Mild 408C baseline run at track

Hey Guys I finally got my car out to the track before it closed for the year. This is a full weight 72 mach 1 with a 250# driver, mild 408 c (10.3:1 comp, closed chamber heads, blue thunder intake, 750 dp, small solid lifter cam 268/274 seat dur, (239/244 @ .050) .615"/.598 lift. Trans is a c6 built with lower 1st and 2nd gear (2.72/1.54), converter is a stock CJ converter with a little more stall, and a 3.50 gear with a trac loc. Tires are 255 60 R15 m.t. et street radials. Headers are 1 3/4" primary into 3" collectors into 2 1'2" mandrel bent exhaust with x-pipe and dynomax ultra flows and tails. This car runs 91 0ctane and was cammed to give enough vac. for the power brakes. This was with a baseline tune with no timing or jetting changes made yet. My best time was a 12.27 @ 109, with a 1.811 6o ft, and a 7.81 1/8 mi @88.96. Carb was rich at 12.2 afr. I was having to feather the throttle off the line and then roll into it. I think that there's more left in it with tuning and driving time. I was hoping to make some passes with the dumps open, but ran out of time. I have a 30 min. drive to track (highway) then run with no cooldown. Any tips or reccomendations appreciated.

Hey Guys I finally got my car out to the track before it closed for the year. This is a full weight 72 mach 1 with a 250# driver, mild 408 c (10.3:1 comp, closed chamber heads, blue thunder intake, 750 dp, small solid lifter cam 268/274 seat dur, (239/244 @ .050) .615"/.598 lift. Trans is a c6 built with lower 1st and 2nd gear (2.72/1.54), converter is a stock CJ converter with a little more stall, and a 3.50 gear with a trac loc. Tires are 255 60 R15 m.t. et street radials. Headers are 1 3/4" primary into 3" collectors into 2 1'2" mandrel bent exhaust with x-pipe and dynomax ultra flows and tails. This car runs 91 0ctane and was cammed to give enough vac. for the power brakes. This was with a baseline tune with no timing or jetting changes made yet. My best time was a 12.27 @ 109, with a 1.811 6o ft, and a 7.81 1/8 mi @88.96. Carb was rich at 12.2 afr. I was having to feather the throttle off the line and then roll into it. I think that there's more left in it with tuning and driving time. I was hoping to make some passes with the dumps open, but ran out of time. I have a 30 min. drive to track (highway) then run with no cooldown. Any tips or reccomendations appreciated.

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Great build and great results! I love when people go fast with factory iron.

Open the dumps, do a little tuning and add a set of Caltracs and I bet you are in the 11's. A bigger carb probably wouldn't hurt either.

Great results, well done! As usual TommyK is spot on. Your build is pretty similar to mine so this may be of some help. On the dyno, my best power was at 34 degrees total advance, best torque was at 36 degrees total advance. Depending on what the lash is set at now, you might try decreasing the lash .002-.004 to make the cam act a little bit "larger". Trying different tire rear pressures may net some improvement. Beware, a cold track and low tire pressures is a scary thing. Raise front tire pressures, take the PS and AC belts off (if applicable), solid rear spring eye bushings, one extra half leaf on the springs, extra spring straps (not solid clamp), pinion snubber set at about 1.5 inches.

Your post has motivated me to get off my rear end and build a different carb for my 408C. I have an old 1st Gen. Holley HP "950" (more like 830) that I'll use because I have it. It worked well on a 405 Clevor engine I built 20 years ago so it should work.

Which track do you go to? Chuck

Nice times. I am impressed. I haven't run mine at the track yet. I doubt I could break out of the 14's.

Awesome man , suprized you are not runing a bit bigger carb with that much lift

Very respectable times - especially for a 250# driver! I resemble that remark!

Your motor description reminded me of Chuck's (c9zx)'s car so I was happy to see his post on this thread.

As many know I have experienced his killer motor a few times. It puts the power down very well.

Hmmm. My crystal ball says Chuck's car will see our local drag strip within the next year.

Sure hope I get to go with. Be even better if I could drive the convertible there... .

Ray

Ray

Nice times.

Who did your cam?

Are your heads ported?

What exactly is your flash stall rpm? . . . if should probably at least 2400 flash for your app.

why do you have to feather it off the line, are your tires spinning off the line or do they hook up and cause the bog?

what exactly is the optimum rpm for shifting?

what rpm is it spinning at the finish line?

Does it bog or hesitate when you take off moderately from a stop lite with 1/4 throttle and around 1/2 throttle?

SPARK PLUGS

I would run Autolite AR 24 plugs.

You can clock the plugs so the ground strap is horizontal to the ground and the open end is pointed towards the intake valve . . You can buy a washer kit to so this.

CARB AND IF IT BOGS OFF THE LINE

If your bogging off the line, it is a bit of a challenge to fix and requires a bit more info and trial and error.

Imo, your carb is about the right size if you are not spinning over around 5800 rpm. If you are bogging off the line because your carb is too big for your app, it’s that simple . . if you go to numerically higher gears it will reduce the bog . . if you go to a higher stall converter it will reduce the big . . if you go to a vacuum secondary cab it will reduce the bog . . if you have a straight leg booster carb then using an annular or down leg booster type will reduce bog etc..

AFR

Your afr is fine, you will not gain or loose any more hp by changing it one point . . it simply will not happen . . it will have around the same power from 11.5 to 13.5 . . don’t live and die by afr readings on a carb because it is impossible to get them perfect under all driving conditions on a carb non computer engine.

TIMING

You can gain and loose a LOT of power if your timing is less than optimal for your app by just 3 degrees.

It costs a lot of money to dyno tune a car properly because it takes a lot of time, however I or someone else here can get your timing curve set very close to ideal for your app if you are Able to change a swt of points . . its very easy but a bit time consuming . . let us know if you want to do this.

if you want you can plug your distributir advanvce forever for now and tell us what your idle timing is, your total timing and what rpm it reaches total timing.

if you advance your timing 3 degrees at idle with the dist vac plugged and your engine rpm increases and it does not run rougher then this is better and will reduce bog off the line

now retard the timing 3 degrees so it os back where you started then rev the engine to around 2500 rpm and hold it there

if your engine rpm increases and it does not run rougher then this is better also and will increase hp and tq and mileage and reduce engine temps providing it does not ping/detonate underhard acceleration.

the more you advance the timing, the leaner your afr will become . . pretty cool huh?

.

Ok guys. I don't have a bog, I have trouble getting hooked up sometimes. I lowered the rear tire press. to 16 (from 20) and that seemed to help. As stated above the converter is a factory CJ (that has been rebuilt for a little more stall). It is a 10" converter that was rated at approx. 3000 stall (it was built for my old 357 c.i. engine) as built by Broader trans. So with the much greater torque of the 408, I'm sure it will stall a little higher. The carb is from Pro-systems it flows approx. 800 cfm. For right now shift rpm is 6000 rpm. Initial timing is 16, total is 32 (all in by 2800). Cranking compression is 215 psi. so I will be slowly increasing total timing. I will jet for mph when I can get more runs in the spring. Then I will try slight timing changes. The main thing I feel I need to do is get a burn out/launch routine with the drag radials. I will also decrease the lash by .004" to lose a little bottom end torque. The only work done on the heads is I smoothed the bowls and short turn. The blue thunder intake plenum has been worked a little to equalize flow between runners, and the divider notch has been enlarged. The cam is from a prominent builder that does not like cam specs disclosed, so I will not mention the name. I would not recommend this little seat dur. with this much .050" duration because it limits rpm with a valvetrain his heavy. This cam requires edm lifters for additional oiling, and is also nitrided. spring press. is 400/170. This was a budget build with a lot of parts I had lying around.


Ok guys. I don't have a bog, I have trouble getting hooked up sometimes. I lowered the rear tire press. to 16 (from 20) and that seemed to help. As stated above the converter is a factory CJ (that has been rebuilt for a little more stall). It is a 10" converter that was rated at approx. 3000 stall (it was built for my old 357 c.i. engine) as built by Broader trans. So with the much greater torque of the 408, I'm sure it will stall a little higher. The carb is from Pro-systems it flows approx. 800 cfm. For right now shift rpm is 6000 rpm. Initial timing is 16, total is 32 (all in by 2800). Cranking compression is 215 psi. so I will be slowly increasing total timing. I will jet for mph when I can get more runs in the spring. Then I will try slight timing changes. The main thing I feel I need to do is get a burn out/launch routine with the drag radials. I will also decrease the lash by .004" to lose a little bottom end torque. The only work done on the heads is I smoothed the bowls and short turn. The blue thunder intake plenum has been worked a little to equalize flow between runners, and the divider notch has been enlarged. The cam is from a prominent builder that does not like cam specs disclosed, so I will not mention the name. I would not recommend this little seat dur. with this much .050" duration because it limits rpm with a valvetrain his heavy. This cam requires edm lifters for additional oiling, and is also nitrided. spring press. is 400/170. This was a budget build with a lot of parts I had lying around.

I built mine a little hotter but all your numbers sound good to me.I managed to get a 315 35 17 under mine without any trouble at all. With 255's I was spinning my tires (I have a stick and 3.89 gears) all the way into 4th gear and it was scary but never hooked up, even with the Caltracs I installed.

My point is get more meat under your car and you'll go faster.

Specs are in my profile for comparison purposes

I'm at 34 degrees all in and my distributor was recurved by a local racer with a shit pile of class records in a manual transmission big block 65 corvette and he's still driving and winning in his early 70's

I'm hoping to get some bias ply slicks and hit the strip this spring. I think it could hit the mid 11's with the right driver, I just doubt that is me. LOL

Awesome first Pass,

You are right about the cam having a very aggressive intake ramp profile (29 degrees intensity). Keeping the valve train from crashing will be a challenge. The 215 cranking PSI seems really high for a static 10.3 CR. It is quite a build for parts you had laying around. Well done and thanks for posting. Chuck

hello;

it sounds like you don't need any advice other than caltracs and drag tires.

Is your initial timing with or without the vacuum advance connected?

Hi that's a good time you got there nice too that's it's a 408"[emoji6] Regards DK73

Sent from my iPad using Tapatalk Regards DK73

Nice work!