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Discussion Starter · #1 ·
What can be done to open up my 99 3.8L for more power?

It currently has milled/ported heads, a ported TB, intake, full 3" exhaust, so just mild things.
What else can I do to open it up more? It pulls pretty strong, but runs out of power around 4500 rpms. The 3" exhaust helped the top end power noticeably, but it still trails off. I'd like to bump power across the rpm range while boosting the high rpm power to eliminate the trail off.

Suggestions?
 

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2008 Chrysler Town & Country Limited 4.0
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What can be done to open up my 99 3.8L for more power?

It currently has milled/ported heads, a ported TB, intake, full 3" exhaust, so just mild things.
What else can I do to open it up more? It pulls pretty strong, but runs out of power around 4500 rpms. The 3" exhaust helped the top end power noticeably, but it still trails off. I'd like to bump power across the rpm range while boosting the high rpm power to eliminate the trail off.

Suggestions?
An aftermarket camshaft, even a mild "RV" cam, would be an improvement. Might need new valvesprings if the lift is more than what the stock valvesprings can handle. Tubular headers might make a little more power, but I doubt anyone makes them. An intake manifold with shorter runners will give more top-end power while trading in some low-end power. A turbocharger would be the best way to add power as you get a bunch of low-end torque and top-end power, depending on how you size the turbo.
 

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Discussion Starter · #5 ·
An aftermarket camshaft, even a mild "RV" cam, would be an improvement. Might need new valvesprings if the lift is more than what the stock valvesprings can handle. Tubular headers might make a little more power, but I doubt anyone makes them. An intake manifold with shorter runners will give more top-end power while trading in some low-end power. A turbocharger would be the best way to add power as you get a bunch of low-end torque and top-end power, depending on how you size the turbo.
I've been debating on pulling an 01+ intake manifold, intake plenum, and cam to swap into my engine as the 01+ engines shifted the power back up in the rpm range, but I don't want to sacrifice too much of my massive low end. It just gets annoying that it falls on it's face 1k rpms before the transmission allows it to shift.

I have thought about boost, but being old school, I would go supercharger over turbo for the linear delivery and wonderful whine.

I thought I read somewhere that these engines (3.8) can’t handle forced induction. Something along the lines of the bottom end being destroyed.
Mopar did some testing back in the day to build a "Turbo 3.3" for more power in pursuit cars while they awaited the 3.5 to become viable.
IIRC they ran something like 6-8 lbs of boost on it and ran it full bost/low rpms for something like 74 hours before it blew up. Something an engine would never see in regular use.
People have boosted the 3.3s and 3.8s successfully since then, but there's only a few obscure write ups on it.

Too bad I can't source the parts for the Can Am engine, that would solve all my issues.....
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Discussion Starter · #6 ·
the cast crankshaft and connecting rods can't take boost, after those the head gasket isn't the strongest for it
They CAN handle low boost. What they have issues with is running full boost/low rpms for extended periods of time, something no engine will actually see in real world use.
 

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Discussion Starter · #8 ·
I strongly debated swapping the powertrain from an srt neon into my 2nd gen before I decided to go the cheap and easy route...
I have a bad left knee, otherwise I would have left my 3.0 under the hood, swapped in a manual, and boosted the 3.0. The 3.3/3.8 are less than ideal when hunting for performance, meanwhile the 3.0 takes extremely well to modding and handles boost without issue.
 

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Yeah my cheap and easy route was replacement 3.0. I've got the one I pulled, just sitting there looking at me, filling my head with bad ideas for a future build 😁
 

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Discussion Starter · #10 ·
Yeah my cheap and easy route was replacement 3.0. I've got the one I pulled, just sitting there looking at me, filling my head with bad ideas for a future build 😁
Pistons and cams from a SOHC Diamante/3000GT are a direct bolt in that boost compression and power.
Heads can be ported.
Intake plenum can be heavily ported.
I've had a couple pretty wicked 3.0s over the years, they're stupid easy to make power with.
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The 3.5L rods will allegedly fit into the 3.8 with some minor work. I never bothered to run the numbers, but I'd read some speculation somewhere that the journal sizes were the same or close, the wrist pin to journal length was the same, and maybe the width of the journal was a hair bigger. So maybe, you just have to remove some width from the journal, figure out a wrist pin, and rebalance it?

There are some superchargers for the Jeep 3.8 V6. Sure, you're not going to be able to put tens of pounds of boost into a stock 3.8, but you could definitely solve the top end issues with forced induction. The limiting factor with nearly all engines, is camshaft profile and cylinder head design. Your block, crank, and pistons are sweeping 3.8L of displacement, no different in final result than a formula one or Ferrari engine that displaced 3.8L. Maybe there's different bore/stroke ratios, rod ratios, rpm capability, or power durability, but at the end of the day your 3.8L bottom end is not what decides the power. The important part of an engine that mostly determines its performance characteristics, is how the top end flows air.

The easiest solution would be to fabricate a junkyard M90 supercharger onto it. You could think of a blower in one of two ways. It is increasing the displacement of the engine, let's say you ran 14.7psi of boost on top of the 14.7psi of atmosphere your engine gets naturally aspirated, now you're force feeding twice the volume of air through it so it is functionally a 7.6L engine. The other way to think about it, is increasing volumetric efficiency, which is how much of the 3.8L displacement actually makes it into the cylinders. Stock, your engine is probably struggling to suck in 80% or more of 3.8L through the poorly designed heads, cheap valves, and economy camshaft. A high performance engine might be breathing in over 90% of its displacement. A race engine might get over 100% volumetric efficiency, where scavenging and tuned intake runners are forcing a greater amount if air than the actual displacement through. Most of the mods to the top end would simply be to increase volumetric efficiency.

Instead, you can just force the air in with a blower to achieve the greater volumetric efficiency. If you had an 80% volumetric efficiency engine, and ran 3psi of boost, you'd bump it up to 100% efficiency, or a 20% increase in airflow through the engine. The stock engine can likely handle a small amount of boost, say 5psi or less.
 

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Discussion Starter · #12 ·
@Special Edy
I'm thinking I'm going to snag a newer 3.8 intake manifold and see where that gets me.
The 01+ engine gained 35hp/5ft-lbs over my engine while pushing the peak up to 5k, which from what I can find was done via the intake and cam. If I can just swap the intake and gain some up top from that, it might just get me what I'm looking for.
 

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I'm not 100% sure what happened between 1998 and 2000. I have a 1997 manual, and 2001+, but none for 98-00.

Chrysler bumped the compression ratio in 1998-2000. There's unique part numbers for the 1998-00 pistons. I think they didn't do anything radical until 2001. In 2001, they put a more aggressive camshaft into the 3.8, a milder cam into the 3.3L. They also increased the valve size and lift for the intake, and made the exhaust smaller.

I believe that your 99 3.8 has the higher compression pistons, without the larger valve heads or better camshaft. Power went up 35 horsepower from 2000 to 2001, no way that's from the intake.
 
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Discussion Starter · #14 ·
@Special Edy I would think the newer intake manifold would have to be good for something over the 99 manifold. I know its not going to give me 35 hp, but it should give me something.

The cam is different from my 99 engine over the pre-98 engines, but I'm not sure how much.
 

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The heads are a bigger improvement than the camshaft. Not sure if the extra lift is derived from rocker arm ratio or cam lobe lift though.


3rd Gen4th Gen
Intake Diameter45.5mm48mm
Intake Lift10.16mm11mm
Intake Duration240°242°
Exh Diameter37.5mm35.5mm
Exh Lift10.16mm11mm
Exh Duration240°244°
Overlap14°17°




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Discussion Starter · #16 ·
The heads are a bigger improvement than the camshaft. Not sure if the extra lift is derived from rocker arm ratio or cam lobe lift though.

Not really looking to tear it back down that far. I'm going to pull a newer intake manifold and slap it on. We'll see what happens.
 

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Not really looking to tear it back down that far. I'm going to pull a newer intake manifold and slap it on. We'll see what happens.
It's the rocker arms. You'd definitely want the complete 2001+ heads, they have the bigger intake valves, better valve springs, 7 bolt rocker arm shafts instead of 4 bolt, and I beam rocker arms instead of H beam, for lack of a better description. Unless you can find a set of roller rocker arms that'd fit onto the <2000 shafts, which is quite probable. Youd probably want to step it up from a 1:1.5 ratio to 1:1.6

The specs for the camshaft bearings are identical. Supposing that the <=2000 timing sprocket fits onto the >=2001 camshaft, it should work in your block.
 

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My 2" aluminum mandrel pipes should arrive in the mail today, to weld up for an intake. My Supercharger is supposed to be built and shipped by the end of the month.

Soon! Soon we will know what a crazy but not too crazy 4.0 is capable of!
 
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