Thoughts on 2.5 head choices?

[Username]

So I blew the head gasket at buttonwillow, nothin serious. I actually think it may have already had a small blow into the water jacket prior to the race explaining some odd problems I was having. (it still ran like a friggen beast, although I did get passed by an acr viper in each session which should have lapped me, but he had more money than skill :eyebrows: )Well now the number 1 is blown into the water jacket even more, and there's also a blow between the #1 & 2. So since this is the first time I've had a 2.5 in the csx-t I'm wondering if I just slap the fast burn back on, or throw in a G head while I'm in there. Here's my thoughts. I'm not planning on drag racing anymore, just road races since the dollar to track time value is a million times better, so I don't need a ton of power.(a nice reliable 200hp would be super) I want to be able to run 15-17lbs of boost on crappy california 91 octane, and I'd like a reasonably clean power band. It seems when I had 2.2's with the g head running 18+lbs of boost the boost comes on so hard it upsets the balance of the car. The fastburn didn't seem as bad, so that's my main worry. On the plus side 17lbs would be safer with the g head. The motor will be pretty much bone stock except for cleaning up the bowls and runners. The exh. manifold is ported, no balance shafts, and there's a windage screen and baffle in the pan. Oh and it's intercooled with 3 inch exhaust, no cat or muffler. Just turnin the boost up a little and addin more fuel. So what's everyone's take?? G head or fastburn? Thanks for your input.-Jarrod

[t3rse]

if it already runs well with the swirl, stick with it

(I've got one for sale :D)

[Juggy]

the benifit of the G head is when properly tuned you can run alot more timing advance.

hit up moparzrule he has alot of experience with the 2.5 G head cal.

[turbovanman²]

Swirl, torque rules, :love: :thumb:

Its also very hard to get a good G-head cal over the counter unless your doing yourself.

[cordes]

the benifit of the G head is when properly tuned you can run alot more timing advance.

hit up moparzrule he has alot of experience with the 2.5 G head cal.

According to Stephane the swirl head actually requires less timing pulled per lb. of boost vs. the G head. I think the added timing allowed by the G head is due maninly to the anemic compression, especially in a 2.5.

[Juggy]

According to Stephane the swirl head actually requires less timing pulled per lb. of boost vs. the G head. I think the added timing allowed by the G head is due maninly to the anemic compression, especially in a 2.5.



timing + displacement = VERY NICE :eyebrows:

[BadAssPerformance]

The G-head has benefits when you port the hell out of it... stock vs. stock take the swirl.

Compensate for the 91 octane swill with lower timing... or octane booster

[turbovanman²]

The G-head has benefits when you port the hell out of it... stock vs. stock take the swirl.

Compensate for the 91 octane swill with lower timing... or octane booster

So does the swirl, ;)

I still don't really see the need for a G-head. Until someone can prove back to back that a G-head is better, then I'll always stay with swirl, :thumb:

The lower compression is really neglible and like I stated, unless you have a way of doing the cal yourself, its super hard to get a G-head to run hard like a swirl and not be doggy around town. Maybe a lighter car you won't notice but a heavy vehicle, you notice it immediately.

[moparzrule]

the benifit of the G head is when properly tuned you can run alot more timing advance.

hit up moparzrule he has alot of experience with the 2.5 G head cal.


I've posted up my 2.5 G head calibration in the repository, it's probably too agressive for 91 octane, not sure as I only ever used 93 octane. It has the flash check engine on knock enabled so you'll know if it's too much.

G head VS swirl....
You can run MUCH more advance in vaccuum and in low boost than a swirl head, but yes it's true once at full boost you pretty much have the same amount of timing pulled. The G head was still less knock-prone though. I was able to get 25 PSI boost on 93 octane with a ported G head, and only 22 PSI on a ported swirl (chambers had some metal removed) and blew the headgasket with that setup from knock. Never blew anything with the G head.
Anyway, going by the old butt dyno, I made MORE low end torque with the G head and mad advance on the timing than with the swirl which I maxxed out the timing also. It seems the swirl gets knock pretty easily when in vacuum and low boost situations, so the timing stays back a good ways compared to the G head. Even with 1/4 throttle and less than 5 PSI boost the tires roasted by 3000 RPM. It had so much torque I literally ditched the 2.5 for a 2.2, no point if you could never get any traction.

Stock for stock head I am a G head fan all the way, make the most power on the cheap. Stock swirl heads just plain suck. But ported VS ported I would favor the swirl head, if ported correctly. The swirl can really come alive with some attention.

[Juggy]

what if they made a G head with the swirl head combustion chamber??? :eyebrows:

[Username]

So even though the g head is barely ahead in the poll, i don't think there's been enough reason to swap to one, especially since I already have the fast burn so I won't need to hit the yard to grab one. Although I like the fact that moparzrule said he's never blown a head gasket with the g head, we only have a pathetic attempt at 91 octane out here, after that is 100 oct. but it's almost 9 bucks a gallon, so that's not happening. As far as power band goes, my csx-t is around 2400-2500lbs, so I don't think any lack of bottom end power would be a huge issue, but like I said origianally I'm fine with the power it puts out right now, so I don't need a ton more boost. Since this is the first time I've run a 2.5 does anyone think that 17lbs was too high and possibly why the head gasket popped? The timing is stock at 12, anyone run 17lbs of boost on a stock 2.5 and know how much timing I should pull to make it happy? I have all the stuff to burn chips, so if anyone has a good cal to make this set up more reliable, I'm all ears. Thanks for al your info!

[moparzrule]

what if they made a G head with the swirl head combustion chamber??? :eyebrows:

Thats why I said stock for stock comparison...

Street car with occasional racing with ported head= swirl

race car only- G head all the way!

[cordes]

So even though the g head is barely ahead in the poll, i don't think there's been enough reason to swap to one, especially since I already have the fast burn so I won't need to hit the yard to grab one. Although I like the fact that moparzrule said he's never blown a head gasket with the g head, we only have a pathetic attempt at 91 octane out here, after that is 100 oct. but it's almost 9 bucks a gallon, so that's not happening. As far as power band goes, my csx-t is around 2400-2500lbs, so I don't think any lack of bottom end power would be a huge issue, but like I said origianally I'm fine with the power it puts out right now, so I don't need a ton more boost. Since this is the first time I've run a 2.5 does anyone think that 17lbs was too high and possibly why the head gasket popped? The timing is stock at 12, anyone run 17lbs of boost on a stock 2.5 and know how much timing I should pull to make it happy? I have all the stuff to burn chips, so if anyone has a good cal to make this set up more reliable, I'm all ears. Thanks for al your info!

The timing you will be able to run will depend on a large number of factors. IIRC someone was running a 2.5 non-ICed at 17PSI very successfully with only a scanner and boost gauge. Many people have probably blown HGs and toasted pistons like that too though.

Patience is the key when tuning. Monitor your knock, AFR, and preferably EGTs and you will be fine. I have run 22PSI on a swirl headed 2.5 for an entire summer before with no ill effects.

[turbovanman²]

The timing you will be able to run will depend on a large number of factors. IIRC someone was running a 2.5 non-ICed at 17PSI very successfully with only a scanner and boost gauge. Many people have probably blown HGs and toasted pistons like that too though.

Patience is the key when tuning. Monitor your knock, AFR, and preferably EGTs and you will be fine. I have run 22PSI on a swirl headed 2.5 for an entire summer before with no ill effects.

Exactly, and there is too many factors in why your head gasket blew.
What boost were you running, A/F ratio? Cal? What turbo? Was it running hot?
Have you checked the deck and head for warping?

[turbo84voyager]

I run both. My g-head 2.5 pulls harder in my caravan than my swirl does in my lighter shadow. The only problem with the g-head is to get it right you need to fine tune it to your application. I have a few versions of matts cals that have been modified for daily driving. Trust me the wrong cal ( and there are some out there, you will have sluggish performance and very high EGT's) If you are looking to just throw the head on and not mess with it stay with the swirl.

[puppet]

we only have a pathetic attempt at 91 octane out here, after that is 100 oct. but it's almost 9 bucks a gallon, so that's not happening. Try (9) gallons of 91oct. and add in (1) gallon of Xycol. Give that a shot.

[moparzrule]

Try (9) gallons of 91oct. and add in (1) gallon of Xycol. Give that a shot.

I'm guessing you mean Xylene (xylol) which is ~117 octane IIRC.

9 gallons of 91 with 1 gallon of 117 gives you 93.6 octane. Not really worth it there. 8 gallons of 91 with 2 gallons of 117 would be 96.2 octane, thats better but...
Xylene used to be $10 a gallon, now it's almost $20 at home depot, now it's really not worth it. So $40 for 2 gallons of xylene, and $15 for 8 gallons of 91, thats $55 for 3/4 tank of 96 octane. Pretty crazy.

One other thing if you do use xylene make sure you stick in 1oz of marvel mystery oil per gallon of xylene for lubrication purposes.

[puppet]

Just try it Mr Professor.
:P

[Aries_Turbo]

i voted Swirl head but im in the process of swapping a 2.5L with a g-head on it in my daytona. motor and head was completely rebuilt by the previous owner so im just swapping it in and trying it.

ive run 22psi on my 2.5L/swirl in my k car on 93octane gas with no knock retard.

[moparzrule]

Just try it Mr Professor.
:P

I've done it several times, last time was when I noticed the insane price jump.