308 QV head porting | Page 6 | FerrariChat
Buy

308 QV head porting

Discussion in 'Technical Q&A' started by mk e, Nov 20, 2006.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

Page 6 of 6
  1. mk e

    mk e F1 World Champ

    Oct 31, 2003
    13,813
    The twilight zone
    Full Name:
    Help me get this thing finished! https://gofund.me/39def36c
    #126 mk e, Feb 17, 2007
    Yes, that's right.

    I don't expect any CR increase due to the valves alone, infact the CR will probably drop. The head flows much better with the valve sunk a bit into the seat. The extra flow will add a lot more hp than the slight drop in CR takes away, so it makes sense to get the heads right.

    On a boosted engine, higher boost always makes more hp than higher CR, so the drop in CR is a plus because it lets me run higher boost...although since it's already well over 500hp, I'm starting to get nervous about the stock pistons and I'll probably replace them, so I can have any CR I want anyway.

    On a NA engine, obviously the best answer is to change the pistons and get the CR as high as you can get away with. I'm sure 10:1 is no problem and depending on the cams, 11:1 is probably just fine too.

    An engine with everything matching will give the best over-all performance. Getting the flow up works wonder for the top end where the engine is starving, but doesn't help the bottom much. On a high rpm engine, like a QV, increasing the CR from 8.6:1/9:1 (or more like 8:1 I'm told in reality,but haven't calculated yet)to 11:1 will add quite a bit down low, I'd guess 10-20 ft-lb torque, so that's good. Between the CR bomp and flow bump, the hp/torque comes up from idle to rpm line.

    The cams are a bit harder. Cams with a little less duration that are a perfect match to the head flow will give more power down low, again 10-20 ft-lb, but because the heads are coming out a touch below ideal flow will hurt up top by 10-20 ft-lb. Everybody likes to see bit numbers on a dyno pull, so ferrari over-cammed the engine and the stock duration cams get effectively even bigger when the low lift flow numbers are fixed on the heads...so on a 3.0, they are 8000-8200 rpm cams. Knocking out 10 degrees to make them 7500 rpm cams makes a better matched engine with a flatter touque curve...but the big dyno number isn't quite as big. It's a tough call.
     
  2. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    #127 snj5, Mar 18, 2007
    An interesting proposition to increase compression ratio was brought up to me today: modifying the valve face (e.g. removing any concavity) to reduce the combustion chamber volume thereby raising the compression ratio. It apparantly does not take very much.
    Has anyone ever heard of this?
     
  3. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    #128 snj5, Mar 25, 2007
    Last edited by a moderator: Sep 7, 2017
    Dropped off the car at Norwoods on Friday to begin the big upgrade:

    port/polish heads - Vic
    bigger intake valves - Vic
    higher lift camshaft - Webcam
    tubi headers - Carobu
    dual s/s exhaust - Norwood
    Final assembly - Norwood

    We are looking at flow increases from around 92CFM to hopefully 111CFM or so for a 15% to perhaps as much as 20% power increase. I am hoping that power will come in sooner as well. As most of you know, the 3.2 already has 40DCNFs with 34mm venturis which are supposedly good up to 330 hp or so, but I do also have a set of 36mm chokes as well if we need them.

    I think we may go to .400 lift from my .367 and shorten the duration a bit to near stock to beef up the lower end. We'll keep the stock exhaust cams as before. Will have to watch valve spring bind.

    Norwood will have the headers ceramic coated inside and out, and will fabricate and externally ceramic coat the new dual s/s exhaust system developed in the performance exhaust thread.

    I am very happy with my reliable single Unilite distributor & MSD 6AL, so no changes to the ignition and anticipate keeping a max advance of 34 degrees or so by 3000 rpm

    I have no hard idea which way the carb jetting will go, but will have an LM-1 mobile A/F on each side to help tune to a running A/F of around 13 under load. The velocities achieved on Vic's test head are also promising for an even more responsive engine. The -12 accell pump cams are more than rich enough to keep up with the new flow.

    I know what the computer modeling says I should get, but we'll see. Some estimates are higher, some lower.

    Watch this space over the next 6 weeks and we'll see how all of this theory plays out...

    For those new to the thread, here is the computer model of rear wheel hp from what I have now to with the new heads. Remember this is rwhp, so divide by 0.83 for the approximate flywheel number. As most of you know, approaching 290 hp at the wheels is almost unbelievable. I think this power increase will well match the chassis, clutch and transmission to give the best street package on street gas.
    Image Unavailable, Please Login
     
Page 6 of 6

Share This Page