Reply With QuoteCheck your valve springs even if they are new, you guys buzz a lot of R's!..
Hey Guys,
Need some help! I race Crackerboxes and at Long Beach 2 weeks ago the motor started loosing RPM. Let me give you a little background on the motor... Due to the rules we are limited to 314 CUI and a 650 Holley. We are direct drive (no overdrive) and build the motors to rev very high. We run a large bore, short stroke configuration, 4.155 x 2.82. The motor has always run up to 9200 on the shoots. At Long Beach we were only able to pull about 8200...
Motor is a Bow-Tie small block, 23 degree CNC ported Brodix Track I heads with Ti valves. Crower springs are new... 13 to 1 compression and we run VP 114 octane. Mag is a Mallory Sprint Mag that was just serviced at Mallory.
The motor is fresh with maybe 12 heats on it. It runs great, pulls real hard off of the corners just doesn't pull the top RPM we're use to. We moniter air with a weather station so we are pretty sure jetting was very close. It's hard to do a good plug check because we have to idle in to the ramp but the plugs looked good.
On the Dyno it made the most power with 40 degrees of timing. Thinking that much timing may be hurting us on the big end we went down to 38 with no results.
The cam has been in the motor awhile. It's a roller and when we freshened up the motor I noticed the rollers were leaving a "whitness" mark on some of the lobes. It wasn't a deep groove or anything and was told that was pretty normal for a roller... I'm thinking the cam may be going away. Any thoughts or suggestions would be very much appreciated!
S&S
Check your valve springs even if they are new, you guys buzz a lot of R's!..
is it losing rpms since you have the mag freshened?----not saying mallory changed anything, but maybe they changed the springs and reset the stop where you are not getting full 38 deg timing----checking the cam should be easy enough using an indicator with 0 lash on a rocker and checking specs as to what it should be----and yes you will see a little noticeable "wear" on the lifter lobes after a bit of use
and most definately check the springs as Go Fast Racer said
Check your valve springs even if they are new, you guys buzz a lot of R's!..Ditto what Art said but I'll go further and say you guys are prob. in need of a spraybar to keep the springs cool or plan on changing springs more frequently. What about fuel pressure, you have a guage in your line of sight, right?
Thanks guys,
All very good suggestions and all we have already considered... The cam isn't crazy on the lift, like .650" Intake. That's only about 2/3 travel until the stacked height. They should last awhile at that lift, but I will check them anyway. Springs was the first thing everyone said to check... Fuel pressure is fine. I changed to a bypassing system this year. That is what was hurting us last year... We have a 2 5/8" gauge on the dash and my rider pays attention and fuel pressure was rock solid.
The mag was suspect as well but we have a spare, just rebuilt, we tried with no results...
I will put an indicator on the cam but any other suggestions will be appreciated!
S&S
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