Engine tuning

[Dieschelan]

Hi

I have a mk1 engine in my lotus elan S3. I have hear that this engine is a little fragile If tuned. Do you can make a reliable engine for fast road? How much power can you obtain for a reliable fast road engine?

Regards

[bill308]

Hi Dieschelan,

I tuned the mk1 engine in my 1966 S2 SE and got good power buy upgrading the cams and inlet valves to sprint specification, increasing the compression ratio to 10.3:1, porting the cylinder head according to Vizard, fitting tubular headers, increasing choke size and rejetting the carbs. I never put it on the dyno but I suspect output was raised to the 130+ bhp level. The engine crank and rods were balanced, shot peened, and assembled with care and a low inertia flywheel fitted.

I did a number of time trial runs with it at Lime Rock Park in late 1980's and it went well, turning up to 7000 rpm in places.

I believe the weakest area was the small diameter bolt (5/16 inch) connecting rods, which I still plan to replace with later rods, that use larger 3/8 diameter bolts. A steel crank shaft and high strength big end bolts would be good additions.

Bill

[Dieschelan]

Thank you Bill.
Is necessary to update the engine to Mk2 specification (crankshaft, Conrods and oil sump) for a reliable engine?

[StressCraxx]

Thank you Bill.
Is necessary to update the engine to Mk2 specification (crankshaft, Conrods and oil sump) for a reliable engine?

I would most certainly replace your connecting rods and bolts with the 125E rods and 3/8" high strength bolts. The rods with the 5/16" bolts are known weak spots. A good sound cast iron crank, properly balanced is absolutely fine for street use. The early oil sump is less susceptible to oil starvation than the Mk2 sump and pickup.

Regards,
Dan

[Dieschelan]

Hi

I have found also another posibility. I can also buy a Big Valve Engine and so it’s not neccessary to do a lot of modifications. The other option is to use the original engine and convert it to 6 bolt and put the later crankshaft.

Regards

Diego

[vstibbard]

I'd buy the Big Valve engine and keep the original engine stock, especially if its the original engine for the car.

Vaughan

[nmauduit]

I'd buy the Big Valve engine and keep the original engine stock, especially if its the original engine for the car.

Vaughan

I would also ...

[rgh0]

You can certainly develop the earlier engines as much as the later ones. How much money you want to spend will determine how much reliable HP you can get.

If you're car has its original engine it may be nice to keep that so you have something to drive while you build a big engine to swap in and have something to go back in if you ever want to return it to original as others have said.

cheers
Rohan

[Dieschelan]

You can certainly develop the earlier engines as much as the later ones. How much money you want to spend will determine how much reliable HP you can get.

If you're car has its original engine it may be nice to keep that so you have something to drive while you build a big engine to swap in and have something to go back in if you ever want to return it to original as others have said.

cheers
Rohan

I want a fast Road engine (140-150 bhp). I have the stock engine and also a late crankshaft with the connectin roads and also a dellortos cabs. All these parts comes from a big valve plus 2 engine. I need for the conversion a pair of cams and also the later oil sump.
Is a updated engine reliable? Is the cylinderhead the same us the later one?

Cheers

[rgh0]

Many ways to build a reliable 140 to 150 Hp twin cam road engine and I have seen lots of good ones and bad ones.

It does not matter much what engine version you begin with, as this HP can be obtained from any engine with limited modifications... but there are a few key issues to consider

i.e
The early die cast heads with the half moons in the plug well can limit breathing due to their small diameter inlet runners. This will have you at the 140 hp end of the range without a lot more work

The 4 bolt cranks original rods and rod bolts will not go safely beyond 6500 rpm, the later 125E rods will do more but if you stay with the cast iron cranks (either 4 or 6 bolt) you still want to limit to 6500 rpm. Better ARP rods bolts give a little more head room but you still have the oil leak issues from the 4 bolt crank rear rope seal. While getting a 6 bolt crank and 125E rods is not that hard or expensive finding the 6 bolt front bowl sump for it is challenging and expensive so buying a complete later engine is probably sensible unless you have all the bits including the sump.

If the engine bottom end needs a rebuild then new lightweight forged pistons and a rebore helps with extra capacity and smoothness at little extra cost even with a 6500 rev limit from the cast iron cranks.

Almost all blocks will go to 1600 cc with standard stroke and 83.5mm bore but you do want to get the wall thickness ultrasonically checked and offset bored to maximise wall thickness. If replacing a 4 bolt crank then worthwhile thinking about going to a long stroke

Having said all the above the key things I would normally do to build a 140 to 150 HP road engine are as below. Not an exhaustive list but covers the bulk of what I would do. More is possible for more HP but costs start to go up.

1. High lift short duration cams e.g. QED 420 or similar with the required valve springs and valve stem length and followers to match. Exactly what is required depends on things like the cam base circle being used, where the valves are seated in the head, thickness of the followers and the detailed dimensions of your individual head as there are many combinations which can be made to work but some are better than others. Others make suitable cams as well as QED but you want a minimum of 0.420 lobe lift and duration less than 285 degrees seat to seat

2. Standard big valve inlet diameter and standard exhaust valve diameter will work and larger valves not needed on a road engine in this HP range but careful shaping of the valve ports and seats to maximise flow and cleaning up and matching the inlets and exhaust to the carbs and manifold should be done.

3. Measuring the head combustion chamber size, matching them all up and selecting the intruder size on new pistons or skimming the head to get a compression ratio around 10.5:1 assuming you are planing to use premium unleaded.

4. A good quality big bore road tubular manifold and exhaust system

5. A rebuild of the distributor and carbs ( with 33 to 34 mm chokes) and time on a dyno to get them set up right with an advance curve and jetting matched to you're specific engine and fuel being used is worth at least 5 hp alone.

6. For reliability baffling the sump properly to avoid oil loss on hard right hand turns is needed. Careful balancing of all components also helps. Otherwise its all about using good quality components and building it right to the right tolerances and then running it in properly.

7. Removing the mechanical radiator fan and replacing with an electric fan also gains a couple of HP.

8. The standard carb airbox costs a couple of HP and a modified deeper cover over the rear carb trumpets eliminates this.

All of this takes time to work through which is why starting with a spare engine is good so you can still enjoy your Elan while working on it

cheers
Rohan

[Craven]

An inexpensive way to a reliable 150bhp engine is to use the later 1600cc 711 block, crankshaft and rods, large square main bearing caps included for free.
All parts needed for T/C conversion readily available.

[2cams70]

The 6 bolt crank and the 4 bolt crank are exactly the same strength wise. apart from the method of flywheel attachment. You can fix that by having the crankshaft machined to accept another dowel pin for the crank to flywheel attachment. Spend up big on a six bolt crank and sump to suit only if a minor oil leak from the rear rope seal is a real concern for you.

Square main caps from the later blocks or steel aftermarket ones and the 125E rods with ARP bolts are a must unless you rigidly stick to a 6,500RPM limit (which is difficult to do!)

With these mods and all components properly balanced engine should be safe at 6,500 RPM with occasional excursions allowable to 7,000 RPM

The QED 420 cam peaks out at 6500RPM so whilst a steel bottom end is nice it isn't essential.

I personally am not a fan of "big block" conversions but that's just a matter of personal taste! See attached QED 420 cam specs.

[nmauduit]

An inexpensive way to a reliable 150bhp engine is to use the later 1600cc 711 block, crankshaft and rods, large square main bearing caps included for free.

I'm not sure an extra 100cc alone will get you to 150bhp - or even 140...

[rgh0]

An inexpensive way to a reliable 150bhp engine is to use the later 1600cc 711 block, crankshaft and rods, large square main bearing caps included for free.

I'm not sure an extra 100cc alone will get you to 150bhp - or even 140...

The long stroke crank enables you to go from 1600 cc to 1700 cc with a 83.5mm bore.

That extra capacity is worth around 6 to 8 hp at 6500 rpm compared to a similalr specification 1600 cc engine i.e. taking 140 to 150 hp engine into the 150 to 160 hp range. You can do it in a standard 1500cc block with suitable pistons, you do not need to use the taller 1600 cc block.

But if starting with a 4 bolt crank engine you will need to find a suitable sump (hard and expensive) and a few other bits (cheap and easy) to convert to suit the 6 bolt crank design

cheers
Rohan

[2cams70]

Remember if you increase the cubic capacity without also increasing the breathing capacity of the head your gains will be less than than expected.