On a 302 I would suggest a combustion chamber size of no more than 60 CC and valve sizes of 1.94 / 1.60. A set of early 289 heads ported and fitted with larger valves would do this but by the time you paid the machine shop bill it would be cheaper to buy new heads.
Edelbrock, Holley, TFS, World Products, AFR and Ford Racing are a few companies that all make and sell either cast iron or aluminum replacement heads for your 302. All are excellent quality. Prices start around $600 for a pair of World Products or Ford iron heads. Contact Jegs (www.jegs.com) or Summit (www.summitracing.com).
These heads are sold ready to bolt on and require no mods of any kind to do so if you order them properly. Spend some time with the order tech person to be sure what you get will be perfect for your application.
There is a serious restriction in the exhaust port from the smog passage cast into heads made from 1968 - around 1986. This keeps you from realizing any serious performance gains. Another problem is the rocker stud on 1969 - around 1982 heads is the positive stop type which needs machine work to change to an adjustable type rocker setup. By the time this machine work and porting was done you would already be driving your car had you bought new replacement heads. Plus the bill for the machine work would exceed the price of replacement heads. Plus the replacement heads would still outperform the reworked stockers. Plus the replacement heads are NEW!
Here are some typical machine shop prices for quality work:
Install 16 valve guides = $80.00
Price of bronze guides = $24.00
Vat heads and magnuflux = $20.00
Install 16 valve seats = $100.00
Price of Stellite seats = $65.00
Performance valve job = $175.00
New Stainless valves = $180.00
Valve springs & retainers $80.00
Hardened 10 degree valve locks $35.00
Total = $759.00
So you have spent $759.00 before any porting has been done. There is still no way to adjust your valves in order to be able to use an aftermarket cam because I did not include the cost for changing rocker studs.
58 cc combustion chambers
1.74"/1.48" valves (?)
BIG thermactor bump in the exhaust port
You say some "mild" portwork on the exhaust side... this could mean anything from some simple gasket matching, to possibly taking out the "smog" bumps. It's hard to put horsepower values to just the portwork on the heads since so many other factors come into play...
Not knowing anything about the condition of your heads... the guides, flatness... I'm inclined to agree with Royce... Go with the World Products Roush 185's or something. Follow his wise counsel on ordering, paying special attention to the cam grind that you have vs. the valve springs that they should use, and the valve rocker/stud boss area, etc...
Not knowing anything else... how much does machine work cost in the Netherlands, your laws regarding emissions and doing stuff other than stock, how much work you could do yourself, etc... that's about all I have.
To clearify my question...
How much power is possible with a set of stock heads in good condition, without spending money on new heads and without spending money on machining and porting the stock ones?
The ones I have have been rebuilt by the previous owner and are in good condition. He milled the gasketsurface flat, new valves, springs and seats, gasketmatched the ports and reduced the "smog-bump" in the exhaust ports. In other words, completely rebuilt with mild porting.
So I was curious to how much I can get without spending "any" money on the heads. Just a ballpark figure, like 250hp/275hp/300hp/325hp(?)
If it's impossible to tell I'll be happy with that ansver too
(I'm not after how much hp I have now, but what's possible to get)
If I was going to spend some money I'd surely get new heads. No argument there!
Seems like with what you have there, depending on valve sizing, you could get into the 300 + HP range with the proper cam, intake, carburation, exhaust/headers, compression, etc...
I have ported 289 heads on my 302, 1.94"/1.60" valves, 0.560"/0.560" lift, 294 duration, solid lifter cam, single plane intake manifold, Holley 780 cfm "racing" carb, etc... etc... and am making about 400 HP. Will be taking to the drag strip in the next week or two to verify with some ET's. Not very user friendly out on the street, but makes LOTS of power.... fun, fun, fun, til' your daddy takes the T Bird (Cougar) away.
The question of "How much horsepower" is much more a function of $$$$ than anything else.
You might investigate the "GT40-P" heads. these are stock on teh 98 and up 302 explorers. They have small valves but are of the fst burn variety and the power range is from about 1500-6000. With a good cam, headers, performer rpm intake and a 65o double pumper, 350hp is not out of reach. These heads are advertised by PAW and are very resonable compared to World Products. I have them installed on a 351W and they work well at medium to high rpm ranges. The only drawback is the plug angles are less than stock 302 heads and require special headers that Ford Racing sells. Or you can use Hedmans with an additional flange installed to space the heddeers out for plug and wire clearance.
Question? what is the rocker setup on the gt40p's? If there pedestals theres more money involved and then with the header problems the worlds look cheaper all the time. Plus with the thick decks the worlds have there very durable compared to any stock ford head. mm
Hey thanks, I got a stock 302 out of I think an 82 granada, not sure on the exact year. it has a 2brl wich will be changed. I just want to know my option of I decide to go full out and make this 302 in to a real monster.
I do believe the GT-40P's are set up for pedestal type rockers. I bought a set on ebay earlier this year, complete w/ valves, and traded the stock springs that were to come with the heads for the $50 worth of machining on the rocker stud bosses to make thread in studs work. I got mine from the folks in the southern tip of your great state of Indiana at Tri-State cylinder head for around $400, with stainless 1.94"/1.54" valves, with the stud bosses milled down 0.300", and without springs or retainers/keepers. The springs/retainers/keepers on those are too wimpy for any sort of decent cam anyway. Someday I may put those on, but for now I don't feel like messing with the whole plug/header thing, and could tell I'd have problems by setting one on my shortblock and holding up a header to it. I've got the old bombers, must be hookers or something, short radius bends.
The guys at world products are smart enough to know what the market will bear; they know the $$$ associated with jacking around with Ford heads, and price their units accordingly.