5.23" con rods

[HCA]

Is anyone using the long con rod in a road engine? There are the odd instances in the archive of the rods being used, but mainly in competition.

I will be putting a set into a tall block with a long stroke crank that Rohan says will be a pretty good build. I am now interested in comments from anyone actually using this combo - not in competition, particularly regarding smoothness.

[2cams70]

Depends whether or not you like truck engines. Make no mistake. There’s certainly some very grunty truck engines but they probably can’t be considered appropriate for a sports car.

[HCA]

mmm. This from experience, yes?
In my research here, I found quite favourable comments on taking the engine up to 1700...

[2cams70]

I really don’t understand why people want to change that which is perfectly good. Sure do a few mods to help the engine breathe better but why change the stroke? A standard Lotus twin cam is a sweet and smooth unit even at high RPM. I know a lot of engines run long strokes these days for emission regs and torque but along with that a lot of tech. is also put into soundproofing and engine mount design. Unless you are going racing do you really need it? I find usually no matter how rapid a car is you quickly adjust to it anyway and things soon no longer feel that way.

[rgh0]

A 1600 tall block with a 83.5mm bore, with a 1600, 77.62 mm long stroke crank, for 1700cc displacement and combine that with a light 5.230 inch / 132.8mm rod (that length is the Cosworth design for a BD motor) and with a light forged piston with modern thin rings and it all works to produce great torque and power for a road engine with the right high lift short duration cam, the right valves and porting and the right carb set up and right exhaust and right ignition and the right balancing details. This comes with no signficant increased vibration versus a 1500 twin cam in my experience at least up to 7000 rpm.....

I have never experienced a build like this at 8000+ rpm but at those revs a 1500 block short stroke Twincam will scream beautifully but it is certainly not vibration free as I know from failed oil pumps, distributors and alternators in race engines as all of which struggle with the vibration in the nose of the engine at 8000+ rpm. The water pump is actually the most reliable ancillary in a race engine as long as you keep the V belt as loose as possible

There are many details you need to get right but I dont believe its a truck engine and I dont think Cosworth designed trucks either

Bore to stroke of 1.08 and rod ratio of 1.71 also say its not a truck engine.

You should get around 170hp or 100 hp/litre at 6500 to 7000 rpm which is certainly not a truck engine and not bad for a modified 70 year old design road engine running on carbs with no 4 valves or Variable valve timing and lift, or knock sensors and electronic ignition or any of the other modern naturally aspirated engine stuff done by people like Honda or VW or Mazda or others and they have not got much better output per litre in the last 20 years despite all of this ( but maybe they are crippled a little by emissions regs unfortunately) .

But all that is just my personal opinion. Everyone needs to make their own decisions about what they do, but all power ot people prepared to put their money into a project like this and breath new life into Twincams and Elans for the current era.

cheers
Rohan

[HCA]

I really don’t understand why people want to change that which is perfectly good. Sure do a few mods to help the engine breathe better but why change the stroke? A standard Lotus twin cam is a sweet and smooth unit even at high RPM. I know a lot of engines run long strokes these days for emission regs and torque but along with that a lot of tech. is also put into soundproofing and engine mount design. Unless you are going racing do you really need it? I find usually no matter how rapid a car is you quickly adjust to it anyway and things soon no longer feel that way.

My original question had nothing to do with stroke - or do you think a longer rod increases the stroke? I am not changing the stroke at all - it is a wide bore crossflow engine with con rods that have been available for many years, that I am using to avail of optimum rod/piston ratio that I have been reading a lot about.

The design is used by many of the Cortina and Escort enthusiasts (and Cosworth before them) who use the crossflow engine with much applaud.

I was merely asking if anyone with a twin cam elan is using the same - I do not know why you decide to go off on a tangent and talk about truck engines and long strokes...

[SimonH]

My intention is to make a xflow based twincam for my plus2. I’m following this project with a fair bit of interest as I think I’ve kind of got the jist of what’s required for it. Xflow crank and rods, either Ford or aftermarket and some shorter compression height pistons although that might be wrong. Using standard spec forged would be easier if that’s what it should be. I hope to not have to deck the block and end up as a 1700, not planning on revs above 6750 or so.

[HCA]

My project, similar to yours, stems from CC's idea of the +2 being able to take a young family 1000 miles in comfort. I am following this, but using modern parts available to me. Now, a Zetec engine might/would be better, but (and please do not tell the purist police this...) I fancied keeping a large presence of the twin cam!

Rohan is better placed to tell you the way forward, but as everything I know is from him, and as it is my idea, I will give you the bones and he can finish with the finer points

You say that you do not want to end up with a 1700 and decking the block. I am with you on not having to deck the block, but what is wrong with having 1700? Nothing like a few extra ccs for easy power and it is easy to do with a crossflow: standard Xflow 1600 711M block, standard Xflow crankshaft and then make up the rods and pistons to suit. After half crank throw, you have 169+mm to fill the bore. Use a 122.58 rod, you will need a 46.9 CH piston, a 125.17 rod needs a 44.31CH and a 133 rod 36.64CH

At this stage, I urge you to read up on two things - bore/stroke ratio and rod/piston ratio. I will say no more, but fascinating stuff and after you will see why an 83.5mm bore and 133mm (5.23") conrod fit perfectly. It maybe shows too how Messrs Costin and Duckworth were ahead of their time in the BDA design. Escort and Cortina enthusiasts are recognising this as an inexpensive way to get some more power and, they tell me, better tractability due to the longer rod changing the torque curve...The brilliance of this combination that you only need 39mm CH pistons, of which there are several, and by skimming approx 3mm from them, the block is nicely filled without decking. Nothing in this creates a truck engine.

As for breathing, I have not a clue what to suggest is best. I have stretched my budget and maybe mistakenly gone for a John Wilcox head - 1.6 and 1.4 valves, ported 45mm with throats widened and polished to 33mm and fast-road cams. Rohan has tactfully remained quiet on this, but a local engineer - one of the few 'Mr Cosworths' in France - sucked his breath in saying that at low revs, the engine might demand my foot be heavier on the right pedal...! His thoughts are that the throats should only have been enlarged to 30mm... We will see! If you see a near new Wilcox head for sale next year, you will know!

How far are you? Do you have a Xflow block and crankshaft?

Lets keep in touch as it seems we are looking for the same result.

[SimonH]

That should have been read as hoping to not deck the block, aiming for a 1700.
I have a 711m block that appears ok. Also a slightly earlier complete xflow which I got to take the front bowl sump pan from. If the crank and rods are good enough for what I want then I’ll use them also. If not a 711 crank isn’t horrendous cost and rods come up occasionally. I think the standard Ford xflow rods are the length you talk about, looking at the burton site for dimensions of aftermarket ones for direct xflow fit.
The head is an unknown right now. I have arranged to buy a good used one from someone who is having it reconditioned so that will be the starting point. It’s a normal big valve head with, he thinks, sprint cams. Might get some qed 420 spec or similar if they are just standard ones. I’ll be running some Weber throttle bodies, fuel injection etc etc, the mapping will be done by me eventually

[rgh0]

As for breathing, I have not a clue what to suggest is best. I have stretched my budget and maybe mistakenly gone for a John Wilcox head - 1.6 and 1.4 valves, ported 45mm with throats widened and polished to 33mm and fast-road cams. Rohan has tactfully remained quiet on this, but a local engineer - one of the few 'Mr Cosworths' in France - sucked his breath in saying that at low revs, the engine might demand my foot be heavier on the right pedal...! His thoughts are that the throats should only have been enlarged to 30mm... We will see! If you see a near new Wilcox head for sale next year, you will know!

Hi Hal

I dont know the details of the Wilcox head modifications or the source of the new head casting itself (though the 3 types of new castings castings are identifiable by detail differences) so its hard to comment on how it will perform in a 1700cc road engine but it will be interesting to findout .

A standard original twin cam head had 29mm ports so going to 30mm only seems pretty conservative to me. I measured one of my orginal older competition heads that has been ported with a 33mm throat and the McCoy head I use now for racing has a more slightly oval shaped throat at around 34mm vertical and 35mm horizontal. There is a lot more than just the throat size when porting a head but I guess it gives some indication of the extent of the work done

What I do know is that 1600cc engines i have built with the McCoy converted heads and similar short duration high lift cams have very good lowdown torque when used with 34mm or 36mm chokes in the carbs. 38mm chokes generate more top end power on the track but struggle to work well at more normal road engine speeds, though perhaps more time on the dyno playing which jetting and cam timing could improve their low rpm performance.

A 1700 cc engine like your building should be even better with the higher port velocities and bigger capacity improving lower speed performance. A similar engine i helped a friend build recently using another old racing head of mine with 33mm ports is certainly a great performing road engine in his Elan with no lack of low rpm torque

cheers
Rohan

[2cams70]

I’ve had time behind the wheel of almost every Mk1 Escort variant, 1100’s, 1300’s 1300GT’s, 1600’s and Twin Cams. Haven’t sampled a BDA unfortunately.

What I can say is that with every step up in stroke - the bores on all these engines are the same whilst you gain in low end torque and power you lose in high RPM smoothness and effortlessness. The “busy noise” factor at high RPM increases. In my mind the standard LTC engine bore and stroke is a really good compromise. If you are building up a Twin Cam certainly do not discount basing it on a 1500 Cortina block and using the original bore and stroke.

[HCA]

That should have been read as hoping to not deck the block, aiming for a 1700.
I have a 711m block that appears ok. Also a slightly earlier complete xflow which I got to take the front bowl sump pan from. If the crank and rods are good enough for what I want then I’ll use them also. If not a 711 crank isn’t horrendous cost and rods come up occasionally. I think the standard Ford xflow rods are the length you talk about, looking at the burton site for dimensions of aftermarket ones for direct xflow fit.
The head is an unknown right now. I have arranged to buy a good used one from someone who is having it reconditioned so that will be the starting point. It’s a normal big valve head with, he thinks, sprint cams. Might get some qed 420 spec or similar if they are just standard ones. I’ll be running some Weber throttle bodies, fuel injection etc etc, the mapping will be done by me eventually

Simon, you have all the building blocks to make up a 1700. One of your 711M blocks, the crankshaft from the complete unit - assuming in good condition, same applies to the rods and camshaft that will become your jack shaft. You then need to bore the cylinders out 0.040" to match suitable pistons.

Before you bore anything, you will need to source correct pistons for which you will need your head to calculate the CR. This where I will duck out as I am not qualified to comment on head or piston selection.. I know though that if you talk nicely with one of our betters, you will get the answers..

[HCA]

but it will be interesting to findout .

cheers
Rohan

This must be a phrase used widely in motor racing.. Bruno, although very impressed with the quality of the work on the head, said exactly the same !!

He looked up some notes and had the throats at 28mm. But has only scant knowledge of the twin cam and would bow to your superior knowledge.

The head is cast by SAS. The spec sounds exactly the same as Tony Ingram's but Tony says that his design is unique to him...and as Wilcox will not give me the spec on the valves he uses, he ain't going to tell me if he is or not using the same head

[rgh0]

The throats were smaller on the Mk1 heads. i have never measured them but maybe they were 28mm ?

In any case I am sure there is some variation in individual castings that could be around 1 mm as sand casting is not a a very precise method.

There are 3 new heads being cast as far as i am aware

1. SAS - you can tell as it has no cam bearing sheels and the cams run directly in the alloy ( like most modern engines). The inlet runners are larger than the orginal heads

2. QED - supposedly made using the orginal Mk2 head patterns but they make heads with larger inlet runners also.

3. USA / Dave Bean - the casting has the half moons in the spark plug well like the original Mk1 heads but with larger inlet runners.

I dont know what head(s) Tony Ingram sources to do his builds but on his Web site i see photos of both SAS and the USA / Dave Bean heads.