High horepower Twin-cams?

[Lotus14S2]

I have a question for the group --
I raced cars in the late ?60s and early ?70s, and a couple of cars I ran were with the Lotus Twin Cam 1600 engine.
Now my information is dated, but I do know something of these engines.
I am hearing of some very high horsepower engines that people are talking about for street cars, and I would like to know what is being one done to gain this power? When the BDA type engines came out, there was only one company attempting to compete with them, with a twin-cam, and that was Brian Hart.. The engine made power above 180 HP. The Hart engine was an all steel bottom end and a highly modified head. His engine was a hand grenade. The head was very fragile, and was opened up so much that the heads were practically useless if you needed to do anything like a valve job. Hart ruined many heads. A failure mode was they would suck valves into the head, which was due to the extremely thin walls left after machining, and very strong valve springs.
The steel bottom ends were pretty much standard, with a steel billet crank, and steel caps.
I had a Kent block in my last engine with the narrow journal Cosworth rods, and all steel, but I had a Vegantune head, which was much stronger, but it probably peaked at maybe 175 HP...Maybe. The engine would have been very difficult to drive on the street, as it was high revving and required a high rpm to get it moving from a standing start.
So I hear of these engines in access of 180 HP; how is this done, with a power band low enough to drive it on the street.
Thanks,
Tim
'62 Elite
'63 Elan

[rgh0]

Yes the Hart heads were very fragile. The ports were bored until they broke through into the spring seat area which was also lowered a little to fit in the valve springs available at the time and then the hole was sealed up with epoxy this left the spring platform weakened to the point that they failed often as you observed

The high horsepower road engines that can be built now come from combining a range of features not available to Brian Hart back in the 416 twincam days.

i.e.

1. Modern new head castings from SAS, Dave Bean or QED or the McCoy Stromberg conversion. These heads have bigger ports and breath much better than an original casting can ever achieve.

2. Modern cam shaft profiles with high lift and short duration combining good top end power with strong mid range torque

3. Modern valve springs that can accommodate the high lift cams without lowering the spring seat thus leaving room for the bigger ports without making the spring seat area fragile

4. Larger capacity engines at 1700cc or more. "There ain't no substitute for cubic inches" . A steel crank and rods and forged pistons good for 7500 rpm also helps make use of the top end power the cams will offer, though with a large capacity engine you can get around the 170 to 180 hp number at 6500 rpm with the standard bottom end.

To get 180 hp out of a road twin cam you need all the above plus a good detail build,paying attention to combustion chamber shape around the valves and compression ratio and good carb and exhaust setup and time on a dyno to get it all dialed in right

cheers
Rohan

[patrics]

Hi Tim,
It?s a good question ? I am no expert so people may disagree but anyway.
I have a 1600 big valve non FIA engine ? 10mm plug and something like 12:1 compression and 183bhp ? will run on 98 plus octane booster. An FIA engine runs smaller valves but nearly same horsepower. I understand this is all down to the compression, so obviously a lot more than 12:1, need special fuel and rebuilding frequently. Cams, compared to yesteryear are higher lift with less overlap so keeping driveability.
Not sure how much power you would get with big valve and FIA compressions.

Regards
Steve

[Lotus14S2]

i guess the other option would be to use the Cosworth 2 Liter block, as was done by some wealthy vintage racers to build an unbeatable twin-cam. They would go so far as to add simulated casting markings.

[rgh0]

Hi Tim,

........Not sure how much power you would get with big valve and FIA compressions.

Regards
Steve

The top end for twin cam power is still around the 190 hp in a 1600cc engine that Hart achieved and its done with valve sizes and porting very similar to what was developed back then . You can do it more reliably these days thats all. Some people claim to have built the mythical 200hp 1600cc twincam so maybe its possible.

cheers
Rohan

[nmauduit]

Hi Tim,
I understand this is all down to the compression, so obviously a lot more than 12:1, need special fuel and rebuilding frequently.

going from 11:1 to 12:1 will only get you a few percent extra power, so it's not only about Compression Ratio



and the consequences very high CR entails are painful, as you mention (high octane fuel to avoid detonation and catastrophic engine failure).

One aspect to ponder in an engine preparation is the target rev range, and as discussed above it is one thing to get a very high power at one single point of a peaky curve (probably widely overlappping cams, tuned exhaust, possibly carb trumpets etc) and it is an other to get a high and wide power band.

[ecamiel]

Early "small port" Hart motors were very reliable and not particularly fragile. Later when they were opened up and run at 9,000 + rpm, they were indeed handgrenades.
Mine was an early small port race motor which after I converted the Elan to the street, I detuned in steps to be streetable. Of course "streetable" is a very subjective term. I did drive it for a while on the street in full race mode and it was generally OK except getting caught in traffic was a disaster. There was basically nothing below 4,500.

[i] "The engine would have been very difficult to drive on the street, as it was high revving and required a high rpm to get it moving from a standing start."/i]

Getting off the line, particularly uphill, used up a lot of clutch before I experimented with cam timing and changed cams, in steps, from .500 to .440 and now .420 lift. The .500 was designed for a 900 lb formula car and the .440 was actually faster on most tracks with a broader torque curve that fit the 1,650 pound (wet with driver) 4 speed Elan.
I too find it amazing that people are able 180 + HP with such broad torque curves.
Eric
64 Elan S1 Hart

[Davidb]

My experience with a Hart 416B was pretty well what others have described. The block was found to be so badly cracked when I bought it-#3 bearing web was breaking out of the block. I got another good block and gave both to a machine shop with orders to exactly copy what Hart had done on the new block. That may have been a mistake! I had 13.5:1 compression (at least) and although the engine was very powerful it was also very fragile. I finally burnt a piston and in the rush to get it ready for the Monterey Historics I fitted a set of Cosworth pistons in place of the original, highly peaked, Mahle. The engine seemed to feel no less powerful but ran cooler and more reliably ...

The new camshaft designs seem to be they biggest reason for so much power in "streetable" engines now--presumably due to computer modelling?

[1owner69Elan]

Just to add a short comment on streetable, high horsepower twin cams.

My engine basically follows the "formula" as outlined by Rohan with a couple of other points to mention:

1. My engine only has Weber 40's with 32mm chokes, 10.25 CR running on pump gas (91 octane (R+M)/2 ) as opposed to Weber 45's and larger chokes as well as higher octane fuel. Presumably the smaller Webers provide a more tractable, responsive, streetable character. Even with the smaller carbs, as shown in the dyno sheet, the engine does not run out of breath up to my 7K redline. Perhaps a testament to the new SAS head and the builder's (Dave Vegher) expertise and head prep.

2. A custom, large volume airbox was fitted. The standard airbox robbed 7 hp on the dyno.

My dyno sheet (apologies, has been posted before):

The broad and low end torque (including below 4000, not shown on the dyno sheet) allows the car to be driven easily in traffic and from standing starts. Also, no need for a close ratio transmission to extract performance.

[RichardHawkins]

Gentlemen,

Does electronic control of ignition and fuel injection make a contribution that was not previously available?

Richard Hawkins

[Lotus14S2]

Thanks to all of you for the enlightening information. It is interesting to see how the engines have changed. But I did notice, you had to buy all kinds of very expensive after market parts in order to obtain that high output.
I do think, though, that I?m glad I got out of it when I did.
My S1 Elan has a pretty much stock engine, and to tell the truth for running around on the road, it is just fine.
In my racing days, I had a great time, and was surrounded by some wonderful people. It was a fraternity and the people were always helpful. One fellow loaned me an engine for a race when mine broke, I doubt that would be the case today. You could run a weekend of racing for about $500 to $700 including travel and lodging.
I bought a factory Vegantune 1600 Twin Cam for about $2500 including shipping from England; I doubt you could pay that, just for shipping today. In fact I would think that an equivalent engine today would cost more than my whole race kit?far more.
I ran everything from production sports cars, formula cars, to sports racers, on a salary, and without breaking the bank. I ended my career running two Formula Fords, as they were great fun and the completion was terrific. The cost was low also; I bought a Lucas Gold Star for about $1200. Now the bare block probably costs more. I remember running a race at Riverside where 140 Formula Fords showed up, and they had to add another race to the program so they could run two 40 car grids; you felt you accomplished something just getting on the grid.
Besides my two Lotus street cars I still have a Merlyn Mk.4A and a Rochdale bodied Austin 7, which won in an endurance race at Silverstone in the ?50s. The racers are left over from my vintage racing days.
I leave the 200 HP engines to the current crop of hot dogs.
Thanks again,
Tim
'62 Elite
'63 Elan

[1owner69Elan]

We are talking about road cars. My upgraded Elan with all the tweaks certainly cost less than a new sports car of similar performance. At least that?s what I tell my wife when she asks how much I have spent! I?d rather tool around in my uprated relatively rare historic vehicle than some new thing. Consistent with my own vintage age!

I would note that the Vegantune TwinCam that you purchased back in the day for $2500 would cost ~$16k in today?s dollars. In the same neighborhood of a high quality TwinCam rebuild today.

[rgh0]

Thanks to all of you for the enlightening information. It is interesting to see how the engines have changed. But I did notice, you had to buy all kinds of very expensive after market parts in order to obtain that high output................
I
Tim
'62 Elite
'63 Elan

You can get most of the increase to the 170 - 180 hp level for a road engine for not much more cost than a full rebuild to standard specification. You can get around 160 hp from a ported standard head at 6500 rpm, and big capacity bottom end at 6500 rpm. The last 20 hp to the 180 hp level is where it gets expensive.

cheers
Rohan

[awatkins]

One-owner ?

Would you please elaborate on the design of the high volume airbox that gained 7 bhp? Any pictures?

[Slowtus]

Every time I see threads like this I tend to smile and somewhat disregard the numbers being flung around unless said numbers are accompanied by a dyno printout - which dyno is known to be properly calibrated and operated.

This is the price I gladly pay for being a cynic.