Editing Openai/695c4a9d-28a0-800d-9f93-cab63ec35c09 (section)

=== Assistant: Perfect. ===
Perfect. With 275/60/15 and a TH400, we can now be precise instead of general. This combo explains your slips almost exactly.

I’ll walk you through the math, then give clear, no-BS recommendations.

==== - Tire: 275/60/15 → 28.0" tall ====
* Transmission: TH400 (1:1 high gear)
* Rear gear: 4.10
* 1/8 MPH: ~99 mph
* RPM at stripe (your report): ~6,000

==== RPM formula: ====

: 

At the 1/8 mile:
* (99 × 4.10 × 336) ÷ 28 ≈ 4,870 rpm

But you’re seeing ~6,000 rpm, which tells us something critical:

===== That is very typical for: =====
* A loose performance converter
* A torque-heavy Buick

So mechanically:
* Effective RPM = ~4,900
* Actual engine RPM = ~6,000

👉 This is not a problem, but it matters for gearing decisions.

==== ### ====

With:
* 28" tire
* Strong torque
* Loose converter
* 1/8-mile focus

You are:
* Running out of RPM right at the stripe
* Forcing converter slip instead of acceleration
* Giving up MPH

This is why MPH is stuck at ~99.

===== Letting the TH400 “granny shift”: =====
* Likely shifting before peak power
* Possibly shifting inconsistently
* Not letting RPM recover optimally

With a Buick, shift points matter more than launch RPM.

==== ### ====

Use the shifter.

Target:
* 1–2 shift: 5,600–5,800 rpm
* 2–3 shift: 5,500–5,700 rpm

Why:
* Buick torque curve likes to fall back to ~4,200–4,400
* You stay under converter flare
* MPH will increase

📈 Expect:
* +1 to +1.5 mph
* −.05 to −.08 ET

===== For 275/60/15 + TH400: =====

====== - 3.73 ======

====== - 3.55 ======

What happens with 3.73s:
* Stripe RPM drops to ~5,400–5,600
* Converter slip decreases
* Engine stays in power
* MPH climbs to 101–102

ET typically improves, not slows.

===== 2,000 rpm footbrake: =====
* Works
* Safe
* Consistent

Only adjust after shift control and gear are fixed.

==== With: ====
* Drag radials
* Open exhaust
* Manual shifts
* Same weather

===== - 6.70–6.75 @ 101–102 mph =====

===== - 10.50–10.65 @ 126–128 mph =====

That aligns perfectly with a ~600 hp Buick on a TH400.

==== This is not a traction problem ====
This is not a power problem

👉 It’s gearing + shift strategy.

You’ve already built a fast car — now you just need to let it use what it has.

If you want next:
* I can calculate ideal shift recovery RPM
* Or help you decide 3.73 vs 3.55 based on how you actually drive the car

Just tell me how you mainly run it: 1/8 only or 1/4 too.