JDM Vs. USDM B6T Intake Manifolds

These are some comparison photos of the early JDM intake manifold Vs. the USDM intake manifold (I think post '86 JDM engines used the usdm design as well) The JDM intake is rumored to provide an additional 15 HP - mostly top end. This comes from the larger plenum, better injectors, and the dual feed fuel rail. There are a lot of minor mods needed to use it - it WILL bolt right up - but most of the hoses won't match right up. The brake booster hose is on the wrong side, the idle valve hoses are different - ect. These pics hopefully will show the differences.

JDM on the left, USDM on the right.

The JDM intake is a lot bulkier than the USDM, its much wider both side to side at the top and front to rear.

USDM with port matching I did myself and painted all nice.

Side profile - you can see the JDM intake is much "deeper". It comes a lot closer to the firewall.

The back of it. You can see the plenum is a seperate piece. The Idle valve is on the bottom middle of the flange.

USDM is a one -piece construction with dual runners. The runners have a divider in them up to the plenum. The idle valve is on the right side in this picture.

Top: single feed USDM injectors and fuel rail. Bottom: JDM dual feed rail and injectors. NOTE: the fuel rails will not interchange between manifolds. Injectors are different (clips, flowrate) but can fit in either rail/manifold.

Closeup of the inlet/outlet

Close up of the dual feed rail.

JDM's pintle on the injector is larger, with a different pintle cap

USDM pintle and pintlecap (the pics arent very good for comparison, side by side the jdm injectors have a larger pintle)

Minus fuel rail. Runners run all the way down, and curve back up into the head.

Runners literally run straight into the head.

Stripped side profile

Believe it or not, it looks like its got equal-length runners!

The plenum pops off and has these circular ports - plenty of room for porting here!

Portmatched USDM port. (enlarged 1/16th" all around or thereabouts)

JDM Port- much closer to the port size on the head - injector shroud is smaller

The runners flow straight in unhindered.

The USDM has to make a bend to get into the head at the right angle - this actually narrows the runners here, and creates a lip at the transition where the flange meets the head. Pretty awkward, but easy to port out.

The coolant for the TB runs into the plenum on the JDM intake, instead of into the throttle body like on the USDM. (it still flows into the TB but the nipples are on the plenum)

I bypassed the coolant on my TB but here are the stubs where the nipples were. If you look closely at the bottom of the JDM TB, There are indentations cast in these positions ready to be tapped.

Exploded view of the dissasembled JDM manifold.


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