How can I get more power for freeway driving from my 3.9 V8 - Page 2 - Defender Source
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  #21  
Old December 8th, 2014, 08:48 AM
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I think the earlier posters were in the right territory when they were talking about gear ratios and where the Rover V8 makes its power.

A clear example for me is my 3.5 will run up a hill at high rpms in 3rd gear at 60mph. I shift it into 4th and the power dies and the speed falls. (4 speed gear box)

Part of my problem is that I installed a very high xfer gear in my gearbox. It gives me great driving on the flats and around town - a lot lower engine speeds / quieter and so forth. I just loose on the hills. Everything is a compromise.

Tune your engine, replace the cam, make sure you have a 1.4 xfer.
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  #22  
Old December 10th, 2014, 03:13 PM
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Tune up.
Gasket match top end and exhaust manifolds.
Upgrade cam...
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  #23  
Old December 10th, 2014, 03:28 PM
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Some dangerous misinformation going on in here. Uncle Doug is the only one who has keyed in on the most important consideration.

Do you have larger than stock tires? A roof rack? Winch bar?

A stock NAS D90 should have more than enough power at highway speeds. How hard are you pushing it? What condition is the engine in? When was it last serviced/tuned?

Also, what is your frame of reference for power up hills?

Huge difference between a well-kept 3.9 and a neglected one. If this thing has never had a tune up and is sucking through a clogged air filter you're probably only seeing 130hp versus 180+

By the way, all the same mods that can be done when building a 4.6 can be done to a 3.9 or 4.0 as well. Forced induction is also well researched and executed in the UK, its us yanks that could never figure it out.
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  #24  
Old December 10th, 2014, 06:11 PM
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What it really comes down to, is how much you want to spend.
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  #25  
Old December 10th, 2014, 06:28 PM
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Aside from all the excellent recommendations already given. Jut buy a really nice stereo, comfy seats and enjoy the scenery. Conversely, plan all trips to be downhill.
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  #26  
Old December 12th, 2014, 10:41 AM
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Quote:
Originally Posted by transientmechanic View Post
Some dangerous misinformation going on in here. Uncle Doug is the only one who has keyed in on the most important consideration.

Do you have larger than stock tires? A roof rack? Winch bar?

A stock NAS D90 should have more than enough power at highway speeds. How hard are you pushing it? What condition is the engine in? When was it last serviced/tuned?

Also, what is your frame of reference for power up hills?

Huge difference between a well-kept 3.9 and a neglected one. If this thing has never had a tune up and is sucking through a clogged air filter you're probably only seeing 130hp versus 180+

By the way, all the same mods that can be done when building a 4.6 can be done to a 3.9 or 4.0 as well. Forced induction is also well researched and executed in the UK, its us yanks that could never figure it out.
I think the 3.9L gets a bad wrap...
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  #27  
Old December 12th, 2014, 10:48 AM
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Quote:
Originally Posted by Uncle Douglas View Post
A valve job and fresh cam typically make a huge difference in waking up a tired engine.
Where I would start. The cam chains stretch and a lot of power is lost. A nice aftermarket cam and proper timing chain / sprocket set usually make a big difference.
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  #28  
Old December 12th, 2014, 11:05 AM
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Since I don't have any insulation at all in my truck, earplugs let me drive a little faster.....Perfectly capable of 65 or more without problem. But then I have an auto plus 1.2 and it probably compensates for inclines.
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  #29  
Old December 12th, 2014, 01:10 PM
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I had good luck with a new exhaust. My cats were starting to break up and it was partially clogging the exhaust.
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  #30  
Old December 12th, 2014, 02:17 PM
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Thought I'd chime in..
I have a 95 SW that had these changes in the following order:
1. 3.9 converted to 4.6
2. 4.6 over heated all the time. swapped out tons of parts until finally stripped the motor, removed AC, but in new radiator and related cooling items. Without AC radiator, ran much cooler and seemed stronger
3. Did a top end and in the process redid timing chain and put in an RP2 cam from RPI engineering in the UK
4. F'ed with air filters, oil weights, making a cold air intake blah blah blah.

The 4.6 does help but the most noticeable change that was literally day and night on my truck was changing the final drive ratio to 4.15. It felt like the truck got another 50HP. Looking back on all the money that was spent messing with the truck for marginal gains, gears are a reliable 1K bucks that will make a major difference in the usability of each gear, especially on the highway. I can now stay in 5th going up long grades without even being to the floor. My tires are 33x12.5 R15 and I turn 2500ish RPMs at 65-70MPH. Looking back on it, this would have been the first thing I did.

Other thoughts. What tires are you running? most people don't ever check the weight of a tire but might switch to something lighter that doesn't suck away WHP. Or remove the cats, slam the timing forward and run it on 100LL
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  #31  
Old December 12th, 2014, 07:43 PM
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My transmission (auto) doesn't downshift up steep grades at all on the east coast, and this is with a 4.6 and Crower cam. The 4.6 that came out of the truck in August that I drove across the country with, had a 3.9 or 4.2 cam. It still only downshifted a few times in the mountains out west. I had no problem accelerating up hills.

For the amount of work, I think putting a new cam in a 3.9 is a waste of time. I would only do that if there is an issue with the current cam. If your head gaskets are leaking, I would say replace the heads with some new style 10 bolt heads that have been machined, and go from there. I personally couldn't justify modifying a 3.9.
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  #32  
Old December 12th, 2014, 07:48 PM
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Quote:
Originally Posted by Jymmiejamz View Post
My transmission (auto) doesn't downshift up steep grades at all on the east coast, and this is with a 4.6 and Crower cam. The 4.6 that came out of the truck in August that I drove across the country with, had a 3.9 or 4.2 cam. It still only downshifted a few times in the mountains out west. I had no problem accelerating up hills.

For the amount of work, I think putting a new cam in a 3.9 is a waste of time. I would only do that if there is an issue with the current cam. If your head gaskets are leaking, I would say replace the heads with some new style 10 bolt heads that have been machined, and go from there. I personally couldn't justify modifying a 3.9.
I think you have to drop below a certain speed before the trans will allow a downshift
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  #33  
Old December 12th, 2014, 08:33 PM
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When i rebuilt the engine in my D90 I kept the 3.9, but opted for the high flow heads and a Kent cam. The engine had 139k miles on it, but as mentioned, i found upon tear down the primary reason for the sluggishness was a very worn timing set (see pic). I replaced the stock nylon timing gear/set with a Cloyes double row set on the Turner reman engine. With this set up, i found the engine ran better with about another 3 degrees of timing (requires mid grade gas). It does not run like an LS3, but the truck pulls strong and has no trouble cruising in 5th gear. Overall, pretty happy with the setup, but I will not win any drag races.
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  #34  
Old December 12th, 2014, 08:49 PM
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Quote:
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I think you have to drop below a certain speed before the trans will allow a downshift
It has a kick down cable, and will down shift under heavy load/throttle. Believe me, I am constantly downshifting on the highway on my way to work passing people.
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  #35  
Old December 13th, 2014, 02:10 AM
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A good slop free timing chain and good Cam makes a big difference in the way these motors run. I for one think a Cam upgrade is a good idea for any Rover V8 motor over 100K . The stock cams seem to wear out of spec and dish the lifters creating less lift and poor performance. I haven't taken a Cam out of any rover motor with 100k miles or over that wasn't worn to the point of visual damage . And a quick measurement shows the wear .

A pic from a buddy's 4.0 with 125k he sent me this pic .

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  #36  
Old December 14th, 2014, 12:02 PM
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The original camshaft on my 4.6 ground an entire exhaust lobe away at 60K miles. Made the cylinder exhaust through the intake creating a really heart warming noise in the process. Here is a photo of the damage to the tappet on the left.
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  #37  
Old December 14th, 2014, 12:17 PM
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The original camshaft on my 4.6 ground an entire exhaust lobe away at 60K miles. Made the cylinder exhaust through the intake creating a really heart warming noise in the process. Here is a photo of the damage to the tappet on the left.
What brand of cam and lifters?
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  #38  
Old December 14th, 2014, 12:39 PM
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Originally Posted by Jymmiejamz View Post
What brand of cam and lifters?
I've been wondering if this cam would work in a 4.6. I doubt it but worth researching.
http://www.thewedgeshopstore.com/pro...Cam-setup.html
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  #39  
Old December 14th, 2014, 12:43 PM
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What brand of cam and lifters?
They were stock.
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  #40  
Old December 14th, 2014, 04:09 PM
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I've had great luck with Crower cams from Mark at D&D in Michigan . I think the cam is often over looked and is the cause of these motors being short of breath .
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