[Stevo440]

Ok this is gunna stir the pot here!!! There is a way to "Play around with"/"Fool" an EFI computer system specifically an SD system when it comes to the "Cam" that will be used.
I don't ever remember anyone mentioning this before on this site, I also haven't been a member since the beginning only since 2009 and haven't done a search for it either.

So is everyone ready for this "Revelation"????
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Here it comes!!!!
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Only scroll down if you dare!!!
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Rhoads "Variable Rate"/"Variable Duration"/"Variable Lift" Lifters!!!!
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Go ahead let the Flames begin!!! Or do I need to Explain how they work or are supposed to work "FIRST"????
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But be ready to have a "FACTUAL" Debate and have Real evidence, facts and proof to present at the Round Table!!!!
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Game on!!!!!

Just adding some humor here to spice up our day!!!!! Something different to argue/complain/cry about other than Jabs, Masks, Mandates and all the other dumb stuff goin on these days!!!!

 

[Stevo440]

They were used in the old days to keep the vacuum up for the brakes on high lift / duration cams

Yes they were and the higher vacuum is what is needed on SD EFI to function at Idle and low rpms/speeds. They also gave better Idle quality which gave the Carb idle circuitry the ability to function correctly which is what it would do for the SD EFI system.

 

[Stevo440]

agree for the reasons to do this.
However the Speed Density is expecting to see a certain vacuum, at idle. While doing this would help, it may not fix it if it doesn't get it within what the speed density ecm is expecting to see. I am not sure what this ## is but would likely take some messing around to get it to work as intended, in these applications...

Yes correct, I agree 100%, I was not intending my Opening Statement to mean they would be a Fix for all large Cams. They are only a Fix or workaround for slightly larger cams then those designed to work with SD EFI systems. If the Cam you are running or trying to run lowers the Vacuum too low than the Rhoads lifters would not be able to recover enough vacuum to Fix the problem/make the Cam useable. They are a workaround for SPECIFIC SITUATIONS within Reason!

 

[Stevo440]

i feel like its an added potential problem and i would not recommend it unless you wanna try and be the test dummy

1: there is no fixed amount of change so you are taking a guess at how much it will be doing. its designed for big cams and high rpm. the bigger cams help force it to leak down more. i doubt you would put in a big enough cam to notice a major change and you probably dont rev over 3.5k rpm very often so are you reaslly seeing any advantage fro mthe bigger cam? from thier FAQ page



2: there is a alot of variables since it relies on leakdown of the lifter. while its designed to be more determined by rpm than oil pressure to when it stops adjusting, im sure things like oil pressure, engine temp, oil viscosity all play into it also. a cold engine making 40psi idle using thicker oil will blead down significantly slower than a hot engine making 10psi idle and thin oil. so when cold starting it might act like a normal lifter and then when it warms up it will start to adjust more.



3: if you do try this and it doesn't give enough, you will probably regret putting in the bigger cam and these lifters. as now you will want to swap them out or still need tuning.

4: if you do decide in the future to tune it, it might makes it difficult to tune correctly when there are variables that can change how they operate.

5: normal lifters do occasionally fail. having a more complex lifter is another potential issues for failure

its an intresting concept but more for large cam carbuerated builds more than trying to make a stock EFI work with a mild cam

Please go back and Re-Read my last post, #5.

I was a Test Dummy with Carbed engines with not so large Cams see below:

I have used these lifters in a Big Block 440 Mopar in a Roadrunner and a Small Block 307 Chevy engine in a boat. In the 440 it gave unbelievable low end torque but it is a big block with 440cid so it should have lotsa torque but there was a problem with the cam in that engine, when I had it rebuilt they put the wrong cam in it, it was suppose to have the 280 deg cam and they put the 268 deg cam in instead. So the theory was with the 280 Cam it was supposed to act like the 268 Cam down low and the 280 Cam up top but with the 268 Cam it acted like a 256 Cam down low and the 268 Cam up top. So the outcome was 21-22 inches of vacuum at idle and gobs of torque down low but it ran out of breath at 4000rpms (because of the too small of a Cam). The 307 on the other hand had "so I was told" a 1/2" Race Cam in it and it wouldn't idle in gear at less than 2000 rpm and was a dog after that. Well I changed out the Cam and put the previous aforementioned Chevy 268 Cam in it being it was a 307cid with Rhoads variable rate lifters so theoretically the Cam would act like a 256 Cam down low and the 268 Cam up top. Well this little 307 was like a monster from almost "0" rpms to over 5000 rpms, it idled so low I couldn't get a reading on the Tach and it pulled to over 5000 rpms we needed a larger pitch prop to utilize all the extra power to keep the Rpms at or below 5000. The vacuum at idle was also amazingly high. Now both these engines had relatively small Cams in them and the Rhoads lifters worked better than what I expected for such short durations and lowish lifts. All Cams shown were Advertised duration not at .050. This was all done back in the mid 80's and both were Carbureted.

Now my point was for a guy building a SD EFI 351 or 302 for a Bronco that he could get away with a Cam with 10 degrees more timing or one with slightly less than the 114deg LA separation recommended and not have to get a tune and just run with the Factory programming.

Yes there are Variables with Leakdown related to rpm, oil pressure, temperature and viscosity but there are no more moving parts in the Lifter to fail other than a Groove or a larger bleed hole.

 

[Stevo440]

My guess here is that most people don't even know about the Rhoads Variable Rate/Duration Lifters or even what their True intent is and what it can do for our vehicles. There will always be "Doubters" but unless you have seen the before and after results and understand fully the dynamics of how they work I think you should do your due Diligence Research and read as many articles as you can find and then if you still "Doubt" then prove it won't work with "Facts" not "Opinions" or try it out for yourself cause you might like them and become "Woke".

 

[Stevo440]

The Rhodes lifters will have variable duration and lift based on rpm, but this will not change lobe separation, which effects engine vacuum. Lobe separation less than the required 114 degrees introduces intake and exhaust valve overlap which reduces the vacuum signal.

There are other ways to fool an SD computer (higher compression or smaller intake ports) to increase vacuum.

I would suggest you read a bit deeper into the workings of said Rhoads lifters. In there limiting the Duration/Lift at idle and low rpms this changes the Degrees of Overlap the Cam effectively has the same way the wider Lobe Separation does. What wider lobe separation does to a Cam is allow the same durations but shortens the overlap, just as shortening the Duration by 10-15 degrees will do. They allow you to adjust the Lift to give a .010"-.040" decrease which in turn decreases the Duration accordingly, you can Tune them according to your needs of course you need an Adjustable Valve Train to do all of this. Do the math or look up cam Charts/Diagrams and enter the numbers in and see what comes out.

Yes you are correct raising the compression is another way to get some vacuum back but it is not adjustable and is hit and miss cause it is hard to calculate.
With the smaller intake ports we already have those flow problems (heads and intake manifolds) we are trying to produce more HP and TQ not less. Good ideas though..

 

[Stevo440]

I feel like at end of day a MAF swap or other aftermarket solution is the real fix here.

Even if you get it to idle and such, your still limited by the 19lb injectors. With any performance style build on these motors, with a cam profile enough to be out of the speed density's "specs" ; your leaving some on the table by sticking to stock injectors and that anyways... 19lb's are only good for around 260hp at 80% duty cycle and 39 psi (what the Fords usually run at, few other generalization there too). My opinion...

I'd rather keep this simple and related to the Vacuum with SD EFI. You can install larger injectors if needed and have someone adjust the constant in the program or whatever is available to correct for the injectors.

 

[Stevo440]

Maybe not keeping with the method of the thread, but within the subject matter of the thread, I'd like to ask a question from the side of ignorance and just thinking out loud...
Anyone know how much vacuum is needed for SD to operate properly? Also is this only at idle or does the vacuum effect it throughout the RPM range?
Where I am going with this, and it's probably a dumb idea...but what about an auxillary vacuum pump plumbed into the vacuum system? If you knew what pressure the SD system liked, you could fool it with small pump maybe?
I'm guessing this may not be a good idea because if i understand it correctly, this also tells the ECM how much fuel to send and you could run into a rich/ lean scenario...but if its only an idle issue and once it gets up enough RPM to make the SD "happy" you could operate the auxillary pump with an RPM activated switch (like use commonly in nitrous applications).

Im sorry, im on a boring conference call

I do not know the vacuum range required for our Bronco SD EFI system for sure but since the Specs call for 15"-21" of vacuum at idle I would assume to say in that ballpark...

As the vacuum drops because of throttle opening you are then getting into FIXED maps because you go into Open loop in the computer. The problem is during Closed loop with a cam swap and the decrease in Vacuum at idle and low rpms...

The Auxiliary Vacuum pump is an interesting Idea but we are getting out of PROVEN technology here, Rhoads lifters are PROVEN to do what they are Designed to do, INCREASE Vacuum and Torque at idle and lower rpms.

 

[Stevo440]

I was/am NOT "TAWKINABOUT" Injectors, Heads, Intake Manifolds, port size, Vacuum pumps or Reprogramming computers, I was/am tawkinabout Rhoads lifters to keep a cam swap in a SD EFI engine with the wrong specs within limits Running with the Stock computer setup/programming. Nothing expensive or Complicated that any knucklehead can "FIX" their Problem with and get their Bronco running so they can use it. I'm tryin to keep this simple. I have a MAF so I can't be the Guinea pig here. It was a thought to help "Someone" on this site if they are experiencing this problem and gathering opinions not other options. We can start another thread about Options.

 

[Stevo440]

If you're going to have to monkey with the programming for the injectors (provided you plan on exceeding the 260 hp mark), might as well go ahead and upgrade the ECM to something like PiMPXS..then you can run whatever cam you want within reason and keep the SD

Also, this particular use of a vacuum pump would be "experimental" i suppose, but they are used quite a bit in forced induction applications, plumbed into a reservoir then all the vacuum operated goodies like HVAC and Power brakes run off of it.

The first Gen Z-r1 corvettes from the 90's had a dual runner setup on their LT-5 DOHC engines, and when you put the engine in "Full" performance mode, this activated a small 12v vacuum pump that would open the secondaries under full throttle giving you all 405hp. I had one of these and that pump in particular is what made me think of the whole "auxillary vacuum pump" idea. 405 HP out of a naturally aspirated 350 engine in the early 90's wasn't too shabby.

BTW that manifold on the Vette I know about that as it came many years after my idea in College. My Senior Paper in 79/80 was going to be about a "Variable Runner Intake Manifold", but I stopped because of Political problems. There is the Variable Venturi Carburetor (Ford) way back when also. It got Really Deep the whole Idea/Concept. Just some Fun Facts from my past!!! Believe it or Not!!!

 

[Stevo440]

@robbz28 they make Roller lifters also so no break-in necessary just remove old and drop-in new, then adjust and button up and go. Basically anyway...
I'll look into the attachment thanks I'm never too old to learn.