Head selection for low rpm 87 octane build

[travis]

I’m building another 351w, for a daily driver F-150, and need max fuel economy/part throttle response in the 2000-4000 rpm range, on 87 octane cat pee fuel. WOT power isn’t important on this...maximum fuel economy is (with the full understanding that it will never be “great”). And of course it still needs to function as a truck once in a while.

I’ve poured over hundreds of builds over the years, and for WOT testing between stock and aftermarket heads, you generally don’t see any significant gains in performance until 3500-4000 rpms or so. Fine for a performance build, but how does this translate into part throttle transition and fuel efficiency at lower rpms? I imagine that a better chamber shape (and aluminum construction) would allow more compression and less timing requirements, which has got to be worth something...but is it enough to justify the expense?

Would a smaller intake valve be more appropriate in this situation...say 1.94” vs 2.02”?

How much cranking compression would you target for 87 octane fuel, keeping in mind the heavy weight and that long hot summers we have in Texas?

I’m thinking very conservative on the cam...like 206-ish at .050. My experience with these trucks has been that fuel economy diminishes much more rapidly than performance increases with increased cam timing.

[Carnut1]

E7's 1.85" 1.6" good valve job and a deep bowl blend. Near 200 cfm small, fast port.

[F-BIRD'88]

8.8:1 cr. Cam 190@.050 or less.
1.94 or smaller valves. Mild porting.
Tube exhaust headers.

[Carnut1]

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E7 cutaway, obvious issues are boss and bowl. Ssr I would just blend for this application. Ssr work will increase high lift flow but this application will not get there.

[Carnut1]

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E7 cutaway, red exhaust needs boss, bowl and that iron on roof removed. 1.6 valve and some cleanup should be 135 - 140 cfm. Which is fine on this mill.
Yellow is intake and you can see blending that is needed. Thanks, Charlie

[travis]

Thanks Charlie...that helps a lot.

Looks like the short turns can get thin pretty quickly with a bigger valve. Any concern with a hardened seat on the exhaust side with a 1.54” or 1.60” valve? Looks like it could be really close to water. For that matter, the exhaust bowl on the long turn side doesn’t look like is a lot there to work with

[groberts101]

I've done both E6 and E7's and would prefer the GT40 heads with bowl cleanup and properly thinned guide-boss with 4 or preferably 5 angle valvejob

rpm-air-gap style intake (helping against that Texas heat) with 1/2 - 1" 4 hole phenolic type spacer topped with smaller venturi 600'ish cfm holley carb

cam in the 205-210 @.050 range with little over .500" lift, 110 LSA and advanced to 106.. or even 105 ICL since this motor will rarely push much past 5,000 rpm anyways

smaller headers with 1.5" primary x 2.5" collector and good mandrel bent 2.25" or 2.5" crimp bent system and decent 2.5" mufflers

If you are concerned about max torque in that lower range with decent mileage, less reversion and added detonation resistance you would be better off to keep exhaust valve sizing on the smaller 1.5 - 1.55" MAX. Bigger 1.6" exhaust valves only serve to help with initial blowdown/reduced pumping losses but come at too high a price for this type of combo. Radius seat with some pocket and port cleanup. If 1.5" I'd use a 32 degree backcut.. 1.55" with no backcut to help control lower speed reversion tendencies. The smaller primary pipes/collectors higher gas velocities will help a ton here. Wrapping them will help a tad more too. Work like hell to minimize squish clearances(.040" MAX) as this will help you to push the compression ratio without quickly exceeding the lower quality fuels octane allowance.. ultimately improving the engines octane tolerance. I'd go no less than about 9.5/1 static and shoot for about 180 psi cranking.

I lived in Dallas for 4 years(1 year being record breaking with more than 30 consecutive 100 degree days) and built a few motors similar to this without any detonation issues. If you build and tune the motor correctly is will rpm more quickly/lug less and be far less prone to detonation than many will assume based on compression/cranking spec's alone.

[mag2555]

Your right in that you don't see notable gains up to 4000 rpm ( pickup truck power range) because it's very hard to trick the motor into thinking that it has more cid then it does by increasing air flow rates that only matter above 4000rpm!
Why it is that folks don't relate decreasing rotating weight like tires and rims as the same thing as adding HP has been beyond me for years!

Maybe it's because it's not a sexy as saying your 351 is making 1 hp per cid I don't know!

[Carnut1]

Thanks Charlie...that helps a lot.

Looks like the short turns can get thin pretty quickly with a bigger valve. Any concern with a hardened seat on the exhaust side with a 1.54” or 1.60” valve? Looks like it could be really close to water. For that matter, the exhaust bowl on the long turn side doesn’t look like is a lot there to work with

For this application 1.54" valve is fine and very little difference over 1.6". Water will be fine because you don't need to remove a huge amount of metal to get a decent shape for the rpm. As far as valve seat recession it is linked to guide clearance. The guides will need to be bored for k line guides or another type of guide and sized before valve job anyway. Short turn will not need much work for good flow with moderate lifts.

[Carnut1]

I've done both E6 and E7's and would prefer the GT40 heads with bowl cleanup and properly thinned guide-boss with 4 or preferably 5 angle valvejob

rpm-air-gap style intake (helping against that Texas heat) with 1/2 - 1" 4 hole phenolic type spacer topped with smaller venturi 600'ish cfm holley carb

cam in the 205-210 @.050 range with little over .500" lift, 110 LSA and advanced to 106.. or even 105 ICL since this motor will rarely push much past 5,000 rpm anyways

smaller headers with 1.5" primary x 2.5" collector and good mandrel bent 2.25" or 2.5" crimp bent system and decent 2.5" mufflers

If you are concerned about max torque in that lower range with decent mileage, less reversion and added detonation resistance you would be better off to keep exhaust valve sizing on the smaller 1.5 - 1.55" MAX. Bigger 1.6" exhaust valves only serve to help with initial blowdown/reduced pumping losses but come at too high a price for this type of combo. Radius seat with some pocket and port cleanup. If 1.5" I'd use a 32 degree backcut.. 1.55" with no backcut to help control lower speed reversion tendencies. The smaller primary pipes/collectors higher gas velocities will help a ton here. Wrapping them will help a tad more too. Work like hell to minimize squish clearances(.040" MAX) as this will help you to push the compression ratio without quickly exceeding the lower quality fuels octane allowance.. ultimately improving the engines octane tolerance. I'd go no less than about 9.5/1 static and shoot for about 180 psi cranking.

I lived in Dallas for 4 years(1 year being record breaking with more than 30 consecutive 100 degree days) and built a few motors similar to this without any detonation issues. If you build and tune the motor correctly is will rpm more quickly/lug less and be far less prone to detonation than many will assume based on compression/cranking spec's alone.

I will disagree on gt40, gt40p over E7's on this application due to port cc. Both are nice heads with some work and I prefer the gt40p chamber for burn but not on this engine. I agree with the rest but I tend to push my luck with cranking psi even with 87, quench and thermal management make a difference. Thanks, Charlie

[Carnut1]

GT40 & GT40P Head Specs


Head Type

Intake Port

Combustion Chamber

Intake Valve

Exhaust Valve

E7 124cc 61cc 1.78 1.46
GT40P 145cc 59cc 1.85 1.46
GT40-Explorer 145cc 65cc 1.85 1.54
GT40 - Cobra 145cc 61cc 1.85 1.54

This pasted a bit funny but you get the idea. Thanks, Charlie

[pdq67]

Might consider using a cam like Chevy's great old -929 hy-cam BUT in a Ford cam!

It's been used in everything from 195Hp/283" engine up to the 400" engine as a baseline cam!

I want to say that it's spec's are:

195/202, 112/108, .390"/.410" lift.

My new '67, 350SS engine had one in it stock and it was a torque monster!

Just a suggestion is all.

pdq67

[Carnut1]

cam.jpg

This was the cam I picked for the 351w in the "Build a Lightning bronco?" thread. Flat tappet for speed density and moderate rpm. Thanks, Charlie

[Carnut1]

For this build I would use an even smaller cam.

[Daniel Jones]

I'd jump to AFR 165 aluminum heads, specifically p/n 1472, along with Crane/Cobra pedestal mount 1.7:1 roller rockers. They are the emissions compliant version with EGR which is good for part throttle fuel economy. 165 ccs but 1.9" diameter intake valve. Should still have plenty of port velocity on 351 cubic inches.

Dan Jones