Engine build sheet: 321 Turbo

Looking Out Co. demo · 2026-10-18 · Computed from user inputs; verify every number with the parts makers and your machinist.

Section	Item	Value	Basis
Engine	Displacement	320.7 ci / 5.26 L	π/4 × bore² × stroke × 8
Engine	Block	Ford Performance Boss 302 big-bore block M-6010-B302BB (your plan)
Engine	Bore × stroke	4.125 × 3.000 in.
Engine	Rod length	5.090 in.	rod/stroke 1.70
Short block	Deck height	8.200 in.
Short block	Piston below deck	0.005 in.
Short block	Pin (compression) height	1.605 in.	deck − stroke/2 − rod − deck clearance
Short block	Head gasket	4.155 in. bore × 0.040 in.
Short block	Chamber	66 cc
Short block	Piston dish/dome	6 cc
Short block	Static CR	9.01:1	exact from volumes
Short block	Quench	0.045 in.
Short block	Top ring gap (min)	0.025 in.	MAHLE bore × 0.006
Short block	2nd ring gap (min)	0.025 in.	MAHLE bore × 0.006
Short block	Oil rail gap (min)	0.015 in.	MAHLE
Short block	Main clearance	0.0025 in.	rule of thumb 0.0017-0.0022
Short block	Rod clearance	0.0024 in.	rule of thumb 0.0016-0.0021
Heads	Heads	Trick Flow Twisted Wedge 11R 205 (your plan)
Heads	Valves	2.080 / 1.600 in.
Heads	Springs	150 lb @ 1.800 in., 450 lb/in, open 402 lb
Heads	Coil-bind margin	not entered
Heads	Rocker ratio	1.6
Heads	Pushrod length	measure (TFS-9501 checker)	Trick Flow
Cam	Cam	COMP 35-312-8 turbo/blower cam (your plan)
Cam	Duration adv / @.050	276/280 / 220/224°
Cam	Valve lift	0.544 / 0.560 in.
Cam	LSA / ICL	114° / 110°	degree to cam card
Cam	IVO / IVC	28° BTDC / 68° ABDC
Cam	Overlap	50° adv
Cam	Dynamic CR	7.03:1 (12.8 boosted)
Boost	Power adder	Turbo (intercooled) @ 12 psi
Boost	Airflow	71.6 lb/min	Garrett
Boost	Pressure ratio	2.09	Garrett
Boost	Manifold temp	124°F
Fuel	Fuel	93 octane
Fuel	Fuel needed	374 lb/hr	hp × BSFC 0.6
Fuel	Injectors	80 lb/hr @ 43.5 psi, 58% duty
Fuel	Pump needed	278 lph @ 56 psi	incl. 20% margin
Targets	Estimated hp / tq	~623 hp / ~599 lb-ft	estimate
Targets	Redline / piston speed	6000 rpm / 3000 ft/min

Open checks / warnings (21)

CONFLICT · Headers vs heads: On3's Fox turbo kit says it "IS NOT designed for HIGH PORT Heads or TWISTED WEDGE Heads". You picked Trick Flow Twisted Wedge 11R heads. Ask On3 first. Options: custom turbo headers for Twisted Wedge heads, or heads that work with the kit (On3 says P-heads are fine).
CHECK · Piston-to-valve: Cam lift/duration (COMP 35-312-8 turbo/blower cam (your plan)) vs piston valve reliefs is not published for this combo. Twisted Wedge heads use their own valve angles; Trick Flow says the 11R works with Twisted Wedge-specific pistons. Clay-check at full lift with the cam degreed. Many builders want about .080 in. intake / .100 in. exhaust (rule of thumb). Confirm the pistons are Twisted Wedge-specific. Verify with manufacturer / mock-up.
CHECK · Crank / counterweight to pan: Canton lists the 15-640 for strokes up to 3.4 in.; your stroke is 3.000 in. Check counterweight-to-pan and pickup clearance at assembly. Verify with manufacturer / mock-up.
CHECK · Oil pan vs K-member / steering / headers: AmericanMuscle lists the Canton 15-640 for 1986-95 5.0 Mustangs including the '93 Cobra (bolts in with the stock K-member). Canton says some long-tube headers need modification, and '94-95 manual cars need clutch-cable clearance work. Your On3 turbo headers aren't covered by that note. Check pan-to-header/turbo-manifold and pan-to-steering clearance at mock-up. Verify with manufacturer / mock-up.
CHECK · Oil pickup: Ford says the Boss 302 block fits the factory Mustang pan with a special pickup (M-6622-BOSS302). Canton says the 15-640 uses a stock rear-sump pickup or Canton 15-641 (15-645 with its windage tray). Confirm which pickup fits the Boss block in the Canton pan and check pickup-to-pan clearance. Verify with manufacturer / mock-up.
CHECK · Heads vs block / head bolts: Ford lists the heads the Boss block was designed for (X306, X307, X2, C3, D3, Z304DA, Z2, GT40P) and says it needs special-length 1/2 in. head bolts M-6065-BOSS or studs M-6014-BOSS. Trick Flow 11R heads aren't on Ford's list (they use 1/2 in. head bolt holes). Confirm head gasket/coolant passage and bolt/stud length for this head-block combo with Trick Flow and Ford Performance. Verify with manufacturer / mock-up.
CHECK · Throttle body / elbow vs radiator & A/C: Charge pipe, throttle body and elbow routing to the radiator and A/C lines isn't published for this combo. Mock up the cold side with the radiator, fan and condenser in place. Verify with manufacturer / mock-up.
CHECK · Turbo / downpipe vs steering, frame, booster: On3 says the kit fits 1986-93 5.0 GT/Cobra, keeps power steering, has no room for the smog pump (off-road only), and A/C lines need tweaking and securing away from hot parts. Check the hot side vs steering shaft, frame rail, brake booster and master cylinder with your exact parts (Cobra booster, brake kit). Wrap or shield as needed. Verify with manufacturer / mock-up.
CHECK · Downpipe / exhaust vs subframe connectors: Downpipe and exhaust routing past the MM subframe connectors isn't published. Mock up before welding the connectors in. Verify with manufacturer / mock-up.
CHECK · Intercooler vs condenser, radiator, bumper: Treadstone lists the TR1045 core at 10.5 × 22 × 4.5 in. (30 in. overall, 3 in. in/out). Owner reports say a 4.5 in. core needs bumper-support/foam trimming, and A/C condenser depth is the limit (unverified). You're keeping A/C. Measure the space in front of the condenser before buying brackets. Verify with manufacturer / mock-up.
CHECK · Injectors / fuel rail vs intake: Holley says the SysteMAX retains the stock injector location. Injector length, O-ring size and connector (EV1 vs other, high-impedance for Terminator X) must match. Confirm injector length/connector and rail fit. Verify with manufacturer / mock-up.
CHECK · Valve springs vs cam lift (coil bind): Trick Flow rates the standard 11R springs (TFS-16306-16) for .600 in. max lift (the 205 listing says .650 in.). Cam max lift: 0.560 in. Trick Flow recommends asking your cam maker for springs on forced-induction builds. Measure installed height and check coil-bind margin (often about .060 in., rule of thumb). Ask COMP for a boost spring recommendation. Verify with manufacturer / mock-up.
CHECK · Pushrod length: Trick Flow requires checking pushrod length on every combo (302 checker TFS-9501) and suggests 3/8 in. pushrods for high spring pressure. Measure with the checker after the heads are torqued.
CHECK · Rocker geometry: Rocker geometry follows pushrod length, lifter preload and stud height. Check the rocker sweep pattern on the valve tip after picking the pushrod.
CHECK · Tires vs fenders: 18 in. wheels with 245 front / 275 rear: fender and strut clearance depends on wheel offset and ride height. Check full lock and full bump with the actual offset. Verify with manufacturer / mock-up.
CHECK · TKX swap fit: TREMEC says a Fox TKX swap needs a TKX-specific bellhousing, a new crossmember, a shorter driveshaft with a 31-spline yoke, and a 26-spline clutch. Shift SST says to locate the shifter hole with the engine at final height. Your plan has the Lakewood bell, Sonnax 31-spline yoke and a rough-range driveshaft + crossmember. Confirm the McLeod clutch is the 26-spline TKX version and measure the shifter hole before cutting.
CHECK · Compression vs boost vs octane: Static 9.0:1 at 12 psi = about 16.4:1 effective (CR × (boost + 14.7) ÷ 14.7) on 93 octane. Rough rule of thumb only: on 93 with aluminum heads, about 15:1 effective is a comfortable ceiling. Intercooling, timing and your tuner decide the real limit.
CHECK · Turbo size vs goal: On3 says its 70mm suits about 500 rwhp and recommends a 76mm for 650-700 rwhp. At 650-700 crank hp (about 550-600 rwhp), ask On3 whether the 68mm (6870) is big enough.
CHECK · Compression (computed) vs boost: Computed static CR 9.01:1 → about 16.4:1 effective at 12 psi. Dynamic CR (IVC 68° ABDC) 7.03:1 → 12.8:1 boosted. Rough rule of thumb ceiling about 15:1 effective on this fuel. Your tuner decides.
CHECK · Coil-bind margin: Coil-bind height not entered. Get it from the spring maker or measure it. Verify with manufacturer / mock-up.
CHECK · Boost needed vs set: Garrett's MAP formula says about 18.0 psi is needed for 623 hp at 6000 rpm (VE 0.85); you set 12 psi. VE is a guess; the dyno tells the truth.