[70RAlll]

Originally Posted by RicksGTO

thanks for posting the figures from the recent races Dennis! Very interesting, especially Weymouth's times between his RAIV and 455HO as his engines would be blueprinted and tuned to the same level and suspensions set up in similar ways. The 12.25 to 1 compression allowed on the earlier 400's is a definite benefit to their times. I'd love to see what the HO's and SD's in this class would run with just that one additional change in compression.

I agree..12.25:1 compression seems to be pushing it. Definitely race fuel vs the HO @ 9.9:1 compression could still run on readily available fuel... to me,and disclosure..just my opinion, not trying to start a fight here, I think that is a bit of a stretch. I get the 1.5 increase in compression on all engines from advertised , but when you take an engine from running on pump gas to racing fuel, well I just think you have lost the spirit of STOCK racing.. would love to see numbers of cars with original stock compression engines. Bet the difference ,especially with the RAlll would be glaring... I have always wondered how stock racing produces such numbers vs what these cars did in period tests..And RAlll getting 12.25:1 vs RAIV getting 12:1?? again, seems like the RAlll got a little benefit that makes its performance look better than it ever did against the RAIV,HO or SD's....

[transam1972]

I do have to say we are really no longer stock vs. stock...however I can appreciate things being changed to get more out of your stocker...but it does get confusing as to modifications...when do you stop?...I am looking forward to a nicely set up carb. and uni. dist. on my 58k stocker!

[SD455DJ]

Originally Posted by transam1972

I do have to say we are really no longer stock vs. stock...however I can appreciate things being changed to get more out of your stocker...but it does get confusing as to modifications...when do you stop?...I am looking forward to a nicely set up carb. and uni. dist. on my 58k stocker!

transam1972,

Some people really get caught up on having a fast pure stocker, while many others are satisfied knowing their car is truely factory stock and learn how to make it faster with tuning and driving technique. Don't forget that drag strips are prepped much better than back in the day with glue for the first 330', so you shave a bunch of et with a proper launch and 60' time. It's still possible to spin, but with some control and practice, 2.1 second 60 foot times (and better) are possible, which are alot quicker than the 2.5 or higher back when our cars were new.

Stock RAIV's and 455 HO's/SD's will run 13.50's @ 105 mph regularly after proper tuning and good driving.

Dennis

[SD455DJ]

Originally Posted by 70RAlll

I agree..12.25:1 compression seems to be pushing it. Definitely race fuel vs the HO @ 9.9:1 compression could still run on readily available fuel... to me,and disclosure..just my opinion, not trying to start a fight here, I think that is a bit of a stretch. I get the 1.5 increase in compression on all engines from advertised , but when you take an engine from running on pump gas to racing fuel, well I just think you have lost the spirit of STOCK racing.. would love to see numbers of cars with original stock compression engines. Bet the difference ,especially with the RAlll would be glaring... I have always wondered how stock racing produces such numbers vs what these cars did in period tests..And RAlll getting 12.25:1 vs RAIV getting 12:1?? again, seems like the RAlll got a little benefit that makes its performance look better than it ever did against the RAIV,HO or SD's....

70RAIII, '69 RAIV's also can go up to 12.25:1 compression since their advertised compression ratrio is 10.75:1 vs the '70's 10.5:1. When I rebuilt my RAIV motor the heads had been shaved by the previous owner down to 66 cc's. and without decking the block and the pistons .003" in the hole, the compression came out to 10.95:1 with .039" head gaskets. My goal was to keep the compression as low as possible and this is what I got with flat top pistons. I could have used a small dish, but I didn't. I'm sure this was the third time this engine was rebuilt. On the dyno it did 445 hp and 475 tq. In my '70 Judge it turns 12.80's @ 109 mph weighing in at 4050 lbs, original 3.90 rear and Turbo 400 trans and its 13" factory convertor. I'm sure with some 4.33's and some minor suspension work it could run in the mid 12's fairly easily.

Dennis

[Formulajones]

Originally Posted by 70RAlll

I agree..12.25:1 compression seems to be pushing it. Definitely race fuel vs the HO @ 9.9:1 compression could still run on readily available fuel... to me,and disclosure..just my opinion, not trying to start a fight here, I think that is a bit of a stretch. I get the 1.5 increase in compression on all engines from advertised , but when you take an engine from running on pump gas to racing fuel, well I just think you have lost the spirit of STOCK racing.. would love to see numbers of cars with original stock compression engines. Bet the difference ,especially with the RAlll would be glaring... I have always wondered how stock racing produces such numbers vs what these cars did in period tests..And RAlll getting 12.25:1 vs RAIV getting 12:1?? again, seems like the RAlll got a little benefit that makes its performance look better than it ever did against the RAIV,HO or SD's....

Even 9.9:1 is pushing the pump gas limits with a cast iron head and stock HO/SD camshaft. I can tell you I'm at 10:1 with mine and it only likes pump gas if I'm conservative on the timing curve. It's needs a mix of race/pump at the drags.

I know what you mean about the compression and wishing to see stock ratios for stock racing, but as I explained earlier, and as Dennis is also explaining, it's not really possible on a 40 year old engine that's been rebuilt multiple times unless you start changing other dynamics of the engine like installing dished pistons (that don't have good flame travel), or ridiculously thick head gaskets (that kill quench )
So now you would be changing other aspects of the engine that will kill performance and again, technically it wouldn't be stock, would it
When you have to overbore, shave heads, shave blocks, all of which are normal rebuild procedures, compression ratios change. Just the nature of the beast. Hence the reason for the allowable change.