Late model intake manifold on 3.9? - Defender Source
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  #1  
Old October 12th, 2005, 10:55 PM
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Late model intake manifold on 3.9?

I was wondering if a late model intake manifold/throttle body would bolt onto a 3.9L. If so, would it provide benefit such as torque/horspower gains as I've been told it might?

Any idea how much trouble this would be to fit onto a '94 3.9L, and if it would be beneficial/worth the hassle? The pic below is from a 2000 Disco II which is for sale on. It looks like this may not be the entire manifold, perhaps part of a 2-piece system and is just the throttle body. I've not seen a newer LR engine up close, so I'm not sure how the top end goes together....
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  #2  
Old October 12th, 2005, 10:59 PM
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I have one on my workbench for that swap in the future, you also need the lower manifold as well since it's a different runner pattern. The one in the picture is just the upper manifold and throttle body.

The thermostat assembly is different, so you would need a remote thermostat off the same year truck. I haven't had a chance yet to see what changes might need to be made for the heater hoses yet either, it's a low priority project right now. You would probably need to make some changes to the throttle cable as well, and the intake tube wouldn't match up either.

I also have no idea if the stepper motor and TPS sensor are compatible with the existing ECU. For me, that doesn't matter, since I plan on going with the Megasquirt.

-Hans
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Old October 28th, 2005, 04:44 AM
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Hans, what crank are you using in your new engine? I have access to a 4.0 rebuildable core (needs pistons) and I think i might build a new bottom end to replace the 3.9 & use my new intake manifold on it. Is the 4.6 a stroked 4.0, or is it bored? Seems to me a stroker would work best in a D90...

I started hearing a new and disturbing noise that sounds distrubingly like piston slap, and I'm really getting fed up with this 3.9 no-power engine. I'm not over the top like Doug though - I don't need a 5.2 racing engine

Did you say that the injectors might need upgrading, too if the displacement went up beyond 4.0? I'd like to stay with the stock ignition system (though a knock sensor seems pretty appealing right now...)
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Old October 28th, 2005, 12:25 PM
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Well, when I redo mine it will be getting a Buick 300 crank actually, put into a 3.9 block bored .030 over and that gives 4.9 liters.

You may need to upgrade the injectors too, if the fuel requirements change a lot. But I don't know if you can use the THOR manifold with the 14-CUX computer, I haven't compared the resistance curves in the throttle sensors, and I don't know if the stepper motor is compatible or not. If those are OK, then I think you will be fine. The only other thing I can think of is that you might have to add a fuel temp sensor in there somehow, but it should be easy on the THOR fuel rails.

-Hans
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Old October 28th, 2005, 01:08 PM
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OK, so the buick 300 crank has a bigger throw than the 4.0. You can use all the same components - balancer/pullies/flywheel, con rods, etc, from the 4.0? Is there a good resource out there which goes into detail about what I can do to this engine in the way of custom mods?

I have heard of people in other situations increasing the fuel pressure to compensate for overdriven injectors - maybe that would work here? Right, I hope the curve on the TPS is the same (if min/max are similar I might be ok?) & no idea about the stepper motor - I'm not sure where to get that info.

It looks like I have more questions than answer at this point...
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Old October 28th, 2005, 01:21 PM
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Check this site out for a little info on parts and stuff

http://www.aluminumv8.com/
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Old October 28th, 2005, 02:30 PM
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I'll second that link as a good info souce (I wonder why I didn't mention it, I normally do when I talk about the stroker), though some of it isn't working right now. D&D is an awesome source for rover engine parts or even complete engines.

Thats where I got the idea for the stroker engine from. It's not a drop-in modification, there are a bunch of other changes that need to be made as well such as different pistons and rods, modification to the crank and an adapter piece for the rear seal.

-Hans
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Old October 28th, 2005, 04:48 PM
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Thanks guys, I'll check that out...it does look like alot of info. ..
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Old October 28th, 2005, 05:24 PM
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I just wish I had found it before I put a replacement factory cam and lifters in mine, I would have definitely gone with the Crower instead of a direct replacement for the original. Next time, I know better.

-Hans
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Old October 29th, 2005, 12:40 AM
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I did a lot of investigation on cranks/pistons/rods before I built my 4.6. I even filled my heads/cyliders with oil to check compression ratio in theory/reality. I think you will find that a lot of the high volume scenarios will have very high compression ratios, above 11:1, which make standard petrol use difficult to say the least.
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Old October 31st, 2005, 10:17 PM
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Yeah, I will be planning to stay below 9.5:1 on compression - I'll have pistons ordered to match the actual volume of the chambers to make sure I stay below 9.5:1.
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Old October 31st, 2005, 11:16 PM
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One more note on compression and that goes to fuel reliability. I want, just like every other small minded power hungry bigger better man, more horse power. Who wouldn't? But, more importantly, I want to drive not walk home. With higher compressions come slightly higher worries in reliability, but not enough to notice as long as you run the right gas. But who can guarantee that? That is why I went with a lower compression than I could have--because in the back country or at some po-dunk place, I want to be ABLE to use the gas--there is a lot of inherent value in that. New gas, old gas, high or low octane. Lower compression allows that. (my '68 400HO convertible Firebird, GRIS, has 11:1 back 10 years ago and I had troubles then and gas has gotten worse, not better, in my opinion).
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