Advice on cam selection

[Cheromaniac]

If you compare the early stock HO cam to the late stock HO cam, the late cam produces more torque up to ~4000rpm but thereafter the early cam comes out ahead. If you want a big slug of low rev torque, the '00+ intake manifold and late cam are the way to go so you can see why Chrysler added those to the 4.0 before it was phased out. The 231 cam will produce slightly more torque in the midrange and about 15hp more at peak but is weaker at lower rpm.
I don't think anyone has tested the 505 Performance roller cams in the real world but I've run a couple of profiles on my Desktop dyno. They have ~50hp advantage over the stock cams and a ~35hp advantage over the 231, with more torque across most of the rpm range.

[Tar2001]

If your engine wasn't smooth at high rpm it could have been an imbalanced, misfire (perhaps linked to the hesitation), etc. Some builders just don't take the time to correctly balance an engine. Close enough is often not good enough. Even though it is internally balanced you still should have the harmonic balancer and flexplate balanced. The last two balancers I took to my machinist were off by 9-16 grams. Two different brands, Professional Products and a Powerbond. I wouldn't even touch a Dorman.

Would any machinist do the job or special equipment is needed. Is it done after or before installing the crankshaft in the block. I assume i have to get another flywheel since im preparing a block to be swap in once completed.

[Tar2001]

If you compare the early stock HO cam to the late stock HO cam, the late cam produces more torque up to ~4000rpm but thereafter the early cam comes out ahead. If you want a big slug of low rev torque, the '00+ intake manifold and late cam are the way to go so you can see why Chrysler added those to the 4.0 before it was phased out. The 231 cam will produce slightly more torque in the midrange and about 15hp more at peak but is weaker at lower rpm.
I don't think anyone has tested the 505 Performance roller cams in the real world but I've run a couple of profiles on my Desktop dyno. They have ~50hp advantage over the stock cams and a ~35hp advantage over the 231, with more torque across most of the rpm range.

These figures are so tempting... I assume the software is taking into consideration the fact that the 505 is a roller cam? How much of this advantage is attributable to the fact that it's a roller cam? In other words, if it was a flat tappet cam but with the same profile, how much gain would be estimated over the 231 instead of +35?

By the way, im obviously not an expert in cams, isn't a cam with longer duration (stock cams compared to the comp cam 231) supposed to have more peak hp instead of more low end torque? Or is this due to the higher lift of the 231 i assume?

Any

[SilverXJ]

Would any machinist do the job or special equipment is needed. Is it done after or before installing the crankshaft in the block. I assume i have to get another flywheel since im preparing a block to be swap in once completed.

Most machinists have a balancing machine. If they don't I am unsure what they are doing. The pistons and then the rods are weight matched. The rods are put on a fixture and each end is measured and matched to the lowest weighting one. The pistons and wrist pin are simply put on a scale and matched to the lowest one. The crank is spun balanced as well as the flex plate and harmonic balance, but separately from the crank.

Also, consider that the 505 roller is a cast cam and won't last past 100,000 miles.

[Cheromaniac]

These figures are so tempting... I assume the software is taking into consideration the fact that the 505 is a roller cam? How much of this advantage is attributable to the fact that it's a roller cam? In other words, if it was a flat tappet cam but with the same profile, how much gain would be estimated over the 231 instead of +35?

By the way, im obviously not an expert in cams, isn't a cam with longer duration (stock cams compared to the comp cam 231) supposed to have more peak hp instead of more low end torque? Or is this due to the higher lift of the 231 i assume?

Any

The software does indeed take the roller cam set-up into consideration, and about 25hp extra is due to that over the flat tappet set-up with the same profile.
The stock cam has a shorter 0.050" lift duration than the 231 cam. Check out my cam spreadsheet at http://www.angelfire.com/my/fan/Jeep4.0Camshafts.htm

[Tar2001]

If you compare the early stock HO cam to the late stock HO cam, the late cam produces more torque up to ~4000rpm but thereafter the early cam comes out ahead. If you want a big slug of low rev torque, the '00+ intake manifold and late cam are the way to go so you can see why Chrysler added those to the 4.0 before it was phased out. The 231 cam will produce slightly more torque in the midrange and about 15hp more at peak but is weaker at lower rpm.

I assume that the 15 hp advantage you are mentioning is when "all other things are held constant", including SCR, but not including DCR? Am I correct?
Well then how about if we shoot at a target DCR and keep it constant by changing the combustion chamber volume. I will give an example based on the site's calculator.

Then what would be the peak power gains for the 96+ stock cam?


Example:
0.060 overbore
Long rods
Combustion chamber + dish volume = 58 + 21.7 = 79.7 cc
Then SCR = 9.55, comp cam DCR = 8.34, post 96 stock cam DCR= 7.88

The same DCR of 8.34 can be achieved with the OEM 96+ cam by reducing the combustion volume by around 6 cc ( SCR of 10.13).

Back to my question, what would be the peak power/torque gains when increasing the DCR from 7.88 to 8.34?
Am i missing something here? Wouldnt the oem cam look more attractive. Any other bottleneck i am missing out in this analysis, like the increased displacement...?

[Cheromaniac]

I assume that the 15 hp advantage you are mentioning is when "all other things are held constant", including SCR, but not including DCR? Am I correct?

Yes, correct. Part of the ~15hp gain is due to the higher DCR with the 231 cam compared to the OEM cam, and the rest is down to improved breathing. In that case you could indeed make the OEM cam more attractive by raising the SCR so that the DCR also raised to the same level as you'd get with the 231 cam and lower SCR. The only downside then is that you'd need to run higher octane gas.

[Tar2001]

The only downside then is that you'd need to run higher octane gas.

I thought the pinging issue would only depend on DCR... I know that 2 similar engines with the same SCR the one with the higher DCR will have more tendency to ping. But from what you're saying i deduct also that it also depends on SCR: 2 similar engines (same quench, disp, etc...) and with the same DCR but with different SCR would not have the same tendency to ping!
Interesting...

[Cheromaniac]

No, I think you misunderstood. The tendency to ping will be the same if you arrive at the same DCR with either the 231 cam or the OEM cam regardless of whether the SCR is different in either case.

The only downside then is that you'd need to run higher octane gas.

Just to clarify, this will happen if you raise the SCR from 9.55 to 10.13 with the stock cam to bring the DCR up from 7.88 to 8.34 (same as 231 cam DCR) as in your example.

[Tar2001]

Ok... So i figured it out correctly at the begining.

So if the stock cam produces more torque below 2300 rpm with a DCR of 7.88 compared to the comp cam with a DCR of 8.34, (and 15 hp less at around 4,800 rpm let's say) then...
Would you go:
1- 9.55 SCR and comp cam 68-231-4 (DCR = 8.34)
or
2- 10.13 SCR and 96+ stock cam (also DCR =8.34)

Then the stock cam would have a torque advantage also above 2300 until ... Which engine speed?
Also, the 231 would have a peak power of less than 15 hp... How much? Are we talking 3-4 hp or 11-12 hp?

Would the comparative advantage of the stock cam decrease as we go for a higher displacement, like 4.7 compared to 4.5?

[Cheromaniac]

Using your own example of a 4.7 stroker with 58cc head, 4.0 rods, and IC944 pistons I get:

SCR 9.70, DCR 8.27 with 231 cam, DCR 8.37 with 96+ OEM cam, and DCR 7.65 with '91-'95 OEM cam using this DCR calculator http://www.projectpontiac.com/ppsite15/ ... calculator which is more correct 'cause it uses advertised cam duration.

So it would be inadviseable to run a higher SCR with the '96+ OEM cam but you could do it with the earlier HO cam, though a DCR of more than 8.0 using this calculator is probably going to require premium grade fuel to avoid pinging.

[Muad'Dib]

Using your own example of a 4.7 stroker with 58cc head, 4.0 rods, and IC944 pistons I get:

SCR 9.70, DCR 8.27 with 231 cam, DCR 8.37 with 96+ OEM cam, and DCR 7.65 with '91-'95 OEM cam using this DCR calculator http://www.projectpontiac.com/ppsite15/ ... calculator which is more correct 'cause it uses advertised cam duration.

So it would be inadviseable to run a higher SCR with the '96+ OEM cam but you could do it with the earlier HO cam, though a DCR of more than 8.0 using this calculator is probably going to require premium grade fuel to avoid pinging.

We have a calculator here that is very similar to that Check the link at the upper right of the webpage...

http://www.jeepstrokers.com/calculator

[Cheromaniac]

Oh yeah, forgot about that. Thanks.

[Tar2001]

We have a calculator here that is very similar to that Check the link at the upper right of the webpage...

http://www.jeepstrokers.com/calculator

Thanks, i did use this calculator

[Tar2001]

Using your own example of a 4.7 stroker with 58cc head, 4.0 rods, and IC944 pistons I get:

SCR 9.70, DCR 8.27 with 231 cam, DCR 8.37 with 96+ OEM cam, and DCR 7.65 with '91-'95 OEM cam using this DCR calculator http://www.projectpontiac.com/ppsite15/ ... calculator which is more correct 'cause it uses advertised cam duration.

So it would be inadviseable to run a higher SCR with the '96+ OEM cam but you could do it with the earlier HO cam, though a DCR of more than 8.0 using this calculator is probably going to require premium grade fuel to avoid pinging.

I think jeep strokers' calculator also uses advertised duration, but i also tried the pontiac calculator which gives very similar results... I used a deck height of 0.010 and a gasket thickness of 0.044, no way to get an SCR of 9.7 it's around 9.56 with both calculators.

Anyway, with an SCR of 9.56 based on advertised duration the comp cam 231 will have DCR 8.35, and the 96+ OEM a DCR 7.89. Reducing the combustion chamber by 5.5cc to 52.5cc (assuming it's doable) will get SCR to 10.13, and then the 96+ OEM cam will also get to a DCR of 8.35! This is where my question comes in...

What i am trying to get at, is a comparison between cams based on a fixed DCR. Of course this implicitly means that i am trying to get an idea about the torque/hp curves by varying not only the cam but also the SCR (in order to compare apples to apples since pinging is a constraint that depends on DCR).
We can afford to have this luxury when designing the engine from scratch, as opposed to just swapping a cam in an already running engine, don't we? I hope you see my point.

I want to start from a target DCR (maximizing it without ping) then i have 3 options to achieve it with 3 cams (and the corresponding combustion volume that would achieve it can be calculated).

At least, to me this would be important to make decision on cam selection.

By the way, Dr. Dino i sent you a PM.