been reading, comp cams 4&7 swap?

[j_eremy]

what is the general concensous about the comp cams 4&7 firing order swap? is this a good design? has anybody ran one of these cams?

[jnjdragracing]

I have installed a 4/7 swap cam in a coupe of 350 for some guy's. No problems encountered and it is supposed to be good for another 30HP. I am planning on re-doing my cam in the near future and plan on going the 4/7 route.

 

John

[WEBEZEEed]

Horsepower T.V. did a Dyno test on one of those cams not too long ago, they got a 30 H.P. increase on a 500 H.P. motor.... (no other changes but the cam)

[280zwitha383]

Were all other things kept the same? Do you have a link?

[jt1]

I don't know if it works or not, but I'm skeptical. You still have two adjacent cylinders firing consecutively, just different ones. How can that help?

 

Crank harmonics are a funny thing though, I guess it's possible.

 

John

[gretchen/jason]

I saw the same Horse Power TV show and if i remember corectly they gained 30 horses around the 5-6 thousand rpm range nothing down low though just in the higher rpms . Dont quote me on this though .

 

Jason

[boodlefoof]

I don't know if it works or not, but I'm skeptical. You still have two adjacent cylinders firing consecutively, just different ones. How can that help?

 

Crank harmonics are a funny thing though, I guess it's possible.

 

John

 

I am also skeptical. Another possibile reason for such a power gain could be the exhaust header design. If you're using headers with primary tubes of unequal length, switching the firing order could have a significant impact... However, depending on the header, it seems that swapping could also cause worse performance.

[sweetride2go]

man, its been a while since ive researched this, but i seem to remember sumthing along the lines of taking some of the 'load' off of the rear mains w/ the change in firing order, as well as a slight increase in power....

[BRAAP]

C’mon guys, this is Hybrid Z, THE source of technical info. You all no better than this. There is NO magic HP in a firing order change. It is what accompanies and complements the firing order change that “frees” up hidden power that was being restricted in the first place! The firing order change in itself does NOT produce more power over what was previously available. (where is Grumpy when you need him?). And at that, totally dialed in setups of comparable displacement will produce similar power, PERIOD, regardless of their firing orders. That crap has all been sorted out way back when these engines were originally designed guys, I’m talking back in the ‘40’s and 50’s! The ‘60’s, 70’s, ‘80’ and the ‘90’s only showed us that there is power to be unleashed in fine tuning and cylinder head design, (port shape and location) of the original design! . Don’t let the magazines snow you into thinking there is free magical HP to be had here…

How many magazine articles have you guys read about a new way to approach the SBC 350 that over the years only proved to be nothing more than, if its tuned right from the get go, it will make power!, i.e. NO MAGIC!!!!!

 

You guys are all looking for that little bit of “magical” HP that these magazine articles reference, in this case, a camshaft that allows a different firing order… (in the engine building/machining trade, we refer this as “Magazine engine builders”, not a positive label to say the least). Please, take what you read in magazines with a grain of salt. A 350 CID engine will produce “so much power”, no matter what its firing order is. Differences in ignition timing have more affect on power produced than the firing order will. There are SO MANY other variables not accounted for that these 30 HP increase claims are just pain BS!!!! Trust me, there is no magical free horse power to be found that hasn’t been found out already…

 

Do a little research fellas. The Ford 5.0 back in the mid to late 90’s came with 2 different firing orders. The Thunderbird/Cougar/Truck 302 had a different firing order than the HO 302 Mustangs. Ever notice how sedate and mellow the exhaust note is on the V-8 Thunderturds vs the HO Mustangs? It wasn’t because of more duration and lift of hte Mustang, it was the firing order! The firing order of the HO Mustang is similar to the old Ford V-8 and typical Chev and Chrysler V-8, (that typical rough sounding rumble.) The 4-7 swap smoothes out the firing pulses to the ear. The LS-x GM engine use the same firing order as the sedate Ford V-8, not only was the 4-7 swapped but 2 of the other cylinders are also swapped. It was for noise, vibration, and harshness reasons, not for free magical power. The LS-x engines do sound “smoother” than the traditional V-8 at full song.. Hmmm.. now if you tuned the induction and exhaust systems to either firing order, they will produce similar power throughout the rev range given similar valve timing specs etc.

What I’m trying to say here is don’t get suckered into thinking you are buying a free 30 HP gain just in a 4-7 swap cam! Also, don’t let me sway you from a 4-7 swap cam. I do feel that it is a step in the right direction if you want a smoother, less audible V-8. But PLEASE, don’t accuse the 4-7 swap of allowing or robbing power just because of the firing order change by itself! That would come for the improper tuning. (Grumpy could clarify this better than I). There are too many other variables to take into consideration. In short, by believing the 4-7 swap alone is worth HP, would be like taking only one verse out of the Bible and using that one and only verse as the interpretation of the entire book. That would be WRONG! Magazine articles do just that all the time. They are paid by parts manufactures, so keep that in mind when you read an article about an engine build-up that is too good to be true. They are selling parts to help pay there bills. Just read between the lines when you read those magazines and you will be well served.

 

If you really want to be different with your V-8 firing order, look into a 180 degree cranks, (also known as a flat crank or single plane cranks for the 90 degree V-8 blocks. 180 degree headers offer similar results, but without having to use a different crank and cam).

Ever notice how a Ferrari V-8 sounds like a high strung sport bike but a domestic V-8 sounds like a Harley V-twin! Domestic V-8 cranks shafts are duel plane or 360 degree in techno speak, and have the firing order in such a way as to be viewed as 4 V-twins sharing a common crankshaft. The Ferrari V-8 is like a pair of inline four cylinder engines sharing a common cranks shaft, hence the exhaust notes…. Supposedly the single plane allows for exhaust tuning, but 2nd order harmonics are greater, i.e. the engine will be buzzier just like a big 4 cylinder. For what its worth, NASCAR has played with both over the years, and are still using the traditional firing order, as well as the top echelons of drag racing…

 

 

You have better chance of freeing up corked HP by building your own 180 degree exhaust system like what is pictured below. The center 2 cylinders on one bank communicates with the outer 2 cylinders of the opposite bank, and vice versa… This allows for exhaust tuning, but any real power gains will only be realized on higher end performance projects, i.e., greater than 120 HP per CID.

 

 

[TravRMK]

Wow that 180 exhaust system is crazy! I like the looks of it, but way too complicated for me. Also would require more room than available, unless you drive a 4x4 Z.

[WEBEZEEed]

No such word as irregardless(double neg.) anyway the ONLY change made was the cam, and they produced more power. How & why it made more I can't tell you but it did,I've watched that episode twice now.

[BRAAP]

No such word as irregardless(double neg.) anyway the ONLY change made was the cam, and they produced more power. How & why it made more I can't tell you but it did,I've watched that episode twice now.

 

I apologize for the grammatical error. My education beyond High school is only an Associates degree (aviation maintenance tech/engine builder/machinist), acquired back in ’91. Since that time, I’m sure I’ve lost a lot of my English and grammar skills.

 

Back to the 4-7 swap hub-bub. I don’t doubt for a minute that engine produced 30 more HP, or even as much as 50 more HP. That is not in dispute at all. That only proves that the previous setup prior to the cam swap wasn’t optimized as a package, and that cam swap only brought that package 30 HP closer to its ideal component-matched configuration, nothing more. Apparently in that particular pacakge, the 4-7 swap matched that induction and exhaust systems better than the original.

 

I’ll say it again and defend it till the bitter end. There is NO magical free HP in a 4-7 swap! As long as the setup is optimized as an ENTIRE package to begin with, no power gains should be realized. Personally, I plan to run a 4-7 swap in my Supercharged SBC T-56 Z car, but only for the smoother less obnoxious exhaust note. If I use parts that are compatible with each other including the cam, then I should realize no magical power increase just because of the firing order change.

[Guest Saylore]

It was previously stated that NASCAR does not use this firing order, the statement although true is not a completly informed one, since Chevrolet does not use this firing order in its V8 production engine it is not legal for NASCAR to use it in thier race motors. As this firing order greatly reduces internal harmonics, and crankshaft deflection force by more than 150%, NASCAR would surely make use of this advantage to increase the survivability of motors. but of course this is just one mans opinion.

[grumpyvette]

the 4/7 firing order swap reminds me of the huge rush to use flat 180 degree cranks about 20 somethiong years ago, yeah, theres BOTH advantages and DIS advantages, but BRAAP COVERED IT WELL yes you can in theory gain a few hp, yes it costs more, yeah, it tends to lower the harmonic loads SLIGHTLY

1-8-4-3-6-5-7-2

1-8-7-3-6-5-4-2

 

think about it, your swapping center cylinders for outer cylinders, in theory spreading the demand on airflow in the plenum and runners but increasing the twist or torsional loads on the crank over a larger length, not much gained IF both are optimized but the 4/7 swap should run smoother as not as much a/f ration harmonics & disruption takes place (in theory)

[WEBEZEEed]

Paul.... no need to apologize, I was just knittpicking!