GT40 aluminum heads

[427supr]

I will be pulling my SVO 351 and stroking it to 408. I really want to use the existing parts if possible. The car is primarily driven on the street, with my rpm's staying down most of the time. I want to stay with my aluminum GT-40 heads. Are they sufficient for my mostly street driving, with the 408 displacement? My engine builder advised that he can port them if needed. I am also running a victor jr. single plain intake.

[RACER X #99]

I have had the same engine as you have and unless you are looking for some track HP save your money and keep the 351. I think the GT40 heads are too small for a 408.

I had the gt 40 heads ported by a pro and they were marginally better on the 351 but not noticable enough to warrent the expense. You can buy a set of Victor Jr's for a little more than a good port job on the Ford heads and they work a lot better.


If you want more power sell the 351 and buy a World products or Dart block and have your engine builder put something together for you with some better breathing aftermarket heads. Jr's AFR.

Putting a lot of money into a stock 351 block just does not make sense to me. The block is weak and you will have to bore .030 over to get to 408 with your 4"stroker and you are really putting a lot of strain on a weak block.

Some will disagree but I have done both and I would not build another stock block 351.

[Curt C.]

Agree with Racer X. Why are you pulling the motor?

[TerrysSPF]

427supr: Welcome back! Glad to see you decided on the 408 - good choice. Like the guys above, I would suggest you sell the GT40 heads and go with an aftermarket brand. The Vic Jr's are a nice choice, but if you really want the 408 to sing then I would go with the AFR 205's.
If you're going to go through all this work, don't restrict the engines ability by re-using the stock heads. I know a few guys that changed their GT40 heads on their 392 crate engines to AFR's and they picked up 70-90 HP. -That's how restrictive the stock heads are.

-Spend a few extra bucks and do it right.

[LoBelly]

Here are some links to sites showing flow rates

http://www.jason.fletcher.net/tech/f...a/aluminum.htm

http://www.racingheadservice.com/Inf...ts_New.asp#SBF

For performance your aluminium GT40 heads are probably about the minimum spec that you'll want for a 351, considering the flow number of heads like the 4V 351 clevos.

However I think that stroking your 351 to 408 puts your engine in new territory so some more flow would be preferable.

Notwitstanding this - if you're anything like me you're probably thinking that the whole stoking exercise is expensive enough as it is. I'd probably go with what I had to start and then look around for a deal on heads when time/budget/circumstances allowed - If I felt it was needed.

The other factor is the cam, if your going bigger on the cam will your existing heads cope - its likely that the 408 will be able to swallow a bit more cam.

It's easy enough to change the heads with the engine in the car but the cam could be a bit more of an effort.

The availability of high flowing heads means that port jobs are out (uneconomical) unless you have a very good reason or the ability to DIY.

Once you start toting it all up have a good look at some crate engines (maybe short motors too) and what you could recover from your own

Good luck with your mods and post some progress pics for us.

LoBelly

[Rickd]

Stroking the motor and staying with the same GT40 heads is a total waste of time. The $$ would be better spent by REPLACING the heads with a set of AFR 185's (around $1400), and you will be adding a LOT of hp and torque, and not stroking the motor. You will then have a much more powerful 351. The GT 40 heads were standard issue on 302's, and the 302 is made a lot more powerful by upgrading to something like an AFR 165. Talk to an engine builder (ie Keith Craft) he will tell you the best routes to take and they also sell the parts to do it. My 331 with AFR 165's dynod 436 hp at 6000 rpm with 400 lbs of torque.

[RACER X #99]

Originally Posted by TerrysSPF

427supr: Welcome back! Glad to see you decided on the 408 - good choice. The Vic Jr's are a nice choice, but if you really want the 408 to sing then I would go with the AFR 205's.


-Spend a few extra bucks and do it right.

Terry , I have had the AFR 205's on my 408 and now the Jr's on my 427. While the cnc ported AFR's do make more HP than the Jr's, in my opinion the Jr's are a better made head quality wise. I particularly like the heli coils in the Jr's.
If 427 supr is looking for a good street 408 I think the Jr's are a better choice.

BTW I do have a set of 205's for sale but they need about $600. in repairs ( the main reason I bought the Jr's)

[427supr]

I will look into the AFR heads. How are the Trick Flow heads for the small Fords? Like most of us, I am trying to save a couple bucks using my existing parts, but if it won't work right, I will have to pull out the wallet. Will the exhaust ports still be the same on the AFR's and the other aftermarket heads as my GT-40 heads? I am hoping to be able to bolt up my headers in the same position.

[ERA2188]

427. Call AFR and ask about the exhaust ports if you are talking 205's. I know the 165's and the 185's are identical to the stock Small Block Ford heads. They bolt right on and you can (should be able to) use the same headers etc. The only reason I bought Trick Flows is that someone from Unique mistakenly told me the AFR's would require a header change. I too was on a budget, so for that reason I went the Trick Flow route. They were wrong, as the AFR 165 and 185 have the same dimensions and same port locations as the stock heads. The AFR is a higher quality head IMO, and they have smaller valves, with similar or better flow characteristic, that means higher velocity which = more power (so I am told). Keith Craft uses AFR's on a lot of SBF motors. I don't know which cam you have, but you might look at it. Although one Fast Ford article I read stated "formula for a touque montser = conservative cam + high flowing heads. For street use I BELIEVE your biggest problem is that you are starving that 351 inch motor with those puny GT40 heads. You can always change the cam later. Ask for Tony at Kenth Craft, or Keith (he is a cobrafile - has a Kirkham).Rickd

[BDR561]

The AFR205 will accept your existing headers. They have two different header bolt paterns.

[Curt C.]

Racer X - why do you think the block is not worthy of a 408 stroke, .30 overbore? If the engine in question is an SVO 351 crate motor, the block should be a Sportsman model. I beleive Sportsman is rated to 700 hp by Ford. The block should be plenty for a stout, street 408 no? I am curious because I have a Sportsman block too and will be rebuilding at some point in the future. I also track the car 4 - 5 weekends per year.

[RACER X #99]

Curt,
Not familiar with the sportsman block, does it have 4 bolt mains like the aftermarket blocks?
I had a 351 Crate a few years back and I beat the crap out of it on the track. I shifted it at 7,500 all day long and it finally blew up and the only thing I salvaged was the manifold and water pump.So I don't have a lot of faith in stock Ford blocks.(for track use)
The World Products and Dart blocks can both be bored to 4.185 and still maintain a .250 wall thickness. I also like the fact that they have priority oiling.

RD

[Curt C.]

X, It has been around for some time and used on the Ford performance crate engines. Part #M-6010-C58. Still a two bolt main with 3 inch mains and not recommended to be bored more than .030 or stoked more than 4.00. Not meant to compete with the likes of Dart or World, but costs a lot less too. Basically it is a nodular piece with some added material. The one you blew up turning 7,500 was most likely a Sportsman. Any 3.0 main Windsor turning 7,500 for too long is going to let loose. Too much heat in the bearings the experts say.

Originally Posted by RACER X #99

I had a 351 Crate a few years back and I beat the crap out of it on the track. I shifted it at 7,500 all day long and it finally blew up and .....

RD

Sounds like you got a decent amount of time from it no? Mine is still kicking strong but I shift at 6,000.

[Curt C.]

427supr. If the motor does not need a rebuild, don't do it. Go with a set of AFR 185's. You will get 30 - 40 HP from it and it will take only 3-4 hours of skilled labor. You can then sell your GT40 heads and recoupe maybe half your investment. If you do want to stroke later down the road, 185's, while on the smaller side for a 408, will work very nicely for the street with an additional 50 HP or so. My $.02 anyway.

[TerrysSPF]

RacerX: Can't argue with you about the Vic Jr heads being good quality. I have Edelbrocks on my engine and I love the fact that they have heli-coils in all holes (except spark plug holes). I just figured (from his previous blog) that 427supr was looking to get as much power as he could for his money - which is why I suggested the AFR205's. -Plus, I don't think the AFR's are a "poor quality" head, (or I wouldn't have mentioned them) they just might not be built quite as well as the Edelbrocks........although still solid, IMO.

The IDEAL combo would probably be to buy the Vic Jr heads and send them to Keith Craft for some of his magic port work, but I know 427supr is looking to do this as cost effectivly as possible!

[Rickd]

I have NEVER heard AFR and "poor quality" ever mentioned in the same sentence. Beautiful heads, just need to insure to put in good springs for your application.

[427supr]

I'm not too concerned about running at 7,500 rpm. I don't race my Cobra. Once in a while on a country road, I may hammer it. My rev limiter is set at 6,000 rpm. The bigger heads will breath better at high rpm's, but what I am looking for out of my future 408 is that low end torque.

[Howard Jones]

I also have a 302 with the GT40X heads and importantly the "B" cam from FMS. This is the basis for the 345HP motor. I have had the car on a chassis dyno and I will tell you that with a 750 DPer, open headers, and a RPM performer I got right at 280hp at the wheels. That is pretty close to 345 at the flywheel give or take.

Now... here's the deal. This setup made 280Hp at 5200 revs and 315 ft/lbs at 3800 ish. It also completely ran out of steam at 5500 making 270hp and 250hp at 6000. Its really a combination of the very soft valve springs that come stock on these heads, the 194 intakes, a sloppy valve pocket casting, and the cam. Both, cam and heads, just don't work above about 5500.

I think you can get maybe 365hp out of these heads if you change the cam and springs but that's with a 302. Asking to feed another 50 inches is asking too much from the GT40X head as cast. I think there is another 30HP with a good pocket port job and a 3 angle valve job but not much more. Going to a 202 intake would be worth maybe another 15Hp but unless you are doing the work yourself for free they just aren't worth spending money on.

The bottom line is I would do a couple of things.

1. Rebalance the rotating assembly and reuse the 351 crank rods and pistons if still in good shape. Do not reuse the stepped Ford rings. Perfect circle makes a good ring set for these metric pistons in these motors. Leave the engine size at 351.I would use APR rod bolts however and a good crank dampener. The FMS ballance job is well known to be a stock ford ballance job and not intended for revs much above 5K or so. A good ballance job is the best money you will ever spend.

2. Pick out a better cam with about .550 -.575 of lift and 285-290 degrees of duration.

3. Replace the heads with the AFR 185's, 2.02/1.60 valves, 58cc chamber volume, and run the comp cam magnum roller rockers. This should be right in the neightborhood of 9.5 to 1 CR. You will need to check valve clearance but you would want to do this anyway. The AFR springs are good for about 6300 and work well with the hyd roller lifters in these motors. Running theses HYD roller lifters beyond 6200-6400 is a just dramma and a waste of time anyway. Limmit revs to 6200 and all will work well together.

This should get you about 1.25HP per inch with a good flowing exhaust and a 750 DP on a rpm performer intake. Be careful here, those side pipes can really eat up a lot of power if they aren't made to flow properly. This should put you right at 435HP on 91 octane gas and thats just about right for 10 inch wide street tires on a roadcourse through a limmited slip diff.

Last thing... If you don't have a limmited slip diff.. do that first.

[TerrysSPF]

C'mon Howard. Everyone knows that the only thing better than cubic inches is..........MORE cubic inches.

Actually, what Howard suggests isn't a bad idea, 427supr. Especially if you're worried about your stock block not being able to handle the extra cubes (although keeping it in the 392-408 range should be fine).
He also brought up a good point about the restrictive sidepipes. You can pick up quite a few HP by changing out those SPF pipes for something better. -But good headers & pipes aren't cheap either.

I guess we could all help you out more if we had an idea of what your budget is. Can you give us a clue? Also, what do you want to do with the car? If it's just a street car (like you mentioned above) then I wouldn't be worried about taking it to 408 - especially with your 6000rpm rev limit.

BTW: If you want "low rpm TQ" like you mentioned above, you need a BB!

[427supr]

Running a roller cam, will require a retro-fit type for my block. I will probably go with the Eagle 408 kit, AFR or Trick Flow heads and listen to the advice of my engine builder. He works for a well known company that does Nascar motors. You guys have also been helpful, I appreciate it. I am currently doing a 1964 Ford T Bolt with a built 600 HP 460. Now you know where my money is going. Thats why I was trying to get away with using the existing parts of my SVO 351.