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Cylinder Head and Camshaft Comparison.

Rockabillyrat

Rockabillyrat

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As I get closer to my engine build I've been spending some time researching head flow CFM and camshaft profiles on the 6.5. When upgrading to a much more efficient turbo I wanted to see if improvements could be made to the engine to make the most out of a turbo upgrade. So I took the time to locate head CFM and cam specs from other diesel engines as a comparison. After all an engine is just a giant air pump, and air doesn't care if its DI or IDI. I was very surprised by what I found and it completely changed my opinion on porting 6.5 heads. I figured some of you might be interested in this information.

CYLINDER HEAD CFM

ENGINE- INTAKE CFM/ EXHAUST CFM/ VALVE LIFT

6.5 - 175/145/@.500
7.3 IDI - 187/163/@.500
7.3 PS - 110CFM
6.0 - 162/122/ @.500
12v - 143/151/ ?
24v - 156/169/?
LB7 - 183/149/@.500

NOTES:
* According to TSP chart the 6.5 did better on the intake at .450 lift (180cfm)
* Could not locate any more info on the 7.3 PS
* Alternate specs for the 12v 131/139/@.500 maybe this is with the integrated intake have not been able to confirm.
* Some claim the 24v does 185cmf stock
* For comparison a ported 12v head flows 184/195/@.500

I was surprised to see how well the 6.5 heads compare to the rest. Especially with the power levels I know the other platforms make with stock heads. . For my build I'm thinking of leaving the intake side of the heads alone, with maybe some slight exhaust port work. Then upgrading to 1.6 rockers to get a .450 net valve lift to max out the flow of the head. Now on to camshafts...


CAMSHAFT

Intake Duration @ .050/ Exhaust Duration @.050/ Lobe Separation Angle

6.5 - 178/201/110
7.3 IDI - 176/184/103
7.3 PS - 177/185/104
6.0 - 167/176/106
12v - 159/204/102
24v - 159/206/107.5
LB7 - 176/176/106

NOTES:
* I found 2 different LSA for the 7.3 IDI once source said 103 the other said 105
* For comparison a stage 1 performance 12v cam is 175/210/104

Again I was surprised to see how the 6.5 compared to the rest. The only thing that really sticks out is the wide LSA the 6.5 cam has. I assume this is because the 6.2 (same cam as the 6.5) was a N/A diesel and they wanted a wide torque curve to go with its 4400rpm operating range. Then once they added a turbo the LSA was also beneficial to deal with the high drive pressure of the stock GM turbo. But with a more efficient turbo I think the LSA could be knocked down to 108 maybe even 107. Most performance diesel camshafts are in that LSA range.

I'm sure some of you will rake me over the coals for this. But my unpopular opinion is that the stock heads and cam are fine just the way they are for 99% of 6.5 builds. The CFM you gain from port work, big valves, and high ratio rockers doesn't make much of a difference on a turbocharged engine. That extra CFM can easily be made up with a turbo. Port velocity is more important than CFM to a point. Obviously your not going to make 1000hp on heads that flow 100cfm. Its a balancing act of CFM, and port velocity to have a responsive engine that makes your power goals in the RPM range of you engine. Look back at the muscle car era, they proved big heads+ big cam+ big carb = port stall and the car was a dog off the line.

To my knowledge these specs are accurate, but if anyone sees something that's wrong please let me know.
 
I think on a basic low modded 6.x things are well balanced as you stated, and more flow is needed in the exhaust side, is good porting necessary, no, can it help in the overall picture, I think so, but only if done right..

I won't post numbers but I can say I'm working with a diesel cam specialist concerning my motor, now he has been doing cams for pullers for many years with a large customer base of well satisfied customers as just a fyi...

He also asked for flow numbers with intake & exhaust bolted on, something only my flow man talked about but I never gave it any thought...

He asked for measurements I never thought would be needed until he explained the computer program. He did say the lsa would change in my case and a regrind wouldn't fix that..

Thankfully, he was a 6.5 guy many years ago and even offered a cam for someone to test but 15yrs ago no one gave much thought to different turbos much less cams, and no one took up his offer...

Good work doing the research, if I can find the link there is a way to figure how much lift a cam/motor will benefit from...
 
Just for reference I flowed a new in the box stock P400 head, pulled numbers every .050" lift up to .500" , below are the numbers..


LIFT​
INTAKE​
EXHAUST​
.000​
0​
0​
.050​
18​
33​
.100​
56​
47​
.150​
82​
64​
.200​
107​
79​
.250​
133​
95​
.300​
152​
112​
.350​
167​
121​
.400​
180​
126​
.450​
181​
130​
.500​
184​
131​
 
Wow thoes exhaust CFM numbers on the p400 are low 😳

Makes sense to ask for flow numbers with the intake and exhaust on. Doing just the heads can through things off I imagine. Thats some exciting stuff. Im looking forward to how this camshaft performs for you. Keep us up to date on that process.
 
My heads are in the 230-240 range . Crane regrind is 198 /202 and .440/.450 lift . The stock dual plane intake is about 20 cfm down from the single which is about 200 cfm . I think what Chris said is true but for the 1% that want to push it , heads and cam work will be on order .
 
Good info guys. I think Littleboy has shown that getting higher power levels than most of us are accustomed to is as simple as adding more fuel with a properly sized turbo. I think he may be on to something in his pumps that others haven't figured out yet. Reliability at those levels is probably measured in hours instead of years!
Seriously though, I am an information junkie. And I appreciate the time and money you and others have poured into this platform for the benefit of us all.
 
Have you flowed any Promaxx heads?

CDD is up to some interesting stuff. .370 H&R is possible with the right parts. The hard part is finding them. The biggest DB2 offered was a .370 4 cylinder AG pump. I haven't check with my stanadyne rep to see if the H&R is still available. But the .390 and .450 are discontinued. Both only offered in the early D series and the rotor requires machining to fit. CDD told me he had a supply of NOS H&R he luckily found. Also he is custom building a .500 and .550 rotor.

I'm working on a few things myself.
20201024_222835.jpg
 
https://www.enginebuildermag.com/2017/03/flow-bench-testing-cfm-numbers-need-know/

Good article, its focused on NA gas engines. But air flow is air flow. The main thing I see EVERY head builder say is the three most import parts of a good ported head is port velocity, port velocity, and you guessed it port velocity. A head can flow more CFM on a bench but if the port shape is wrong you can actually hurt HP.

With a turbo engine CFM becomes less of an issue because your not relying on atmospheric pressure to push air into the engine. Lets say head A flows 200cfm and head B flows 250cfm. Head A made 400hp @ 20psi of boost. And head B made 400hp @ 15psi of boost. Boost is a result of restriction in the head. So a lower CFM head will have a higher boost number with the same turbo vs a head with more CFM. But they still made the same HP. That's because the turbo will force feed the engine with whatever CFM it makes at a given RPM. Both heads are getting the same amount of air into the cylinders. Just head A has more boost pressure thus more air density. So if your just going off CFM numbers on your heads you making a big mistake. and in some cases you might be hurting HP and turbo spool.

So far we have seen 450 WHP out of stock promaxx heads @ 20psi from Banghart's truck. I just don't see a point in porting 6.5 heads unless you are pushing 500+ hp. We might learn more as they data log the truck.
 
Interesting that you made the statement about atmospheric pressure " pushing " air into the engine . Most think it " sucks " in air .

As far as boost is boost , most people think that way . I do not . 15 lbs of boost on a smaller turbo vs larger turbo will have a much higher IAT and the resulting effect is less dense air . Some say mass flow , I'm not sure . If this were not the case , why run an intercooler ?
 
I'm not talking about different turbos. Same turbo on different heads. They will have diffent boost numbers due to different head flow CFM. Of course 15 psi on a big turbo is different than 15psi on a small turbo because of the CFM differences between the two turbos. My point is 50 CFM differences in heads with the same turbo wont gain you anything.

If you want to get into the thermodynamics of it then yeah small heads will make more heat. But I highly doubt a small difference in head CFM is going to drastically change that.

Turbo Ls guys proved years ago they can make the same power no matter what heads they ran.
 
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That was a good read by Darin . One of the items I wrestle with is comparing gas to diesel boost numbers and the resulting gains or losses from boost . Not really impressed with turbo numbers as I could put one on a weedeater and make power . More of a NA guy but I don't overlook the results either . I'd be willing to bet the LS guys just ran more boost to get their numbers . That being said , my porter made the claim that 40 CFM was worth 100 HP . Some how does this cross over to diesel ? I'am not sure . I started my engine a long time ago because no one did anything with porting a diesel , at that time , along with camshafts . I didn't look at boost , just more air in and out . Boost by itself can be good and bad but the result is just more air . What you do with that is up to you . More air and you can run more fuel and that is the main advantage , more fuel . More fuel , more power . If the boost is hotter and less dense , then you need an intercooler . Would this happen with just the heads being ported ? Not sure but my thinking was maybe with the extra flow that might help to cool the cylinders some resulting in lower EGT numbers . I should get my engine running as I have a Banks kit and aside from the cam and heads , we know what to expect as far as numbers and performance .
 
The rule of thumb on CFM to HP is what ever your heads flow you double that and that is the supported HP in a NA application. So 200cfm heads support 400hp give or take on a NA engine. Say you port the heads to 250cfm then they are going to support 500hp. That all goes out the window on a turbo engine. Because again your not relying in atmospheric pressure. If your running 15psi you basically doubled the pressure entering the engine. So now you can make more that 400hp with the same 200cfm heads. Want more power, turn up the boost and increase the air density just as long as you stay in the efficiency range of the turbo.
 
I would question the theory or where it came from . If you are talking about gas , with the fuel in the air , then yes . We don't have that with the IDI so it is basically a " dry " intake . Swirl , tumble , etc all come into play with gas engines along with the " wet flow " benches . The fuel will displace some of the air in the manifold , IDI does not . So in theory that should mean more HP will be supported if you could get the fuel in . Agreed on the efficiency of the turbo as that is or could be a problem .
 
Here is the math. Like I said CMF flow x 2 is close to the HP the heads will support. Its not perfect but its easier to do in your head.

" HP=. 257 x (peak) airflow x number of cylinders. If we plug in flow data from a CNC-ported small-block cylinder head that offered a peak flow of 304 cfm, we get the following: HP=. 257 x 304 x 8 or 625 hp"

Straight from Google.
 
You're missing the point . Those are formulas for a gas engine that carries fuel in the air . Even if this was an injected or TPI engine , it carries fuel . Fuel helps to cool the air mixture and by being injected into the air , it helps to breakup the mixture . Injector placement is critical , checkout some of the vids of the Renault F1 engines on the dyno . Wild stuff ! My main point is that we don't really know what more airflow does in a diesel . With this extra flow , thru porting , you now have the potential to run more fuel into the engine . How you use this extra air is up to you .
 
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