What intake flow #'s do I need for a 306?

[Nitrous Al]

I want to have enough cylinder head intake flow for a 360-380 hp, naturally aspirated, fuel injected 306 motor I'm building. What kind of numbers do I need? 220 cfm @ .500" lift, 240 cfm @ .500" lift or 270 cfm @ .500" lift? Can I use a aluminum head with a 1.90" intake valve or 2.02" intake valve?

[Jeff Chambers]

The rule of thumb is to have an intake that flows 15% more than the heads. That way you've sure that the intake isn't the restriction in the system.

[lx mike]

i think he means the intake port of the head not the intake manifold.

i'd talk to a shop that specializes in head porting and ask them, but heads aren't the only part to making hp although they are a key piece.

[Nitrous Al]

Jeff - I was asking about cylinder head intake flow numbers. The TFS TW head flows 251 cfm @.500" lift. The Performer 6037 head flows 223 cfm @ .500" lift. I just found out the X303 head flows 249 cfm @ .550" lift. What's the ideal flow numbers for a fuel injected 306?

[Nitrous Al]

Jeff, this is going to be the rest of the engine combo. Starting with a stock 302 block, machined to a 306 or 308, I'm going to put in a M6303A50 cast steel crank, PRO-Line 5140 "I" beam rods and TRW forged pistons. I want the whole rotating assembly balanced after the builder removes some material from the pistons just like in the Pro Stock engines. This engine combo in a street Mustang won't run 10's like Pure Street cars, but hopefully it will scare a few LS1 GM cars out there.

[Jeff Chambers]

You don't mention what compression ratio you're aiming for. Flow numbers for the heads are the end-all. I'm shooting for over 400HP (crank) this year and my heads only 200cfm. You've got to look at the entire combination and match the components well. I know many guys that slap some TW heads on their car with a .560" cam and still can't turn elevens with their car. One of the best things that you can do is to look at others combinations and try to discern what makes them work. I also rely on Destop Dyno quite a bit. Not necessarily for quantitative numbers, but for comparison of changes..ie does a change take me in the right direction from a baseline.

At any rate, you should be able to make 360hp (crank) with either of the heads you mention. I also wouldn't ignore the AFR 165's, they have an excellent intake/exhaust ratio.

[Nitrous Al]

Jeff, what engine combo are you running (400 hp at the crank)? How much will a "street legal" cam make the power drop off from the 400 hp #?

[NewAge 5.0]

well.. Using desktop dyno as he stated. My heads flow 225/170 my cam numbers and all intake flow numbers 10:1 comp longtubes w/mufflers EFI car makes 360-380 depending on intake CFM. so explain to me what Variables you would put in for the Intake on say the HOLLEY or RPM Intakes.. Nitrous Al, what times are you looking for out of your car? 11.90-12.30's what?

[Nitrous Al]

New Age 5.0, I want to go as fast as possible. My original plan was to build a Pure Street Mustang for street and strip fun. They run 11.00's with a N.A. 310 motor and a drag suspension. I'll try to keep up with the big boys, but it doesn't look promising. I just want to build a killer street car and beat anything that pulls along side of me. Hopefully I can learn a few Pure Street secrets and use them in my Mustang.

[Jeff Chambers]

Can't divulge all my secrets Al, but its a P-headed combination with good compression and a race cam. For N/A, probably the two biggest impacts you can make are in compression and cam selection. If you're going for an off-the-shelf cam to retain street characteristics, its probably going to cost you about 30HP over a race cam. The .500" lift restriction also holds you back a little with the TFS/Edelbrock/AFR heads since they'll continue to flow at the bigger lifts. In S/W, we're limited to cast iron production heads (GT-40/GT-40P/E7TE/289/etc) and can't port them so we really try to concentrate on the entire lift band; maximizing flow at the lower lift numbers, just not peak flow. You'll also need to think about the rest of your induction system (MAF, injectors, TB, etc.) I've seen a lot of people dial back the fuel curves because they don't want the rich idle that comes with larger injectors, only to hurt themselves on the big end of the power curve. You might consider an Optimizer or a tunable EEC system like the PMS, EEC Tuner, etc.

[Nitrous Al]

Thanks Jeff! How high of a compression ratio can you run? 11:1, 12:1? I can also always have a custom cam made, right? Something just on the edge of race cam, but still street legal. If I forget about P/S and just go for a "killer street car", what do you suggest? Do you ever bolt on the street legal tires and surprize the local street racers?

[Jeff Chambers]

That's all I'd ever run is a custom cam. I've worked with Ed Curtis from FTI and Cam Motions both on cam and they've always gotten me alot more HP than any catalog cam could hope to. Talk to either one of these places, explain your intentions and see what they recommend.

[red82gt]

For a street car I'd be weary about going above 11:1 even with aluminum heads, you never know what your gonna get with pump gas. My combo is a shade over 10:1 with Iron heads and every now and then it'll detonate with 92 octane gas and 13 degrees of timing.

[Nitrous Al]

What about using 104 + Octane booster with the Sunoco 94 (around here it's available) all the time?