GT40 Alum heads on 351W stroked 408?

Rpollard · #1 (**permalink**) 11-22-2003, 06:20 AM

I have a set of GT40 M-6049 Y303 Alum heads. Can they handle a stroked 393 or 408 stroker? or should I stay with 351W 60 over. No need for 500HP.

blykins · #2 (**permalink**) 11-22-2003, 07:17 AM

You're gonna get gobs of more hp and torque if you stroke it, and sure your heads will handle it...but not as well as some of the other aftermarket heads out there such as Trickflow, AFR, Edelbrock, etc. The valve size and the port sizes are too small to really support good flow. There are people that do it though.

Rpollard · #3 (**permalink**) 11-22-2003, 07:30 AM

blykins,

Can I port these heads with out changing valves. I just don't want to spend another grand on new heads.

blykins · #4 (**permalink**) 11-22-2003, 09:09 AM

Sure you can. Do you know what intake you're using yet? If so, whenever you get it, buy your intake gaskets, and see how far you're off. You can always port match the intake to the heads (or vice versa).

There's none really around here, but I'd say in your area, there are plenty of competent machinists that can really port heads and do valve jobs.

What are the valve sizes? 1.94 and 1.55?" I can't seem to remember....

How much horsepower were you wanting? What other components were you planning on using? Dual plane or single plane intake? How fat of a cam? Roller motor?

Rpollard · #5 (**permalink**) 11-22-2003, 09:26 AM

The block is at the Mech shop being prep. Yes, the valves are 1.94 and 1.54. As far as horsepower, if I had 400 hp It would be enough to get me in trouble.
I have a Edelbrock Performer Intake. Performer Plus Cam and lifters. Performer Carb.
Also Crane Roller Rockers.
I think I will go with the smaller Stroker like 393.

Thanks for your help
Roy

blykins · #6 (**permalink**) 11-22-2003, 09:50 AM

Give me a sec...I'll put it in Desktop Dyno and give you a rough estimate...

What's the bore on the block?

Rpollard · #7 (**permalink**) 11-22-2003, 10:28 AM

60 over.

blykins · #8 (**permalink**) 11-22-2003, 10:45 AM

Roy,

I couldn't find a file to duplicate the GT-40 heads, so I used an AFR 185cc head with the same valve sizes as a GT-40. Maybe one of the other users can provide me with the correct file. I really don't know if this will affect the outcome or not...

Anyway,

With a 4.060" bore, and a 3.78" stroke, that's about 398ci. I used a 10:1 CR, a 750cfm carb (I forgot to ask what size carb you had), a dual plane intake manifold, and I looked up the cam that you had in the Summit Racing catalog....it's a split duration/lift cam.....with 204 and 214 degree durations with a .448/.472" lift. I input hydraulic solid lifters also.

Basically the cam and the heads are killing you. Based on the inputs that I gave it put out a max hp of 351 and max torque of 454. By just changing the cam alone, it raised the hp to 397 (same Comp Cam as I have in my 425ci stroker) and made the torque 431 lb-ft.

For this size of engine, it just needs to breathe better. I'll go ahead and give my disclaimer that I may not be the best Desktop Dyno operator out there...some of the others may wanna chip in here. But I input the specs as I could find them.

Like I said you might wanna go with a different cam at least...Even a single plane intake made the hp go to 420 with the cam I just mentioned.

Hope this helps. I'll be glad to help you any way I can.

blykins · #9 (**permalink**) 11-22-2003, 10:52 AM

OK....I was looking at the wrong cam in the catalog...You have the Performer RPM set...right? I was just looking at the Performer set. The specs for that cam are 224 and 234 durations with a .496 and .520 lift.

With the dual plane Performer RPM intake, you get 389hp and 437 lb-ft of torque.

Rpollard · #10 (**permalink**) 11-22-2003, 11:00 AM

Thanks blykins.
I think I'm good to go.

Roy

blykins · #11 (**permalink**) 11-22-2003, 11:06 AM

Hey Roy...one thing you might wanna look at...instead of paying the bigger bucks for a stroker crank, different rods, etc....It's showing on Desktop Dyno that you could keep around the same horsepower with a stock stroke (3.5"). That could potentially save you a lot of money up front. It made just a few horsepower less, but it made it at a higher RPM because of the shorter stroke. Just a thought.

408cobra · #12 (**permalink**) 11-29-2003, 11:13 AM

I built a 408 stroker with probe pistons manley rods and an eagle 4 inch forged crank. I ported and polished the gt-40 x-303 1.94 1.6 heads with a fresh 3 angle valve job (use the intake and exhaust gaskets when porting and also concentrate on the bowl areas of the heads.) and run a 236 248 @.050 trick flow roller cam and a TWM stack throttle body sequential fuel injection setup. It makes awesome torque and horsepower. The stroker crank really gives you so much extra torque.

TerrysSPF · #13 (**permalink**) 11-29-2003, 12:08 PM

You could stick with the stock displacement (351) and just go with AFR heads and a better cam and easily get 400HP. Then you could stroke it in the future if you are looking to get more power. Or, if you are set on a stroker, go with the AFR 185 or 205's. The Ford 392 crate engine makes over 400HP (430-450) and they use GT40x alum heads. They also use a Comp Xtreme Energy cam, and the intake is a copy of the Vic jr. single-plane with a Demon 750 carb. I've read articles that say you can get another 75+HP just from switching to the AFR185 heads (from the GT40x) on the crate 392.
.....Once you get used to the 400Hp, you'll want more!

Rpollard · #14 (**permalink**) 11-29-2003, 12:38 PM

I sold the heads. And bought Edelbrock Performer RPM heads. Edlebroch Tech heads told me. With the RPM series Intak,Heads,Cam and Carb. That the engine will make 450 HP.

Thanks Guys

blykins · #15 (**permalink**) 11-29-2003, 04:33 PM

Well good...I think you'll be much happier...the engine will breathe a lot better with those bigger valves.

Jack21 · #16 (**permalink**) 11-29-2003, 05:18 PM

Well, that's what this Forum is for. Teamwork in action.

The GT40 heads may add something to a more or less stock 302, but when you start approaching 400 ci, the equation changes. These things need to breathe, and 1.94"/1.54" won't cut it.

TFS, Ede, and AFR with 2.08/1.60 is a good starting point. The 2V Cleveland heads had this configuration.

Take a look at the Blue Thunder 351 Cleveland aluminum heads on a 400+/- CI engine and see if anything "stirs" inside you! Play with some numbers using Dyno 2000, and see if there are any potential ""Chevy" beaters with these compnents.

stevehaygood · #17 (**permalink**) 01-03-2004, 11:27 PM

There was an article in either Car Craft or Hot Rod recently. Gt-40 iron heads bolt right on a 351, but the GT-40 has 7/16 "bolt holes and the 351 has I/2". So the GT-40 has to have its headbolt hole made bigger. Also the GT-40 has small exhaust ports which makes for a higher exhaust speed exiting, which is a function of creating torque. I was told to port match the heads and get a 3 angle valve job. A Comp Cam and edlebrock performer and a holley 4 barrel. No more than a 750cfm though on the carb. Should get between 350Hp & 400HP and around 350 ft/lbs of torque