"Pinning" the secondaries open.

[robbz28]

I have found mixed replies to this question on the internet but nothing as direct as I would like. I had a vaccum leak and it was causing my secondaries to only open some of the time. So I pulled my plenum, did some checking and managed to get the leak down to a manageable amount, but I went ahead and used a tie strap and tied the actuators open on both sides. (My car has the LPE 530 kit on it where it is in "full" mode at all times) I figured what would it hurt, what's the difference in this and removing the guts completely. Anyone else done this? Any adverse effects? Been running my car like this for about 500 miles and no issues yet.
One more question, anyone ever run any 100 octane low-lead aviation fuel?

[GOLDCYLON]

I believe Dominic has pinned back his butterflies. XfireZ51

[mike100]

100LL used to be a cheap way to get some octane to run nitrous on an 11:1 street-strip carbed muscle car I had, but if you still have catalysts, look out, it will quickly break the substrate up into rattling chunks.

[robbz28]

100LL used to be a cheap way to get some octane to run nitrous on an 11:1 street-strip carbed muscle car I had, but if you still have catalysts, look out, it will quickly break the substrate up into rattling chunks.

I'm not 100% certain on the cats, I think they are there, but one tank probably wouldn't hurt. My car has 12:1...but it runs good on 93, just wondering if there would be a noticable difference with the 100.

[Kevin]

100LL used to be a cheap way to get some octane to run nitrous on an 11:1 street-strip carbed muscle car I had, but if you still have catalysts, look out, it will quickly break the substrate up into rattling chunks.

i knew the 02 sensors would have a problem but gas + flame fixes tat

[XfireZ51]

Was your calibration modified to run 2 injectors all the time? By opening the secondaries permanently, air is moving through the secondary runner as well. I suspect there some loss of velocity thru the primary runner but primary injector is spraying fuel only into one air stream while secondary air is getting into chamber without any fuel. You're getting enough fuel but not an even mixture IMO.

[XfireZ51]

I believe Dominic has pinned back his butterflies. XfireZ51

I did originally and modded the cal. Now they are completely out.

[GOLDCYLON]

I did originally and modded the cal. Now they are completely out.


Good man

[robbz28]

Was your calibration modified to run 2 injectors all the time? By opening the secondaries permanently, air is moving through the secondary runner as well. I suspect there some loss of velocity thru the primary runner but primary injector is spraying fuel only into one air stream while secondary air is getting into chamber without any fuel. You're getting enough fuel but not an even mixture IMO.

Dont know...i will call LPE and find out tomorrow...makes sense with my hesitation.

[PhillipsLT5]

You should be able to buy 100 unlead race gas, it will be pricey, $6 to 8 per gallon
This should help
http://www.osbornauto.com/blend.htm

[robbz28]

You should be able to buy 100 unlead race gas, it will be pricey, $6 to 8 per gallon
This should help
http://www.osbornauto.com/blend.htm

The only reason I asked is because my cousin has a crop dusting service just down the road from me and he has a big ol tank of 100 LL.

[Hib Halverson]

If drag racing is your thing, disabling the port throttles might make sense.

Otherwise, on 350s and 368s, the car will probably accelerate quicker, if the port throttles are working. This is because at low rpm, with the port throttles open or removed, air velocity is very low and that decreases torque at the low end and the beginning of the mid range. Engines larger than that are, for the most part, immune from the low air port velocity problem.

As for 100LL, do not run leaded fuel if you have cats or oxygen sensors. It renders both useless in short order. Also 100LL doesn't work as well in a high-rpm LT5 as it does in a low rpm aircraft engine. Finally, it greatly decreases spark plug life.

You're much better off mixing 100 unleaded race gas with pump gas.

[Paul Workman]

If drag racing is your thing, disabling the port throttles might make sense.

Otherwise, on 350s and 368s, the car will probably accelerate quicker, if the port throttles are working. This is because at low rpm, with the port throttles open or removed, air velocity is very low and that decreases torque at the low end and the beginning of the mid range. Engines larger than that are, for the most part, immune from the low air port velocity problem.

Hib...

From the perspective of one that is running sans SPTs, you'd be (pleasantly) surpised to know that ain't so!

Referring to the FSM related to conditions for the secodaries to open, accelleration so light as to keep the SPTs closed is such that velocity is more a factor of the TB plates than runner cross-sectional area. In other words, even moderate throttle demands and speeds will trip the secondaires open - making the arguement of whether to eliminate the SPTs or not becomes MOOT for practial purposes.

However, something I think we'd all be interested in is the affect running sans secondaries might have on emissions compliance. The question has been posed several times, but perhaps Sammy being the exception, to my knowledge nothing in the way of conclusive data has come to light.

From my experience in driving w/ and w/o secondaries in traffic the difference is subtle, BUT it is there. Running w/o those pesky things really makes the LT5 behave in traffic soooo much nicer...is/was my opinion. And, then there's the benefit of having the secondary port valves constantly being washed by fuel. Clean valves are always better than dirty ones from a performance perspective.


P.

[scottfab]

... snip...
. And, then there's the benefit of having the secondary port valves constantly being washed by fuel. Clean valves are always better than dirty ones from a performance perspective.
P.

Depending on how you drive, washing the secondary port valves is not a problem. WOT was made for that. (Wash Out Tube)
I have more trouble with the wipers hardening for lack of use. I could just rip them off and toss them but I think keeping things in good working order is best. :-D

[Paul Workman]

Depending on how you drive, washing the secondary port valves is not a problem. WOT was made for that. (Wash Out Tube)
I have more trouble with the wipers hardening for lack of use. I could just rip them off and toss them but I think keeping things in good working order is best. :-D

Parts that don't exist don't cost much and they NEVER fail.

I've had it both ways - have real (not hypothetical) knowledge and I'd not go back to them even if it were an option (not in my case).

I'd bet once you pulled them too, you'd need a much better reason than "working order" to go back.

And nowhere has the topic of performance @ WOT been discussed.

Well, do whatcha want. The pros for NOT having them (for me) outweighs the cons by a wide margin. But, your mileage may vary!

P.

[scottfab]

... snip

Well, do whatcha want. The pros for NOT having them (for me) outweighs the cons by a wide margin. But, your mileage may vary!

P.

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.

[Blue Flame Restorations]

Parts that don't exist don't cost much and they NEVER fail.

I've had it both ways - have real (not hypothetical) knowledge and I'd not go back to them even if it were an option (not in my case).

I'd bet once you pulled them too, you'd need a much better reason than "working order" to go back.

And nowhere has the topic of performance @ WOT been discussed.

Well, do whatcha want. The pros for NOT having them (for me) outweighs the cons by a wide margin. But, your mileage may vary!

P.


Having less chance for vacuum leaks is what motivated me to have Pete remove mine. Glad we removed them.

One less thing......

[mike100]

I would be curious to try a before and after emissions test.

[Fully Vetted]

Having less chance for vacuum leaks is what motivated me to have Pete remove mine. Glad we removed them.

One less thing......


Yep. Pete gutted mine as well.

[sammy]

i will tyr to get ahold of john and see if he has a copy of the test or can give me the new owner

[Paul Workman]

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.:icon_scra So...There's that for fair and balanced.:p

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...:blahblah:

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!:icon_thum

@ 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!" :dancing

[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.:icon_scra So...There's that for fair and balanced.:p...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]

...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 :-D
But so is keeping them in good working order and well exercised.
"but officer I was just exercising the secondaries" [-X

[Paul Workman]

[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.:icon_scra So...There's that for fair and balanced.:p...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.