Horse Power Potential of Cylinder Heads
Hi Moper,
I don't have Pipemax, but I have a friend who does. In any case I don't have the scratch to do custom headers, which is the only way I'm going to improve on the Early A-body TTIs. Given that I'm not fully exercising the heads (smaller dual plan manifold, 10.25:1 compression, 93 octane tune) I suspect there is little to be gained until I commit to 110 octane (after I retire 4.5 to 13 years from now). After all the Dart does get street driven to local autocrosses and cruise-ins (and Carlisle). Given the torque "curve" shift points by feel work just fine.
I'm still dialing in the chassis and trying to fit more vintage legal rubber under the Dart's rear. The SVRA and VRG rule books spec' 15"x8" wheels (HSR requires 15"x7"... Ouch!) I'm running American racing 15"x8" - 4.5" backspace (0 offset) Ansen Sprints, which weigh the same as the more popular Torque Thrusts but are stronger and about $50 cheaper (an important consideration when your buying 12 of them). VRG points to SVRA for tire rules so here's the list:
Size Make Designation Height Section Tread Rim
======= ==== ========= ==== ====== ===== ======
6.00-15 GY Bluestreak 25.5 10.6 8.4 8 ( 8 )
7.00-15 GY Bluestreak 26.7 11.6 8.6 9,8 ( 9 )
25.5x8.5-15 Hoos Hoosier TD 25.4 10.3 8.7 8-10 ( 8 )
225/60D-15 Hoos Street TD 25.8 10.0 8.0 7-8-9 ( 6 )
245/60D-15 Hoos Street TD 26.4 10.4 8.0 7-9.5 ( 7 )
26.5x9.5-15 Hoos Hoosier TD 26.6 11.0 9.5 8-10 ( 8 )
275/60D-15 Hoos Street TD 27.6 11.2 9.5 7.5-10 ( 7.5 )
(Wish this editor would respect fixed length blank spaces)
HSR just allows the Goodyear 6.00-15 or Hoosier 225 60 15, I'm currently running the Goodyear 6.00-15s all around, but hope to cram the 7.00-15s under the Dart's rear soon. This will move the top speed with the 3.55:1 rear from 145 to 152, provide better corner exit forward bite and possibly allow me to not use 4th gear anywhere but the front straight at Summit Point, which would eliminate 6 shifts per lap.
Vacuum pumps are a grey area in the rules, I CAN run a dry sump (just can't afford it), but a vacuum pump is not addressed.
My real problem with this car is getting weight out of it. the Minimum weight with a 318 is 2800# with end of race fuel but no driver. Currently the car weighs 3400# with me in it or about 400# over weight. There is very little left to do to get more out of it. Easy stuff includes an aluminum case trans & dif, and an aluminum water pump (requires a new radiator too); and removing a lot of the bracing that is extraneous given the cage. That might take 100# off of the car. A longer term, pricy, option is to get the iron bell housing (122 tooth flywheel) copied in magnesium that would likely save 25# by itself.
I'm sure my ring package is in the ball park, keeping in mind that it has to last as well as be quick.
Anyway, it's a long term project. I plan to road race until I can't pass the physical anymore, then do track days until I kick.
Dave
Dave - do you have Larry Meaux's Pipemax program? You're obviously pretty interested in the specifics... It's a fun program to play with and might help you with the limited intake rules and things like shift points and final gearing choices for various tracks, and maximizing your exhaust system.
In terms of frictional loss the biggest is the ring package you run. Low tension is good in terms of the oil ring, but the 2nd ring (scraper) should be a Napier, and all three can be reduced in width. (I'm also assuming you can't run a vacuum pump?) There are big gains there.