| Author |
Message |
    
eric
| | Posted on Friday, October 04, 2002 - 03:35 pm: | 
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Hello,
What would be a good cam for a replacement? I'm in California, so it can't be too radical and screw up the emissions test.
Just looking for your basic low-end torque/economy cam, idle to 4K. Something other than the stock.
Thanks for any ideas,
eric |
hey
| | Posted on Friday, October 04, 2002 - 04:24 pm: |
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http://www.rpi-engineering.co.uk/ |
Jason Vance (Jason)
| | Posted on Friday, October 04, 2002 - 05:03 pm: |
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Crane still makes cams (and lifters, etc) for the buick 215 that should fit the Rover. Find a cam with greater lift than stock, but minimal increase in duration (keeping the overlap low and the powerband low where it needs to be). It should be cheaper than RPI as well (especially when you consider the shipping). |
hendrik
| | Posted on Monday, October 07, 2002 - 02:43 am: |
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How much difference is to be expected from such a Crane camshaft. The standard Rover cam should be designed by Rover to do just what eric wants.
I´m just asking (no expert as you know, but there is many times a possibility to improve things and many times one to share money  ). |
Ali
| | Posted on Monday, October 07, 2002 - 06:34 pm: |
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I don't suppose anyone here has the specs on the 3.9/4.2 LR cam? |
eric
| | Posted on Monday, October 07, 2002 - 07:55 pm: |
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For a stock 3.9 cam:
valve lift - .373 in./ex.
duration - 256 degrees for in./ex.
Compare to the RPI Piper cam:
valve lift - .432 in./ex.
duration - 260 degrees for both
Crane:
lift - .416 in. / .432 ex.
duration - 260 in. / 268 ex. |
eric
| | Posted on Monday, October 07, 2002 - 07:58 pm: |
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The 4.2 cam is different than the 3.9. I don't have the manual in front of me, but the info. is under the 4.2 engine data section. |
Jason Vance (Jason)
| | Posted on Monday, October 07, 2002 - 11:46 pm: |
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FWIW,
don't fear the split-duration Crane cam. The stock 3.9 cam is on weird lobe centers (retarding the exhaust...? I hafta check...); but it looks like the Crane specs addresses a restrictive exhaust port design. Both the Piper and the Crane should offer an increase in low-end torque that will increase drivability. Total increase in peak HP won't matter too much since the auto t.ranny usually shifts well before the engine's peak HP anyway; but the overall increase in torque and HP across the typically used RPM range should beneficial. |
Randall Smith
| | Posted on Tuesday, October 08, 2002 - 08:40 am: |
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One thing that's interesting:
Many people have told me that the 4.2 cam is "better" than the 3.9 cam. But when I look at the specs for the 4.2 cam in the service manual, the 4.2 cam is actually more conservative. The service manual could be wrong though.
If I were buying a cam today, it would probably be the Optimax.
Randall |
Jason Vance (Jason)
| | Posted on Tuesday, October 08, 2002 - 11:23 am: |
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Randall,
that's not surprising, but I don't know enough about the 4.2 engine (e.g. did LR change the porting on the heads, valve-size, rocker-ratio, etc.?). What may be 'more conservative' on the 3.9 might be very-well matched on the 4.2. There's more to it than just looking at the advirtised duration and peak lift. Duration at 0.050" valve lift will tell you if the cam has steeper ramps (e.g. cam could have less duration, but could allow more flow through heads by reaching peak lift sooner and holding it near there longer); lobe-centers and how (if) the cam timing is advanced or retarded can certainly optimize a "conservative" appearing cam for the particular engine combination. If LR didn't change the heads/induction at all, a conservative cam may be the better choice since the heads would probably limit any gains at higher RPMs.
Since the 4.2 is stroked, the air-flow dynamics will be different than the 3.9/4.0; increase stroke + shorter rod = smaller rod ratio...pistons accelerate quicker at TDC which aids sucking in the air/fuel mixture.
A lot of stuff to consider, especially if you are making a drastic change. However, going with a conservative cam will probably yield conservative gains...those you can feel, but for the most part will not detriment the powerband, especially at lower RPMs where it is needed. |
Ali
| | Posted on Wednesday, October 09, 2002 - 09:10 am: |
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I've heard the same thing too about the 4.2 cam being a better cam if you have the 4.6/4.2 combo. Randall, can you publish the specs on the 4.2 cams here? I also heard that the 4.2 heads have better flow characteristics such as improved port matching for instance. |
Randall Smith
| | Posted on Wednesday, October 09, 2002 - 05:27 pm: |
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Ali
Nice to meet you last weekend. Will try to hang out with you some next time.
All the numbers below should are degrees and were taken from the 1993 "engine tuning data".
INTAKE 3.9 4.2 EXHAUST 3.9 4.2
opens 32 28BTDC 70 72BBDC
closes 73 64ABDC 35 20ATDC
duration 285 272 285 272
valve peak 104 108ATDC 114 116BTDC
My assumption is that the block and heads were the same. But the cam, crank, rods and pistons were different. The compression ratio went up from 8.14 to 8.94.
The ECU program was also different. The 4.2 ECU increases overall fueling by about 7%. However the steady throttle fueling is less, and the increase fuel comes when you accellerate. This is a closed loop system though, so it will tend to provide the correct fueling no matter how you are driving. |
Randall Smith
| | Posted on Wednesday, October 09, 2002 - 05:30 pm: |
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The post above was supposed to be columns under 3.9 and 4.2, but it got compressed when it posted. |
Ali
| | Posted on Thursday, October 10, 2002 - 03:17 pm: |
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Randall,
It was good to put a face to the name last weekend. You have a nice looking rig. Based on your comment, it stands to reason that using a rising rate fuel press regulator with the 4.6/4.2 heads combo is a good idea. What do you think? Why do you like the Optimax cam from RPI over other cams? |
eric
| | Posted on Friday, October 11, 2002 - 11:04 am: |
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I believe RPi sells Piper cams. Optimax is a Crane design. |
eric
| | Posted on Saturday, October 12, 2002 - 12:42 pm: |
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I believe I should not have sent the last message.
Ali, you're right. |
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