12HT improvements

[Rocher]

Hey All,
After much research I think I have finally decided on a 12HT over a 1HDT/FT to go into a 40 series I'm looking at building once I sell my current HJ47.

One thing i noticed while researching the engines is that there are a number of people with various mods to the exhaust and intake manifolds of the 1H* series engines that seem to increase boost response and/or efficiency. There are no threads about any of this on the 12HT though, can anyone see any benefits in custom fabricating new manifolds? I would ideally like a twin scroll housed turbo for the better boost response but haven't been able to find an appropriate sized housing to suit.

FYI main reasons for the 12HT are the chain driven cam and potential better fuel economy. Not keen on the rotary pump and multi-stage injectors on the 1H* series either. Still open to other engine suggestions, although I'm after something with minimal electronics (hence no 1HD-FTE)

 

[HJ61 12HT]

A 12ht in a 40 pulls it around just fine, no need to mess about with manifolds.
You should just stick one in with a 3 inch exhaust and turn the fuel and boost up just a tiny bit and you will be golden.
Cam is gear driven, no electrics at all needed, truly is a simple engine.

 

[BOOSTED80]

I wouldn't bother doing manifold mods either on a 12HT ..3" exhaust & boost , ip tweak.

 

[watrob]

If you want to go straight to 3" from the turbo then buy one of these specially made for the 12HT.

I have bought one for my second 12HT but I did this on the first with 316 staineless.

 

[Rocher]

I was hoping gbentink may have been able to give a little insight if larger valves and stiffer valve springs would be of any benefit for efficiency or in case the boost gets turned up quite a bit... (Check his thread "12HT performance build" if you don't know what i'm on about)

"The valves are only 43.5mm IN instead of 42mm and 36.5mm EX instead of 35mm. I only increased the valve size because when cleaning up around the valve seat, the casting matching to the machining/seat inserts was really rubbish and I had to machine away some of the inner diameter of the seat to have a smooth transition from the casting to the insert; thus the bigger valves are required to seat correctly"
"Will the porting and bigger valves and stronger seating pressure be worth it???? I am gonna find out!"

Did he or anyone else find out?

 

[David*BJ70]

If you want to go straight to 3" from the turbo then buy one of these specially made for the 12HT.

View attachment 967273

I have Google «4057DP exhaust»… only 2 results !


This part seems to be sold only in a kit at +/- 1400$ (aus) (http://www.exhaustsaustraliawide.com.au/). Did you know the value of this part alone?

 

[watrob]

http://www.ebay.com.au/itm/111361339547?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
$170.00

 

[BOOSTED80]

I would like to see the difference with a nicely ported head and G-turbo & boost , to a stock one as well.

 

[niffa]

Subscribed! Keen to hear of any benefits to 12ht

 

[watrob]

The 12HT when fully rebuilt you will find is a very quick revving engine, although it's called the bigger brother of the 2H it is totally different. It's more suited to a Auto transmission as the manual 5 speed's first gear is only used for few seconds.

Throttle response is touchy and requires a throttle dampener, it will rev straight to the rev limit whereas the 2H finally gets their. Having a narrow quick rev range already, with your changes you have to be carefully you don't end up with an un-driveable engine because it's too touchy or you will be trying to change up thru the gears quickly in a 5 speed box which has a slow gate.

 

[niffa]

Quick revving in comparison to what? I would say its slow in comparison to my 1hzt. Agree with sensitive throttle but its easily overcome as u said.

 

[watrob]

It's more than three times as quick as my 2H, so it's damn quick, but then everything has been done, head, valves & springs, pistons, IP, new injectors, etc, plus the 3" exhaust. And I can define quick, have a 3 turbo M50D and that's the yard stick to compare it with?

Quick to 8,500 revs in one thing but when its to 4000 revs in a light fibreglass tub it can be a problem, specially on the beach where you have no traction.

 

[Crick60]

Everything watrob says is true and I don't entirely agree with the comparison to the 1hzt niffa...1hdt on the other hand...

 

[BOOSTED80]

Everything watrob says is true and I don't entirely agree with the comparison to the 1hzt niffa...1hdt on the other hand...

I wouldn't agree with that comparison either..I haven't had any drama smoking some stock 1HDT's.

My 1HZT is no slow revver.

 

[niffa]

Lets compare apples with apples.. watrob is pushing a short 40 with a glass body and im pushing a 61...not exactly evens here. Im sure ur tri turbo bmw would scream thru the revs too if it was attached to the same rails as ur 12ht. I think you would find the revs slow substantially by having a full size 4wd around it. Not to say your beach weapon isnt sweet but it isnt exactly what the 12ht was inserted into from factory

 

[Crick60]

12ht doesn't have the lag the 1hzt has, no doubt the z develops for power but at the expense of lag.

 

[Crick60]

Lets compare apples with apples.. watrob is pushing a short 40 with a glass body and im pushing a 61...not exactly evens here. Im sure ur tri turbo bmw would scream thru the revs too if it was attached to the same rails as ur 12ht. I think you would find the revs slow substantially by having a full size 4wd around it. Not to say your beach weapon isnt sweet but it isnt exactly what the 12ht was inserted into from factory

Can't disagree there, watrob's virtually powering a shopping trolley with a V8. She's a very nice looking shopping trolley though.

 

[niffa]

12ht doesn't have the lag the 1hzt has, no doubt the z develops for power but at the expense of lag.

mmm thats a tough one, my 1hzt has a front mount and my 12ht has a top mount so its hard to compare again.

 

[Radd Cruisers]

The stock turbo outlet on the 12HT is fine running in to a 3 inch pipe.

There may be a lot to be gained from cleaning up the shrouding under the valves. There is a lot of material to be removed there.
cleaned up (lots of material removed from the port and under the valve.
original casting before clean up

Biggest disadvantage to the 12HT is the very touchy throttle response compared to any of the others. It's very challenging driving a 5 speed 12HT off-road because of this.

Personally, for general driveability and off-roading I would choose the 1HDT or the 1HDFT before the 12HT, but the 12HT is a great engine - more of a highway engine though.

John

 

[watrob]

Rocher, is talking about dropping a 12HT into a 40 (after he sells his HJ47), so, he might end up being 600lbs heavier than mine but nowhere near the weight of a 60 series.

Rocher is also talking about trying to get say another 25bhp out the engine as well, a under powered 40 is just as bad as a over powered one.

PS. When the head planned how much was taken off?