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mini streetvan #2

1K views 19 replies 6 participants last post by  strtvan 
#1 ·
Morning,
Is there any new news on how to get G-head to run well on a 2.5\auto ?
 
#2 ·
Not really. The combo just does not work right especially on a heavy van. Best thing is to keep the swirl or if you have a g-head on the motor pull it and install a swirl before installing the engine otherwise you will be swapping the head in the near future. The cal Matt and I worked on appears to be one of the better running 2.5G cals but it has its issues. Best thing I did to resolve them was to install a swirl. This is after screwing with the cal for almost 3 years and then one day I said thats enough of this nonsense and pulled the head. The only way I can see a 2.5G engine in a van working ok is on a race only van. The timing is too tempermental for a daily driver. Too much and it knocks, too little and it is a complete dog and there is an extremely fine line in between these.
 
#3 ·
my pet theory is that the dish in the 2.5 piston won't work with the G head's combustion chamber as the 2 were never designed to work together

a custom piston with the small dish of the 84-5 motors and the needed valve reliefs might work much better

screwing up flame propagation might be what makes these timeing sensitive
 
#4 ·
I agree.

I have heard people over the years preaching run a g-head on your 2.5 so I did. Like I said above unless its a drag only vehicle I think the combo is horrible and I had zero luck with it. Mabe others have but I would honestly like to see the numbers to prove the performance increase with it.
 
#5 ·
Yes, having control over the cal is VERY important, but making the hardware work together is also important. One thing to keep in mind is that the compression ratio is going to be reduced by using the g-head. This combined with the fact that there is NO quench or swirl and yeah, you've got a total turd down low. Now, if you were to shave the head (cam timing MUST be corrected if this is done enough to make a significant change in compression ratio), or get custom pistons (no more expensive than off-the-shelf, they just take longer to get), or a combination of the two, now you're going somewhere. Of course the cal is going to be completely different for a set-up like this.

Other things to consider: what turbo, where does it spool, what FD ratio, what transfer gear ratio (auto only), what is the TC stall (auto only), cooling (I highly recommend installing an oil cooler, and the 4th-cylinder cooling mod might also help in this case), what cam, cam timing, what exhaust size.

Now, so far I've inferred that the head is stock (except being shaved if you were to do that). However, a good port job and chamber work can make a pretty big difference. If you don't know how, or don't have a lot of experience doing this work, especially with our heads, this is best left to someone that does know. Really, if you want a good head without a lot of trial and error, suck up your pride and pay for somebody to do it. It's not cheap (usually), but in a lot of cases you get what you pay for in this department.

Anyway, my overall point is that there are a LOT of dials to turn to make a combination work. Get it right and you'll love the results. Get it wrong and you'll want to burn the thing to the ground.
 
#6 ·
Wow am I happy I stumbled on that old info. I'm a 45 yr old Mopar guy but this is only my 3rd TD, 88 conquest, 03 Ram and current mini.
I'm being tested enough already so I'll stick with a proven recipe.
Since I have a rebuilt 782 on the shelf the decision is easy.
New 445 G-head with slider cam for sale !
Lol . I have $500 invested- make offer.
 
#8 ·
I have a MP +1 mm head,(G head) on my 2.5 but it's in an Omni
My first time out I went 12.13@112 running a tad rich, about 10.8 on the wideband
Compression might be lower but that's what the Holset is for.
Gotta crank the boost next time to lean it out
 
#9 ·
Morning,
Maybe i should have mentioned this is a fresh rebuild with forged wisco's, s60 turbo and inj's, 2 piece IT , 52 tb, fmic, full 2.5" exhaust ( no cat ) straight through muff, built 413+quife ( not sure about what stall speed yet ) and after it's together a boost button cal.

Does this change things ??
 
#10 ·
Ran the same setup but with a 46 trim hybrid and a TU header. It was horrible. Almost felt like I was starting I 2nd. Keith may have gotten away with it because the Omni is lighter and he still had to be running a custom cal and or quite a bit more timing because with a stock 2.5 cal EGTs easily hit 1750 - 1800 even in low boost due to timing. I will be honest. I was able to get mine to run quite well after working on a cal for 2 years but the problem is the cal is too tempermental with climate changes. For a race only vehicle it can work for a driver no. Get a good ported 782 and trust me you will be much happier. I wasted too much money and time playing with the g head and I try to save others from going through the same thing.

Another thing is are you running stock bore or 30+ pistons. Reason I ask is because there was ( at least I was told by others) a ring problem with the std wiseco's at one point. I have a set of the bad ones because my engine burns about 1 qt every 600 miles and has blow-by. Now it is possible I could have hurt it trying to tune the g-head or when my walbro pump took a crap at 18 psi and I heard it ping but others have had the same problem so I doubt I hurt them. Mine were purchased about 6 years ago. Im going to pull the engine this summer but a 2.4 is going in.
 
#12 ·
I dont understand how we are not comparing apples to apples here. You are not going to find a closer combo. My engine was fresh when I had a g-head on it. Compression was right where it should be and it did not burn oil at first just like everyone else with the wiseco problem. Even with the blow-by issue and oil burning the swirl will outperform the g-head any day. And I also have the exact same build in my shadow convertible but I used a 782. Night and day difference between performance of a 782 and g-head 2.5.

Simon had the same problem running a g-head on his mini, I’m not the only one. Matt (Moparzrule) had tuning problems on his shadow and I’m sure the list goes on.

Stall speed might help the low end power but it still will not fix the fine line between not enough timing and too much timing. On a driver it is almost impossible to get it to the point where there is enough timing but no knock unless you live in an area where the temps are pretty consistent.

As for a cal, I believe Rob (Shelgame) is using my timing and fuel tables in his turbonator g-head cal. This was one of the better street able cals for this combo. You will not find a cal out there where you can just plug and play. It will need tuning. Matt (Moparzrule) had a good g-head cal which I based mine off of but his was race only and when I tried it I heard some knock even out of boost. It was too radical for a driver on 93 pump gas.

I’m not trying to be rude use the g-head but don’t complain when you run into knock issues and or low power. I don’t know where all of this great talk about the g-head is coming from it sucks on a 2.5. The swirl only flows a very small amount less and even with some minor porting can flow as good as the g-head. It has a better combustion chamber. These small flow differences are overcome by the lowered compression and poor burn characteristics of the g-head especially with the 2.5 pistons. If you really want to make some major power invest in a Menegon head or go 16-valve. Otherwise a stock or mildly ported 782 is the only way to go on a 2.5 especially a heavy van.

Like I said earlier I’m just trying to save you the headache, you don’t have to listen if you don’t want to. I am not going to go any further into this. I only wish someone did the same for me and Simon would say the same as well. I am not new into these cars and have built and involved in tuning quite a few of these for myself and others over the years including 12 second cars. I have learned a lot over the years. I am not claiming to be the expert but I am also by no means an amateur.
 
#13 ·
I'm not questioning you ! I read it as if the bad ring was always there.
I wouldn't think anyone could tune a engine burning oil.

My 782 is already at the machine shop being inspected ( came with the van,no history on it ).

I appreciate the info and the call !!
 
#17 ·
when buying forged pistons and you intend on using a G head why not buy the higher compression pistons?

You need more timing with lower compression, I bump up to 14-15 from 12 as a start. Then adding 2-4 degrees of cam advance can also help.

After good porting the 782 flows well, well enough that a G head isn't worth it. The nice thing about a G head I suppose is that any chimp that can operate a banana can port one, easy.
 
#18 ·
Just wanted to note something about ignition timing.

When you set the timing of the distributor to 12*, this is simply a reference for the computer. The calibration knows that the engine is supposed to be set at 12* and ALL of the timing is based on this. By changing the base timing you will be moving the entire timing "map" in whatever direction you changed it because the computer has no clue that you did that. So, if you are having issues with ignition timing, yes...this might help, but it could also hurt. It is best to have the calibration altered to give you the timing curve that works for your set-up.

Once a calibration is made for a certain set-up, it will only work the way it was intended with that set-up. If something is changed, then in order for things to work the way they are supposed to the calibration should be changed as well.
 
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