jrb55gh

There have been several dynos published on various forums showing that installing a VQ35HR upper manifold on the VQ37VHR engine increases mid range power. Since the VHR engine is used in both the G37 and 370z, this article applies to both cars.

A used HR upper manifold can be adapted to the VHR lower manifold with a few alterations.

The HR and VHR engines have an upper plenum/manifold made of black plastic material and a lower manifold made of cast aluminum. Photo 1 is a side view of the upper and lower VHR manifolds fitted together. The ports and alignment holes in both the HR and VHR upper manifolds match the VQ37VHR lower manifold perfectly. Photo 2 is a side view of the VQ37VHR lower manifold for the G37 and 370z showing the ports and alignment studs.

Photo 3 is a side by side view of the underside of the HR and VHR upper manifolds. The HR is on the right and the VHR is on the left. Notice that the outlines of the HR port runners are longer than the VHR’s. The longer runners tune the intake to make more torque and power in the 3000-7000 rpm range compared to the stock VQ37VHR upper manifold. This results in faster acceleration when accelerating through the gears when shift points are held to the stock 7300 rpm for the 7AT.


Here is the step by step process to adapt a VQ35 upper manifold to your VQ37VHR:

1. Acquire a used HR upper manifold. Thoroughly clean the oil residue from inside the HR upper manifold with carb cleaner. Then use a degreaser like Zep 505 available from hardware stores to clean the dirt and grime from external surfaces as in Photo 4. Be careful to wash the exterior without introducing dirt or grit to the inside of the manifold runners and plenum. A clean manifold is much less likely to trap dirt and machining chips in the runners and plenum. Check to be sure all the vacuum ports are still in place and clear of residue. There are 2 ports on the rear and one on each of the throttle body mounts. The Photo 8 top view shows the vacuum port locations on the HR (right) and VHR (left). Photo 9 shows a close up of the 2 rear vacuum ports on the HR manifold.








2. Elongate the 4 bolt holes in the HR upper manifold that must be matched to the VHR lower manifold. Cover the port openings and throttle body mounts with masking tape tape. Drive the shoulder dowels out from the bottom of the 4 holes to be elongated. Place the upper manifold on the lower, note the direction of the hole mismatch, remove the upper manifold, cut the holes with a rotary cutter or a coarse round file. Repeat this process as necessary. Be careful not to remove any more material than necessary so as not to break into a gasket groove, a runner or the plenum area. Cut the holes in the plastic to the proper shape so that the shaft of an 8mm hold down bolt will fit through. Photo 5 shows the underside of the HR manifold with the 4 holes that were elongated to match the VHR lower manifold.

I elongated the holes the easy but more expensive way and had a friend with an NC mill cut the holes to the pattern of the lower VHR manifold. No matter how you do it the end result should be the same: cut the upper manifold so that the shanks of all the bolts that fasten the upper to the lower manifold will fit through the upper with about .007” side clearance.

3. The HR upper manifold must be cut to clear the passenger side fuel rail fastening bolt that protrudes above the mating surface of the lower manifold. Photo 6 shows the interference with the HR upper manifold. Photo 7 shows the material removed from the HR manifold to clear the fuel rail bolt.

Continued in next post…….

jrb55gh

4. Make a plate to clamp the upper plenum to the lower manifold from a piece of aluminum to 5.25” x 9.0”x ¼” thick. The machine shop that cut the upper manifold bolt was able to drill the plate with holes to match the 4 elongated bolt holes. I also had them spot face the area for the head of the hold down bolts at the 10 degree tilt of the upper manifold. Photo 10 shows the upper clam plate. The 8x1.25 mm bolts required to clamp the plenum to the manifold are shown in Photo 11. The additional bolts required are 2ea 75mm, 1ea 110mm, 1ea 120mm, 1ea 130mm, 1ea 140mm. Photo 12 shows the lower manifold, plenum and clamp plate assembly.

5. Reroute vacuum hoses to connect to the vacuum ports on the HR manifold. Fabricate a new hose linking the rear lower vacuum port on the HR manifold to the 2 pcv hoses that normally connect to the front vacuum ports on the VHR manifold. Insert a tee fitting in the vacuum line going to power a/c vents. Connect the MAP sensor to this tee. Photo 13 shows these hoses and their fittings. Photo 14 shows these hoses and fittings connected to the HR manifold.


6. Photos 15 and 16 show the HR manifold, vacuum hoses and fittings installed in my 370z.

Ape Factory

iTrader: (3)

Thanks for the post!

jrb55gh

You are welcome! The info in this thread can save you several hundred dollars relative to buying an M370 manifold.

hotdawwgman

iTrader: (1)

Awesome!

jrb55gh

PM me if you have questions about doing this project.

rotarymike

iTrader: (4)

I know I'm bringing back a dead horse...

Any reason not to use the VQ35HR lower intake manifold as well? Different mounting / injector style etc?

BULL

It's almost been a year of this.
And would like further info.

It appears injectors and fuel rail might be different on the 35, can anyone confirm?

rotarymike

iTrader: (4)

I can confirm the fuel rail is different. Basic visual is the VQ37 rail is round tubing, the VQ35 is square. They mount in different places on the lower intake manifold - the clearance cut made in the original DIY for this thread is one mounting tab.

I've got a VQ35 lower intake manifold too and I'm planning on putting that on with the upper. By feedback and gasket fitment it looks like a direct bolt-on.

The injectors look the same - they're all the skinny plastic type - but might be differently flow capacities.

BULL

So I think I found the answer. Z1 sells a VHR ported package for the HR that consists of Upper and Lower from the VHR and fuel rail can be exchanged. The rest is finding the correct ports.

So the same can be done viceversa, I've seen many Upper and Lower HR that can be had for pennies.

rotarymike

iTrader: (4)

I have an extra VQ35 upper. I think I have an extra VQ37 lower. Have spare throttle bodies too. PM if interested.

This weekend I need to spend some organizing time in the garage; I'll see if I can get comparison pics of it all.

rotarymike

iTrader: (4)

Wanted to add - it would be easy if you had a TIG to build up the bolt bosses on the lower manifold, and drill/tap those to match the earlier upper intake rather than slotting holes and using a clamp plate. My closest reasonable and free access to a TIG is 6 hours away, so I started looking for later year G35s in the junkyards.

If you're looking at ebay for lower intakes, the top side of it has square runners and not round. The older DE engines use round runners where they connect to the upper.

BULL

Visit any JY you'll find an untouched HR. The best method is upper and lower from the HR, this avoids any drilling, plates, etc.

rotarymike

iTrader: (4)

At least around here, cars sit in the junkyards for about one week before someone pulls the engine and puts it on ebay. The pick-n-pull / LKQ yards have created a group of middlemen who strip any car that comes in of anything valuable for resale online. Lights, motors, wheels, doors, seats, etc. I see the guys walk around a car with their phone, checking ebay prices on parts to see what to strip.

BULL

Yeah, I tend to do that at times. Especially with 37's
You can download lkq app and check it. In our end it ends up working out due to the HR not being as popular.
Once you get the email, you'll know what to do. You might end up paying $50-$100 depending on all that you take and how generous the cashier is.