[Spridgets] the engine catasrophe
mhagopian at hoppetool.com
Thu Sep 25 14:14:40 MDT 2008
thanks for all of the advice guys,
sounds like to me that we will be building a whole new engine this winter..
new cams, new springs, new rocker arms. i just read somewhere that when you
install a new cam you need to install new pushrods and lifters, is this
Any suggestions for some good kits? race car only. and would like the most
hp and decent reliablity. there was a lot of head work done already. intake
and exhaust valves are larger.
On Thu, Sep 25, 2008 at 9:11 AM, John Caffrey <jdc6 at lehigh.edu> wrote:
> Matt Hagopian wrote:
>> what one of
>> those pics doesnt show is on the piston, there is a 1/2" dent in the top
>> the piston. cylinder walls are a little gashed. freshen up the motor this
>> winter. compression is only 160 in that cylinder and 165 in two others and
>> one cyliner is 185. kind of low for 13:1 pistons, rocker arm has a crack
>> it... seems to have held up for this whole weekend. I put flat valves in,
>> know thats not as good of flow but it allows for more clearance. I dont
>> the spring pressure im running tho... how do i find out?
>> The high duration cam with it's increased overlap lowers the actual
>> compression, and that's why these cams require more CR. For example, 286
>> degrees cam edneeds at least 10:1, and a 300 degree cam might need 12:1. The
>> difference in your readings is worrysome and the cylinders may need to be
>> re-sized to get rid of the gashes. There are small spring testers available
>> that work with a bench vise, but you will need a telescopic gauge to precise
>> length measurements from your head with valves and retainers installed.
>> There are spring testers available that the stock car guys use on assembled
>> engines to check seat pressures at the track, but I can't say if they'll fit
>> our rocker arms. I do all of the prep on the bench. With a matched cam kit
>> you'd only need to setup the pressure on the seat for all of the valves, but
>> mixed components may have you also calculating the spring pressure over the
>> nose of the lobe using your cam lift, rocker ratio and geometry. With the
>> wrong springs you can have the correct seat pressure and be excessive over
>> the nose, and just bolting 1.5:1 rockers on a race cam made for 1.28 rockers
>> could give the same problem. Potential problems are excessive wear,
>> frictional HP loss, and component breakage. The top end details must be
>> correct for reliability. Just about any of the engine building books out
>> there will show the tools and procedures needed.
> Fogelsville, PA
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