How to build a motor for top end power ?

[dieselfuelonly]

What rocker arm ratio does the 6.5 use?

The 6.5 has a 1.5 to 1 rocker arm ratio. That's according to specs right out of a GM Service Training Book I bought a few years back...dated 11/92.

 

[EWC]

OK , first thing is to get a starting lift number ie .004 , .020 , .050 or ? Without this you have no idea of what you are starting at . Lift is the same for the intake and exhaust . Rockers are 1.5 , lobe lift bares this out . My Crane :

.004 lift

Intake

20 degrees BTDC opens , 54 degrees ABDC closes , advertised duration 254 degrees

Exhaust

62 degrees BBDC opens , 16 degrees ATDC closes , advertised duration 258 degrees

.050 lift

Intake

6 degrees ATDC opens , 24 degrees ABDC closes , max lift 105 degrees ATDC , advertised duration 198 degrees

Exhaust

36 degrees BBDC opens , 14 degrees BTDC closes , max lift 115 degrees BTDC , advertised duration 202 degrees

lift @ cam ; intake .2934 , exhaust .3000

 

[6.2 turbo]

---

Here are my GEP cam specs

Exhaust opening @.050 = 40 degrees BBDC

Exhaust lift .282

Exhaust centerline 116 BTDC

Exhaust duration @.050 = 203 degrees Exhaust closure @.050 18 degree BTDC

Intake opening @.050 =12 degrees ATDC

Intake lift .280

Intake centerline 102 ATDC

Intake closure @.050 11 degrees ABDC

Intake duration @.050 =180 degrees

Lobe separation 109 degrees
Ground in advance 7 degrees

​

 

[EWC]

The DSG is ground in advance . Don't remember what it was but 4 degrees sounds right . I used an offset key to degree mine when I installed it and yes I used a degree wheel .

 

[6.2 turbo]

How does the Crane cam work for you ?

 

[buddy]

CIL6's numbers were taken at .05" lobe lift, thats the industry standard. And I know the lift is the same, as I already pointed out that discrepency. The numbers aren't perfect, but it can provide a basis for comparison until another set on a stock cam is posted, either from a degree wheel or datasheet.

The cam I had custom made is similar but a little more exhaust duration to that Crane cam, but its not been installed.

 

[EWC]

6.2 , don't know how it runs as the truck is still in pieces . I was happy to find a cam as this was started 5-6 years ago and never heard of Delta . I was only the second person to get that regrind and couldn't talk to the first . Comp Cams basically gave me the WTF response cause it was for a diesel . My heads have been ported , almost 30 & 40 CFM improvement , the intakes were tested , single plane worth almost 20 CFM over the dual plane , DSG , 4911 , etc . Can't wait to get it started but it's going to be next year . If you really want to go higher RPM's , port the heads . Get a set and cut one up . See how much you can get into the runners without hitting water . My porter didn't care if it was for a diesel , he just was concerned about air flow . I don't think the cams today are big enough and I don't agree with the " turn the boost up theory " . Everyone told me that putting a cam in a diesel was a waste of time but look where that thinking is now .

Buddy , I fail to see the point in comparing wrong specs for the cam . This just leads you down a different path and that is not good .

 

[6.2 turbo]

What was the total intake port cfm @ what valve lift ? Do you know what the intake port volume is in cc's ? I can check the cc's,but not flow. The GEP intake ports look smaller,will have to look into this.

 

[EWC]

Head : Intake before porting : 176 @ .400 . After porting 208 @ .450 & .500 . Exhaust before : 151-155 @ .400-.500 . After porting : 165-183 @ .400-.500 .

Manifold

Dual plane : 177 @ .450-.500

Single plane : short runner 202 @ .500 , long runner 194 @ .500

 

[THEFERMANATOR]

This what I was getting at early on when I said porting would be a HUGE RPM limiter. Just because you have boost in the intake, it doesn't mean the air is getting into the cylinder in enough time at the higher RPM's. Boost ISN'T the key here, airflow IS.

 

[buddy]

Buddy , I fail to see the point in comparing wrong specs for the cam . This just leads you down a different path and that is not good .

When you or someone else posts specs of a stock cam that came from GM or a degree wheel to compare then we will know if the specs wrong. And not until then, so sorry if youre getting confused by it. Its a set of data, from a stock cam, from a degree wheel. Post what you got.

 

[EWC]

That's basically what I was thinking when I had them ported . At the time the current thinking was just turn the boost up . Boost to me is a resistance to flow . One of the car mags did a test with 2 blowers , a smaller one like a BM and something like a 6-71 or 8-71 . Both were set up to put out maybe 6 psi boost . Obviously the smaller one had to work much harder ie spin faster than the larger one . This related to a hotter mixture and not as much power . Same thing applies to the diesel , more air can be moved for a given amount of boost , pressure etc . A good example of this is the amount of work people will do to the exhaust system and realize performance increases while not going to the same lengths on the intake side . Yes you can do filters and elbows but to get a really good increase in power you need to go further into the engine and most people will not do that . That's one of the reasons I don't agree with posting wrong specs on the cam . This is not a knock on CIL6 , it's just information that should be factual so that we can make an informed decision on parts that may be used . I did some research before I bought my Crane and I can tell you those are not the numbers for a stock cam .

 

[THEFERMANATOR]

The 6.5 has a 1.5 to 1 rocker arm ratio. That's according to specs right out of a GM Service Training Book I bought a few years back...dated 11/92.

My question is though, are they actually 1.5:1 or are they 1.47:1? GM has been known to say they are 1.5:1, but in reality they can vary DRASTICALLY! I know in a SBC it wasn't uncommon to have rockers varying from 1.45:1 all the way up to 1.57:1 in a single set of 16 rocker arms. This is why we need to know are these specs measured at the lifter, or valve? How many were checked to average them against each other? Also were the hydraulic lifters swapped out for solid ones and adjusteable pushrods used? There are alot of variables to consider when degreeing a camshaft, espescially when you are working on OEM factory parts with such a variance allowed in them.

 

[sshewins]

IIRC, and I think I do, didn't Bill Heath use 6.2 valves because they are larger? I would have to think that if we're going for every last little bit, then the larger diameter valves, with a 3 angle valve job in addition to porting and polishing, or if funds allowed, extrude honing the runners for the ultimate in flow.

 

[EWC]

OK Buddy , I did post them on the "other" site . I'm not confused , got them out of a NAPA book . That's how I know that the Crane is different . Tell you what , why don't you check a cam and let us know what you find ? That way we don't have the " he said she said " situation going on and we can come straight to you for the answers .

 

[EWC]

Good point Ferm , the cam card for my Crane says tappet lift when starting at .004 and .050 .

 

[THEFERMANATOR]

IIRC, and I think I do, didn't Bill Heath use 6.2 valves because they are larger? I would have to think that if we're going for every last little bit, then the larger diameter valves, with a 3 angle valve job in addition to porting and polishing, or if funds allowed, extrude honing the runners for the ultimate in flow.

Larger valves are not always the answer. A larger valve can make it flow LESS unless you open up the intake runners and everything above it as well as make sure the valve isn't shrouded inside the combustion chamber. A valve can only flow what the intake runner can flow, putting in a bigger valve without opening up the runner simply means you put a bigger obstacle for the same amount of air to go around. Bigger isn't always better, but volumetric efficiency is the key.

 

[THEFERMANATOR]

Good point Ferm , the cam card for my Crane says tappet lift when starting at .004 and .050 .

Most cam specs that I am used to seeing will list lift at the lifter, and in some cases will also list a lift with X ratio rocker arm. Measuring at the rocker arm, or multiplying it out at 1.5:1 isn't a true representation of the camshaft. It would be nice to find somebody who could check both a GEP and a GM with the same set-up at the lifter in the same block to know if there is a difference. I stil lhave my 95 short block out in teh shop, I'll see if I can find time to drag it out and put my degree wheel on it and see what the lifter lift is on it as well as get some baseline degree specs for it.

 

[sshewins]

Sorry bout the confusion Ferm, you're absolutely correct. Valve size is meaningless if the rest of the runners aren't wide open as well. Both in the head AND intake manifold. And the exhaust side of the equation isn't being overlooked either. A lot of little pieces here and there add up to a great piece of work.

 

[EWC]

Shop manual lists lobe lift @ 7.133 mm + or - 0.05 . That's .281 inches lobe lift multiplied by 1.5 rocker ratio = .421 . This would be easy to check , just mic the lobe and the base circle . That I can do on a stock cam .