Why did my peak rev range change?
 

My 3.0 with 20/21 cams had peak HP @ 6400 and torque @ 5500.

My 3.4 was built with the same case and heads using the same 20/21 cams has peak hp @ 6100 and torque @ 5200.

The 3.4 used the same heads, a bigger throttle body, half mooned cylinders, lighter rods, lighter pistons, Ti keepers with HD valve springs and a boat tailed case.

Both used the same CIS system.

Why did the rev range drop on the 3.4? I would have thought it would have went up 300rpm, instead of down 300 rpm, with the weight drop on the internal parts and better breathing from the case/cylinder work.

It probably has to do with the bigger displacement itself. The bore to stroke ratio is different and the amount of air being sucked in per revolution is more on the bigger engine. It reaches the capacity of the intake system at a lower RPM.

-Andy

Also the weight of the internal parts has no bearing on the power the engine produces other than a slight effect from the way an inertial dyno would measure it. The internal case mods probably don't have a noticable effect on the RPM the torque and HP peak at.

-Andy

I think the primary reason is that your induction/exhaust (intake runners, ports, HEs, muffler) did not "get bigger" in proporition to the displacement increase.

I agree.

Your heads still flow the same and choke the output. Actually, your whole torque range is probably elevated compared to original engine but starts tapering down at high revs when heads cannot flow enough.

The increased torque range was given going from a 3.0 to a 3.356l (3.4). Torque at 2500rpm on the 3.4 is 175#. Max torgue at 5500rpm on the 3.0 was 168.

If you graph the two engines the 3.4 leaves a max of 8 to 10 hp on the high end of the rev range but doesn't drop off as sharply as you close in on 7K rpm as the 3.0 did. The torgue drops off 500 rpm sooner but graphed leaves a good 25# in comparison to the 3.0. I have 250# of torgue by 4000rpm which happens faster than some of the stock 3.6s and it stays there till 5200rpm so I am not complaining.

So the question is would keeping the same cam to clear the MM P&Cs and replacing the CIS with Motronic or a Varioram system
add much to the rev range, the HP or Torgue? How about head work? These are '79 heads btw.

SSIs and a Danke 2/2 are the exhaust.

What is the ultimate set of upgrades in induction and head work to help out my cams and P&Cs?

My opinion?

So the question is...
1) ...would keeping the same cam to clear the MM P&Cs and replacing the CIS with Motronic or a Vario cam system
add much to the rev range, the HP
>>> In both cases I believe the answer will be yes as long as the new induction system flows better then the CIS system.

2) or Torque?
>>> Most likely not much, but it might shift the torque curve around some, or broaden it in the case of the Vario Ram system. I doubt that you could retrofit a Vario-cam system onto your engine without a lot of effort.

3) How about head work? These are '79 heads btw.
>>> I'd start with the induction system first. Once you have reduced the restriction there, you might find a smaller improvement in your heads given your current configuration.

Yepp. Your midrange torque would probably stay the same but changin those CIS-friendly mild cams for something hotter (Motoronic won't mind) would extend your torque curve upwards which would ultimately yield more top HP.

If you spend most of your driving between 2000 and 4000 RPM then it's probably not worth the money.

If you race and need those extra 20-30HP (my guesstimate on how much you would win) on top then it's a good idea.

I wouldn't mess with heads before doing what was previously mentioned. Individually, they usually flow quite good actually, it's a combination of mild cams and CIS flapper door that chokes the most.

Thanks John.

"I doubt that you could retrofit a Vario-cam system onto your engine without a lot of effort."

Sorry, my mistake, typing varioram not the vario cam. The varioram has been done on a 3.2 with good results giving 220hp at the wheels. And even better torque IIRC.

dane, you are thinking of varioram, not variocam.

The Max Moritz Pistons won't take much more than a 20/21 or GE40 cam. So changing cams is not an option as mentioned in the previous post.

Engine spends a good deal of time between 4 and 7.


Thanks, Goran.

Sorry Andy, I was thinking Varioram induction off the later model 993s as an option since one of the local shops has done it.