Purely hypothetical...

What does it take for swapping the cam in an OEM roller block to LS Firing order?
I can find retrofitted ones, but not OE roller, why?

Kind regards,

Chris

 

Are you asking about running an LS firing order in a SBC? Any particular reason?

 

Yes, for OE roller block. I love the sound of the newer firing order. There is no performance wise reason to swap that in a 300hp engine. Why dont they have such cams for 87+ Up SBC Gen 1 engines?

 

Summit has SBC roller cams with the LS firing order.

https://www.summitracing.com/search/...ller-camshafts

 

which are all retrofit. I think the point the op is making is that oem roller cams aren't available that way. And as someone who has done ZERO research on it, my guess would be lack of demand. They don't make it if no one is buying it. I have no doubt if you request a custom cam, they'll make it that way.

 

Anybody that makes cams will custom grind you one with the 4-7 swap. Piece o cake.

What's the big deal?

 

I don't know if there was ever a definitive study on any difference that makes whatsoever.

 

Can get a custom grind. Problem is finding a core to use. Its not a popular thing and im very surprised summit has retrofit ls firing order cams. Thats crazy but cool at the same time

could run one of those with a different cover and chain tho

ls firing order is suppose to be better for engine/crank harmonics. But likely not noticeable since sbc has run for 100’s of thousands of miles without much issue before

 

Thats the problem. I wrote to howards and to Jones cams. Both cant grind me a custom cam cause of it's lack for cores of that kind. And I want the complete firing order of the LS, not just 4-7 swap. I think there is no possibility in the moment then just wait for it to come.

 

If you're dead set on the LS firing order, just run the retrofit cam, matching lifters, longer pushrods, an old style timing chain and a cam button. I know that's considerably more expensive but that looks like about the only way you're going to get it done any time soon. Getting parts right now is a nightmare.

 

The crankshaft in an LS series is a different animal from the Gen 1 SBCs. The LS basically has a "mirrored" firing order, the same as a Gen 1 but flipped end-for-end. A Gen 1 with 700,000 miles or LS with 700,000 miles don't seem to reflect substantial design problems.

 

Crank stays the same on a 4/7 swap. Racers have been doing it for a long time now, benefit is more even loading on the crankshaft to my understanding. may not matter on a 300hp engine, but might make a difference at 700hp.
you are probably looking at a custom billet cam to get the correct stepped nose on the cam. $$$$$$ if you just want it to sound different, i think you would see more of a difference manipulating the lobes than just changing to the other firing order. or do an ls swap like most everyone does now.

 

Hey, and thank you all for the answers.
So just a 4/7 swap is possible with the SBC crank?
For the complete firing order the crank would not work cause of it's crank journal? Or other reasons? Could you please explain that for someone who wants to learn. (=

https://www.thirdgen.org/forums/tech-general-engine/783766-firing-order-swap-cam.html


Ahhh, you already answered that in another thread.
The question with the custom cam manufacturer would be nice to get answered, so I can write more E-Mails out.

Besides that, who makes custom cams for SBC in general except howards and jonescam?

 

Complete firing order swap also works. My 8.1L had the LS firing order as built. Changing only the cam and moving some injector/coil wires around at the PCM changed it to the old school 1-8-4-3-6-5-7-2 firing order. LS firing order sounds like crap, old school sounds better. There are like 4 or 5 common firing orders on a 90* V8 using the same crank throw arangement. For example my Nissan V8s are 1-8-7-3-6-5-4-2. Same as a SBC with a 4-7 swap.

 

All of those swaps are unaffected by the crank, and vice-versa.

THIMK about a 4-stroke V8 engine for just a minute... The crank has 4 journals. Each journal has 2 pistons attached to it. The crank turns two full turns for each engine cycle, since each cyl makes 4 strokes during one full cycle (suck, squeeze, bang, blow), each of which is ½ turn of the crank. Thus, at all times, each cyl is doing the EXACT OPPOSITE of what the cyl 4 cyls away from it in the firing order is doing. In the traditional GM firing order, for example, then (18436572) when #1 is just beginning the suck stroke (intake) its piston is at the very top of its travel, starting to descend. #6 is just beginning to bang (power); its piston is at the very top, beginning to descend, being pushed by the freshly ignited gases. And so on, for EVERY event, and for EVERY one of the 4 pairs of cyls. Which one of those 2 events is occurring in each cyl at the moment that their pistons are both doing the same thing, is determined by the action of the valves; i.e., the cam. Therefore you can take any 2 cyls in the firing order that are 4 cyls apart, and exchange them, without altering anything but the valve train. So, to get from 18436572 to the LS firing order of 18726543, no changes to the crank are required; only the cam. The events are swapped between #4 & #7 (4 cyls apart in both orders), and between #2 & #3.

Cyls 1 & 2 share a journal, as do 3 & 4, 5 & 6, and 7 & 8. Note that in the traditional layout, out of those 4 pairs, 3 pairs fire sequentially, and only 7 & 8 don't fire right next to each other; but in the LS layout, it's exactly the same, except that instead of 7 & 8, it's only 1 & 2 that don't. I'm not seeing where there's much advantage there.

AFAIK practically ALL of the racing cam mfrs do custom grinds. Comp, Bullet, Crower, to begin with. The problem then is getting CORES: in order to "grind" a cam, there has to be metal there to grind off, but if you want the lobes to be quite literally turned around backwards, then either you have to start out with COMPLETELY ROUND ones and grind 3/8" off of them, OR you have to start out with a cam that has rough lobes nearer the right size and shape but pointed the right way. With cast cores somebody has to cast them that way, which is a problem. With billet cores the possibilities are greater but still tedious.

Comp has some 4-7 swap cams that are off the shelf designs although not always kept in physical stock. Billet solid rollers. https://www.summitracing.com/parts/cca-12-843-14 for example. Note that it's also on a small base circle, for rod bolt clearance.

 

ls firing order does not require a special crank

 

yes. Step nose cores are had to find in billet. The cast cores comp uses are around. I ordered my cam from Jones back in January and my cam showed up a couple weeks ago. That blows my mind as Mike had even said it probably would not be until mid summer so that was unexpected. But I was in no rush to have the part either.

If you call comp you more than likely can order any shelf grind custom with the firing order swap done. Last I checked the price was about the same. That is if you don't mind a cast core.

 

Thanks for clarification, guys. Need to read the text twice or more to understand, but those are very good informations!
I already have seen the comp cams 4-7 swap cams, but there waaaaay to radical. Pity, no one does have a hydraulic oem roller with acceptable duration and lift numbers just for sound and technical enthusiasts like me with those crazy ideas with the LS cam swap. Will contact more cam manufacturers though and see what they say.

 

Don't even need to change the lifters. Run OEM lifters on the retrofit cam. Easy Button....for something I don't think is worth it, but....personal preference.

 

Personal preference here, but I don't like the LS firing order sound. I wish someone made a traditional firing order swap cam for a LS. Then again my 8.1L is a hybrid and like a big cubic in LS, so who needs a LS anyway while there are good old 8100s on the market.

 

Will that work? Won't the lifters drop down too far to use the OE dog bones?

 

How/why would they do that? The cam base circle is the same.

 

A retrofit cam has a smaller base circle…

 

Where are you seeing a spec that shows a different base circle?


I don't think that differences in the base circle would be enough to cause the lifters to slip out of the dog bones.

 

Every single retro fit camshaft I’ve ever bought from Comp or Howards had a reduced base circle. It says it right in the description.

 

Since when? This is all news to me. But I've only been using retrofit rollers for around 30 years now; maybe I missed something?

 

I don’t know how you haven’t noticed, lol. It’s obvious when you pull it out of the box…

 

IDK. The link for the cam that you provided back in post #4 or so, doesn't say anything about the base circle.

On the one from your phone app, what is the "smaller base circle". The answer to your question is simply in the base circle spec for a stock cam, vs. the base circle on your proposed cam. What is the base circle on your proposed cam? :bigears

 

I thought the reduced base circle cams were offered for clearance purposes in stroker applications?

 

 

They make small base circle cams for strokers, yes, but retro fit cams also have a reduced base circle.

 

I thought it was common knowledge.

 

Here it is straight from Comp Cams…

 

So....

"specialized base circle". What's the base circle dimension? :bigears

 

Hell if I know.. Call them and ask them lol. I’ve never measured it. It’s obvious from just looking at them that it’s smaller. The base of the lobe is almost even with the shaft.

So you want to argue about it when even Comp and Howards both say they’ve got a reduced base circle?

Really?

 

Really? Really? Really? Am I arguing? THINK!

OR...am I asking a question? Go back and READ my posts. YOU said, it has a smaller base circle...you asked: would the lifters go too low and fall out of the dog bones? Right? RIGHT.

Did I argue? Nope, I did not. What I DID do is ask for specs on the base circle....and I pointed out that knowing that, and comparing that to the stock cam, would provide us with the answer to your question. Right? RIGHT.
That's quite a lot better than guessing, right? RIGHT. Think. Don't be a dumbass and don't call me out for that which I didn't say or do. Cool? COOL. As you were.

 

Maybe, the difference is .010"(for example)...and not enough to cause the lifter to drop down out of the dog bone....or enough to affect anything else in a meaningful way -so you didn't notice? If the base circle is 1/8" smaller in diameter, well...that might be enough to cause a problem and/or be noticeable during assembly. But if the base circle is .005" (for example) smaller....it's probably not going to affect the lifters in the dog bones, or anything else in a meaningful way.

SO....how much smaller is the base circle? :bigears

 

I posted the info from Comp and you said “specialized” and kept asking the dimension like you don’t believe what’s posted.

I don’t care about the dimension nor do I care about trying to use OE lifters on a roller cam. If that was standard practice, there’s be no need for link bar lifters…

The issue at hand is whether the retrofit cams have a small base circle and the fact of the matter is YES, they do.

if anyone here is a dumbass, it’s the one that doesn’t know a retrofit cam has a smaller base circle than a cam designed for an OE roller block…

That’s been common knowledge since they designed them…

So if you want to get pissy and act a fool, do it by yourself. I have no desire to listen to you flap your gums like a 3rd grader throwing a tantrum.

As you were…

 

And I said, if you’re that freaking curious, CALL COMP or HOWARDS..

It’s not .005” difference, smartass..

It’s OBVIOUS by looking at the cam that the base circle is SIGNIFICANTLY smaller… and it isn’t .005”…

More like .100”.

As I’ve said before…

CALL THEM if you want to know.

Again, I’m NOT concerned about putting the OE rollers and dog bones on a flat tappet block with a reduced base circle cam. I don’t think it’ll work. Maybe it will.

What I know for a fact is retrofit cams ARE small base circle cams.

Don’t believe me? Don’t believe Howards? Don’t believe Comp?

I don’t give a ****.

 

Yes...yes....it's obvious that you "don't give a ***".
SOOO? WHAT IS IT? You're the expert on Retro Rollers here, apparently. Right? Tell us what the base circle is!



You don't care....you say. Then why'd you ask:
^That's^ what not caring looks like? :bigears



That's NOT what link bar lifters are for. Sorry, but nope.



NOPE. AAAAAAAAA! Wrong. The issue, is the very question that YOU brought up! My god...."Won't the lifters drop down too far to use the OE dog bones?" That's the issues. It doesn't matter WHAT the f'n base circle is....as long as it's close enough to the OEM cam's base circle to not matter! THINK!! Think.

SOooo.....What's the small base circle of the cam you picked out? :bigears



A dumbass....AND a copy kat to boot! Strong qualities in this one.

 

Look ********, I don’t know why you’re such a *****, but here’s the deal.

Why I’m God’s name do you think they came up with link bar lifters???

Because they needed something to keep the lifters aligned in blocks that don’t have a provision for the dog bones…

Jesus, for someone that thinks they’re so smart, you sure do make some idiotic comments…

As far as the measurement, I’ve told you I NEVER measured the base circle. WHY WOUKD I NEED TO???

It’s VISIBLY smaller…

If you’ve built any engine with a retrofit camshaft, and it’s obvious you haven’t, you wouldn’t even be flapping your gums right now.

If you want to know so bad, crawl out of mommy’s basement and ask to use her phone and call Comp, Howards, Lunati, etc and find out for yourself…

You keep running your kawksucker wanting to know the dimension, well then put that kawksucker to work and make a phone call…

 

Yeah....it's obvious that "you don't GAF". LOL

I'm a ***** b/c you had to be a ***-tard and call me out for "arguing" when I was simply asking an exploratory question that would lead us to a clear answer to YOUR question. That douchey malfunction on you part? Yeah, that soured me on you, so the prickery is flowing now. YOU picked the cam....YOU are the self proclaimed "roller expert"....right? RIGHT! YOU asked the original question....YOU call 'em and you'll have a clear answer to your stupid question! Geezus.

 

I don’t know how many times I need to explain this but I don’t care about putting OE rollers on a retrofit cam. I asked a question and it was rhetorical. It may indeed work but I doubt it.

The issue here is you arguing about base circles…

You can huff and puff until you can’t breathe anymore. You’re just making yourself look like that much more of an *******.

Can you please point out here I claimed to be an expert…

I’ll wait.

 

Do you know the definition of irony???

If you had any functioning neurons between your ears, you wouldn’t have suggested trying to run OE rollers on a small base circle cam…

Making a stupid comment and then calling someone else stupid???

IRONY

🤣🤣🤣🤣🤣🤣

You’re “soured” on me???

Oh woe is me! Whatever will I do? How will I ever go on?

STFU… 😂

 

Yeah? Why, exactly. TELL US WHY. Show us what an astounding, brilliant, Roller-retard you are....

:BIGEARS......

 

For the rest of the peeps here who do care, the normal base circle on a cam is slightly smaller than the cam bearing diameter minus the lobe lift.
Thus, most any after market cam with more-than-stock-lift, will have a smaller base circle.

But let's investigate Billy-bob's question, since he doesn't GAF....but asked the question, anyway.
On the stock cam, lift is what? ABOUT, .410ish? So, .410/1.5= .273" lobe lift.
The journal diameter of a Small Block Chevrolet is 1.868”, so 1.868 - .273 gives you a base circle of 1.595"

Billybob's cam has .565" lift, so .565"/1.5=.376. 1.868-.376=1.492"
A difference of ~0.103". a tenth. Since that's dia, the lifter will lose 1/2 that, elevation, so ~.05" lower than with the stock cam.

I'll go ahead and say that the lifter won't fall out of the bottom of the dog bone if the lifter goes ~.05" lower on one cam than another....and that's probably why people have successfully swapped in aftermarket (smaller base circle) cams for decades, w/o lifters falling out of dog bones. I think it'll be all right, but surely it's always good to investigate to understand it fully. <That may never happen, for Billy-bob, the roller-retard.

 

Why don’t you go back up to Sonic and brag to all the high school kids about your vast knowledge…

Maybe you all can get your Fast and Furious coloring books out and compare notes…

Still waiting to hear where I claimed to be a retrofit expert…

Whats that I hear? Oh it’s silence…

Because it didn’t happen, brainiac.

 

Quote:

Why don’t you go back up to Sonic and brag to all the high school kids about your vast knowledge

BWAAAAAAA-HA-HA-HA-HA-HA-HA-HA-HA-HA-HA-!!!!!! That^.....was.....AWESOME!
That wasn't an answer. That was just a bunch of immature bullsh!t. Why didn't you answer the question? That's OK. That's where people go when they're wrong and embarrassed. I get it.

I don't know everything about cams....but I know more than you, and more importantly, I know how to figure out the answers!

 

You obviously don’t if you don’t even know retrofit cams are small base circle cams…

Thats engine building 101…

Yeah, you know sooo much! 🤣🤣🤣🤣

 

All cams with higher lift use a smaller base circle. Like I said, I don't know everything....but I know more than you!