[Mark Weymouth]

Your welcome and I understand how hard it can be to wrap your mind around the numbers these cars are producing. With the exception of a person or two who come up to me each year and say I used to go faster in mine back in the day and I never even touched anything...

70 RA III you are correct that the biggest gain likely comes from the exhaust if your motor is already well tuned. The next half is split between the motor and chassis/track prep.

To give a good example an early HO that was dyno'd was Dan's original T-37 motor. It had a +.030 over bore and no other machining or changes from factory spec. It used all factory GM parts. It was well built and tuned. Ultimately it pulled 370 on the dyno with about 500 lb-ft of tq. We have now pushed these same motors with the knowledge we have gained to just over 400 hp and just over 530 tq. Ten hp equates to about one tenth on the track in our racing. BTW with our conservative dynoing method 370 is a good number let alone 400.

Take your RA III for instance. The exact same rebuild was done to it and it made 370 hp also and 455 tq. We now have these motors making so far north of that it is incredible. This latest motor we are doing will hopeful push the 440 hp barrier. We have already pushed to the 430 hp mark with one that had just 10.8:1 compression and A body manifolds. We have also pushed over the 500 lb-ft mark when using the 068 cam. The 744 cam gives tq up to get hp and rev but can only be used on '69 4spd cars. The 068 cam has taken us over 420 hp in well prep trim. RA III's respond even better than HO's do.

RA II/IV's are big improvers also. The same +.030 over bore with all else remaning as the factory built with GM parts took us to 390 hp and 440 tq. My Judge which leaves a point of compression on the table pulled 446 and 488. The T/A motor was even higher with lot's of compression to give still and a smaller bore than the Judge hitting 455 hp. We saw some items on the Judges motor we thought would improve it and they did but we had never intended the T/A motor for racing and did not max items. When the numbers came back we smiled and ran it down the track. It has the matching numbers block so it likely will not come out to play often but it has been out twice at test and tunes and proved to be a strong runner.

Ultimately I think 465 hp could be done in a maxed to the nth degree 1970 RA IV as they seem to carry about 10-15 hp advantage on the '69's. Their heads flow a bit better from what we have tested and they are allowed more compression.

In the case of the RA III and RA IV I would suggest that the motor can be made to equal a great exhaust setup for improvement but would also be harmed more by a poor exhaust. On a HO and SD the exhaust has a bit more value then the engine.

We have played with exhuast combo's on the dyno and it is imperfect at best but take a Gardner Show exhaust vs. a highly thought out X system and depending on motor you could see in the neighbor hood of 50+ hp improvement depending on which motor combo you have. On a RA IV even more.

We did a full test on an L79 Corvette and tested factory 2.5" manifolds, 2.0" later L-79 manifolds, NOS large and small side pipes, and NOS under car exhaust and 2.5" under car exhaust. We built couplers so we could test all the big and small combo's together. The best combo was the small manifolds and big under car exhaust. Next best small manifolds and small under car. This is why I say it is imperfect the big/big side exhaust was third and one might have thought it to be a player or any combo of big/big. Every car truly has its own desires and it takes time and testing to find it.

I am glad people have enjoyed this conversation. If any of you find yourself at the races (this year Martin in June, Stanton in Sept, or Virginia in October) or Woodward Cruise look me up I would love to say hello and put a face to the names and thanks for the venue to exhange thoughts and ideas. Everyone here seems so much nicer and kinder than some other boards. It is a joy to see people treating each other with high regard.

Mark