"Ford Kent Engine Back In Production"

[bcmc33]

Until someone buys one we won't know. Anyway spend your money and build the engine the way you want to.

I've ordered a 711M block - delivery promised in 2 weeks.

Short rods are a good thing for torque, long rods benefit horsepower. If it were a street engine I would build the lotus replacement block where torque is a fine thing to have in excess.

I always believed that a longer stroke to get 1700cc gives more torque and not necessarily more power - which is what I'm after.

[msd1107]

Belief is one thing. Mathematics is another.

Some years ago, I wrote a paper "The effect of rod to stroke ratio on the theoretical volumetric efficiency of an internal combustion engine"

Theoretically, a very short rod can have a 3% or greater volumetric efficiency improvement over a long rod, with other possible improvements. However, there are other considerations including increased side thrust due to increased rod angle, increased loads at TDC, and reduced time for combustion in the period around TDC. F1 engines go to the opposite extreme, with very long rods, despite all the structural inefficiencies. With the computational resources available to F1 engine builders, maybe they know something!

This is all academic considering the small differences in rod length with which we have to play in our TCs.

The shorter rod can be lighter and stiffer than the longer rod. Specify the piston pin height to be compatible with the block height, stroke, and rod length. I think the Dave Bean catalog covers these possibilities.

The question of long stroke vs short stroke has a long history. Legislative requirements for declaring and taxing horsepower led to small bore long stroke sedan engines for decades. The first generation of short stroke engines were more oriented to mid to high rpm power, not low rpm torque. So long stroke engines oriented around low speed running have better low rpm torque than short stroke engines designed for high rpm power output. The details of the cylinder head and valve train design control the relative distribution of torque up through the rpm range.

David
1968 36/7988

[rgh0]

I had a chance to measure up a couple of the new Ford blocks today that a friend of mine bought as he has been going through secondhand blocks at a rapid rate in the last couple of years - 9000rpm and 190 hp puts a bit of stress on these aging blocks so with the Aussie dollar at a high level he bought a couple of new blocks from the USA to supplement his stock of spare blocks

The blocks are the standard Lotus height for use in historic racing here not the tall block. The castings have the claimed modifications around the main bearings that should help and are very much similar to 701M blocks externally including having that casting number and all the other usual Ford casting numbers present and Ford logo so no problems with "eligibility". The claimed "reinforcement" to the clutch bell house bolt location is questionable as it appears to be like the earlier 120E blocks in this location and actually thinner than the original 701M blocks. However I have never had a problem in this area so it is probably not much of an issue.

I measured the bore wall thickness on the 2 new blocks and compared it to my data on other original blocks. It is close to the average of all the blocks I have measured ( numbering 20 plus blocks in total from all casting numbers 116E,120E, 681F, 701M, 711M). This does not surprise me as the bore casting outside diameter is limited by the sand casting technology used and the OD is typically in the 90 to 91 mm range depending on casting tolerances and corrosion. These new blocks are no differrent with one averaging 90.45mm and the other 90.24 mm across the 4 bores outside diameters. An 83.5mm bore is comfortably doable but still requires offset boring to get consistent wall thickness over 3 mm. An 85 mm bore in these new blocks would have around 2.5mm minimum wall thickness which is the very bottom end of what is just tolerable in a road engine and I would expect a failure over time in a full race engine at this thickness.

The myths about L blocks and 701M blocks AX blocks and now these new blocks having thicker walls are still just that "myths". Most blocks from the earliest to these new ones can safely take beyond 83.5 mm but it needs careful offset boring to do that and still get 3 plus mm wall thickness consistently and going beyond that while possible requires careful selection of a suitable individual block. An 85 mm bore really requires a 91mm bore casting OD which is at the top end of the range i have seen which neither of these new blocks have.

cheers
Rohan

[elandoc]

Hi Rohan,

Well, there goes my 2 litre cheater. I couldn't wait for the new blocks after blowing up at Bathurst 2 yrs ago, so pulled apart my spare TC and half filled the water jacket with Blockfill - basically concrete, from what I can see. Running 83.5 mm. Hopefully strong enough now. Not yet run in, and no overheating issues - runs a bit cool, actually. My next mod will be an oil/water heat exchanger, as the oil can get very hot, even with cold water - when I get time... and money. I'm glad the new wonder block doesn't measure up - I've been worried I should have waited.

Cheers

Patrick

[rgh0]

The new blocks are good if you want to build a new race engine and dont want to worry about finding a decent block to base it on

Biggest advantage of the new blocks is no corrossion especially at bottom of water jackets where old blocks have most corrosion after sitting in wrecker yards for 30 years. Also the opportunity to offset bore from scratch to centre the bores in the casting and maximise wall thickness and not having to deal with poorely centred orginal bores and later over bores makes it simpler. The improvements around the mains support will not hurt either

But the new cast iron blocks are not the answer for a big bore race engine - you really need that 2 litre alloy block like Jay Leno!! - in reality the alloy blocks are not that expensive when you look at the total cost of a new race engine.

cheers
Rohan