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  #61  
Old 05-22-2006, 05:48 AM
dynomatt dynomatt is offline
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I'm new...but have some general experience with cams.

In my experience aftermarket cams are often sold with either an advertised duration or a 0.050" duration.

The intent is that at 0.050" (remember that's 1.27mm lift) it's taken up most of the slack in the valve train, and is a repeatable indication of the cams duration.

Advertised duration varies wildly based on things like hydraulic pump-up effects etc and is unable to be reverse engineered to a 0.050" result.

www.tighecams.com.au who are cam grinders of repute in Australia utilise the 0.050" system, as do others...it's not limited to the US.

And Trevor, all your comments about how the duration is related to TDC positions etc, in my experience, doesn't have much relevance. Lobe centrelines or angles or LCA or whatever you want to call them, become the important issue....and they can be set (assuming vernier wheels) however you want. That's where you can also effect overlap as Tom mentioned.

The other thing that's been bugging me is the cam suggested earlier, with a duration of 247 degrees, and then it being suggested to be retarded 7 degrees...I don't think this will have the desired effect. Duration is a function of the lobe profile, and retarding the cam timing doesn't alter that...it just means that the cam will be retarded with the associated losses.

Having just been through a fair bit of grief to do with cam selection on a recent rally car project, I'm comfortable with what I'm saying.

This page (http://www.billzilla.org/4agmods.htm) by example has some information regarding 4 valve per cylinder performance mods specifically for the 4AGE. Obviously there are marked differences between the EG33 and the 4AGE, but some of the core theories can be applied. He talks about common 4 valve twin cams having about a 240 degree (seat to seat, not 0.050") duration which is close to the EG33. He then suggests that going to something like a 264 degree (seat to seat) starts to be the limit of the standard ECU. Having read elsewhere on this forum, I suspect MAF's become a problem before that. Combine that with the guy who built the WRX with the stock EG33 and ony an aftermarket ECU, which yielded 212ATWHP, I suspect the standard EFI system is a limiter.

Based on that, my theory is that I suspect EG33's could absorb more than 247 degrees...and maybe more like 260 which is the kind of duration for Tom's originally proposed "little more radical" cams.

If I had a spare complete head, I would be happy to get another set of cam measurements to get the standard profile (if only to support prior work), but more importantly, I have access to a flow bench, and could continue Bill and VTSuby's work in order to start to more accurately realise the potential of this motor.

Matt
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  #62  
Old 05-22-2006, 07:58 AM
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Greetings Matt,

You certainly appear to be an authority on cams and you are a welcome addition to the thread. In fact I would accept that I am no longer required.

I have never seen figures set out as has been described and accept your superior knowledge and have been wrong in doubting Harvey, even though his evidence is far from convincing. I fully understand the reason for including the 0.050" figure but this does make it very difficult to relate specifications.

You have provided the required figure I needed to enable the relationship to be ascertained i.e. 0.050" equals 1.27 mm lift. This is the exact information required and had it been known and provided there need be no arguement.
With this on hand it is possible to put figures together. It would appear that my assumption that the figure shown as BTDC is in fact ATDC, the negative sign indicating this.

I gather what you are saying is that the lift and closing ramps are probably of a different shape and hence the lobe need not be centred. Please confirm. Even so there must be a relationship established/existing between piston position and valve timing. We appear to be simply at cross purposes in the way we may be describing this issue. However I am sure that I clearly made lobe centre lines the important point as you do.

We are in accord regarding the possible ammended timing figures particularly the suggested 7* retard figure which I could not relate to. What is more I agree 260* duration should not be out of the way.

Your further comments will be appreciated by all.

Cheers, Trevor.
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  #63  
Old 05-22-2006, 04:17 PM
dynomatt dynomatt is offline
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No flattery required...but thankyou.

I'm unsure whether lift and closing ramp shapes differ...I would suspect not. In fact most cam graphs I've seen show a perfect arc...suggesting that both ramp shapes are identical. I expect it may also be a machining issue.

A relationship does exist with cams and piston position. It is referred to as the lobe centre angle, centre line etc. This is always quoted as a degree of BTDC and ATDC eg 110-115 degrees. For example, for inlet cams, 110 degrees AFTER TDC is the point that the inlet valve is fully open. Adjustment of these centre lines changes things like overlap etc. Longer duration cams usually mean the centre angles are reduced...but then other problems arise, like idle etc.

My reading of the site says that this is usually where the "interference engine" issue arises...but you'll notice that the valve is fully extended when the piston is 110 degrees after TDC...hence it's 2/3 the way down the bore (or 50mm when we are talking about 8-10mm lift ).

Where I am curious is that given the exhaust cam drives the inlet cam in a geared arrangement, just how much adjustability do we have to select optimum centre angles assuming a vernier wheel is fitted...I suspect not much. A vernier cam wheel will only allow mutual advancing/retarding with both cams acting as a unit...rather than individual adustments which is optimum. This could be a limiting factor but I suspect if it is, it would only be a minor one.
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  #64  
Old 05-22-2006, 06:25 PM
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Lobe centers.

There are two forms of "lobe center" talked about. One is the angle formed between the inlet and exhaust cam lobes, and the one that I use, is the inlet valve fully open position, in relation to the crankshaft position.
This has more meaning that just the relationship of the inlet and exhaust lobes, to each other, which is just the result of positioning the two individual cam positions.

The main objective of timing the inlet cam is to match the maximum open position of the inlet valve to the maximum air speed in the inlet tract. The fully open position of the inlet valve is fixed by the gearing. The maximum air speed in the inlet tract varies with the engine speed. The maximum piston speed is achieved at about 85* ATDC. At say 1000 rpm the maximum air speed will follow the piston, but as the engine speed increases the maximum air speed lags behind the piston speed. So that at say, 5000 rpm the maximum piston speed is at 85* ATDC, but the maximum air speed will not happen till say 115* ATDC.

So to get the engine to develop maximum torque at 5000 rpm we have to have the inlet valve fully open, at 115*to allow the maximum air speed to match the fully open valve position. As we change the engine speed for maximum torque, we have to change the inlet lobe center to bring the two to the same speed. Move the torque peak up the rev range requires the lobe center to be retarded. Bring the torque down the range needs the lobe center to be advanced.

The duration used, is a function of the engine speed that the maximum torque is required. The higher the engine speed, the longer the duration needed to allow the cylinder to fill.

This outlines the 3 stages that I purposed, some time ago.
http://www.subaru-svx.net/forum/show...ghlight=stages post 164.

Thanks for joining the thread Matt.

Harvey.
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  #65  
Old 05-22-2006, 08:10 PM
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Matt,
Ditto what Harvey and Trevor said regarding your joining the thread!
What I believe I'm reading now is that the 7 degree of "retard" used when installing the DeltaCams in Chike's old car, Tom's old car, and ShotgunSlade's car is, most likely, reducing the Hp increase possible with these cams?
Thanks.
-Bill
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  #66  
Old 05-22-2006, 10:05 PM
dynomatt dynomatt is offline
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I'm not sure...I believe that advancing the cam generally improves the low end torque. Within limits obviously.

The only way you can tell if it's doing anything is to dyno it back to back.

So much of this stuff is trial and error.

Matt
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  #67  
Old 05-22-2006, 10:06 PM
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Oh and Bill...what would help is more flow information!!!
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  #68  
Old 05-22-2006, 10:31 PM
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Quote:
Originally Posted by SVXRide
Matt,
Ditto what Harvey and Trevor said regarding your joining the thread!
What I believe I'm reading now is that the 7 degree of "retard" used when installing the DeltaCams in Chike's old car, Tom's old car, and ShotgunSlade's car is, most likely, reducing the Hp increase possible with these cams?
Thanks.
-Bill
Yes Bill, I explained that back in Chikes thread here.
http://www.subaru-svx.net/forum/show...8&postcount=97
Harvey.
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  #69  
Old 05-23-2006, 04:04 AM
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Final Figures

An important object of this exercise, now well off track, was to analyze the differences between the cam grinders figures and Subaru's specifications. At long last here are the figures :-

Subaru's figures relating to the standard cam are shown as, SS

Grinders figures relating to the standard cam are shown as, SG

Grinders figures relating to the modified cam are shown as, MG

All figures should be read as degrees of angle.


Relating the figures SS and SG:-

Duration: SS 180 + 2 + 54 = 236. SG 180 - 27 + 33.8 = 186.8.

Overall Difference = 49.2. At each end of the cam, 24.6

Therefore 24.6 is the estimated rotation relative to 0.05" valve travel.

Inlet, SG 27 ATDC - 24.6 = 2.4 SS 2 BTDC and error = 4.4

Exhaust, SG 33.8 ABDC + 24.6 = 58.4 SS 54 and error = 4.4

Corrected 0.05 travel figure = 24.6 + 4.4 = 29

Comparison between SG and SS figures:-

Opening SG BTDC (-27) Correction 29 = 2, SS = 2 ( No change)

Closing SG ABDC 33.8 Correction 29 = 62.8, SS = 54 ( 8.8 increase)

N.B. The correction figure has been calculated on absolute values and it is probable that Subaru's figures provide for some slight valve/lobe clearance, in which case the figure of 29 could be accepted as say 27.5. This would bring the figure of 8.8 increase, down to 7.3 which is near the obscure figure mentioned several times in the thread.

Relating the figures SG and MG:-

Duration: SG 186.9, MG 180 - 23.4 + 36.2 = 192.8, Increase = 5.9 = 3.2 %

Relating the figures MG and SS:-

Duration: MG 192.8 + 29 + 29 = 250.8, SS 236, Increase = 14.8 = 6.27%

The end result of the cam grind, as anticipated, indicates only a very limited degree of change which appears hardly worth the effort and expense.

The increase in lift shown is .784 mm which amounts to 11% increase.

Edit:- The actual effective increase in breathing can be shown as less than 3%, due to the limited time when the valve is fully open. However there could be some additional very limited advantage, due to a slight increase in the terminal speed of the gas flow.

Going for the reasonable maximum and to make a real difference, I will stick my neck out and suggest:-

Based on Grinders Measurements:-

Duration: 202, Opening 24, ATDC, Closing 46 ABDC.

Edit. I think you could go as far as say:- 210, 20, 50.

Based on Usual Measurements:-

Duration; 260, Opening 5, BTDC, Closing 75 ABDC.

Edit :- 268, 9, 79

Are there any takers ?
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Last edited by Trevor; 05-27-2006 at 08:39 PM.
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Old 05-23-2006, 05:59 AM
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Actually, I believe my cams were ground to Harvey's suggestion for the 5MT with 3.9 ratio

"8mm lift, 247* duration and 118* lobe centering, per Harvey's recommendation for use with 3.9 5MT."
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  #71  
Old 05-23-2006, 06:26 AM
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Quote:
Originally Posted by shotgunslade
Actually, I believe my cams were ground to Harvey's suggestion for the 5MT with 3.9 ratio

"8mm lift, 247* duration and 118* lobe centering, per Harvey's recommendation for use with 3.9 5MT."
Where he recommended those specs?
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Old 05-23-2006, 09:09 AM
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If my duration is 247 degrees and the lobe centering is 118* ATDC ,then opening would begin at 5.5* BTDC and closing would be at 62.5* ABDC, assuming that the opening and closing cam profiles are symmetrical. If this is correct, then I may be beginning to understand the geometry of this issue.
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  #73  
Old 05-23-2006, 02:10 PM
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Quote:
Originally Posted by dynomatt
Oh and Bill...what would help is more flow information!!!
Ouch

I've got to get the right bolts (yes, M10-1.5 bolts are NOT the right bolts to put an EG33 up on an engine stand ....M10-1.25 on the way...) so I can get my spare engine on the stand and pull the heads off and get moving on them. The heads I already have will probably be sliced up...
-Bill
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Old 05-23-2006, 04:29 PM
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Quote:
Originally Posted by shotgunslade
Actually, I believe my cams were ground to Harvey's suggestion for the 5MT with 3.9 ratio

"8mm lift, 247* duration and 118* lobe centering, per Harvey's recommendation for use with 3.9 5MT."
As I understand it all of the cams which have been ground are in accordance with the grinders specs as posted in this thread. My figures are based on these. If you doubt their accuracy please check them out and advise. If there are errors these should be corrected as a matter of urgency.
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Old 05-23-2006, 04:45 PM
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Quote:
Originally Posted by shotgunslade
If my duration is 247 degrees and the lobe centering is 118* ATDC ,then opening would begin at 5.5* BTDC and closing would be at 62.5* ABDC, assuming that the opening and closing cam profiles are symmetrical. If this is correct, then I may be beginning to understand the geometry of this issue.
It would appear that you are using the usually quoted figure for duration and the grinders figures for lobe centre. This has been a problem through out and is the very reason I have gone to considerable trouble in producing figures which clarify the position. I leave it to you to use them.

BTW as far as I can see Harvey has not produced figures which exactly indicate positions relative to TDC/BDC. Could someone please point out exacly where these can be found. There does appear to be absolute confusion regarding these figures.
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Last edited by Trevor; 05-23-2006 at 04:52 PM.
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