TECHNICAL INFO  

 CYLINDER HEADS 

Calver Special Tuning Mini Spares Centre head range 

I'm often asked about the range of cylinder heads I do for Mini Spares, so here's the low-down… 
 
Although the following range of heads accommodate specific fitments - like pre-1992 where by-pass hoses and heater take-offs on the clutch end of the head are used and post-1992 where neither of these exist, and on SPi (single point injection) heads where they don't usually have a threaded hole for the temperature sender - in reality it is easy to convert almost any of them to fit any other engine since holes are easily blocked off - or by-pass hoses not used, water pumps blanked off and drilled thermostats fitted (see articles on cooling/engine transplants). A list of which is what and what to do to each to convert is at the end of this article. 
 
For more in-depth descriptions of the head specs, see article 'Cylinder head - About Calver ST Heads' - basically the valve sizes used have been decided on after extensive and in-depth flow testing/dyno testing. The sizes used provide the best balance of airflow and gas speed for their typical uses to give optimum all-round performance. Typically the large-bore heads have consistently proven to provide sufficient induction flow to produce up to 120 real crankshaft BHP (quality fast road 1380, single 1.75" HIF SU, MSC inlet manifold, RE13OT cam). Finished specifications will change/evolve as and when anything new/better is discovered. 
 
 
 
C-AHT88 Small-bore 'stage 3' spec head. 1.218"(30.93mm) inlet & 1.043"(26.5mm) 
exhaust valves in EN214N stainless steel, manganese-bronze valve guides, A+ 
spec stem seals, 200lb (nominal) double valve springs, nominal 23.5cc chambers. 
Suitable for all fast road/track day small-bore engines and lead-free fuel use. Has by-pass 
hose and heater valve take-offs. 
 
C-AHT133 Road-Sports large-bore 'stage 3' spec head. Modified, standard MG Metro spec 
1.406"(35.7mm) inlet & 1.151"(29.2mm) exhaust valves, cast iron valve 
guides, A+ spec stem seals, 200lb (nominal) double valve springs, nominal 24.5cc 
chambers. Suitable especially for fast road large-bore engines of 1380cc type 
capacity where extra chamber capacity is required to keep compression ratio 
sensible and lead-free fuel use up to 6,500rpm continual peak rpm limit. Has by- 
pass hose and heater valve take-offs for pre-1992 engine types. Near zero flow- 
loss from modified standard valves when compared to race-spec valves. 
 
C-AHT135 Road-sports large-bore 'stage 3' spec head. Modified, standard MG Metro spec 
1.406"(35.7mm) inlet & 1.151"(29.2mm) exhaust valves, cast iron valve 
guides, A+ spec stem seals, 200lb (nominal) double valve springs, nominal 21.0cc 
chambers. Suitable for fast road large-bore engines and lead-free fuel use up to 
6,500rpm continual peak rpm limit. Has by-pass hose and heater valve take-offs for 
pre-1992 engine types. Near zero flow-loss from modified standard valves when 
compared to race-spec valves. 
 
C-AHT136 TPi Road-sports large-bore 'stage 3' spec head. Modified, standard MG Metro spec 
1.406"(35.7mm) inlet & 1.151"(29.2mm) exhaust valves, cast iron valve 
guides, A+ spec stem seals, 200lb (nominal) double valve springs, nominal 21.0cc 
chambers. Suitable for fast road engines and lead-free fuel use up to 6,500rpm 
continual peak rpm limit. Near zero flow-loss from modified standard valves when 
compared to race-spec valves. 
 
MSE3 Large-bore Super-sport spec head. Race-spec stainless steel 1.406"(35.7mm) inlet & 
1.161"(29.5mm) exhaust valves, manganese-bronze guides, A+ spec stem seals, 
200lb (nominal) double valve springs, nominal 21.0cc chambers. Suitable for fast 
road/occasional hill-climb/sprint/auto-test/track day engines and lead-free fuel use. Has by- 
pass hose and heater valve take-offs for pre-1992 engine types. 
 
MSE4 Large-bore Super-sport spec head. Race-spec stainless steel 1.406"(35.7mm) inlet & 
1.161"(29.5mm) exhaust valves, manganese-bronze guides, A+ spec stem seals, 
200lb (nominal) double valve springs, nominal 21.0cc chambers. Suitable for fast 
road/occasional hill-climb/sprint/auto-test/track day engines and lead-free fuel use. Has NO 
by-pass hose and heater valve take-offs for post-1992 non-injection engine types. 
 
MSE5 Large-bore Super-sport spec head. Race-spec stainless steel 1.406"(35.7mm) inlet & 
1.22"(31.00mm) exhaust valves, manganese-bronze guides, A+ spec stem seals, 
200lb (nominal) double valve springs, nominal 21.0cc chambers. Suitable for fast 
road/occasional hill-climb/sprint/auto-test/track day engines and lead-free fuel use. Has by- 
pass hose and heater valve take-offs for pre-1992 engine types. 
 
MSE6 Road-sports spec large-bore head. Modified, standard MG 
Metro spec 1.406"(35.7mm) inlet & 1.151"(29.2mm) exhaust valves, cast iron 
valve guides, A+ spec stem seals, 200lb (nominal) single valve springs, nominal 
21.0cc chambers. Suitable for fast road large-bore engines and lead-free fuel use 
up to 6,500rpm continual peak rpm limit. Also limited valve lift use (max 0.420" 
valve lift). Has NO by-pass hose or heater valve take-offs for post-1992 cars 
including single point injection. Near zero flow-loss from modified standard valves 
when compared to race-spec valves. Can be up-rated for more valve lift by simply 
fitting C-AEA526 double valve springs. 
 
MSE7 MPi large-bore Super-sports spec head. Race-spec stainless steel 1.406"(35.7mm) 
inlet & 1.161"(29.5mm) exhaust valves, manganese-bronze guides, A+ spec stem 
seals, 200lb (nominal) double valve springs, nominal 21.0cc chambers. Suitable for 
fast road/occasional hill-climb/sprint/auto-test engines and lead-free fuel use. Has 
NO by-pass hose and heater valve take-offs for post-1997 twin point injection 
engine types (alternator bracket bolted to head). 
 
MSE8 Large-bore Super-sports spec head – same as MSE3 but done on a brand new MPi casting. 
Race-spec stainless steel 1.406"(35.7mm) inlet & 1.161"(29.5mm) exhaust valves, 
manganese-bronze guides, A+ spec stem seals, 200lb (nominal) double valve springs, nominal 
21.0cc chambers. Suitable for fast road/occasional hill-climb/sprint/auto-test engines and 
lead-free fuel use. Has by-pass hose, temp sensor hole and heater valve take-offs for 
pre-1992 engine types. 
 
MSE9 Large-bore Super-sports spec head. Race-spec stainless steel 1.406"(35.7mm) inlet & 
1.161"(29.5mm) exhaust valves, manganese-bronze guides, A+ spec stem seals, 
200lb (nominal) double valve springs, nominal 24.5cc chambers. Suitable especially 
for fast road/track day large-bore engines of 1380cc type capacity where extra chamber 
capacity is required to keep compression ratio sensible and lead-free fuel use Has 
by-pass hose and heater valve take-offs for pre-1992 engine types. 
 
 
To change pre-1992 head to post-1992 fitment (except TPi) - 
Fit heater take-off blanking plate (p/no. 2A180) and gasket (p/no. 88G221) and fit by-pass hose blanking cap (p/no. CAM4126) or remove by-pass hose adaptor and fit blanking plug (p/no. 88G619). For single point injection only - blank water temp gauge sender unit hole off with 5/8"UNF threaded plug (p/no. 5/8UNF). 
 
To change post-1992 head (including TPi variants) to pre-1992 fitment - 
Drill 9/16"/14.5mm hole through counter-bored heater take-off hole (1/4UNF heater tap retaining stud holes are already in place) or remove blanking plate if fitted. For by-pass hose, either drill/tap 5/8" UNS (16TPi) port in required place and fit by-pass hose adaptor p/no. 12A2075, or drill/tap 5/8"UNF and fit adaptor p/no. 12H1405, or blank water pump port off with blanking cap p/no. CAM 4126 and either drill 6 1/8"/3mm holes around thermostat periphery or fit blanking sleeve (really not good for road use - recommend thermostat is fitted). For water temp gauge sender unit either drill/tap port out to 5/8"UNF thread or remove 5/8"UNF socket headed grub screw if fitted. 
 
Anything beyond this - i.e. for specific applications like full race and so on, contact me direct.