Need cal advice for g head swap.

[Shelby]

Okay so I have a stock 1988 CSX-T that I'm going to be putting a Garret T2, FMIC, and maybe a 287 g-head on. There is nothing wrong with the swirl head on the car but I have heard that g-heads flow about 10% better and produce about 10% more torque. My question is will the g-head work fine with my current calibration or will I lose performance? If I lose performance with current cal/g-head combo, how hard would it be to make a custom g-head cal and would it be worth it? Thanks in advance.

[4 l-bodies]

By bolting on g-head on swirl bottom end, for starters you will be sitting at approx. 7.6:1 compression and not 8.1:1 compression, so loss there. There is a 6cc difference between g-head and swirl head. The swirl head can be made to easily outflow a stock g-head with just a few hours of port work. Then you can have original compression, and have benefit of higher flowing head and not have to have custom cal made. If I were you, I would spend my money on your current swirl head and have a good multi angle valve job done. For increased performance, find someone to unshroud valves in chambers a bit, do some light pocket porting in throats, and concentrate on short turn radius of intake and exhaust ports. If you want to do a bit more, straighten out walls of ports a bit. Do it correctly then your swirl head outflows a stock g-head without a doubt. I would also buy a ported exhaust manifold from one of our vendors.
Todd

[Shelby]

I had a ported and polished swirl head with 1mm oversize valves on another car that I was going to use, but it got deep cracks between valves and was letting water into my oil. I have the stock swirl head on the CSX and a g-head laying around, so I don't have to spend any money. Can I take my swirl head to a machine shop to have it ported or should I have a someone do it by hand? Also, I already have a ported exhaust manifold that I'm going to be putting in this car too (sorry, forgot to mention that).

[4 l-bodies]

If I were you I would have someone that does good machine work do a nice valve job on your spare swirl head. As far as I know only Forward Motion has a CNC program for porting swirl cylinder heads. Everyone else does it by hand. That does not mean doing it by hand is inferior. I used to finish LS cylinder heads at a nationally known SBC engine builder after it was machined by CNC program.
If you still have +1mm swirl head that was cracked you could use those valves. Decent quality replacement +1mm stainless valves are only around $130 for the set. There are better options but they are about twice that amount. The nice thing about +1mm valves is your not having to sink valves into head (which hampers flow) like you would using the same size valve. The better quality valves combined with being +1mm larger is a gain. It is impairative that you unshroud valves and open up throats when you add +1mm valves or you will see no gains or could lose some flow! Ask around your home town to find out who does good port work. You should be able to get a decent head with 3-4 hours of port work done. Your best option would be Steve Menegon or Brian Slowe. These two guys are in your home state and they do fantastic work! You could contact them and see if they are interested or to get a time line on doing the job.
I would offer to do this for you but I am recovering from two hand surgeries this past year. Still licking my wounds from the surgeries. Besides shipping cylinder head two ways would just add needless cost to your project.
Todd

[contraption22]

I thought that the legend of stock G heads outperforming stock swirl heads had been debunked. Even if they did outflow them by a small margin, it's nto worth the compression loss and tuning issues that seem to come along with the swap from swirl to G.

[4 l-bodies]

I thought that the legend of stock G heads outperforming stock swirl heads had been debunked. Even if they did outflow them by a small margin, it's nto worth the compression loss and tuning issues that seem to come along with the swap from swirl to G.
Out of the box the g-head will slightly outflow a swirl on the flowbench. I agree Mike, the loss of compression for sure outweighs any CFM flow gains from running the 287/455 g-head. Then there is the infamous 655 G-head which a few people on left coast view as the Holy Grail of 8V heads. Out of the box it has a larger volume CC intake port. So bigger has to be better right? This certainly was proven to be false. The intake and esp. the exhaust has a terrible short turn radius that cannot be fixed with porting. IMO, a really poor choice for a performance head. It can easily be surpassed by 287/455 or swirl head with minimal effort. My advice to anyone reading this is don't drink the kool-aid (hype) on the 655 head. Your just shooting yourself in the foot running one.
Todd

[turbo84voyager]

Best advice I can give is Don't do it. I fell for this a few years ago. I believe you can get away with it better with a 2.2 then a 2.5 but still a ported swrl is the way to go. As for a cal, im not sure about the 2.2 but without one on a 2.5 the thing will barely run right trying to set the timing if you try to set it to stock 12 degrees and it is a complete dog. I have heard that it is not nearly as bad on a 2.2 but I dont have personal experience with that combo. All I know is I spent 2 years trying to tune my g-headed 2.5 in my van and after all the time, and trying everything possible to fine tune the timing ( very small window between too little timing and high EGT's and knock from too much timing) I pulled the head and put a ported swirl on. Performance was as good or better and much better driveability.

[Shelby]

Alright. Thanks guys. Swirl head it is. I will contact Bryan Slowe and Steve menogen and see what they can do. My only questions now is how do I "unshroud valves and open up throats when you add +1mm valves"?

[bakes]

De-shrouding the valve is best done when you know the curtain height between seat and valve face . The cam you choose will dictate this . once you have this measurement then you are ready.

[Shelby]

What's a curtain height? pic? I was just going to use the stock cam.

[bakes]

The height the valve lifts of its seat , measured for valve seat to valve face when open.
http://images.omegaowners.com/images/faq/miscpics/Valvearea.jpg

[bakes]

http://www.calaisturbo.com.au/showthread.php?p=3044417

[4 l-bodies]

If your planning on having Steve or Brian do the head, leave the unshrouding and throat cutting to them. Money well spent! You can easily lose all the gains made on a well ported head by making throat too large or too small or not unshrouding correctly. Even having the wrong cutter cutting seat angles can cause a 15 CFM or more loss. What works for a Harley (or fill in the blank) isn't necessarily the hot ticket for our motors.
Like I said earlier, concentrate on those few areas mentioned earlier. The first few cylinder heads I did actually turned out decent. After getting more brave with the carbide roatary files, I took a step backwards according to the flowbench. So until you really know what your doing, most of the time less is more when your making mods to a cylinder head. Resist the urge to try to reinvent the wheel. For the weekend warriors porting heads there is some advice for you (lol).
Todd

[OmniLuvr]

you said you have a csx-t, so is that a 2.2 or 2.5? im still a big fan of the g-head (not 655), and run them on all my l-bodys with 2.2's, all i did was crank my timing to 15* advance. with the lower compression you can run more boost without having to run higher grade fuels, 18-20 psi no problem with 91 (stock head). in the lighter weight cars like l-bodys and shadows the loss of torq from less compression was just a bonus for me.

now if you hav a 2.5, or a heavier car, swirl is the way to go. i will admit i did get a little better mpg with a swirl head, but with a proper cal, i had very similar mpg with my g-head cars.

you said you didnt have much cash, a steve m head is not cheap, you could get an f4 cam, ported 2piece, ported exhaust mani, and valve job on the g-head for similar/cheaper than that... just an idea, but a steve m head would be awesome!

[crusty shadow]

Then there is the infamous 655 G-head which a few people on left coast view as the Holy Grail of 8V heads. Out of the box it has a larger volume CC intake port. So bigger has to be better right? This certainly was proven to be false. The intake and esp. the exhaust has a terrible short turn radius that cannot be fixed with porting. IMO, a really poor choice for a performance head. It can easily be surpassed by 287/455 or swirl head with minimal effort. My advice to anyone reading this is don't drink the kool-aid (hype) on the 655 head. Your just shooting yourself in the foot running one.
Todd

I have flow bench results that prove otherwise

[4 l-bodies]

Then there is the infamous 655 G-head which a few people on left coast view as the Holy Grail of 8V heads. Out of the box it has a larger volume CC intake port. So bigger has to be better right? This certainly was proven to be false. The intake and esp. the exhaust has a terrible short turn radius that cannot be fixed with porting. IMO, a really poor choice for a performance head. It can easily be surpassed by 287/455 or swirl head with minimal effort. My advice to anyone reading this is don't drink the kool-aid (hype) on the 655 head. Your just shooting yourself in the foot running one.
Todd


I have flow bench results that prove otherwise

I see someones had too much Kool-Aid from the Poop. I'll bite. What does your 655 head flow? Stock then ported vs. a 445 or swirl. Post up those #'s.
Todd

[crusty shadow]

I see someones had too much Kool-Aid from the Poop. I'll bite. What does your 655 head flow? Stock then ported vs. a 445 or swirl. Post up those #'s.
Todd
already did over the summer, everyone here ignored it.

[85boostbox]

Repost it.

[Dr. Johny Dodge]

Best advice I can give is Don't do it. I fell for this a few years ago. I believe you can get away with it better with a 2.2 then a 2.5 but still a ported swrl is the way to go. As for a cal, im not sure about the 2.2 but without one on a 2.5 the thing will barely run right trying to set the timing if you try to set it to stock 12 degrees and it is a complete dog. I have heard that it is not nearly as bad on a 2.2 but I dont have personal experience with that combo. All I know is I spent 2 years trying to tune my g-headed 2.5 in my van and after all the time, and trying everything possible to fine tune the timing ( very small window between too little timing and high EGT's and knock from too much timing) I pulled the head and put a ported swirl on. Performance was as good or better and much better driveability.

I can say that the G head runs fine with an 85 DC lm/pm and 86 style mediun sized dish pistons (2.2) - quite well in fact in a 12# log motor
I don't even like the look of the 2.5 piston tops - no way would I expect them to work with a compleately different old wedge / bath tub style combustion chamber

[crusty shadow]

Repost it. go find it, it was right under everyone's nose.
when that makes an appearance I will post up charts from a 782 taken from the exact same flow bench....