Performance Research Industries
Triumph TR4
Triumph TR4 Engines


Triumph 4 cylinder Engine Rebuild

At Performance Research Industries, we have been applying our tried & true performance techniques that have won so many Superbike races in the past to our Spitfire engine rebuilds with astonishing dyno and racetrack results.  Our "entry level" stage one Spitfire rebuild is nearly doubling the horsepower of these engines in their original state. (Spring issue of "Spitfire & GT6" magazine)

For custom specs and availability please call (541) 459-5442



Our stage 1 engines are precisely machined and meticulously assembled. They are built with care and attention to detail.

Cylinder Head Work

  • Hot tank cleaning
  • Magnafluxed for cracks
  • Blend porting
  • Performance valve job
  • C.C. combustion chambers and Surface head to desired compression ratio
  • Rebuild rocker assembly
  • New rocker shaft
  • New rockers
  • New valve guides
  • New intake and exhaust valves
  • New valve springs
  • New spark plugs
  • New freeze plugs
  • New paint
  • New hardware if needed
  • New gasket set

Block Work

  • Hot tank cleaning
  • All parts magna-fluxed for cracks
  • Line bore main saddles if needed
  • Rebuild rods, resized big end, re-bushed small end, polish beams, match weights
  • Bore and hone cylinders
  • Turn (if needed) and polish crankshaft
  • Regrind camshaft
  • Degree camshaft
  • Set piston deck height
  • Match piston weights
  • Balance crank assembly  
  • New piston set
  • New rod bushings, bearings and bolts
  • New cam bearings if applicable
  • New main and thrust bearings
  • New lifters
  • New cam chain (gear if needed)
  • New oil pump
  • New water pump
  • New seals and gaskets
  • New oil galley plugs
  • Paint
  • Freeze plugs

*This price does not include re-sleeving block if necessary.

A new clutch assembly is recommended for balancing with the newly rebuilt crank assembly. P.R.I. warranties only non-upgraded stage 1 engine packages on a "conditional" 12 months or 12,000 miles.

All parts for the stage 1 rebuild are o.e. type and not P.R.I. parts. All P.R.I. parts are discounted 10% with in-house precision rebuilds for performance upgrading.
(Any performance upgrades other than what is listed below will void this warranty)


  • CARBURETION: Single Weber, 2 barrel draft progressive. Keihin CR, side draft quad set 31mm only.
  • EXHAUST SYSTEMS: Any header and free flow exhaust is OK but must be in optimum condition. We currently offer "modified" PaceSetter headers and our own tuned performance exhaust systems.
  • P.R.I. modified PaceSetter header  
  • P.R.I. performance exhaust systems for Spitfire
  • Replacement catalytic converters  

Catalytic converter systems: must be new with no cracks in manifold, or replaced with a performance header. We have after- market rebuilt cats for those unfortunate cars that may still require them.

Speciality Built Engines - Stage 1, Triumph TR4 = $5,050.00 USD

 Triumph Spitfire Cylinder Head



All that is done on the Stage 1 Engine Rebuild plus the following:

Cylinder Head Work

  • Extreme performance cylinder head conversion kit
  • Roller rockers chose from 1.55 or 1.65 ratio
  • Maximum port work flow bench tested

Block Work

  • Complete engine ARP hardware set
  • Exterior oil line to feed rocker shaft
  • Stock rods are lightened, polished and shot peened
  • Light tubular push rods
  • Lightened lifters
  • Lighten flywheel

Additional parts 10% Discount
(with the exception of the ARP hardware already discounted)

Speciality Built Engines - Stage 2, Triumph TR4 = $7,050.00 USD

High Performance Cylinder Valve Kit



Professional Race Application

All that is done on the Stage 2 Engine Rebuild plus the following:

Cylinder Head Work

  • P.R.I. Pro comp series head conversion kit (Titanium valves available)

Block Work

  • 4340 Chrome Moly steel, or Titanium connecting rods.  PRI designed
  • ltra-light JE piston set with gapless low friction ring package
  • PRI Stage 3 cam
  • PRI tubular Chrome Moly "heat treated" push rod set
  • PRI crank case venting kit w/K&N filter

Stage 3 engines are also built in street-able specification.

Speciality Built Engines - Stage 3, Triumph TR4 = $10,750.00 USD

We do not email info about our engines.
Please call if you are seriously interested. 541-459-5442

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As noted on the Policy Page, all shipping charges (national and international) are calculated and applied at time of shipping due to the uniqueness of each part and all payments must be made by check, money order, or through PayPal. Additional fees apply (3% US and Canada) (4% all other international orders)for PayPal transactions. (Calculated and billed with shipping charges).


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