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Big cam small head vs small cam big head

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Big cam small head vs small cam big head

Postby MikeD » Fri Nov 23, 2012 4:10 pm

I've narrowed my build to one of two engine builders. I'm looking to have built a Ford FE 427. 4.250 bore 3.78 stroke. Single Holley. For a cobra kit. In discussing heads builder A wants to go with a Medium Riser ported to flow 360 cfm intake 260 cfm exhaust. Cam is 240/244 @ .050 with 110 LCA. Builder B suggested a head that flows 300 cfm intake and 220 e haunt. Suggested a cam of 252/260 @.050 with 110 LCA. Both suggested an 11:1 static compression. Which is the better approach?
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Re: Big cam small head vs small cam big head

Postby bigjoe1 » Fri Nov 23, 2012 4:21 pm

Is this build for street driving only, or for a street race application ??? Do you want to run pump gas ( 91 octane ) ????


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Re: Big cam small head vs small cam big head

Postby ou812 » Fri Nov 23, 2012 4:35 pm

MikeD wrote:I've narrowed my build to one of two engine builders. I'm looking to have built a Ford FE 427. 4.250 bore 3.78 stroke. Single Holley. For a cobra kit. In discussing heads builder A wants to go with a Medium Riser ported to flow 360 cfm intake 260 cfm exhaust. Cam is 240/244 @ .050 with 110 LCA. Builder B suggested a head that flows 300 cfm intake and 220 e haunt. Suggested a cam of 252/260 @.050 with 110 LCA. Both suggested an 11:1 static compression. Which is the better approach?

Neither.
Your basing head choice off of flow, not size or airspeed. Big mistake. 11:1 is pushing it for 93 octane, so if your using less than that, I would drop it down some. Because Corbas are light, you can use a bit larger head than typical for a build like this, but there are things you need to tell us like header size, intake manifold style, rpm range, etc...
Plus what gears and is it a 4 speed, 5 speed, or ???
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Re: Big cam small head vs small cam big head

Postby PackardV8 » Fri Nov 23, 2012 5:55 pm

Tell us how you will be using the car. The main thing to do is be honest with yourself. What percentage of the use is it going to be driven in anger on the road course or the strip? If the answer is seldom to never, then small head and small cam and lower compression is your answer.

As previously recommended, 11:1 is just asking for trouble on the street. Again a 427" Cobra is so overpowered for street driving, it doesn't need to be ragged edge.

Don't know where you live, but there's not much room to play any more. FWIW, a friend wanted my opinion of his Cobra replica. We drove for an hour looking for an opportunity to run it out. Just too much traffic everywhere these days. Up through one or two gears and we were gaining on the gomers so fast it was time to hit the brakes. These days civilians with cell phones will sic the Five-O on you if you blow by a bit enthusiastically. Seen it happen.
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Re: Big cam small head vs small cam big head

Postby MikeD » Fri Nov 23, 2012 6:06 pm

Mostly street driving. I live in a relatively rural area so I'd like to take it out on some country roads and enjoy it. I was thinking peak power around 6000 and max rpm 6500. 2" head pipe. 2500lbs. 4 speed. 3.54 rear. Dual plane intake.
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Re: Big cam small head vs small cam big head

Postby MikeD » Fri Nov 23, 2012 6:25 pm

93 octane fwiw.
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Re: Big cam small head vs small cam big head

Postby PackardV8 » Fri Nov 23, 2012 8:00 pm

Several of us can point you away from mistakes, but let's get it from the resident FE expert. Barry should be along any time now to point you exactly where you need to be. He'll get here sooner if you can change the subject line to something like "Ford 427" FE in a Cobra".

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Re: Big cam small head vs small cam big head

Postby ou812 » Fri Nov 23, 2012 9:06 pm

MikeD wrote:Mostly street driving. I live in a relatively rural area so I'd like to take it out on some country roads and enjoy it. I was thinking peak power around 6000 and max rpm 6500. 2" head pipe. 2500lbs. 4 speed. 3.54 rear. Dual plane intake.

10.5:1, smaller heads, decent cam should meet your goal. A large runner head will push that rpm range up considerably. Which heads are you looking at?
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Re: Big cam small head vs small cam big head

Postby ou812 » Fri Nov 23, 2012 9:08 pm

I'm pretty good friends with A.T. Francis of Blue Thunder heads, so I would try to find a cylinder head from him that fits the build. Very good quality product. I'm actually talking to him now about building more engines around his heads and helping with customer relations as right now they have almost none.
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Re: Big cam small head vs small cam big head

Postby MikeD » Fri Nov 23, 2012 9:20 pm

Brian

I was thinking of the edelbrock heads. Their are a few guys out there who use the pro port versions. Supposed to be good. As far as the blue thunder goes I've read a lot about then inasmuch as the quality is very good but supposidly the ports are too big. (Medium riser). It's my understanding they haven't made them in a while. I heard customer service is pretty bad too
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Re: Big cam small head vs small cam big head

Postby RW TECH » Fri Nov 23, 2012 11:17 pm

If the car really weighs in at 2500 lbs. it isn't going to take much over 450 HP to make it a ridiculous blast to drive on the street.

If you did an aluminum block & heads you can get away with a lot more on the compression ratio because it'll run dumb cold if you use the same radiator & fan you'd use for an iron engine.

If the block is iron don't bother with anything above 9.5 to 1 because some day out in the country you will pull into a station & pump 87 octane gas out of the 93 octane pump into your ride. Promise.

Truthfully, if it was mine and all I planned to do was drive it on the streets & spin the tires once in a while I wouldn't get too carried away with big bad heads or a camshaft with over 240° @ .050" duration.

Instead I'd build a 9.5 to 1 engine with a 230°/240° @ .050" hydraulic roller camshaft, a set of smaller port package heads that have been checked over & valve job touched up, a good cast alum. road race oil pan, cast valve covers, and a weber look-alike setup with EFI. Here's a link to something that might work: http://www.inglese.com/WhatsNew/whats-new.asp
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Re: Big cam small head vs small cam big head

Postby ou812 » Sat Nov 24, 2012 1:10 am

MikeD wrote:Brian

I was thinking of the edelbrock heads. Their are a few guys out there who use the pro port versions. Supposed to be good. As far as the blue thunder goes I've read a lot about then inasmuch as the quality is very good but supposidly the ports are too big. (Medium riser). It's my understanding they haven't made them in a while. I heard customer service is pretty bad too


RW has it right, but I would just use the std performer heads, mild port work...mostly valve job/chamber mods, 9.8:1 even on 87 octane with such a light car, cam around 232@ .050 on a 109lca. Keep it simple, you'll love it!
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Re: Big cam small head vs small cam big head

Postby mdross1 » Sat Nov 24, 2012 1:41 pm

These guys are right.Our Cobra with 460ci 9.5to1 Aluminum MotorSport heads mildly ported 235@.050 with TKO and 3:70 gear is an absolute blast the 295/50's under a scaled suspension makes a believer out of passengers.Motor runs 190 degrees just about all the time.Have fun good luck with your build.Mike
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Re: Big cam small head vs small cam big head

Postby PackardV8 » Sat Nov 24, 2012 3:35 pm

Another FWIW, a friend with a Cobra and a big cam/big heads is constantly fighting the carb/ignition tune. When the weather turns cooler or he takes a trip up into the mountains, the unburned fuel smell takes all the fun out of the ride. His buddy with a milder cam never has to touch the carb or ignition and never smells.

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Re: Big cam small head vs small cam big head

Postby plovett » Sat Nov 24, 2012 7:08 pm

I'd go in between the two recomendations on both cam and heads. Something like a 320-325 cfm intake cylinder head and a 246-248 intake duration cam. And drop the static compression to around 10.5:1. A half point of compression might lose only 6-9 hp, but you'd never have to worry about detonation under "weird conditions". The above recommendation is a generalization and dependent on specifics, but that said, I think it would be THE sweet spot.

JMO,

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