Advice please on a 1972 HC engine

[ernie100]

Hi
I have just purchased a 1972 Mark 111 7.2 litre HC engined Interceptor. Details to follow in the next couple of weeks. It has been off the road for 30 years and has the bodywork redone. Over the next 12 months or so the car will have the rebuild completed, including full mechanical overhaul/ recommissioning (lots of new parts already fitted)...as well as a repaint
I know that the engine will have to be rebuilt (70k miles low oil pressure but compression ok?). As its an HC engine in the car (the car is not an SP) with the more traditional carb set up, I appear to have some options...(Grant put that train of thought into my head with his excellent suggestion). Firstly the car comes with a brand new (unsed Edelbrock..dont know which model yet) so instinctively I may wish to retain this...are they good with this engine?
Also as the engine will have to be rebuilt thus I assume that SP spec pistons etc can be easily done during the rebuild..thoughts gentlemen..as to a good spec, I want to balance longevity with performance
Also do I want to rebuild the car to SP spec with different carb set up?..I read that the SP is a bit tricky to keep set up/ tuned...whats it like to live with an SP?
If I go SP spec, apart from the badges, is there anything else I should look to upgrade to at least SP spec...engine, brakes etc
Finally, from what I have read low octane fuel and HC engines do not mix...would this be addressed by the traditional unleaded conversion for the valve seats etc? or should I do more...I am brand new to Jensen and have a limited engineering knowledge so please be gentle in your res ponse....
Thanks David

[Dave782]

Hi Dave, my car must be very close to yours (August 72), and has an HC designated engine, but that does not refer to high compression as I understand it, it's just a code designation. Also, I had an edelbrok on my car when I bought it and it was not good so Dave Barnet refitted the thermoquad which makes the car much better to drive.
That's all I can offer but would be interested in replies o your thread too.

[Richie]

Welcome on board Ernie.
Good luck with the car, looking forward to seeing some pics.
In the meantime, I'm no engineer but...
Dave782 is quite correct in his belief that HC is a date code. It certainly doesn't refer to high compression. The HC in standard form should therefore be fine on 95 octane fuel.
If however it does need a full rebuild, the world is your oyster -the set up you choose would be dictated by your requirements and budget. As the old saying goes "speed costs money... how fast do you want to go?"
The "tricky" reputation of an SP is down entirely to the "six pack" (sp) carburation. I've an edelbrock 1460 on my standard 383 and it runs fine. Whether yours will work as well would I guess depend upon the spec you go for on the rebuild...

[ernie100]

Hi Dave, my car must be very close to yours (August 72), and has an HC designated engine, but that does not refer to high compression as I understand it, it's just a code designation. Also, I had an edelbrok on my car when I bought it and it was not good so Dave Barnet refitted the thermoquad which makes the car much better to drive.
That's all I can offer but would be interested in replies o your thread too.

Thanks, thats interesting, the vendor said "as there was a six month window in the second half of 1972 when Jensen fitted the more powerful HC (High Compression) 7.2L engine. My car was manufactured in November 72 and first registered 12/1/73." I will check his source of information and when I get the final documentation I assume that I can track down the specific build information.
My main requirements is for drivability rather than outright straight line performance...the rebuild will at a minimum include porting/ etc, do these engines respond well to mild tuning to improve efficiency etc...the car will come with its original thermaquad, so if that is rebuilt is that better for day to day work rather than a after market replacement? Your insights are welcome as are comments...
Meanwhile any comments gratefully received...
David

[Richie]

Lots of discussion on the matter here

/www.joc.org.uk/forum/viewtopic.php?f=4& ... e&start=15

To summarise however...

H = 1972
C = Chrysler

HC definitely does not refer to high compression.

According to the guru that is Richard Calver, aside from SP units, all 440s fitted to Jensens were low compression units.

If you're embarking on a full rebuild, it doesn't have to stay that way.

[hlequippe]

My car is also a HC version as it came out in July 72. I had a rather strange carb setup on mine with a Carter AVS which was in need of a full rebuild on a Edelbrock performance manifold. Was getting even per Jensen standards very low MPG (my trip to Le Touquet from Paris last year to meet the Turin trip folds was a full tank for 200 kms driven on motorways at 70 MPH) So after various advice and considering the fact that the rebuild cost would be in the same ballpark as a complete new carb, I bought a Carter Thermoquad from Summit Racing in US.

In any case, in terms of driving feelings, the car feels very very torquey, but does not provide the same acceleration as say my Porsche. Apart from the weight difference, I believe the main difference is coming from the gearbox.

That Torqueflite gives the impression of endless acceleration with almost unnoticeable gear change. but you do not really get the kick in the bu... feeling. So here are my impression after 18 months of ownership

Car accelerates plenty enough. Remember that whatever amount of $€£ spent on the engine will also require extra $€£ spent on cooling, suspension and brakes. And brakes are not that great to start with compared with what we are used today. Not even mentioning tires which cost more for the Jensen than on the Porsche. But these are your only contact with terra firma so spending money for good tyres is a must. When I got mine, it had 15 years old Pirelli. they were OK on the dry but a disaster on the wet. Taking roundabouts at 45° angle is not fun in the middle of trafic

If I wanted extra driving feelings I would change the gearbox to either a Manual or at least an auto box with overdrive allowing lower ratios at the bottom and lower revs at speed.

good luck and remember that whatever your decision it is Your car

[Chris_R]

Totally agree with Richie.
The vendor either didn't really know what HC meant or was being inventive!
H being the engine year designation, Jensen started fitting the 1972 440 H series engine in April 1972 and then in December that year started fitting the 1973 "3" or "J" series engines, so yes, there was an approximate 8 - 9 month "window" when they fitted the HC engine but HC doesn't mean High Compression, it means as Richie posted. The engine was designed for use on US premium gasoline which was from 91 - 94 octane. US Gasoline was always lower octane the UK / European octane levels.
In original specification the performance of an Interceptor III was, as Rolls Royce would say, "adequate". That means top speed in excess of 125mph and acceleration to match. So, to answer your rebuild question, what do you want from the car? Sometimes it's nice to have extra performance but in reality where and when can you use it (legally) in this country?
You say your main requirement is driveability, on that basis I'd say rebuild as standard with the Thermoquad. You will get differences of opinions on carburetors, some will swear by the Carters, others will rubbish them and say only a Holley is any good and yet others will say ditch all that and fit an Edelbrock. Phillip Lochner from South Africa who has posted on this forum will assert that a good Thermoquad, properly setup and tuned is almost unbeatable. Search out his posts as he has two Interceptors, both 440s and one has EFI fitted and the other runs a Thermoquad.
One small point, you say it has good compression but still needs a rebuild on account of low oil pressure. That low oil pressure may be due to a faulty oil pressure sender or due to a worn or damaged pump. If the engine runs and unless there are lots of other reasons to rebuild the engine it might be worthwhile getting a direct pressure gauge and connecting it to the pressure port to get a proper reading. It might be that the electric sender is faulty and sending a faulty reading. If the pressure really is low then it might be worthwhile simply replacing the oil pump with a high volume pump and see what difference that makes. If the low pressure is your only problem this might save yourself an engine rebuild and be able to use the car sooner. I had a low oil pressure problem on mine when I bought it, changed the oil pump and 18,000 miles later it's still going well.

[ernie100]

Thanks to all on really useful information...I will keep you all posted. I expect it will start to go under surgery in six months with full mechancial check/ refurb..and then reprime block and paint..will post pictures in a coyple of weeks
Cheers to all.

[hlequippe]

Do not get too stressed about low Oil pressure reading on your dash. Matting a sender to thegacuge is a nightmare as it seems US senders do not match Uk supplied gauges. I would as previously said put a gauge direct to the block to see hat is going on. I had that sa me nightmare last year. I have bought an extra oil pump and all that, but it is still in garage as finally, my gauge was wrong

[Chris_R]

Herve, Andy Brooks is currently getting the correct senders made from a company in Wales. Made with modern internals but in the original specification casing and working to the original specifications. Will fit straight into the engine block and match correctly to your gauge.

[Lee Grover]

P1010026.JPG (150.1 KiB) Viewed 4818 times

Hi David,

Some inspirational reading for you. Any one will tell you all about what you have....and some hints regarding what you might want to do. Cheap tuition for the education gained. Have fun

Lee

[Sheila J]

Hi Ernie,

Not sure where you are in Warwickshire but I'm near Alcester and have a 1973 Interceptor III with 7.2 engine (3C11357) if ever you need to check anything out.

[ernie100]

Hi Ernie,

Not sure where you are in Warwickshire but I'm near Alcester and have a 1973 Interceptor III with 7.2 engine (3C11357) if ever you need to check anything out.

Hi I have PM'd you...seems that we may be neighbours

[Richard Calver]

Leaving aside gauges and senders and worn pumps, don't forget that oil pressure is governed by the relief spring. The pressure cannot exceed what the spring allows. Springs weaken with age and the indicated pressure slowly declines. It doesn't necessarily mean the pump is bad or the engine is worn. If it makes you feel any better, shim the existing spring or change it for a new spring or fit a Hemi spring, which has a higher pressure limit. Either way, you'll 'see higher pressure on the gauge but as said you'll only know what that pressure is in reality by hooking up a direct reading gauge. 10 psi per 1000 revs is plenty good on these engines. The H motor was a low compression unit built for low-lead petrol and did not have the induction-hardened exhaust valve seats. If you are rebuilding it and changing things, you may as well fit hardened seats.

[Twright55]

It also depends on when you get the low oil pressure.
My HC motor had 50 psi at over 2500 rpm (which was what the pressure relief valve was governing it at) but near zero at idle. From what I've read, that can be caused by worn cam bearings.

What is your oil pressure at idle and what is it at say 3000rpm?