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I just bought a 1975 De Tomaso Longchamp. It needs work on various things, but at the top of the list is having the blown head gasket fixed. Since both heads are going to come off the engine, I was thinking is there something else that would be a good idea to get done while they are at it.

After the car is finished I´d like to end up with an economical 350hp engine, so I can piss off a friend of mine who has a Jag XJ-S..
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I have been thinking about the fuel injection systems (Mass-Flo), but now I´m leaning more toward a LPG-conversion, if the consumption gets too high.

Right now the car is in Italy with the vendor I purchased it from. The vendor will do the sills, head gasket job, and some interior work. After that the car will be shipped to Finland. At the moment I can´t afford to go the whole hog on the engine, as the car will need more spending on other items.

If I have understod it correctly, in the current specification the car should have an output of 270hp(not counting wear and tear). Earlier versions had 310hp and 330hp(don´t know if 330hp versions were actually produced). I can´t see any reason why I shouldn´t have at least 330hp..
Will the car need to meet (stringent) emissions standards? Valve job, cam change, and carburation can provide nice gains for modest cost but it's difficult to say without knowing your starting point.

If it's configured like the relatively low compression 74 US engine, just advancing the cam events 4 degrees with a timing chain that can be indexed can help, but again difficult call without knowing compression ratio and other details.

What's the starting specs for Euro Longchamps of that era? Is it unaltered?
There are no emission testing for pre-1977 cars in Finland. I believe the engine is unaltered. Longchamps of that era should have 8,5:1 compression ratio with 270hp at 5000 rpm.

Problem here is that I need to brief the guys in Italy fairly soon on what to do to the engine, without the possibility of taking my time to check out the engine properly. The company is a very well known general classic car dealer, but it is not naturally a specialist on Detroit power. It makes sense for me to let them do the head gasket work over there, as it makes it so much easier for to have real running car when it´s shipped to Finland. Now I just need to figure out what else would make sense considering my goals when the car is "finished".

P.s. From Finland with six dollars per gallon..

P.s, p.s. Sorry for bothering you guys while I really don´t know what I´m talking about..
when the head or heads are removed, the mechanic shall find the pistons have either flat tops, or dished tops. This will distinguish with certainty which motor the Longchamp is equipped with.

If the pistons have flat tops, the compression ratio is nominally 8.6:1, the heads have the large valves, and the cam is installed at zero degrees (neither retarded or advanced).

If the pistons have dished tops, the compression ratio is nominally 8.0:1, the heads have the smaller valves, and the cam is installed 4 degrees retarded.

The work I advise you to have performed to the motor is:

(1) cylinder head improvements consisting of replacing the valves in both cylinder heads with 1 piece, single groove, stainless steel valves. The valves should be the large size 2.19" intake, 1.71" exhaust. Replace the valve spring retainers with chrome moly steel retainers and the appropriate keepers. Install Boss 302/Boss 351/429 Cobra Jet valve springs. Install silicone bronze valve guides, and replace the valve guide seals. Replace the stock rocker arms with Ford "bolt down" roller rocker arms, part number M-6564-C351.

(2) Rebuild the crankshaft dampener (a company in the US called Damper Dudes can perform this service).

(3) Replace the camshaft timing chain with a "RollMaster" timing chain. If the motor has dished pistons, set the timing chain to advance the camshaft by 4 degrees.

(4) Upgrade the ignition to a breakerless system. It is recommended to use the Ford Duraspark ignition for reliability and parts availability. The donor motor for this ignition will be a 1976 - 1982 Ford 351M, 400 or 460.

(5) Not knowing what intake is installed at this time, I would advise you to use the cast iron spread bore intake manifold originally equipped on the late 1971 - 1972 351C Cobra Jet motors; plus the Autolite/Motorcraft 4300D spread bore carburetor.

The original valves were of 2 piece construction and are known to occasionally come apart and ruin the motor. The same goes for the valve spring retainers. The stock rocker arms are junk and create unnecessary valve train wear. The silicone-bronze valve guides are more durable than the iron valve guides. The Boss/Cobra Jet springs will improve the motors rpm capability a small amount.

The original camshaft timing chain sprocket had nylon teeth, and the teeth may strip off the gear and leave you stranded. It is best to replace it, and the RollMaster is the best. Plus the RollMaster allows to retard or advance the camshaft.

The rubber in the crankshaft dampener is rotten by now, and it could come apart anytime. It is critical to have it rebuilt.

The breakerless ignition will not go continually out of adjustment like the oem breaker point distributor, you can set it once and forget it. This improves performance, reliability and fuel economy. The car will start easier, idle smoother and have more rpm capability.

The Autolite spread bore 4300D carburetor is the best carburetor for a stock motor. It flows about 700 to 750 cfm, gives the engine more rpm capability than the Holley 600 many European DeTomasos are equipped with. Plus the carburetor is tuned more precisely for the motor, returning better drivability and better fuel economy.

With these improvements, and just regular maintenance afterwards, I would expect your cleveland motor to give you years of uniterrupted, reliable service. With about 280 net SAE bhp on tap (about 310 DIN), the performance is decent too. However, if the bad head gasket is the result of over-heating, the motor may have other issues.

Last edited by George P
Fuel injection is something you should consider for the future.
With fuel prices at $1.80 per litre (about $6.80 for a US gallon) this is something I would like to do.

In the UK the tax on LPG means that it's not really worth it. Hopefully in Finland the government have more sense.

Also be careful when looking for an LPG system, some systems will reduce the power of the engine by 10 to 20%.

Thank you very much for your advise. I think I´m going to let the Italians to do the step 1 in your post with the exception of the roller rocker arms installation. Then after the car is in Finland I´ll proceed with the rest of your list.


LPG is very cheap in Finland at the moment, but then again it was probably pretty cheap in the UK before it became more widely used. LPG would be cheap way to get economies, while FI would be a more elegant way.

In any case, settling the FI/LPG decision is waaayy ahead in the future...
Jani & Rapier and all who are also interested,

Converting to LPG is popular here in Holland. Considering that petrol is about $6,50 a gallon and LPG $ 2,45 a gallon over here. With conventional LPG systems i.e. for carburetted cars the powerloss is 5 to 10% depending on how well the system is adapted to your engine and how well it is tuned.
Over here it makes sense as all cars over 25 years don't have any roadtax. If this wasn't the case I would have to pay about $ 400 every 3 months if I were to run it on LPG.
My Deauville will have a system in by this summer, consisting of an 18 gallon ring tank which replaces the spare wheel and will use the original drivers side filler neck. The left side fuel tank will be taken out permanently. This setup will give me the added benefit of almost no gain in weight. The LPG system does add about a 100 LBS.
Total costs? About $ 2.100 for the whole system, installation and setup.
Worth it? For me it is. The savings in petrol will have me earning back the system about 6 to 7.000 miles.
I have seen it to be realiable in a number of 351C engines under normal conditions. If you want full power for an Autobahn run or trackday, just flick the switch to petrol and your ok.
Well things have not gone quite to the plan I laid out in the earlier posts. The car is finally in Finland (delay not due to seller - not blaming them). The interior is done and the power steering is fixed. Engine will be opened tomorrow. According to the Italian registration paper the car should have the 270 hp version of the engine.

Findings so far. Car has three radiators and an extra electrical fan for the main radiator. Something tells me that the original radiator is not working to it´s fullest capability..

It seems my thread title is not correct. The head gaskets are just fine. It is definately the first time I´ve bought a car with a seller confessed problem that doesn´t exist.

It seems that the car has had some issues with overheating, and the solutions for these problems have been amateurish to say the least. There was even an useless radiator for the power steering! Other findings: The kilometers on the clock seem to genuine (50000km), car is equipped with a Holley carb. Carb port to intake match is awful. Should I get an Autolite to replace the Holley or just grind the intake to match. I think George mentioned that the Autolite is superior to Holley.

I'll offer some advice about the cooling system.

there is a good probability that your Longchanmp's motor has the wrong thermostat installed. this is a very common problem even here in the states. Auto parts stores, Ford dealerships and even Pantera vendors dispense the incorrect thermostat. The Cleveland thermostat is different than the Windsor (351W) thermostat, but most parts vendors dispense the Windsor thermostat for 351C applications. The correct thermostat is a Robertshaw model 333-180. This is a picture of the Cleveland thermostat:

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I don't know where to advise you to purchase one in Europe. They are available via mail order from Summit Racing, stock number BRA-333-180 (Summit will refer to it as a Flow Kooler thermostat).

Drain the radiator and visually inspect the core for scale deposits, if scale is visible the radiator will require chemical cleaning or replacement.

Another common error with 351C maintenance is the improper orientation of the head gaskets during assembly of the motor. This can be detected by a gurgling & surging sound coming from the motor as it heats up.

Assuming the head gaskets are installed properly, a good clean radiator and the proper thermostat should resolve any overheating problems. If the car continues to overheat you can increase coolant flow with an Edelbrock water pump. This pump is unique in that it employs a cast, curved vane impellar which pumps coolant more efficiently than the usual stamped steel "paddle" type of impellar.

A final solution to resolve overheating problems would be to install a new radiator with a more efficiently designed core. Modern radiator cores have fewer rows composed of wider tubes (33 - 38 mm wide) for less restriction to coolant flow and a better fin design for improved air flow.
Last edited by George P
At normal operating temperature the brass cup shaped bottom of the thermostat extends downward and blocks the hole in the brass orifice below the thermostat. That hole is the recirculation passage, the passage that bypasses the radiator during warm up. Without a thermostat to block that hole when the motor is warm the motor will recirculate coolant uncontrolled. When coolant is recirculated it is bypassing the radiator, and the motor will over heat. No thermostat is a bad thing in a cleveland, because it was designed to recirculate a larger volume of coolant than other engines of that era.

Last week my biggest worry was looking like an idiot about the thermostat thing I posted earlier. This week has moved the game to a new level.

New findings:

The engine has been in a crash. The water pump had actually bended the plate covering the timing chain.

Engine is overbored already to .030 with signs of more overbore to do.

Camshaft is worn, and it´s front bearing is shot too.

So, instead of a top end rebuild along the line of what George recommended, it seems that in the end we´ll end up replacing everything , bar crankshaft, rods, heads, and maybe the block(my mechanic has suggested a trade to a better block too).

To cure my depression, I am asking if the kind people in this board have any suggestions, as far as piston and cam choice goes. Or any suggestions how to proceed with this renovation/mild upgarde project. When the car is ready, it should be a Grand Turismo that will be used as a Grand Turismo.

I wouldn´t mind 350 hp either..
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