Out to the track today. Got four runs in and got the car weighed. Car weighed 2800 even with my 180 lb son in it. He drove it for two runs. 12.45 and 12.41 both at 109 mph. My tech Jerry drove it for two runs. He weighs 230. He got 12.51 and 12.51. Temp was 60 to 70 over the course of the day. Altitude of the track is 2800. 60ft times were in the 1.8 to 1.9 range. The car hooked and ran straight. I think I'll do some carb work this week to see if I can find a bit more power. May need a bigger accelerator pump shot to drop the 60ft times. 302/5.0 9.7 compression, 91 non-ethanol, dyno-ed at close to 400hp but I don't think I'm getting all of it now. C-4 3000 stall. 9" 3.89 gears, locker. 28x9 Hoosier slicks.
395 at the flywheel. 86 5.0. Stock crank and rods. Stock flat-top forged pistons reversed and new valve reliefs cut. AFR 185 heads, upgraded springs. Comp hydraulic roller XE282 232/242 608/610 lift with Comp 1,7 roller rockers, stock roller lifters. Dougs 1 3/4 headers. Holley 750 vacuum secondaries, 70/80 jets. Victor Jr. MSD distributor locked, no advance. 38 degrees timing. MSD 6AL
That's about right. Mine (306) made 360 @6,000 with AFR 165's, a Summit 600 CFM, an E303 roller , 1.7 RR, MSD 6AL, 34 degrees of timing and a Stealth intake. This was with a stock water pump and alternator installed, but no PS pump. I was disappointed and could have made more power with some tuning, cold air and a better set of headers (dyno time =$$$). My Hookers hit the dyno cradle, so we had to use an old set of small port dyno headers that restricted the AFR exhaust port. The thing was so responsive and pulled so clean that I didn't want to mess with it. I'll save all of my tuning for when it is installed. Congrats on the mid 12's. Me thinks there is a lot more to be had from that combo once you start tuning it. Keep us posted.
Just off the top I would have to guess that front to rear jet spread is too wide. Unless it's a mileage type deal 4-6 number spread would be better suited towards a vac sec drag car. And that much power would likely respond to a tad fatter on the fronts.. around 72-74.. and pull around 2 sizes out of the rear. Also consider that if the 70's have had some bleed tuning to get them flowing like they should be on this motor?.. the emulsion droplet size is likely pretty large and may need to be retuned a bit for the larger jet size. This will help add more torque and improve booster response. Also damned hard to put too much squirter on a vac sec drag car as well. Fill it up till she starts puffing a bit of black and then back off 2 sizes and/or a bit less pump cam.
I'd try lowering the timing a bit and see how it responds. I'd start at 30 or 32 and walk it towards 34. 38 seems like a lot for a SBF...worth a shot, and costs nothing to try. I think you're leaving a lot on the table. What CC heads do you have? 28" tall slicks are probably hurting your 60 ft as well with the 3.89's. I also run 3.89's, but I have 26" tall slicks to help make it think it has a lower gear. I think you should be seeing 60's in the 1.7 range at least. Lowering the timing could fix part of that...playing with jetting will get it even closer. Still, it sounds like you're off to a good start! Keep us posted...There's enough folks on here with track experience, that we should be able to give you some decent advice.
The heads are 58cc. Calculated 9.7 CR. I'm using 28" slicks because I'm rpm limited to 6000 (valve float at 6200). I have the shift light at 5700 to keep it off the rev limiter, shift light is on through the traps and rpm is 6000. I will try 34* timing, though.
I talked to my dyno guy this morning. He said he only tunes for air fuel ratio on the dyno, therefore based on my 60ft times I need a bigger accelerator shot. That's where I was leaning and what you are advising so that's where I will start. He recommended staying with the 30cc pump but going to a .040 orifice in the bowl body and a blue cam, so that's what I will do. .020 off my 60ft times should get me to the 12.00 range, which is where I want to be (top of Sportsman bracket). I think I can also get another 20 lbs or so out of the car and I'll also do that.
Seems to me that 282HR should be making power to 6,500 RPM if you had enough spring to support it. My itty bitty E303 roller made power to 6K before it fell off.
Personally speaking?.. and I only offer this as helpful advice because I obviously have no personal stake in the matter.. ego and pride included because I'm certainly old enough to not mind being wrong.. but that's a horrible way to tune any motor as various combos will almost always show more or less power at various AFR's. IOW.. there is no tried and true optimum AFR number that you shoot for and stop at since some will make peak power at 12.5.. while others still keep making power at 11.8. Weight, gear, and leave rpm also plays into it as well. So it's best to simply give the motor what IT prefers.. rather than what the tuner wants. And the accelerator shot should ONLY be used to fill holes(such as the one created due to transition time and lack of secondary squirter on your vac sec).. not for supplementing lack of main jet. If he thinks different than that?.. I would highly recommend finding another dyno operator. I've had and tuned dozens of similar and even lessor powered combos with far less head than that and not one ever took a 70 main jet. The problem with a vac sec carb is that you need to try and leverage the primary's to greater degree because the secondaries will never hit as hard and quick as a double pumper could all else being equal. Again.. only trying to be helpful and hopefully you take no offense to the input or assume a knowitall attitude.
To be clear he only has an engine dyno so he can't account for weight, gear, leave rpm, etc. A chassis dyno will do a better job at that. He knows what he's doing. He also built the engine for me. I normally do it myself, but I was living in AK at the time and it was not practicable for me to do it. He just tunes for power and a A/F ratio in a range that gives best power on HIS dyno. I fully expected to do more tuning at the strip. He made 21 pulls on the dyno for this engine looking for power. BTW, he's a past record holder in both Stock and Super Stock. He also builds engines for sprint boats and drag boats. He's the best available within 200 miles. I totally agree with giving the engine what it wants; so does he. That's what I'm in the process of doing.
Ok.. got it. Sounds much more reasonable when you put it that way. As for the lifters.. comp cams and others have considerably better short travel designs the rpm much better. Getting the weight off the valve side of the equation will also help considerably more than losing weight off the lifters too. Titanium retainers also allow less spring to carry the rpm a bit better while simultaneouslysimultaneously easing the stress on existing rocker guts too. Being close to where you want to be for ET makes life much cheaper and easier for you.. so that's good.
What's the 6000rpm limit for? A short quick timing curve with around 32-34* total. More gear to. There's a guy on here with a comet with a very similar engine going mid 11's.
