My D90 heater box mod
- Thread starter Jeff B
- Start date
WreckITFrank
Technical Excellence Contributor
Forgive my ignorance, but did LR use the same bulkhead for different models or something? I would assume all D90's are the same way, with partially blocked hole. Just trying to understand why they would do that. Thanks.
It is that size, because when the heater is on the left side for right hand drive, the duct in the lower dash ends at that point. Opening the hole won't make any difference with a stock heater. I've actually measured air flows and heat output with different changes. The biggest restriction with a stock heater is the lower dash vents.
The reason was that the original 110's had the same opening on both sides. The steering column hole and the heater box hole were the exact same. These early bulkheads were truly ambidextrous ie the pedal holes were on both sides and the factory simply covered the unused side with thin aluminum plates riveted on. The early bulkheads also had the steering column lugs welded to the top of the bulkhead on both sides. Bulheads became "sided" in the mid to late 80's. They eliminated the second steering column lug, and second set of pedal holes and closed up the steering column hole but kept the small damn heater box hole.
Open it up but also do the gm blower motor swap
Jeff B
Well-known member
Yep, that is my next mod...
But it has to help even the stock blower to have that bigger opening.
Do you know the part # for the GM fan?
I think Lav did a writeup w/ pictures a while back...
Not unless you open up the lower vents and even then it won't do much. The fan inlet is 14 square inches. The stock bulkhead hole is 14.6 square inches. You can get a bit as the hot air is 10 to 15% more volume than the inlet air.
Both lower vents add up to 7.9 square inches total, so this is where the real gains can be had.
The stock fan is actual not bad for the size. It pushes 240 cfm with the heater out of the vehicle, which is around 40 feet/s velocity at the inlet and that is quite decent for this type of fan.
That all said, the biggest problem with the stock heater is the inefficient heat exchanger. This prevent the air from getting really hot and limits its effectiveness in really cold weather.
Jeff B
Well-known member
Napalm00
Technical Excellence Contributor
allisport or similar uprated heater matrix. We just put one in James' truck locally its about 2x as thick as the standard one and the fins are much more dense.
https://www.allisport.com/product-category/performance-products/heater-matrix/
The late style box it is a significant upgrade, the early box the upgrade is not as significant due to the size limitations of the early heaterbox
Both boxes need alot of trimming to the sheetmetal for them to fit, the bulkheadhole is a easy mod to to when its out, as well as the GM heater fan upgrade
https://www.allisport.com/product-category/performance-products/heater-matrix/
The late style box it is a significant upgrade, the early box the upgrade is not as significant due to the size limitations of the early heaterbox
Both boxes need alot of trimming to the sheetmetal for them to fit, the bulkheadhole is a easy mod to to when its out, as well as the GM heater fan upgrade
MountainD
Technical Excellence Contributor
What do you do, just cut to match the plastic covers? I haven't looked yet. Is there a better, more effective thing to do in lieu of the stock covers?
Cut the holes bigger, make up larger deflectors and attach larger pieces to the flaps. Nice and easy when it is apart like in this thread.
The stock covers do restrict a bit and it is common to remove them, but it is better for heating to have deflectors in place.
These are the deflectors I use, but I also have a heater that is much larger than stock.
The stock covers do restrict a bit and it is common to remove them, but it is better for heating to have deflectors in place.
These are the deflectors I use, but I also have a heater that is much larger than stock.
Jeff B
Well-known member
Some more firewall heater hole pics.
These show the corresponding hole on the dash air box(plenum).
Also, picture showing bulkhead pre-cut/prepaint.
The cut is actually straight on the bottom and sloped on the top; it'll make sense when you see the shape of the heater core piece on the engine bay side.
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These show the corresponding hole on the dash air box(plenum).
Also, picture showing bulkhead pre-cut/prepaint.
The cut is actually straight on the bottom and sloped on the top; it'll make sense when you see the shape of the heater core piece on the engine bay side.
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Attachments
I think the heater is more than adequate, the main issue is the rest of the truck is so drafty and poorly insulated. At low speeds the heater will cook you out of the truck, even in sub-zero temps. The heat in my truck good on the highway down to probably about 0F. Once it gets colder than that it gets chilly in the truck.