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Feb 11, 2018 21:36:17 GMT
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I’m building a 1725 Hillman Hunter Race engine. Wanted any advice. Doesn’t seem to be many people getting good figures out of these engines. Has anyone used liners in these engines? Cylinder head porting, big valves, vizard mod? Oil pressure problems? Any help much appreciated.
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Feb 12, 2018 10:27:48 GMT
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Feb 12, 2018 10:52:56 GMT
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Cheers. Yh I will definitely get reading them
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Rob M
Posted a lot
Posts: 1,915
Club RR Member Number: 41
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1725 Hunter Race EngineRob M
@zeb
Club Retro Rides Member 41
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Feb 12, 2018 11:50:29 GMT
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IIRC, the 1725 lump is not too fabulous for tuning. The 1600 Avenger lump is very good, apparently, much of the tuning parts back in the day revolved around the Avenger and the 1600 lump. Ive no idea how easy it would be to drop the 1600 into the space where a 1725 normally lives but, essentially, it may be the best way forward?
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Feb 12, 2018 15:44:57 GMT
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Cheers for the advice gonna stick with the 1725 as I know 1600 are easier to do but I like a challenge and with some carful work I don’t see a reason why they can’t make good power
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Darkspeed
Club Retro Rides Member
Posts: 4,845
Club RR Member Number: 39
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1725 Hunter Race EngineDarkspeed
@darkspeed
Club Retro Rides Member 39
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Feb 12, 2018 19:25:44 GMT
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In the Vizard Book - Theory and Practice of Cylinder Head Modification - there is a small section on modification with detail to gain a few BHP - And the official FIA homologation papers are always a good read historicdb.fia.com/search?key=Hillman
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vitesseefi
South West
Posts: 2,286
Member is Online
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Feb 12, 2018 19:49:29 GMT
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Holbay......
Nick
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1967 Triumph Vitesse convertible (old friend) 1996 Audi A6 2.5 TDI Avant (still durability testing) 1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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stealthstylz
Club Retro Rides Member
Posts: 14,926
Club RR Member Number: 174
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1725 Hunter Race Enginestealthstylz
@stealthstylz
Club Retro Rides Member 174
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Feb 12, 2018 21:03:51 GMT
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More air in (carbs, cam, porting, bigger valves), squeeze it harder (compression) and get it out quicker (exhaust) same as any engine. Depends on parts availability.
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retrolegends
Club Retro Rides Member
Winging it.....Since 1971.
Posts: 3,726
Club RR Member Number: 94
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1725 Hunter Race Engineretrolegends
@retrolegends
Club Retro Rides Member 94
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Feb 12, 2018 22:40:48 GMT
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As the man said - H120 with an alloy head but try finding one these days, i think there's been a couple of Mazda conversions done on here so personally that's the route I'd go, can't fault you for sticking to originality though.
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1974 Hillman Avenger 1500DL1992 Volvo 240SE1975 Datsun Cherry 100a flying custard1965 Hillman SuperMinx Rock N Roller1974 Austin Allegrat Mk1 1.3SDL1980 Austin Allegro Mk3 1.3L1982 Austin Allegro Mk3 on banded steels2003 Saab 9-3 Convertible 220bhp TurboNutter1966 Morris Minor 1000 (Doris) 2019 Abarth 595C Turismo (not retro but awesome fun) www.facebook.com/DatsunCherry100a
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Seth
South East
MorrisOxford TriumphMirald HillmanMinx BorgwardIsabellaCombi
Posts: 15,538
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Feb 12, 2018 23:16:56 GMT
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The Holbay heads have smaller inlet ports than the standard 1725 heads. My understanfing is that this is because Rootes weren't happy that, as originally developed by Holbay, the engines were very 'streetable' and the smaller ports helped with lower rpm running & idling. So you could take from this that if you don't care about driveablility or practicality the ultimate factory based head (in terms of max flow potential) might be a standard 1725 one with the larger ports but with the combustion chambers modified to the Holbay sort of shape.
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Follow your dreams or you might as well be a vegetable.
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Gonna be using a standard engine I do have a Holbay but the smaller ports just increase spread that the fuel/air enters. But with some careful porting and making the exhausts a lot bigger it should pull it through nice. I’ve been told to do bigger valves which is fine only I can’t see them fitting withought massive amount of work. I’m gonna be using pop up pistons and a custom head gasket to get around 11.5/1 compression ratio. Does anyone have a photocopy of the vizard book head modification. (Would I be best doing my own design?) Cheers guys
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v8ian
Posted a lot
Posts: 3,824
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Feb 14, 2018 19:39:03 GMT
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Atmo V8 Power . No slicks , No gas + No bits missing . Doing it in style. Austin A35van, very different------- but still doing it in style, going to be a funmoble
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Darkspeed
Club Retro Rides Member
Posts: 4,845
Club RR Member Number: 39
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1725 Hunter Race EngineDarkspeed
@darkspeed
Club Retro Rides Member 39
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Feb 14, 2018 21:40:20 GMT
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The FIA detail papers show the inlet port sizes of the Holbay and the GL and GT models the same at 1.3" the exhausts on the Holbay are 1.25 compared with 1.12 on the GL a good 1.3" port will feed a 1.6" valve. A Key description on the papers is that the Holbay port finish is Hand Finish. I wonder what standard head had the bigger inlet ports. Or is it just optical due to the Holbay having bigger exhaust port making the inlets look smaller and the stock engine having a couple of ports with look like spigot machinings. Vizard does detail one difficultly when improving the chamber shape in that the tappet chest holes prevent too much being taken off the head to increase the compression. Holbay in the GLS also had better pistons photo looks like solid skirt with a max listed RPM on the papers of 7000 RPM Has gross power of 110 listed for the GLS which at 1725 - also note the different capacities in the papers - is around 62BHP/lire which is pretty heathly for a non crossflow push rod so getting that higher will be an ask and probably only really be possible with capacity - if managing 70BHP/ litre - not easy at all - and an increase to 2.0L which seems a listed maximum - then 140BHP would be theoretical possibile and not cheap. Holbay GLS motor was bloody good.
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Holbay inlet ports are definitely smaller quiet a lot smaller. The only reason I can think of why they did that is to increase speed in and increase speed out (scavenging) they certainly wouldn’t of had any problems getting the air fuel mixture in with twin 40’s
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1725 Hunter Race Enginepeteh1969
@peteh1969
Club Retro Rides Member 107
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PDGough in Nottingham can make you a full flow manifold in Stainless for a 1725 Holbay engine as the built one for me back in the late 90's and they still have all the measurement to make another.
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Definitely will get in touch with them
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