Eliminating the secondaries

[WARP TEN]

Originally Posted by Hib Halverson

With a 350, I've never been a fan of deleting the secondary port throttles because it degrades dirivatility and decreases torque output on the low end.

During the 20 years I owned Barney, my purple '95, the two times I had trouble with the SPTs, I repaired them rather than eliminated them.

For a 368...maybe, bigger than that, yeah, I'd get rid of them along with appropriate cal changes.

For the record Hib I had Marc remove mine on my '95 when he did his porting. I never had a driveability problem and the engine always seemed to have plenty of torque. Of course there were several variables involved besides the elimination of the secondaries. But I was happy with the way the car performed around town and on the track. --Bob

[Perry Mitchell]

This is how I keep my secondaries open at all times after removing the vacuum actuators.

[Paul Workman]

Originally Posted by Perry Mitchell

This is how I keep my secondaries open at all times after removing the vacuum actuators.

Sooo... It appears you removed the actuator(s) and replaced them with a flat tab bolt, yes? Nice. Oh, but to be safe, it might be worth considering to dab some BLUE lOCKTITE on the threads under the nuts to prevent them from vibrating loose, resulting in the secondaries (possibly) creeping closed insidiously.

[Perry Mitchell]

I used a 1/4'' threaded rod and flattened one end using a hammer then drilled a hole in it for the linkage pin to slip into. Loctite on the inboard nut might be a good idea. I used a nylon lock nut on the outside.

[-=Jeff=-]

Originally Posted by Perry Mitchell

I used a 1/4'' threaded rod and flattened one end using a hammer then drilled a hole in it for the linkage pin to slip into. Loctite on the inboard nut might be a good idea. I used a nylon lock nut on the outside.

I like your solution and either locktite or a hole to pint he outer nut from backing off (like the crown nut setup for hubs (crowned nut is not really needed but the pin idea would work well)

[Paul Workman]

The obvious advantage to doing what you have done (used a modified bolt to hold the SPTs open) or a zip-tie as many have done, is the ease at which it can be reversed at a later date.

However, maybe for the sake of discussion, in my research on laminar flow and reversion caused by obstructions, I opted to remove the SPTs and the throttle rod entirely and plug the (now) empty bearing recess with a (Dorman) freeze plug. Admittedly, I have no "before and after" data to document the improvement to be had by so doing - that and extending the tapering of the IH runner down to the injector boss - but intuitively I feel it helps (just like smoothing the outside radius of the curves in the intake runner has in the porting fundamentals).

But, increasing the porting modification beyond 36mm (in one fashion or another) has been shown to be beneficial to many of the porting schemes (including mine which are now @ 37.5mm).

[-=Jeff=-]

Originally Posted by Paul Workman

The obvious advantage to doing what you have done (used a modified bolt to hold the SPTs open) or a zip-tie as many have done, is the ease at which it can be reversed at a later date.

However, maybe for the sake of discussion, in my research on laminar flow and reversion caused by obstructions, I opted to remove the SPTs and the throttle rod entirely and plug the (now) empty bearing recess with a (Dorman) freeze plug. Admittedly, I have no "before and after" data to document the improvement to be had by so doing - that and extending the tapering of the IH runner down to the injector boss - but intuitively I feel it helps (just like smoothing the outside radius of the curves in the intake runner has in the porting fundamentals).

But, increasing the porting modification beyond 36mm (in one fashion or another) has been shown to be beneficial to many of the porting schemes (including mine which are now @ 37.5mm).

I don't disagree, but if the goal is to allow for reverting to stock, I would do what Perry did. if the goal was max power and I was porting, then yes remove them cause once you port those butterflies will not do their intended function

[Paul Workman]

Originally Posted by -=Jeff=-

I don't disagree, but if the goal is to allow for reverting to stock, I would do what Perry did. if the goal was max power and I was porting, then yes remove them cause once you port those butterflies will not do their intended function

And, point of (further) fact, the Gen-III LT5 went so far as to Siamese both runners (into one). And, with the help of some tricky (dynamic lift) lifter scheme and variable fuel pressure, a single injector was used instead of two. IIRC Graham (in his presentation on the motor at the 2016 or 2017(?) Gathering) said that this 350 cid motor made 550 chp on pump gas. My point is, performance improvements via porting developments pioneered by Pete Polatsidis and Marc Haibeck and others showed just how badly the stock LT5 was starved for air: acknowledged (IMO) by the changes Lotus made to the gen-III motor's intake plenum/heads: AND, NO SECONDARIES.

Note of interest: Someone correct me if I'm wrong, but I believe this gen-III motor was (IIRC) installed in a car owned by Graham Behan (former engineer for Lotus and Lingenfelter before going out on his own).

[grahambehan]

Paul, et al
Engine made 528 hp
Ken owns the car that this engine was installed in.
I will put more info on the fb page, including video

Graham

[XfireZ51]

Originally Posted by grahambehan

Paul, et al
Engine made 528 hp
Ken owns the car that this engine was installed in.
I will put more info on the fb page, including video

Graham

And this makes me shake my head when I read stupid comments on the C8 forum about how DOHC motors need to spun like a sewing machine to make any power. 528chp from a 5.7L NA motor. And one designed 30years ago.

Graham, what cams did u use for this?