Do the 4 valves run better than the 2 valves?

[Outbehindthebarn]

Curious to hear from guys who've driven both the old 2 valve Macks and the 4 valve Macks. I'm talking mostly about multi-speed higher horsepower engines. Was there any real noticeable differences. I had a guy telling me that the old 2 valves would smoke 4 valves when the fuel was jacked up...

[220cummins]

I've been told by a couple guys that had 350 2v they would walk a 425 cat back them. I like the 350 2v, it has a good crack to it.

[theakerstwo]

Anymore you may hear anything.Turn the radio off.

[ws721]

All I can say is back in the day we had a 82 Cruiseliner with a 2 valve 350 and a 87 Freightliner with a 425 cat. I put the hired guy in the Mack. I worked my butt off but could never get away from that Mack. On a long pull I could SLOWLY pull by the Mack but never get out of sight of it. That's when I stared respecting Macks. Then when you went to fuel them you really saw the difference! Mack with its 676 C.I. verse the cat's 998 C.I. The Mack was quicker off the line got better mileage and never let that cat forget who was king, even after I had the cat turned up!!

[Mackdaddy2030]

What year did they switch to the 4 valve?

[Outbehindthebarn]

The guy told me you could never get the manifold pressure up on a 4 valve like you could on a 2v...

[mackey58]

My boss just bought a 90rf690s em300. Seven speed is it or how can you tell if it's 4 or 2 valve and I'm gonna assume( we know what that means) that it does have a puff limiter

[220cummins]

I think 86 or 87 was the 4v. The 4v has wider valve covers than a 2v.

[mackey58]

Ok will look at them Monday thanks

[farmer52]

I believe the 2V engines used a stamped steel valve cover. The 4V engines used a cast aluminum cover. 4V engines started production in the mid 1980s.

Most 2V engines used a "high swirl" combustion design. In other words, the intake air flow (along with piston bowl design) created a swirl in the combustion chamber to promote good mixing of the fuel and air. 4V engines typically use a non-swirl combustion process and designed the piston bowl to do the fuel/air mixing (along with higher fuel injection pressure). I think the switch to 4V design was "increased power" due to the fact you could "push" more air into a 4V cylinder. As for 2V engines being more responsive.....it depends on the turbo and fuel pump along with basic engine/combustion chamber design.

As for CAT (I will put my CAT hat on), remember, CAT's engine experience was based on off-highway operation. They had a lot to "learn" about on-highway engine operation. CAT engines for many years were low cylinder pressure (BMEP) design versus Mack which had a high cylinder pressure design.

CAT was about "finesse" whereas Mack was "brute force". Hence a purring kitty cat versus a barking dog.

[Underdog]

I've been told by a couple guys that had 350 2v they would walk a 425 cat back them. I like the 350 2v, it has a good crack to it.

A buddy of mine bought an '84 MH last year with a 350 2-valve... IMHO Mack's best ever engine. I also worked with the previous owner and this truck could run with any CAT or Cummins... We used to enjoy aggravating those LARGE cars with our little Macks.

Gregg

[Glensts]

I had an 84 2 valve and an 87 4 valve, both 350's. I always thought the 4 valve pulled harder.

[Outbehindthebarn]

Those later 2V 350's seem to be really uncommon. Were they chassis mount charge coolers?

[jakebrake86]

I think they went to a chassis mount CAC in '82, and the 4 valve came in '84-'85. I had an '87 R model with a blown up motor so I dropped in a 2 valve 350 from an '82 model. I sold the truck but I still borrow it from time to time from my friend, and it will straight up SMOKE my 4 valve. I think it's got the peppiest throttle of any truck I've driven. The MH I got from Mr. Harbison seems to be running a close second.

[ws721]

Those later 2V 350's seem to be really uncommon. Were they chassis mount charge coolers?

My 82 Cruiseliner was chassis mounted charge cooler but I seen what I was told to be a 350 with the engine mounted tip turbine. The 82 350 2 valve had a 10 speed roadranger and other than maybe a 2 stroke joke with an Allision tranny id say that Mack was the quickest truck off the line id ever driven. It would s@#t & git!!!

[mrsmackpaul]

I dunno about 2 valve verses 4 valve I got my injector pump done up 7 or 8 years ago a bloke in western Melbourne ( he is yank cant remember his name ) did the job and as I recall he set the injector pump to the injectors he believed that was the correct way to have it done or at least thats the way I remember it

what a difference and the bark when pulling hard up a hill its like a gun shot going off (well maybe not quite) but you get my drift and pull my god it was like a different truck

what does all of this have to do with 2 or 4 valve not a lot but I feel a lot of what makes these trucks go hard is how good the bloke is at setting the pump not the amount of valves the size of the turbo the exhaust ect

no good spending bucket loads of cash if the basics arent right just some thoughts

Paul

[j_martell]

<SNIP>CAT was about "finesse" whereas Mack was "brute force". Hence a purring kitty cat versus a barking dog.

**LIKE**

[wingman]

The first antique truck I bought about 4 years ago was a 84 MH613 w/ 350 2v and T2090. I also drove both Ford 9000 and Int 9200 with 425 Cats at work, and I'm sorry but there was no comparison. The 350 2v was very peppy, and I always felt guilty when I chowed down on it because with dual pipes it blew so much smoke you couldn't see the cars behind you! It was one way to make them back off! The Cats were just plain awesome. They had so much torque in the Fords(3406'Bs) they had problems with drivers ringing off the driveshafts and trans output shafts. The 9200's were computer controlled and you didn't get full power until top gear. The mack did put out a lot of power for the size of the engine though.

[fifth wheel]

The 4V are better with cooler egt's, unlike the 2V's that get in the danger zone.

FW

[Dieseldriver65]

As much as I love Macks,I've owned mechanical 300-350's as well as CATS from the era.As a previous poster said there really is NO comparison.Anyone saying they "walked" over 425s or even were about equal is quite frankly full of it IMO.

[Enck762]

I'm with dieseldriver, there is no way a 350 mack competes with a true 3406b setup at 425hp. Maybe you were running with 3406a which commonly in error is called a 425. We have had numerous macks with 300 and 350's and pound for pound they are one of best ever. With a 6 speed I definately don't agree, maybe a 12 speed you could hang in there.

[Bigdogtrucker]

I've driven plenty of both, would have to say the CAT's made gobs more torque also.

[farmer52]

The original 3406DIT was 325hp and 3406DITA was 350hp or 380hp. Spent many a day "pulling the throttle" on those engines at the Testicular Center. The DITA used a water to air charge air cooler. It was years later when CAT went to air to air (ATAAC CAT).

Better torque on the CAT is mainly attributed to the larger displacement.

[ws721]

Well we ALL have stories. As for my case, I DO know the difference between an A model cat and a B model cat. Both trucks had similar trannys. Mack had 3.85 and the cat had 3.90 ratio same size tires. The Mack had a lot more get up and go. Like I said earlier, on a long pull, say like I88 from the NY Thruway down to Binghamton, NY. Then the cat would pull past the mack. But never did get away from it.

Yes its a common mistake that all 3406 cats are considered to be 425 hp. Just like folks will tell you that an 8V71 Detroit is automatically a 318 hp. We have several 8V71's and none of em are 318 hp.

[Timmyb]

I was wondering about the difference between the 2v and 4v also. On paper, the 4v has more torqure. I even bought a worn out 4v with the intent on rebuilding it at a later stage. But the difference in real world performance would be hardly noticeable.

The fact some guys are comparing them to a cat just tells you how great these little engines are.