: DOHC theory, any new information?



Pontiacivan
09-30-13, 01:22 PM
I wanted to discuss some of the issues I seem to be having regarding camshaft specs for the Northstar 4.6, specifically my 05

design L37 engine. It seems that traditional

cam selecting techniques don't apply, most notably duration and overlap. After reading

http://www.cadillacforums.com/forums/northstar-performance-technical-discussion/122654-northstar-cam-specs.html

I was surprised to note that the early L37 had "long" 266 degree intake cams and 26 ,low by traditional

standards but apparently huge in the DOHC world. Comparing this to my 05 with 10.9 degrees of overlap

and cams smaller than the original LD8 it appears as though the L37 got crazy efficient. Even the 00-03 cams have more duration and

overlap, in fact the LD8 from those years has duration numbers close to the later L37 but with more overlap. Several things come

to mind first of which is: What does the torque curve for the 04-05 L37 look like? There is a popular dyno

graph for the early

engines that makes the L37 look "soft" on the bottom end compared to the LD8, but I would bet that the torque curve for the 04-05

L37 looks a lot better, though I cannot find a dyno graph for this year engine. Second, based on the cam specs given it appears

that all the 00-05 cams are installed retarded but one would like to assume the factory placed the centerlines in the optimum

positions after much dyno testing. I would hope. Third, getting back to overlap, this engine revs to 6400 RPM with only 10.9

degrees of overlap. So much for exhaust initiated intake. This seems to be the norm with other DOHC engines regardless of make

or displacement. And of course, duration is no where near what conventional cam theory suggests. I have searched the internet

looking for someone to say "The rules for DOHC cam selection are different because..." The best I could find was David Vizards

statement that DOHC engines tend to draw the intake charge through the combustion chamber meaning that normal amounts of overlap would be a bad

thing, in my opinion. I sincerely want to run some performance cams ( I am going to use Comp Cams regrind service ) If regrinds

are good enough for CHRFab, they are good enough for me. I am currently looking at the XE258BH-116 profile used on their F@#D

4.6 4v cams, though lift will be slightly lower due to our 1.68 followers vs the F@#D's 1.8. This profile is computer friendly and has 26 degrees of overlap, no more than the early L37

David Vizard has a chart for calculating correct

LSA based on intake valve size and CID. Though I hate selecting cams based on LSA, converting the area for two Northstar intakes

to a single larger intake results in a LSA of 116 which happens to be the LSA for this grind. The intake is at 114, or a traditional

advanced setting, in this case 2 degrees. I/E advertised durations are 257/259 with lobe lift being ground

to .250 for .420 valve lift. This profile makes good numbers in all the car mag "build ups" for the F@#D and

with ported heads from CHRFab, I would like to believe the lowest of these at least is within the grasp of

the Northstar. I realize a lot of the power will come from improved exhaust and even though the solutions

are few and crappy, I have a workable plan that should increase the front to rear flow.I do not recall the

Northstar intake ever being listed as a power limiting item. I have 32lb injectors and a modified PCM tuned

currently. Wondering about anyone's input regarding this path. Thanks!

98eldo32v
09-30-13, 02:29 PM
The things that you are talking about, MOST will not dabble in because they aren't trying to extract as much as they possibly can from their motor while going that deep into it.

Ironically, the things you are talking about I can appreciate but there is little to next to none for motorsport parts for this motor.

While it has it's quirkiness to headgaskets at times, this motor in stock trim in my opinion is severly de-tuned.

It gets the job done fairly decently in the massive bodies it has been placed into but yet, no tuning per se', no adjustable cam sprockets to dial in the motor as one sees fit. No decent exhaust systems that actually improve power versus exhaust note/sound.

I have a 2.3 quad 4 "A" engine in my 93 grand am gt . At one time Olds Rocketparts offered indexed cam sprockets for this engine. You could tailor the timing from 4 degrees advanced to 4 degrees retarded. Allowing one to "tune" for what they liked. Try find those things now........

I guess no one figured there would be some that would like to extract more power out of their stock set up.

Yet, I feel the biggest issue with the motor and maybe I'm wrong is that cross over pipe that joins the front exhaust manifold to the rear section. It's a tad bit small but conisdering it was packaged for a fwd platform, what is one to do.

When I finally start working on my eldo, I plan to disassemble the heads and clean up the bowls just under the valve seat and look at how much the exhaust port is possibly choked off.

As for sucking more power out of the set up, I suppose I can try to get pcm tuned for my 98 but I'd have to see some real world proof that it's worth it.

Till then I guess we sit and wonder how much potential the stock trim will really have.....

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If you haven't discovered these guys yet........

http://chrfab.topic-board.com/