Some GT-40 y303 questions

Tubo(2-bo) · Sep 7, 2005

I recently got a set of GT-40 y303 heads w/1.7rr's(used eBay), after doing searches here & at corral.net, I've got more questions than were answered.
Search revealed- All aluminum GT-40 Turbo Swirls begin with the same casting. The y's are the least machined. Stock pushrods can be used. The 1.7's should fit under my cast aluminum valve covers if the baffle are removed.
Now my questions; Can ARP154-3601 headbolts be used?? will they need bushings like 351 heads?? If so what bushings??? Anyone have a cheap set??
What comp ratio will an otherwise stock 92 EFI 5.0 have? And what size combustion chamber will yield a ratio of 9.5??
The final home for this is my 2700lb.1965 Mustang 2+2, mated with 70mm Cobra MAF, 65mm Exploder TB & intake, Everything port matched, Jacobs ignition, JBA shorty's, 2.5 BBK no cats X pipe, AOD, & 3.25 rear. Is low 13's dreamin?

txstang84 · Sep 7, 2005

the 1.7's will fit under stock valve covers w/o modding the cover..

yes, they will need the bushings...they're standard bushings Edelbrock part #3680...they're actually made by ARP anyway, and if you buy the head bolt kit to fit the heads, they will come with those exact same bushings...they cost $46 from Jegs.

the cr will actually go down just a hair, the Y heads have a 64cc chamber, the stock heads were advertised as being a nominal displacement of 62cc...a negligible drop

getting 9.5:1 with a stock 5.0 will need approximately a 58cc chamber.

with that combo, given good traction, a quicker set of gears (like 3.50's or 3.70's-I'm assuming you have an 8" rear), a little bit of a stall (stock cam-go for a 2200-2500), you should be in the 13's...

...just my opinion

ha ha-exploder intake

FourG63 97GST · Sep 7, 2005

whats the stock compression?

txstang84 · Sep 7, 2005

9:1 on a HO 5.0...from 87-95

Tubo(2-bo) · Sep 7, 2005

Thanks Txstang84

The car is to be a weekend-sometimes driver, with rare track visits. I was thinking a slight milling to bump the CR would be an inexpensive way of maximizing the heads for the street. Kinda like the port matching I"ll be doing. Though I dident buy GT-40x's a little machining will get these y's closer to x's. I realize that the y's have plenty of meat to allow milling. How much would need to be milled to get to 60cc.?? or 58cc?? Or is this information a reliable machinest would already have, or be able to determine??

txstang84 · Sep 7, 2005

Tubo3 said:
...Or is this information a reliable machinest would already have, or be able to determine??

yes, a good machinist should be able to mill and cc your heads to figure out where they are at...but, the only down side is, for every thousandth you shave off, you bring the valves an equal amount closer to the pistons-since you're running a stock cam, you shouldn't run into any problems whatsoever, but it's something to keep in mind if you go with a bigger cam...

but, if you're running a stock '92 shortblock, they have forged slugs, why not put a little spray to it? ...would help you get closer to your goal

Tubo(2-bo) · Sep 7, 2005

txstang84 said:
but, if you're running a stock '92 shortblock, they have forged slugs, why not put a little spray to it?

Hehheh, I've still got body work, paint, & a ton of other $hit to do before NOS. That would be a long way down the road, but your right . Something to remember!!

txstang84 · Sep 7, 2005

gotcha-understood!

dastang2 · Jan 24, 2006

do y303 heads require any special headers or anything special to run them. what kind of rockers can be used

Michael Yount · Jan 24, 2006

I run the Y's - you can run any kind of header that will fit the older chassis -- it's only the GT40-P iron heads that require changes to clear the spark plugs. The chamber in the Y is 64 CC's -- probably slightly bigger than a stock E7 head -- so a milling will be necessary to bring the static CR up into the 9.5 range. You machinist should be able to tell you how much he'll have to mill to hit a certain cc target -- but to know your actual compression you'll need to measure your motor -- see how much in the hole (or out of) you are.

Remember if you cut the head you potentially alter port alignment with the intake, pushrod length, valve train/rocker geometry, bolt hole alignment on the lower intake and may need to cut the bottom of the intake depending on how much is cut from the heads. A thorough machinist will want to mock it up to see what impact a significant cut is gonna have.

I ran ARP bolts with mine with no bushings at all -- 3 yrs. and 18k miles ago.

04sleeper · Jan 24, 2006

Michael Yount said:
Remember if you cut the head you potentially alter port alignment with the intake, pushrod length, valve train/rocker geometry, bolt hole alignment on the lower intake and may need to cut the bottom of the intake depending on how much is cut from the heads. A thorough machinist will want to mock it up to see what impact a significant cut is gonna have.

I would also add reduced deck height to go along with that list that can hurt head gasket retention in some applications.

Topdowncruise · Jan 24, 2006

Yes,the y303 heads have a nominal chamber size of 64cc but can actually range from 62cc to 64cc just like the stock heads.I increased the CR on my setup to about 9.5 by going with higher compression pistons when I rebuilt the engine.Don't regret getting the Y's versus the X's.With the money you saved you can get the Y's ported to flow at least as well as out of the box X's;plus I think the smaller Y ports make them fun in day to day lower rpm driving.They have excellent bottom end torque.
.

Michael Yount · Jan 24, 2006

Kev - he was talking about cutting the heads, not the deck -- or did I miss that?

04sleeper · Jan 24, 2006

Michael Yount said:
Kev - he was talking about cutting the heads, not the deck -- or did I miss that?

I was refering to the deck height of the heads. Y's come with 5/8" thick head deck so cutting them would give you even less.

AFR's for example have a 3/4" thick head deck. Better for boost or N2O.

A friend of mine who races Street Warrior had some GT40p's cut so much he had to make custom brackets to keep the head from flexing and popping a gasket. This is before they allowed aluminum aftermarket heads.

The best bet for getting the lower cc head is to buy one thats already close to what you want so you don't run into those issues.

Some GT-40 y303 questions

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