SN2000 HO installed on 406 SBC

[Buck-Strickland]

3.90 gears, 28" tire, through the traps around 5600 rpm. It could use 3.55-3.73 to harness the torque of the 406.

[Buck-Strickland]

I took the car back to the track last night. Went ahead and leaned out the jetting a little from 95 rear jets to 88’s. It made my AFR solid 9.8(still room to go) the entire trip down the track. Last time the AFR was 9.00-10(mostly 9.0) and would move around. Fighting a 20MPH head wind this time compared to a 5MPH head wind last week the car went 12.01 @ 109.8 with a 1.593 60’ time (on Drag Radials). The short times really improved with the leaner jetting. Waiting for a boost retard to arrive, then I will continue to tune on it. I think there is an 11 second pass in the combination. What is amazing is the little blower was pushing almost 7psi through the traps at 5600 RPM.

[444]

Thanks for the updates! Sounds to me with some practice and some tuning you definitely have enough to get well into the 11's.

[Buck-Strickland]

MSD Boost Timing Master on the way.

Last time I used one of these I had good results. I should be able to bring the timing back to the NA curve then set the boost retard to pull out timing. I think this will help make some power early and at each shift recovery. Plus I will get my mileage back when driving out to the track. 26 degrees total kills the MPG.

Then another step colder on the plugs. I think I will go to Champion RC7YC before I start taking out more fuel. Just to be on the safe side.

Lastly I will make a pass without the air diffuser and see if it makes a difference. It was recommended that I add a diffuser on top of the carburetor in the box for drivability, but I'm wondering if it's hurting performance. The diffuser looks just like a flame arrestor from a boat.

I am please with the consistency so far, I made 5 passes Wednesday night over the course of 5 hours and the car ran 12.01, 12.02, 12.04, 12.02, and 12.01. Which for a street bracket race car is a really tight grouping!

[CiDhed]

Why so low on the rpms?

[Buck-Strickland]

Not sure what you mean by low rpm?

It's a 406 with a small camshaft, so it's not going to pull a lot of rpm. Especially with a small intake runner head like the Edelbrock RPM's.

[CiDhed]

Not sure what you mean by low rpm?

It's a 406 with a small camshaft, so it's not going to pull a lot of rpm. Especially with a small intake runner head like the Edelbrock RPM's.

I guess I could of wrote my question better. You answered it.

And just for the record, my dad's mustang doesn't have a diffuser in the carb box and it drives just fine on the street.

[Buck-Strickland]

Thanks for the heads up on the diffuser.

Is your Dad's carburetor a standard Holley with the choke tower or something different?

[CiDhed]

Thanks for the heads up on the diffuser.

Is your Dad's carburetor a standard Holley with the choke tower or something different?

Autolite 4100 with the choke tower removed.

[Buck-Strickland]

I took the car back to the track last night for some more testing. I think the car has decided to torture me by running low 12's.

I installed the MSD BTM set it for 1 degree of retard per pound of boost. Total timing was set to 33 degrees, so at 6psi the total is dialed back to 27 total.

Also, leaned out the jetting, got the AFR to 10.8 now (still more room).

Unfortunately, I was chasing a short the entire evening that was messing up my tachometer signal. The shift light kept triggering at different rpm, so repeatability was hampered.

Long story short with a 12mph head wind and about 60' degree temperature outside it again went 12.012 @ 105 on the brakes. Looking at the 1,000' time it would have run around 11.97. I had to hit the brakes because we were in elimination rounds and I had caught the guy just before the traps, I took the stripe but broke out on my 12.02 dial in. Had I known I would have kept my foot in it. Bummer.

It will be a few weeks before I'm out again, so I will just pull more jetting until the AFR gets into the 11.5-8 range.

[pavement pounde]

I am a firm beliefer that anything richer then 11.5 afr is not good and anything leaner the 12.5 is not good either on supercharged engines.
If it is detonation you fear then better pull more timing and considder water injection or the like.

[Buck-Strickland]

I'm just guessing, but I was thinking that 27 degrees of timing on a SBC with 6psi boost was conservative. I know the SBF’s use 3-4 degrees less than the Chevy’s

I agree with the AFR, I would really like it to be about 12.0, which I will inch up to. The 10.8 was a vast improvement over the 9.0 from the first time out.

The funny thing is you would think that with 6psi it would have improved the ET by more than 4 tenths of a second and 5 mph, I was thinking 6-7 tenths. However it does pull the left front tire off the ground on launch now, so it must be making more torque. Another strange thing, it seems to run quicker when I shift it earlier than NA. It liked 5400 NA but seems to like 5000 with the blower?

I wonder if I have too much gearing. 3.90 gears are putting me through the traps at 5600rpm. Maybe 3.55 would be faster/quicker?

[Buck-Strickland]

Back to the track again. Leaned out the AFR to 11.8-12. Unfortunately it was 100 degrees out, so it went a best of 12.148 at 109.48 with a small 5MPH head wind.
I did setup an IAT sensor it was showing 180 degree air temp at 7psi through the traps. These things get hot. I wonder if an Air to Water intercooler, like the Vortech Aftercooler design, would help?
FYI: I have a 4.5” blower pulley with a 7” crank pulley and go through the traps at 5600-5800rpm, so blower speed is around 40,000rpm.
2nd gear seems to be slipping so; I will pull the Th400 this weekend and have it checked.
Damn elusive 11 second time slip is irking me!!
BTW: I’m in the market for a VR4 kit or blower if anybody has one they would like to sell.

[69fury]

i'd really recommend either a cooler or meth kit. get those temps down- the boost will read lower, but that's just a number on a gauge and not indicative of true air being crammed in. Sounds like your getting it dialed in bit by bit.

[Michael]

BTW: I’m in the market for a VR4 kit or blower if anybody has one they would like to sell.

Buck, have you taken a look at the sticky at the top of the "SN Series" section re: the VR4 group-buy that's going on? Used VR4s are tough to find it seems, so if you're in the market for one you might want to consider getting your name on the list for a new VR4 kit.

Just a thought.