Horsepower numbers

[sapphire shelby]

Hello all,

I am trying to get an idea of some horsepower numbers. There is not a dyno locally so I figured this would be just as good. I know it will not be exact but like I said, I am just trying to get a better idea of the numbers. Here is my set up:

306 cubic inch with flat top pistons

Twisted Wedge street/strip heads with 2.02/1.60 valves and 61cc combustion chambers

Comp Cams solid lifter cam with 576 intake/ 570 exhaust lift and 255 intake/ 266 exhaust duration @.050

Cobra dual plane high rise intake

Holley 715 Shelby carb

Tri-Y headers

I mostly run this car on the street with several trips a year to the drag strip. I know the cam is a little much, but since I got the new cam and lifters for free I wasn't going to turn them down. Besides it helps me on the big end at the track. I ran this set up with the stock cast iron heads for over a year and am getting ready to put on the aluminum heads as soon as they come in. I am thinking around 325-350 at the flywheel. Is that being too generous? What does everyone else think?

Thanks for the input.

 

[D.Hearne]

I'm not going to guess on the HP numbers, but you DO need to find out just which flat topped pistons you have before bolting on those heads. Not all 302 F/T pistons are the same. The compression height varies from 1.585 to 1.620, that's enough to vary the comp ratio by the better part of a full point. Add big chambers like 64 cc's to a 1.585 comp height piston and you'll have a sub 8 to 1 comp ratio. And with that cam, you're going to have an extremely lazy engine on the bottom to mid range.

 

[A66Auto]

From what I have read, if your car is tuned, you should have that at the flywheel.

I also have the same heads, when you get the new pistons, make sure they are cut for the large valves that are installed in your Twisted Wedge heads. I remember reading that you do not need to cut the pistons as long as you stay under .550 lift, so make sure everything clears before you start it up.

Let us know how it goes!!

 

[htwheelz67]

#1 hopefully you have 10-11.1 compression, #2 get rid of that intake manifold and either get an edel air gap or a vic jr, #3 the carb is oK but on the small cubes with a big cam a 650-750 mighty demon annular will be WAY better and put a set of 1 5/8 long tubes on it. With your mismatch you may make 325-350 hp peak with crappy low end, if you make the parts work together I could say 400 fwhp can be made around 6500-7000 rpm.

 

[Bosscat]

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[sapphire shelby]

I'm not going to guess on the HP numbers, but you DO need to find out just which flat topped pistons you have before bolting on those heads. Not all 302 F/T pistons are the same. The compression height varies from 1.585 to 1.620, that's enough to vary the comp ratio by the better part of a full point. Add big chambers like 64 cc's to a 1.585 comp height piston and you'll have a sub 8 to 1 comp ratio. And with that cam, you're going to have an extremely lazy engine on the bottom to mid range.

D.Hearne,

Thanks for the info. The engine kit was purchased several years ago from PAW by my father. He no longer has the paper work for it so I have no idea what flat top pistons they are. Can you tell me if there is a way to check that with the pistons in the motor? Like I said, I have ran this motor for almost two years with the cast iron heads and wanted to upgrade to aluminum.

 

[D.Hearne]

D.Hearne,

Thanks for the info. The engine kit was purchased several years ago from PAW by my father. He no longer has the paper work for it so I have no idea what flat top pistons they are. Can you tell me if there is a way to check that with the pistons in the motor? Like I said, I have ran this motor for almost two years with the cast iron heads and wanted to upgrade to aluminum.

Yes, pull the heads, clean the deck surfaces then get a piston at top dead center, then using a straight edge, measure the gap under the edge to the piston top using a set of feeler gauges. With what you're going to run, you're looking for as close to zero clearance under the straight edge as possible. Certainly no more than .005". If you have more, you'll need to mill the heads to get the chambers smaller in volume to make up for the piston clearance volume. On a 306 short block with .040 gaskets, 64 cc chambers and a .005 deck clearance, that works out to an 8.83 compression ratio. Too low for your cam. You want as close to 10-10.5 as you can get with that cam. To get that, you need a zero deck, .040 gaskets and less than 58 cc chambers. 58cc chambers will net you 9.7 to 1 with a zero deck and .040 gaskets.

 

[D.Hearne]

Here's one more ratio with the 1.585 pistons: 8.55 with a .020 deck clearance and 64 cc chambers.

 

[htwheelz67]

are you sure about the cam specs? I wouldn't think you could run such a big duration high lift cam wih stock heads and flycutting pistons.

 

[sapphire shelby]

Here's one more ratio with the 1.585 pistons: 8.55 with a .020 deck clearance and 64 cc chambers.

D. Hearne,

Thanks for the info on how to check the pistons. One thing I want to note is that these heads have 61cc chambers and not 64 cc chambers. I know that is not that big of a difference but I am sure it has thrown off the calculation somewhat.

 

[sapphire shelby]

are you sure about the cam specs? I wouldn't think you could run such a big duration high lift cam wih stock heads and flycutting pistons.

Htwheelz67,

Yep, I'm sure about the cam specs. I took them right off the cam spec card that came with the cam. I have never had any troubles with them. The car ran well with the cast iron heads, but I knew better flowing aluminums would be better for it.

 

[D.Hearne]

D. Hearne,

Thanks for the info on how to check the pistons. One thing I want to note is that these heads have 61cc chambers and not 64 cc chambers. I know that is not that big of a difference but I am sure it has thrown off the calculation somewhat.

You're still going to need to mill em to get the ratio where it needs to be on a 302. Just to give you an idea of what 302 had a 10.5 to 1 ratio, only one was the 68 J code 302 with 54 cc heads.

 

[Bullitt]

you need to replace the valve springs too because the stock TFS heads aren't rated for lift over like .54" (check your install sheet).

Hard to say since your cam is a bit bigger than mine, but my car made 325 HP / 317 lb-ft to the wheels with a very similar combo. Peak power at 6500 RPM.

306 w/ 9.6:1 comp.
1 5/8 longtubes
TFS heads (stock)
218/228 w/ .536 lift roller cam
performer RPM
750cfm edelbrock carb

Setup correctly, upper 300s should be no problem. Make sure you check your Piston to Valve clearance as recommended though.

 

[57fairlane]

If you are going to keep the cam, get a victor jr on there, put at least 3.70/3.73s out back and make sure the rest of the stuff matches.

Personally on the heads I would mill them .030-.040" and run a .027 cometic.
It'll keep your compression up and you won't sacrifice the heads if you decided to sell them later on. Few people want a tiny chamber head nowadays . . .

 

[sapphire shelby]

you need to replace the valve springs too because the stock TFS heads aren't rated for lift over like .54" (check your install sheet).

Hard to say since your cam is a bit bigger than mine, but my car made 325 HP / 317 lb-ft to the wheels with a very similar combo. Peak power at 6500 RPM.

306 w/ 9.6:1 comp.
1 5/8 longtubes
TFS heads (stock)
218/228 w/ .536 lift roller cam
performer RPM
750cfm edelbrock carb

Setup correctly, upper 300s should be no problem. Make sure you check your Piston to Valve clearance as recommended though.

Bullit,

Thanks for the info. I talked with the techs at Trickflow and they recommended the street/strip head for my cam. The springs are rated for a lift of .600 so they said I am good. I will be flycutting the pistons though.

 

[sapphire shelby]

You're still going to need to mill em to get the ratio where it needs to be on a 302. Just to give you an idea of what 302 had a 10.5 to 1 ratio, only one was the 68 J code 302 with 54 cc heads.

Ok, so I am confused now. I have been doing some research myself and here is what I have found. The cast iron heads that were on my motor are 69 castings. I found this casting number on a website for Ford engine parts and it shows them to be 63cc heads. With the exception of the heads you talked about, it shows nine different 302 castings from 68-70 having the 63cc heads. I then crossed referenced that to an original shop manual that says the 69 302 (I made sure it wasn't the Boss 302 that I was looking at) has 9.5:1 compression. With that being said, how does your formula keep coming up short on compression when the Trickflow heads are smaller with 61cc chambers?

 

[SadbutTrue]

Bullit,

Thanks for the info. I talked with the techs at Trickflow and they recommended the street/strip head for my cam. The springs are rated for a lift of .600 so they said I am good. I will be flycutting the pistons though.

What P/N are your heads? Some of the Twisted Wedge heads have .600 lift springs (p/n 51400005, i believe... which are the ones I have, and are designed for 351w's because they have the 1/2" head bolt holes rather than 7/16). However, the vast majority have springs rated for .540" of lift, as was said earlier.

Not saying you're wrong just make sure.

 

[D.Hearne]

Ok, so I am confused now. I have been doing some research myself and here is what I have found. The cast iron heads that were on my motor are 69 castings. I found this casting number on a website for Ford engine parts and it shows them to be 63cc heads. With the exception of the heads you talked about, it shows nine different 302 castings from 68-70 having the 63cc heads. I then crossed referenced that to an original shop manual that says the 69 302 (I made sure it wasn't the Boss 302 that I was looking at) has 9.5:1 compression. With that being said, how does your formula keep coming up short on compression when the Trickflow heads are smaller with 61cc chambers?

You have to take into account the different piston pin heights used over the years. Here's the numbers I used for yours: 64 cc heads, 9 ccs for the gasket, 5 cc's for the valve reliefs and area around the piston to wall down to the top ring. That works out to a 9 to 1 ratio. Add in more volume for a less than zero deck and you're in the 8's. The factory rating of 9.5 to 1 may not have been 100% accurate either. I know it wasn't with some others, like the 4 bbl 390's. 61 ccs, with another 14 ccs for the reliefs and gasket works out to a 9.36 to 1 ratio, with a zero deck. Might be more or less a couple tenths for differences in reliefs.

 

[D.Hearne]

Just did the numbers for a 68 4 bbl 302 and they work out: 54 cc heads, 14 ccs for the reliefs and gasket with a zero deck and 618 ccs for the swept volume (yours will be 627 ccs) works out to 10 to 1, just what the books list it as.

 

[sapphire shelby]

What P/N are your heads? Some of the Twisted Wedge heads have .600 lift springs (p/n 51400005, i believe... which are the ones I have, and are designed for 351w's because they have the 1/2" head bolt holes rather than 7/16). However, the vast majority have springs rated for .540" of lift, as was said earlier.

Not saying you're wrong just make sure.

The heads the Trickflow techs recommended are p/n 51400010