Finding GT40 heads, but are they worth the trade from 58cc chamber to 64 ?

Even if I can pull it off, it will be inferior to aluminum in all ways. I think I am resigned to a 2.79 8" and a c4 with a stock converter. Expensive upgrades under the hood will be thwarted by the rest of it. Before this project, I never even used a wire feed welder. I never heard of POR15, or Ospho. When I bought this car, I thought it was fairly rust free . I am finding out there is SO MUCH I dont know, and finishing this project as a learning experience will help me carefully plan every phase of the next one. LOL, maybe the next one will have a 250 in it.

 

Hey Stu:
What you're experiencing is commonly know as OTJT .. On The Job Training.. Most of us here have had these courses also . You sound like you got a grasp of what you're doing .
Cometized
(Chip)

 

I like seeing what i can muster out of cheap parts too.. so i get it. Unless they're warped.. save your money and put it towards some thinner Cometic MLS head gaskets that are .030 over at the largest.. standard bore is best if the block is same. They come as thin as .027 thou and will make a much more substantial bump in compression than milling the heads the same amount. Or.. if you are wanting to bump compression even more?.. and I highly advise it as money well spent.. you want to mill those heads as far as possible before getting into the intake valve seat.. .050 thou or more even. The intake flange is 90 degree face so no milling required there. Intake manifold end rails that meet the China wall on each end can be ground off or easily filed with a body file if those areas get too tight. At only -.050" they shouldn't be an issue though and just needs less grey or black RTV sealer.

PS. Don't use course lapping compound except for heavier removal/roughing work or you will end up collecting carbon on the seats. Best to use an ultra fine compound to shine them up real good. Comes in many grit formulas. I typically use 1000 - 1500 grit after all my fine seat stone work grinding is finished up.

 

I appreciate all the knowledge and support from everyone here. OTJT for sure! GRoberts, I have read so much internet stuff about milling heads, and how some say every .0045 = 1 less cc in the chamber? Ford heads? it is dizzying. I got a head as level as I could, poured in 63 ml of water, and put in a tiny smidge of dishsoap to break the surface tension of the water, and had it running out enough to get the surrounding surface wet about 1/4 inch away. There is still some carbon in there, so not an exact measure.....but very close to 64 cc or one less. The intake valve is about .040 below the head deck (when the head is upside down), and another .010 would not cut into the seat. The sheet brass in the pic is .040 and when resting on the intake valve is even with the deck of the head. So, I have also read about block deck heights which I understand to be the distance from the piston top (flat top piston) to the surface the head sits on. If I have a 71 block that has not had any milling to the deck, what distance can I assume is between the piston top and deck? And thank-you BTW for the lapping grit recommendation.

 

Deck clearance is probably somewhere in the range of .015 - .020. Milling should net you about 1 cc per .006 - .007 milled. Mill as much as you can and it is what it is. If you want more.. use the thinnest gaskets you can find. Cometics are pricy but give tons of options to squeeze that last little bit out of the whole deal. Be sure to tell the machine shop you will use MLS so they give a smoother finish for compatibility. The block should be 50 Ra or better too but you can cheat by using spray on gasket dressings or high heat aluminum fortified spray paint. Just dust it up real thin on the block side of the gasket and you will be fine with no leaks or fretting.

 

I need some more real world input. After lots of cam research, and additional thought, and some price calculations, The importance of doing things with a plan (and hopefully once) is rising to the top. I have decided that I dont need a motor to rev over 6k. I want good, or better than good low and midrange torque. I would also like 20+ mpg if possible.

I would prefer to use a carburetor vs fuel injection. I have long tube headers, stock C4, 3.25 trac loc, 1971 302 block with a torker 289 on top and internals that are completely unknown ( compression test: high 170 low 155 and most just above 160). I also have a set of stock GT40 (non P) heads that could become part of the mix.

Now, here is the question.....Do roller cams generally enable better mpg vs. flat tappet? If I choose a cam grind along the lines of a mustang HO, would a roller have a significant advantage? The extra cost of Link bar lifters, dist. gear, and timing chain are not necessarily a deal breaker if the results are good. I am reading that the roller cams can deliver both a smooth idle and some decent grunt.

My problem is I have zero real world experience with this stuff, and ultimately will make a decision on my best guess. Whatever you guys have to say will be appreciated.

 

If you don't have the stuff to convert it I wouldn't mess with doing a roller cam. I'd definitely go with 1.7 roller rockers though. On a stock cam it's a nice little bump in performance.

 

VS flat tappet of same grind, a roller cam will give a slight increase in milage, but for what it costs you'd never recoup the difference in price...

 

I think these guys have it right. Roller conversions aren't usually all that cost effective from a $$/HP comparison in a little street motor. Bigger motors get more bang for the buck from the swap.

OTOH, wipe a flat tappet cam out just once in your lifetime and you'll quickly see the longer term benefit of a roller conversion. Plus, if you like to fine tailor your engine builds and use a custom grind anyways?.. there is a lot more left on the table with a roller cam vs a flat tappet. Just about ALL engines need faster valve action and can typically benefit from higher lifts. Only a roller can allow you to push these boundaries and still maintain reasonable lifespans. Flat tappets are lighter but rollers can also survive a hell of a lot more spring pressure to easily compensate for their heavier lifters.

 

I have read horror stories of flat tappet cams ruining a motor when the lobe got polished off.....does this generally happen with more radical grinds? I think I am leaning toward a flat tappet that will maximize the relatively smaller GT40 ports, the torker 289 manifold that was designed (according to most opinions) for the smallish ports of 289 heads?, holley w/vacuum secondary, and headers with fairly free flowing exhaust. Considering a stock converter and 3.25 gears, I think I should avoid anything that begins making power above 2000. I am probably over thinking all this, but it is interesting anyway. I will probably just get a roller motor with aluminum heads for the next go round, and leave this one flat tappet.

 

Don't be afraid of a flat tappet cam. They were around for decades before the roller cams became popular with the car manufacturers. Just be sure you do the break-in correctly and use the proper oil.

For your build I would just use what you have available, or if you like you can get all matters of expert opinion on this site from which intake manifolds are superior to your Torker 289 to which manufacturer makes the best oil pan drain plug!!!!

 

Flat tappet cams were the only cams for years. I wouldn't try the conversion to roller. WAY to much cost for what you're wanting to do. There's no need in it. Get a good brand flat tappet cam and use good quality oil and a zinc additive. Oil has changed through the years and some additives that were present in oil when flat tappet cams were in every engine, have been removed from today's oil. So use the zinc additive. Cheap and effective.

 

The cam is like the heart of an engine and its importance towards output and overall character is hugely important. The bigger the heart?(within reason from a longevity standpoint).. the better it runs and keeps paying dividends for a long time after. I often think of and weigh out the differences between a cookie cutter lazy ramped small opening shelf cam and a good custom roller design(which is typically a free service, BTW). It is a night and day difference when you keep in mind that just about any street oriented engine lives in a narrower powerband and pays you back in AVERAGE power production. 20+ ft/lb gains at several rpm points across 2,500 rpm spread feels WAYYY different than 20 ft/lbs of peak output at elevated rpm levels. A well matched roller cam can end up feeling like a mini-nitrous kit that never runs out of bottle.

And aside from that.. a roller conversion is cheaper now than it's ever been. Tons of decent SBF parts out there now. And far less chance for dusting you motor full with metal flakes in the long run and no special oil/zinc diet required. Then add the fact that roller setups are actually worth something used and/or can be swapped over to other motors. Pretty much hit or miss to do that with a flat tappet even if you keep all the lifters mated to their original lobes. OEM lifter bore geometry variations are downright horrible. Rollers can easily pay you back with more average power and much added longevity. Are years of enjoyment and greater piece of mind worth another $300 up front?

JMHO, but people wayyy too much underestimate the added value of a closer to optimized cam and/or cylinder head. Bigger lungs make more power everywhere in the powerband. Yep.. costs more up front but the long term dividend is considerably better overall. You will never EVER utter the words "I wish I would have just saved some money on a flat tappet cam".

If you must save the cash and run flat cams then I'd be looking at the most aggressive ramps you can find for the rpm range the motor is designed around. The general rule is that the weaker the cylinder heads are the greater the gains to be had from faster valve action. Keeps you from having to throw too much duration at it to get the airflow up. Comp cams extreme energy, Lunati Voodoo, or Howards various Rattler series are state of the art when it comes to off-shelf fast action/high lift flat cams. For example, Howards has 230-240 degree @.050 flats that are getting up near the .600" lift range from a factory 1.6 rocker ratio. Not saying you should try and stuff a cam like that into this motor.. just pointing out that you have more options now than ever before. Just depends on how much you want to spend and how much power and longevity you care to leave on the table, is all. Persoanlly speaking, if I could go back and do it all over again?.. I sure as hell wouldn't be doing it with a flat tappet design. Life's just too damned short to be running sliding lifter cams these days. Might reconsider the use of some really large mushroom style lifters but that has nothing to do with longevity though. lol

 

This thread and those GT40 heads have been sitting for about 2 1/2 years. I finally took the valves out and did some "bowl blending" as per strategies outlined at http://www.diyporting.com . Nothing will be flow tested, just rounding the short turn a little and smoothing out the transitions between casting and machining under the valve seat. I am using only stones and those cheezy sanding cones. Also shaping the valve stem boss a little bit. Will it turn out great? lol...I wont know until I get them on the car. I am toying with the idea of a comp cams XE262H flat tappet, but I might wait and see what I have in there before I buy something new. I also want to get rid of the torker 289 and get a dual plane intake, maybe this one. https://www.summitracing.com/parts/sum-226030 . I have 100 in the heads, $15 in drill powered grind stones, will have to spend some on valve springs and valve stem seals, and will lap in the valves. If getting them milled doesnt cost too much, I might do that; but cometic .027 gaskets WILL happen.

C4 will retain stock converter, and 3.25 rear gear will not change. I am in no hurry as you can tell, but grinding on those heads is fun and I do want to test them!

 

Personally, I would go with the Summit Stage II manifold. You will easily outgrow the Stage I unit.

Stu, I can't wait until 2020 or 2021 when you make your next posting on this thread. lol