the Secondaries? If I get my intake manifold off I only want to do it once, not multiple times. If there is power to picked up that is not costly here I would like that.

[Hog]

Originally Posted by Billy Mild

How hard is it to eliminate the Secondaries? If I get my intake manifold off I only want to do it once, not multiple times. If there is power to picked up that is not costly here I would like that.

I believe that power simply from removing the port throttles would be minimal, other reasons for their removal would carry more weight.
I suggest reading this entire thread and theeh other on Secondary removal, removal of secondaries, or secondary port throttle removal.

It also makes sense to do all maintenance work that can accomplished once you get the plenum pulled.

Others will have more valid input than myself.