"Pinning" the secondaries open.

[Paul Workman]

Originally Posted by scottfab

I think that's it in a nut shell. I value being able to disable the secondaries per the original engineering design because I like the idea of removing temptation from my sons and others AND because I just don't seem to have as many issues with that system as others.
You're right about fewer failures with fewer parts. Still I choose to leave the wipers on the car even though that would be fewer parts to fail.
Each to his own and we owe it to newbies to see a clear picture of removing systems IMHO.

You're not alone - far as keeping the SPTs intact. None other than Marc Haibeck suggests keeping them in place, and has them in his car. (and I STILL haven't gotten a good answer from him as to why. So...There's that for fair and balanced.

But, the analogy of comparing the wipers to the SPTs is overly severe to exageration. Of course you'd keep the wipers!

With regard to the secondaries specifically (excluding wiper or ashtray analogies, etc), or to the point of keeping them or not, the topic is way over wrought, IMO. Keep 'em if ya want, chunk 'em if you don't. But, for me (and many others, including most of the FBI gang) it comes down to this (and others can decide)

1) Da bastards will never fail me (again), including actuators, check valves, tubing, rubber connectors, or the vacuum pump: secodary issues in general WHICH is one of the most commonly mentioned problems on this forum, e.g., "My secondaries don't appear to be working...

2) Performance?? The SPTs span the center of the air flow column, creating turbulance and theoretically (at least) some impedance to flow, i.e., HP loss. I have no "before and after" data to refer to, I admit. But, referring to laminar flow characteristics of air in a runner column, the highest velocity is in the center of the column. Mathematically, the impedance increases with the square of velocity. (Guess where the SPTs exisit??)

SO! in pursuit of best performance, I know them being gone is not impeding air flow and thus performance (tho I just can't quantify it at the moment, the principal remains valid - at least IMO).

3) In my case, and that of "a few" FBI motors, the stock SPT plates are now too small to seal the post porting column anyway, making the issue of keeping them or not rather moot.

4) CAREFREE drivability! Woo Hoo!

@ this point, I feel like to do or not to do SPT delete has run its course. One has (at this point) enough info to decide, one way or another, with the exception of one last point: As I pointed out before, the next phase for the LT5 eliminated SPTs all together, going to a single injector per cylinder. This was a substantial change from the previous design, and being a frustrated automotive engineer, I have to ask myself, "if the dual runner design was initially used for "some" reason, what changed the minds of the engineers to revert to a siamese runner and single injector?" (which is essentially what we have when SPTs are eliminated and BOTH injectors run continously, no?)

An engineering friend of mine used to say, "Simple and elegant always trumps complex and wonderful!"

[WARP TEN]

[QUOTE=Paul Workman;154486]You're not alone - far as keeping the SPTs intact. None other than Marc Haibeck suggests keeping them in place, and has them in his car. (and I STILL haven't gotten a good answer from him as to why. So...There's that for fair and balanced....QUOTE]

In corresponding with Marc about my winter work, he just sent me a note saying that removal of the secondaries and all related hardware and system is included in the Haibeck 500 (now 510) package as a matter of course. Don't know if he has removed them from his car yet. --Bob

[scottfab]

Originally Posted by Paul Workman

...snip...
But, the analogy of comparing the wipers to the SPTs is overly severe to exageration. Of course you'd keep the wipers!

... snip...

Very well written list of advantages and of course my comparing to removing the ash tray and windshield wipers is mostly absurd but for some not.
If drag racing was the goal then not only secondaries would go but many many other unnecessary object with weight would too. Hell even the air filter goes. And as memory serves back in the 90s someone drilled holes all over the frame and front valence supports to lower weight.

It really is a mater of how extreme you want to go away from a well documented (FSM) car.
Removing secondaries is a completely legitimate decision to make once you've gone to the dark side
But so is keeping them in good working order and well exercised.
"but officer I was just exercising the secondaries"

[Paul Workman]

[QUOTE=WARP TEN;154492]

Originally Posted by Paul Workman

You're not alone - far as keeping the SPTs intact. None other than Marc Haibeck suggests keeping them in place, and has them in his car. (and I STILL haven't gotten a good answer from him as to why. So...There's that for fair and balanced....QUOTE]

In corresponding with Marc about my winter work, he just sent me a note saying that removal of the secondaries and all related hardware and system is included in the Haibeck 500 (now 510) package as a matter of course. Don't know if he has removed them from his car yet. --Bob

Well, now, THAT is an interesting development. I hadn't heard that before. Mebbe he will chime in and give us a peak at his current thinking? I do recall (I think) Marc saying his experience with and w/o the SPTs was around 5-6 hp (pls don't quote me) in his test. Just how one would pull that off; pulling the plenum and each of the plates, stems, and bearings, and sealing them, then reassembling the top end and making another pull or two while maintaining a close run to run engine temp...IF that is even what was done...would be difficult, I recon - even for the amazing "Marcster!"

OT, but in the same vein, Marc did some testing and determined (I think it was) about 6 hp increase on a 350 motor when opening the TB from stock to 63mm. Just for grins, I used an electronics analogy model (using resistors substituted for values of cross-sectional air impedance of a ported top end) and calculated the output power in watts and converted watts to hp. Voila! 6 hp increase!

Coincidence? Likely, at least to a degree. But, considering it costs about $475 to have a TB bored and trued up to gain about 6 hp (on a 350 motor) it makes me curious how much of a flow difference there is in a set of heads before and after SPTs are removed. Just a wild guess, but from what you say if Marc's 510 package includes removing the SPTs...there may be a few more ponies that he's discovered in his porting (he said as much, on one of my visits to his shop). So (me rambling on out loud here), if one is going to a 63mm TB (along with porting a 350 motor) - if removing SPTs buys another 4-6 hp, combined with a 63mm TB were looking at another 10+ rwhp, plus 5 or so more for some porting nuances (he mentioned), and there ya have an example of the continued refinement of the LT5.

Just rambling...

P.