The off idle launches are wierd. I noticed when I stab the gasthere is a slight delay and I mean slight (left on 3rd yellow)and poof off it goes. Possible the brake pedal still hanging up. Possible I have a carb issue when I do a full throttle stab, Need to figure that out. I also noticed from watching the videos a slight amount of black exhaust, so I'll definitely be messing with the carb for the next time and bring the jet kit with me.^^^the only thing that looks "soft" is the almost half second it took him to remember to take off! LOL
I had the same slight delay/hesitation also when flooring it, been messing with carb jetting, pump shot etc and have seen improvements on acceleration especially on the top end, but the slight delay was still there. Turned to timing, was at 18° initial, with 16° mechanical, used a vacuum gauge to increase initial to get the highest vacuum, backed it off slightly. Readjusted the idle screws and idle speed.. Now at 22° initial, reset the FBO plate to 10° mechanical. Better idle vacuum, still pulls strong, and no slight delay any more. Throttle plates were open too much into the transfer slots. Might be worth checking all that to eliminate the possibility?The off idle launches are wierd. I noticed when I stab the gasthere is a slight delay and I mean slight (left on 3rd yellow)and poof off it goes. Possible the brake pedal still hanging up. Possible I have a carb issue when I do a full throttle stab, Need to figure that out. I also noticed from watching the videos a slight amount of black exhaust, so I'll definitely be messing with the carb for the next time and bring the jet kit with me.
I have a full MSD ignition, initial is about 16, with the 18 degree stop (msd billet distributor no vacuum advance). I'll have to play with it some and order the 14 and 10 degree stops from FBO. I will start messing with the mechanical advance spring rates too, honestly I think I still have the light springs in it bringing the advance it early and fast. Lots of stuff to tweak!I had the same slight delay/hesitation also when flooring it, been messing with carb jetting, pump shot etc and have seen improvements on acceleration especially on the top end, but the slight delay was still there. Turned to timing, was at 18° initial, with 16° mechanical, used a vacuum gauge to increase initial to get the highest vacuum, backed it off slightly. Readjusted the idle screws and idle speed.. Now at 22° initial, reset the FBO plate to 10° mechanical. Better idle vacuum, still pulls strong, and no slight delay any more. Throttle plates were open too much into the transfer slots. Might be worth checking all that to eliminate the possibility?
Well then gimme some info and I can order oneI have the bushing for less than the other guys!
Ok. So I tweaked a few things, jetted the carb for altitude, timing basically went back to where I had it as that seemed to be the sweet spot that it liked.
Best run with 5600ft da was 12.52/106, so basically same run with a slightly worse da. Honestly I think the 750 just isn't enough. The thing launches good and dead hooks, 1.7 60fts but at the top of the run it doesn't nose over it just kinda stops pulling so hard. I also noticed a small oil leak from the front of the intake. So I pulled the intake to fix the gasket and decided to port match since I had it off, it was an easy 3/16 off in some ports, now the head and intake are much much closer. I do believe the next test n tune I'll try an open header/header muffler run and swap to the 850dp.
I really really want to try and get this as close to an 11 as I can at this altitude. Hopefully with the 3.55s, but I think the 3.91/4.10 swap is inevitable.
If you guys have any ideas to get this thing closer to the 11s without power adders, throw them at me.
I have also looked at the DA calculators and they say with these runs at my DA - sea level I would already be 11.60's. But since I haven't taken it down to cali test that, I'm going to take it with a grain of salt.
I don't expect to run 11.60s at my elevation but if I can get closer to the 12 flat area that might make me feel a little better. I know 410 gears will help but I don't think it's going to help to get to the 12 flat mark on their own.To run 11.60's at your elevation you need to find 9-10 MPH and the hook to go with it. That's quite a bit of power to find from a carb. I do agree the 750 is on the small side.
I almost think the 4.30's would be a touch too much for the 27" drag radials. I have noticed that I got my best times shifting at 6200rpm.. I haven't tried any higher, it makes me nervous. lol, but there really isn't much of a difference between 4.10 and 4.30 I would think the difference only a couple hundred rpm.4.30's and that 850DP as you mention should get you much closer to 12.00's and you should be trapping@around 6300 depending on how much slip you got in that verter, just hope that HR cam is up to those rpms...not a fan of hyd. cams, roller or not....
When I ran 3.55's and a 3500 verter, a 750DP, .484 hyd I made 301fwhp and ran [email protected] then went to a .590" solid purple cam, 850DP, 4200verter and 4.30's it ran [email protected] and made 366fwhp, trapping@6300 in a 3550lbs car. Adding 65hp to the motor is not a 9/10ths gain in ET if you see what I mean. We also put the 750DP with that spec back on as all the racers told me it was too big just to shut them all up.....we lost 2/10ths!!.....
I'm not making any hasty decisions, tweaking and changing as I learn about the car. I want to get it as far as I can with the 3.55's. My build plan was originally for 4.10's, just haven't gotten the extra 489 case I have built yet. I'm actually impressed with the 3.55's, 12.51@5600ft is a pretty stout street car at sea level. Next TnT I will have both the 750 and the 850dp's on hand along with all my little carb goodies for some more tweaking.IMO do not throw gears at it until you get, the ignition timing and carb dialed in. WOT jet for max MPH, then accelerator cams and nozzles for best 60'. After tune is right check rpm thru the trap and select correct gear.
Every combo is different. Try idle, +200 rpm intervals and see what gets the best 60'.I'm not making any hasty decisions, tweaking and changing as I learn about the car. I want to get it as far as I can with the 3.55's. My build plan was originally for 4.10's, just haven't gotten the extra 489 case I have built yet. I'm actually impressed with the 3.55's, 12.51@5600ft is a pretty stout street car at sea level. Next TnT I will have both the 750 and the 850dp's on hand along with all my little carb goodies for some more tweaking.
I have noticed though, If I load up the converter some, launching from 2000 and up the 60ft suffers.. I get the best ET and 60fts launching off idle and letting the converter flash. I'm not really sure if that is something I can tune out or if that's just how the cookie crumbles.
Ok. So I tweaked a few things, jetted the carb for altitude, timing basically went back to where I had it as that seemed to be the sweet spot that it liked.
Best run with 5600ft da was 12.52/106, so basically same run with a slightly worse da. Honestly I think the 750 just isn't enough. The thing launches good and dead hooks, 1.7 60fts but at the top of the run it doesn't nose over it just kinda stops pulling so hard. I also noticed a small oil leak from the front of the intake. So I pulled the intake to fix the gasket and decided to port match since I had it off, it was an easy 3/16 off in some ports, now the head and intake are much much closer. I do believe the next test n tune I'll try an open header/header muffler run and swap to the 850dp.
I really really want to try and get this as close to an 11 as I can at this altitude. Hopefully with the 3.55s, but I think the 3.91/4.10 swap is inevitable.
If you guys have any ideas to get this thing closer to the 11s without power adders, throw them at me.
I have also looked at the DA calculators and they say with these runs at my DA - sea level I would already be 11.60's. But since I haven't taken it down to cali test that, I'm going to take it with a grain of salt.
Just to clarify my previous post, I'm not saying a bigger carb is a bad idea, it could help quite a bit....but it is not the magic pill that some folks think.
What I mean by that is, if your current carb is well tuned, on the OP motor there probably won't be a big difference due to the poor flowing heads, small cam, low-ish RPM range....in a nut shell, the demand for air/fuel mix is not as high as it would be for a motor that uses more RPM range, better flowing heads, bla bla bla.
I hope that makes sense. I too am a fan of the 950dp carbs (and I really would like one), and it might help some, or a LOT...but that help could be from the previous carb not being tuned correctly in the first place.
A good example of this comes from my buddies car. He has a well dialed in stroker Valiant, runs 6.60's in the 1/8th. He thought a 950 dp would be better than his smaller (not sure on the size) Demon carb...long story short, he tried for half a race season to get the 950 to out perform his other carb...and it didn't happen, it was not any better, but his wallet was lighter...he ended up selling it within a few months.
Its not your heads that are a major issue at this level assuming they are the ones that flow in the region of 253cfm, its your gears, shifting@6200 where you say it likes it is the rpm you should be pulling at the stripe, only way thats happening is with 4.10>4.30's NA, thats where your 12.00's are along with that 850....your not using all the hp that motor has, as you say it goes flat. As I posted earlier adding 65hp to my motor didn't get me the 9/10ths gain in ET, around .4 of that was in the converter/gears upgrade and the better 60 from it, my mph from 101>107.8 shows the 65hp increase.