The SB2.2 project hit a small snag and the bottom end had to come apart but it made 590rwhp on motor first so that's a good sign. While apart I am trying to determine if the combination I have can be run on 93 pump fuel. When I say "run" I mean only to drive to cruise shows, etc... not run hard. It has a Gen 7.

I used Pat Kelley's calculator and it yielded a strange result:

Solid Roller Cam specs @ .050"
270 intake, 279 exhaust, 113 LSA 109 centerline. The numbers I used were the .020" numbers for duration which are 307 Intake, 322 exhaust which gave a figure of 82.5 degrees ABDC. I was told that there are really no seat numbers for solid cams because of lash and was given the .020" number from Cam Motion. Were these the correct numbers to use?

In addition, it is a 4.030" bore, 3.875" stroke, 5.85" rod, 46cc chamber, .045", 4.060" gasket, 0 deck, 8.65cc total piston valve depth.

When run the calc I get 13.61-1 static and 9.18-1 Dynamic. Is this right???

Going with the theory that 9-1 is about the upper limit for pump gas, couldn't I work the tune, pull some timing perhaps and cruise around on 93 and use 110 for the track? The alternative is to have new pistons made with a small dish but that's $1000 and 3 weeks to build. Can it be done with this combo?

Thanks for all your help in advance.

Dave

 

Calculations are the same as I got....not sure about the second question.

 

I get 13.83 static and 9.90 dynamic with a .039 gasket.
Get the chambers opened up and increase your quench area for NOS.
The 82.5 IVC does not appear right according to my cheat sheet

 

What's your lash? That plays a big part in SR DCR calcs.

 

Thanks for the replys. To answer some questions.

1racerdude: The gasket is .045" compressed. Opening up the chambers is not an option at this point due to cost and time constraints. Why does the 82.5 not sound right?

Brett: Cam Motion spec'd hot lash at .025. My engine builder has them set cold at .018, how would this factor in?

There really is no second question. Just thinking aloud I guess. The main question is can I get this thing to cruise on 93?

*(when we built this motor having a race gas only combo was o.k., after much debate we concluded that it would be nice to be able to take it to some shows and fill it at the pump for such occasions and since it is apart and going back together real soon I have a narrow window in which to decide. Opening up the chambers is going to require some sinking of the valve seats wich throws off valvetrain geometry creating an extra problem I'd like to avoid for the moment. Bear in mind I'm not planning on running it hard on 93, but being able to cruise around at up to half throttle would be acceptable. I'm willing to create a seperate tune for this but I need to know if it is even feasable based on the numbers provided.)*

Thanks for the help guys.

Dave

 

More lash will effectivelly shorten the cams duration, causing the IVC to be less then calculated, hence increasing the DCR.
I've built an LT1 around that DCR and it had very little knock retard, mind you the fuel around here is not as good. You could mix fuels if it detonates with 93.

 

Good info. Thanks. I was thinking if my lash is .018 and the cam specs are at .020 wouldn't the IVC I gave be very close or am I thinking about this backwards? Could you tell me about that LT1 you built and what the DCR was? Thanks.

Dave

 

I'm betting that it would be fine. The SB2 combustion chamber is more efficient than the LT1. Don't go WOT with it or put it under too much load. It might help if you put a rock under the pedel when you run pump gas With good tuning, you can probably make it work.

 

Dave,
I had a personal combo, antique BBC. With much higher DCR than you are talking..that has performed many a burnout in OC on pump fuel. low load high revs and light load cruising never showed knock. My only concern was the valvetrain....as I would get greedy and show it north of 9k sometimes in burnouts. Pac 48 springs over 1k lb's over the nose...5k miles and 200 track passes...still good!

keep everything in perspective..and you will be OK.
Dennis

 

Thank you all very much.