Betsy the B2300- Bluej's Build

¯\_(ツ)_/¯ said:

In reply to gumby :

Too light!

Best reason ever!

The owner of the red ND Miata in that picture also has a 2.5 swapped Mazda....3, which spent the day parked in Betsy's paddock spot after you left.  I was amused.

In reply to RedGT :

That GIF is now my favorite way to sum up how I feel about this truck.  Thanks again for getting me a good work assignment so I could get home early, and for the used tires!

The autocross is sort of summed up in pictures on the previous page but a quick writeup seems appropriate.  I got to Warminster bright and early, parked next to a really nice ND Miata, felt slightly inferior, and did this to compensate:

Caught up with a few autocross friends I hadn't seen in a while, picked up some challenge wheels for Stampie and tires for the Merkur from RedGT, did my work assignment, and got Betsy through tech.  No issues meeting the stability rule but for some reason they decided my class letters needed to be bigger, as if anyone was going to call it in as anything other than "the truck" anyway.

I got to run in first heat, so I set the tire pressures to 31psi and went for it.  Betsy handles remarkably well, tending towards understeer but quickly transitioning to oversteer with some trail braking.  Warminster courses are typically a series of slaloms and a few pinch points with a big U-turn at one end, and today was no exception.  The truck transitions well and does fine when things tighten up, but the big sweeper had me producing a large amount of one-tire-fire thanks to the open diff.  I ran a 46.6 with a cone, which I was very happy with given that the fast cars seemed to be running in the low 40s.  It was also enough to beat the Tesla next to me and a number of the big fat CAM things.

With the tires warm, I dropped the pressures to 31psi again before my next run and was rewarded with slightly better handling and a 45.4 +2 cones thanks to some overly aggressive driving.  The tire wear looked good so I left everything where it was.

Third run, 45.6 clean, no complaints but I definitely overdid it in the turnaround and smoked the inside rear tire too much.

Fourth run, 45.1 clean and I don't feel like I really left a ton of time out there.  Betsy was still running well, I was happy, and it was good enough to beat the only other car in CAM-S (a C5) as well as 56 other poor souls who were raw timed by a truck.  Couldn't ask for much more so I loaded up the goods and went home.

I'm super impressed with what this little truck can do on a suspension made of cut up stuff and parts from other vehicles.  There are probably ways to make this chassis go faster in autocross but I can't imagine any of them are this cheap, and it's really a lot of fun to toss around the way it's currently set up.

Can't tell you how happy that makes me to hear 

Especially this part, haha!

Betsy was still running well, I was happy, and it was good enough to beat the only other car in CAM-S (a C5) as well as 56 other poor souls who were raw timed by a truck.

How far out of the question is an LSD?

In reply to AWSX1686 :

I believe there's a complete rear end with discs and an LSD sitting at casa bluej waiting to go in, but I'm not sure it's within budget or that I want to go down there and swap it.  It's really not bad unless you get stuck accelerating out of a big sweeper.

You hear that, challenge course designers?  Decreasing radius only! 

In reply to ¯\_(ツ)_/¯ :

yep, exploder stick w/ LSD, better gearing, discs, and a swaybar.

it seemed like the budget hit ($130, plus some brake re-fresh parts $) wasn't worth the gain over sticking with the lighter stock axle, especially with a pair of 275's to put what power Betsy does make down. I was very curious how that would actually play out in practice, and it sounds like it was the right call so far.

In reply to ¯\_(ツ)_/¯ :

Thanks for picking up the wheels. I owe you a big hug or a beverage of your choice. Whichever you prefer. 

In reply to bluej :

I think it was a good choice also, I can't imagine it would transition or turn in as well with a heavier rear axle and the wheelspin only really hampers it in one specific scenario with the current amount of power.  Well, at autocross anyway.

In reply to Stampie :

Are you setting up the parking lot bar again?  I'd like to purchase whatever whiskey you have on hand using these big shiny 17x8.5 "Stampie coins" I'm bringing.

It looks a lot flatter at auto-x than I would have imagined!

In reply to ¯\_(ツ)_/¯ :

That's the plan. The bar is currently my workbench but it will be a bar again. 

Used nitrous bits mostly tested ok. The fuel solenoid was leaking when presurized w/ air. Need to see what the deal is there.

In reply to bluej :

Should I try to find a spare plastic intake manifold for when the existing one inevitably goes boom because nitrous?

That's... not a bad idea, haha!  The used kit came w/ jets for a 30 shot, so thinking we need something in the 55 and 75 range on top of that, w/ the 75 being a call made on site if you think it's worth risking (close to a time threshold, or to beating another drag time). This is assuming colder plugs and race gas.

I need to confirm what all the rest of the safety requirements are for using it. It looks like the bottle has a 3kpsi blowoff plug thing, but I'm not sure if that particular part meets the NHRA requirements, or other additional things are needed. Triggering plan is to use a main switch in the cabin (need to add), the throttle switch it came with, and use the IMRC circuit w/ relay to limit it to appropriate RPMs.

In reply to bluej :

If at all possible I'd want to keep being able to flat shift, that was worth nearly a full second in testing and any increase in power is going to add a shift to fourth.

If the 30 shot adds a legitimate 30hp dumb online calculators seem to indicate that should get us in the lower 16s.  50 shot in the mid 15s.  Who are we chasing in Gastropods, maybe the NX2000?  I think a stock Miata is in the 16s as well.

These solenoids aren't complex devices, i'm going to tear down the fuel one tonight to see if there's any obvious, and fixable, issues.

Re: flatshift, we could add a switch to the clutch pedal so that it shuts off the spray as soon as you start to depress it. What RPMs was it dropping to, again?

In reply to bluej :

Drops to about 4k rpm if shifted right near 6k- the drop going into 4th is going to be larger, though, probably winding up around 3600rpm.

Ok, so that would still be in spray range. Need to think about this..

In reply to bluej :

I could just use it in 2nd and 3rd and get to 77mph quicker before letting off the nitrous and hanging out at redline for the remaining 500' or whatever.  Also, instead of all these safeties we could just live dangerously and do a simple button like total asshats.

I don't know why doing a big shot of nitrous just to get into the 15s seems totally appropriate. 

My worry is about the nitrous coming in to strong when you let off the clutch after the shift into 2nd/3rd.

What if we just put a big button on top of the dash so I have to take my hand off the shifter to use it?  Guarantees the truck gets a moment to settle out before I can hit it again 

In reply to Stampie :

"I blew it up with too much nitrous" sounds cool as long as you don't mention that it's because you were trying to catch a stock Miata with two dudes in it.