Head milling vs. flow change numbers?
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Launching!
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From: Winnipeg, Manitoba CANADA
Head milling vs. flow change numbers? Something I have always wondered is how dramatic every cc removed from the head deck negatively affects flow numbers. Example if AFR's come stock 67cc and get milled down to 58 or 59cc. How much flow are we talking about losing here. What I'm trying to say is does the compression increase in horsepower get cancelled out by the theoretic hp loss in cfm when milling excess material off the heads? Where is the bigger benefit?? Would you make the same power bolting the heads on with the stock chamber volume keeping the original cfm of the head intact? Sorry for getting too wordy. Have been wondering a lot about this lately. Not sure if I wanna mill my TFS 215's too much and lose the great stock flow numbers. Or am I overreacting here?
Derek
Derek
I recently inquired about this and didnt get any answers on here (no offense ls1tech). What i do know is you will get more out of milling (to an extent) then what you would loose from cfms. I personally am having my stock 241s sent to AI and have them port and mill them to 59cc. It really varies in your setup. I would recommend calling trick flow or a company that specializes in head flow. They will fully explain that to u. Good luck
A lot will depend on the head you start with. Your results with a TFS head may be different than what someone would get milling a stock head. As stated above, your best bet is to go direct to the manufacturer, or to someone with extensive experience with their heads, to see what they recommend.
As an example, Tony Mamo usually recommends milling AFR 205's no more than .040" to bring up the compression. Beyond that, the flow begins to suffer enough that you negate the gains from more compression.
On a side note, if you are milling 241 heads from 67cc down to 59cc, that is a significant reduction in PTV clearance, approx .050". You might be ok with the reliefs in those pistons, but wouldn't hurt to check
As an example, Tony Mamo usually recommends milling AFR 205's no more than .040" to bring up the compression. Beyond that, the flow begins to suffer enough that you negate the gains from more compression.
On a side note, if you are milling 241 heads from 67cc down to 59cc, that is a significant reduction in PTV clearance, approx .050". You might be ok with the reliefs in those pistons, but wouldn't hurt to check
You will see a reduction in flow from milling heads. Reducing the chamber volume while maintaining the same chamber shape increases valve shrouding. With that you are going to have to increase the lift of the valve to achieve an equal point of the valve being completely unshrouded.
How much of a loss of flow you will see is completely dependant upon the heads you are talking about. Different chamber designs, valve angles, swept volume, etc... will all have an effect on this. I'm not sure how many places do this, but a corresponding deshrouding cut really helps.
In regards to which is better in LS applicaions you will typically see a greater gain through millinf. No matter how amazing all of the new heads out there are our intake manifold options are still lacking. A head will only flow as much as the intake will feed it. You may mill a head and flow it to see if there was a loss. Then, attach a crappy intake to it and not see a loss at all, but you will gain power through the added compression.
In regards to what you are doing I say mill away. The only time there are better options out there is when you are building an engine and you have a large selection of pistons, head gaskets, and in .
/out of the hole options.
How much of a loss of flow you will see is completely dependant upon the heads you are talking about. Different chamber designs, valve angles, swept volume, etc... will all have an effect on this. I'm not sure how many places do this, but a corresponding deshrouding cut really helps.
In regards to which is better in LS applicaions you will typically see a greater gain through millinf. No matter how amazing all of the new heads out there are our intake manifold options are still lacking. A head will only flow as much as the intake will feed it. You may mill a head and flow it to see if there was a loss. Then, attach a crappy intake to it and not see a loss at all, but you will gain power through the added compression.
In regards to what you are doing I say mill away. The only time there are better options out there is when you are building an engine and you have a large selection of pistons, head gaskets, and in .
/out of the hole options.
Thread Starter
Launching!
iTrader: (5)
Joined: Aug 2008
Posts: 273
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From: Winnipeg, Manitoba CANADA
Thanks guys very much for your opinions and knowledge. Much appreciated! I had planned on milling around .024" for a 60cc chamber on my TrickFlows with GM MLS gaskets which are listed at 0.51" thick. Shooting for around 11.25:1 static comp. with calculations. Won't be getting around to this for another couple months probably. Still collecting parts. $$
thanks again all !!!
Derek
thanks again all !!!
Derek
A lot will depend on the head you start with. Your results with a TFS head may be different than what someone would get milling a stock head. As stated above, your best bet is to go direct to the manufacturer, or to someone with extensive experience with their heads, to see what they recommend.
As an example, Tony Mamo usually recommends milling AFR 205's no more than .040" to bring up the compression. Beyond that, the flow begins to suffer enough that you negate the gains from more compression.
On a side note, if you are milling 241 heads from 67cc down to 59cc, that is a significant reduction in PTV clearance, approx .050". You might be ok with the reliefs in those pistons, but wouldn't hurt to check
As an example, Tony Mamo usually recommends milling AFR 205's no more than .040" to bring up the compression. Beyond that, the flow begins to suffer enough that you negate the gains from more compression.
On a side note, if you are milling 241 heads from 67cc down to 59cc, that is a significant reduction in PTV clearance, approx .050". You might be ok with the reliefs in those pistons, but wouldn't hurt to check
