L jet on 2L heads, how to fit Options

[rfinegan]

How are people fitting the Ljet intake manifolds to work with 2.0L heads? FWIW this will be on my 2056.

[rfinegan]

Chat GTP 5
on throttle body size for 2056:
Short version: pick your target peak-RPM and volumetric efficiency (VE), estimate the engine’s peak airflow, then size the throttle so the airspeed at WOT near peak power lands in a reasonable range (usually ~250–325 ft/s for a single throttle). Here’s the quick way:
How to size it
Convert displacement to cubic inches
CID
=
cc
16.387
CID=
16.387
cc
​

For 2056 cc: CID ≈ 125.5
Peak airflow (4-stroke NA engine)
CFM
peak
=
CID
×
RPM
peak
×
VE
3456
CFM
peak
​
=
3456
CID×RPM
peak
​
×VE
​

Choose a target airspeed through the throttle at peak power
Common choices at WOT: V = 250–325 ft/s (lower end for torque/driveability; higher for top-end bias).
Solve throttle diameter from volumetric flow
First convert to ft³/s:
Q
=
CFM
/
60
Q=CFM/60
Then area
A
=
Q
V
A=
V
Q
​
and diameter
d
=
4
A
π
=
4
Q
π
V
d=
π
4A
​

​
=
πV
4Q
​

​

Convert ft → inches → mm as desired.
Worked example (2056 cc, NA)
Assume peak ≈ 6500 rpm, VE = 0.90 (healthy street/track build).
CFM
peak
peak
​
=
125.5
×
6500
×
0.90
3456
3456
125.5×6500×0.90
​
≈ 212 CFM
Q
=
212
/
60
=
3.53
 
ft
3
/
s
Q=212/60=3.53ft
3
/s
Now pick a target velocity:
V = 250 ft/s → d ≈ 1.61 in (41 mm)
V = 275 ft/s → d ≈ 1.54 in (39 mm)
V = 300 ft/s → d ≈ 1.47 in (37 mm)
So for this 2056 cc, a single throttle around 37–41 mm is right in the pocket, depending on whether you favor midrange (bigger bore / lower velocity) or peak power response (smaller bore / higher velocity).
If you’re using individual throttle bodies (ITBs)
The math above assumes steady flow, which underestimates ITB size because each cylinder inhales in pulses. Practical rules of thumb for a ~2.0–2.1 L 4-cyl NA:
Street/track cams: 40–42 mm ITBs
Hotter cams / higher RPM: 42–45 mm ITBs
Pick near your intake port diameter (or slightly larger) and consider a gentle taper for signal and atomization. ITBs smaller than ~36–38 mm on a 2.0 L often choke the top end; larger than ~45 mm can soften low-speed torque and throttle resolution unless the combo truly needs it.
Practical adjustments
Add ~10–15% headroom for shaft/plate obstruction, filters, and real-world pressure losses.
Re-run the calc with your intended peak RPM and a realistic VE (0.85 street, 0.90–1.00 well-sorted NA).
Match the throttle to cam, port CSA, and target RPM; the smallest “non-restrictive” bore that meets your power goal usually drives best.
If you want, tell me your target redline, cam/VE estimate, and single-TB vs ITBs, and I’ll plug your exact numbers and suggest a specific size.
You said:
single throttle body target rpm 6000 redline
ChatGPT said:

Thought for 32s
Nice—thanks for the details. Using 2056 cc (125.5 CID), single throttle, and peak ≈ 6000 rpm:
Peak airflow (NA):

CFM
=
CID
⋅
RPM
⋅
VE
3456
CFM=
3456
CID⋅RPM⋅VE
​

VE = 0.85 ⇒ ≈185 CFM
VE = 0.90 ⇒ ≈196 CFM
Throttle sizing from target airspeed (good WOT targets for a single TB: 250–300 ft/s):
d
=
4
(
CFM
/
60
)
π
 
V
  
  
(
ft
)
→
mm
d=
πV
4(CFM/60)
​

​
(ft)→mm
Results (rounded):
VE 0.85 → 250/275/300 ft/s ⇒ ~38.2 / 36.4 / 34.9 mm
VE 0.90 → 250/275/300 ft/s ⇒ ~39.3 / 37.5 / 35.9 mm
Add ~10% area headroom (shaft/filters/real losses) → diameters increase ~5%:
VE 0.85 → ~40.1 / 38.2 / 36.6 mm
VE 0.90 → ~41.2 / 39.3 / 37.6 mm
Recommendation
For a 2056 cc at ~6000 rpm on a single throttle, you’ll be right in the sweet spot with a ~38–40 mm bore.
Favor ~40 mm if you want a bit more low/mid torque and softer tip-in.
Favor ~38–39 mm if you want slightly higher airspeed and snappier top-end response near 6k.
If you share the cam/VE estimate or intended manifold (long-runner plenum vs short), I can tune that to a specific part number.
You said:
long runner and .465/465 lift/ 288/298 duration: lobe center 108
ChatGPT said:

Thought for 36s
Great—thanks for the cam and runner info.
That cam (0.465/0.465", 288/298 adv, 108 LSA) with long runners will keep VE strong in the midrange and still breathe to ~6000. It points to VE ≈ 0.90–0.95 at peak for a well-sorted NA 2056.

Sizing at 6000 rpm (single throttle)
Using the airflow method and a sensible WOT target velocity (250–300 ft/s) through the throttle:
VE 0.90: 39.3 / 37.5 / 35.9 mm (250 / 275 / 300 ft/s)
VE 0.95: 40.4 / 38.5 / 36.9 mm (250 / 275 / 300 ft/s)
Add ~10% area headroom for shaft/plate, filter, and real losses → diameters rise ~5%:
VE 0.90: 41.2 / 39.3 / 37.6 mm
VE 0.95: 42.4 / 40.4 / 38.7 mm
Recommendation (for your combo)
Aim for a ~40 mm single throttle (39–41 mm window).
Pick ~40–41 mm if you want a touch more low/mid torque and gentler tip-in with the long runners.
Pick ~39 mm if you want a bit higher airspeed and crisper pull right at 6k.
Quick setup notes
Keep throttle bore ≈ runner/port CSA “projection” to avoid a step. A slight inlet taper toward the plenum helps signal and atomization.
Long-runner plenum: don’t undersize the throttle; the runners already boost velocity. Your ~40 mm choice won’t dull response but will avoid top-end choke.
If you share your runner inner diameter/CSA and plenum/throttle neck geometry, I can double-check the match and fine-tune the exact bore.