Of these heads, all Dart Pro 1's - 325 CC, 335 CNC or 345 CC would you use on a 540 SCI running a max 5500 RPM. 871 blower EFI. Cam is 248/256 duration .637 lift. I'm getting mixed reports, one say use 325CC to keep flow velocity up, others say go with 345 cc for more air. Many say 335 CNC ported because they move the most air. Cruise performance is most important with an occasional run to 5500 RPM. Again heads are Dart because i have access to these three styles. Thanks,

Really depends what you are looking for. First off only turning motor 5500 ocassionally you won't need as much head. I will tell you this though:
Dart 325's flow: 281/210 at .400 lift/353/249 at .600 lift
Dart 345's flow: 272/210 at .400 lift/359/249 at .600 lift
Until you go past .700 lift the 345's offer you NOTHING, they actually flow WORSE at the lower lift numbers and as you can see the exhaust flows the SAME because they all use the same exhaust port.
I would pick the 325's UNLESS your looking to make as much hp as possible, if that's the case buy the CNC'D 335's as they outflow the other ones by a mile as in
306/235 at .400 and 383/282 at .600
flow translates to hp: the 335's flow 8% better on the intake and 13.5% better on the exhaust. Remember, a blower motor can force air thru a mdiocre intake port but you need good exhaust flow to get it out and make the big hp numbers, Smitty
http://users.erols.com/srweiss/table...hevy_Big_Block

i would use either of the PRO 1 CNC 335 or 355 with a blower motor...like articfriends said you need great flow on the exhaust port to get it out

Give JimV (Valako) a call on the dart heads. He use to work for Dart and I would say the resident expert on them. It will be well worth the call.
616 889-0928

My opinion. Stay with the smaller cc intake port 325-335 cc versions for better out of boost-low boost port velocity and a good wider rpm torque band and put the work in the exhaust side to get hose standard exahust cfm's up to those 285-300 cfm areas that are needed in higher rpm supercharging operation. Try and use a good exhaust system to assure this good exhaust flow the supercharger needs for best power generation. Make sure the exhaust valves have a good backside (tulip)angle , Inconel and are in a properly radiused port throat with a minimum angle in the exhaust port short side radius.

Best Regards,
Ray @ Raylar

I have a set of 325's sitting on the shelf. Can those be ported on the exhaust to achieve 280-300 CFM? Might be dollars ahead to sell those and buy the CNC 335's. Not sure
Thanks,

The earlier 325's will flow over 300cfm on the exhaust side at .600 lift with the right valve and combustion chamber porting. I don't know why but the later Dart exhaust ports have the short turn radius laid down and don't flow as much air at lower lifts. Im not saying stay away from the newer ones but the old flow more air in the usable lift range for boats.
http://www.youtube.com/watch?v=C9AQzI-pfdo













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[QUOTE=JimV;3552100]The earlier 325's will flow over 300cfm on the exhaust side at .600 lift with the right valve and combustion chamber porting. I don't know why but the later Dart exhaust ports have the short turn radius laid down and don't flow as much air at lower lifts. Im not saying stay away from the newer ones but the old flow more air in the usable lift range for boats.
http://www.youtube.com/watch?v=C9AQzI-pfdo

Thanks Jim. The 325's I have one the shelf are barely used less than a year old 4/2011. I'm thinking that I would be dollars ahead buying CNC 335's rather than spending $1k per set for porting 325's. Sell 325's to re-coup a portion of the 335's cost. Opinions welcome. Thanks

I would go AFR's CNC 335's, most flow, best velocity, and best quality.

No offence but the AFR exhaust port doesn't flow anywhere close to the Darts. Here is a no BS video of the AFR exhaust port without and with a cheater pipe cnc ported from AFR.

http://www.youtube.com/watch?v=lefrYoaVsCk


Here is a video of a reworked exhaust port.

http://www.youtube.com/watch?v=9SP9vzIFifc

The port is not very effiecent compaired to the valve size. If your looking for velocity, I would change to a smaller valve 1.8 or 1.825. My experience, the port will flow close to the same as the 1.880 with that particular port. They (AFR) do flow good on the intake side.
So it makes me ask the question Why are there numberous choices for intake volume runners/valve sizes and only one exhaust port choice? The same for combustion chambers. There is one choice for CNC chamber size or bore size. Most all CNC'd heads fit a 4.250 to a 4.6+ doesn't make sense to me. Before you assemble your short block bolt the head on the block and look up at the combustion chamber and it will be obvious, especially if you have a larger bore. I think Tyler did some back to back dyno testing on the stock Darts vs. CNC AFR's.