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#251 SJ Lambert

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Posted 11 November 2014 - 11:49

These days the big engined cars run with the twin cams as long as they don't run wings - last weekend Peter Strauss's BT 31 (ANF1) ran as a Group O entrant with 2.5 RB V8, Bill Hemming ran with the open wheeler Group Os in his Elfin Type 400 (4.4 RB V8) listed as an O Sports. There were even a few Group O entrants listed with 1970 manufacture dates.......... Never have had the run on rule explained to me....... Not that that's necessarily what's going on with the 1970 built cars....

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#252 Ray Bell

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Posted 11 November 2014 - 12:42

But what about capacity distinctions?

Are there none?

#253 Bandola

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Posted 11 November 2014 - 20:02

The CAMS historic groups make no distinction between racecars of different capacities. They just have to have been raced in the stipulated periods and meet the group description.

 

The run-on rules allows a car built/raced after the end of a group period but of exactly the same type and specification of the car  originally built in period to be classified as of that group. eg the Brabham BT29 was built from 1968 to 1970 but 1970 versions can be classified in Group O so long as they are of the same specification as those built up to 1969. 

 

This is the general description of Group O from the CAMS Manual:

 

 

Group O

HISTORIC RACING & SPORTS RACING CARS (1966-1969)

The classification of vehicles within this group will be at the absolute discretion of CAMS. This group is intended to cater for racing, sports racing and sports cars with a competition history

established in the period between 1 January 1966 and 31 December 1969, excluding vehicles fitted with aerodynamic devices as defined under “specific requirements” below. Formula Vee, Formula Ford, Sports Sedans and Formula 5000 cars are also specifically excluded from this group which is intended to reflect the development of wide treaded racing tyre technology and its effect on suspension and chassis design but stopping short of the period when external aerodynamic devices became a major design feature with a significant impact on cornering performance.

Consideration may also be given to the classification within this group of vehicles constructed between 1 January 1966 and 31 December 1969 but with a competition history established subsequent to 31 December 1969, or in some cases without a competition history, provided that the specification of the vehicle is consistent with the general standard of technology evident in vehicles raced during the group period and the vehicle is compatible in appearance with such vehicles.

 

CAMS doesn't record lap records. These are generally recorded by the track owner or the clubs running the meetings and they can distinguish between different capacities and car types if they wish.



#254 SJ Lambert

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Posted 12 November 2014 - 20:33

image.jpg

Geoff Vary running the ex Brian Lear 6550 for the first? time.

Edited by SJ Lambert, 14 November 2014 - 10:03.


#255 Ray Bell

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Posted 14 November 2014 - 14:13

It didn't have the radiator exhausts when built, did it James?

It just doesn't seem right that Brian is no longer the owner/driver, but time marches on and cars change hands...

#256 SJ Lambert

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Posted 15 November 2014 - 12:52

I think it did actually Ray, I seem to recall seeing a shot of Norm Butler attending to the car with Garrie in the cockpit when new. As it is the Mk2 prototype and Garrie's personal car I presume it was the first to get that bodywork upgrade - even though at least one later car (ours) was fitted with a non vented nose.

Squared off engine covers came later again.

Yes, seeing that car, one automatically recognises it as Brian's, I had a chat to Geoff - he's a nice bloke, loves the car & must have got the thumbs up from Brian!

#257 SJ Lambert

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Posted 07 December 2014 - 11:12

I see Chuck Krueger diligently went about amassing a reasonable point tally in the North East Division SCCA Formula B standings of 1967 in our 6653 chassis.

http://www.oldracing.../fb/1967/nediv/

#258 SJ Lambert

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Posted 21 December 2014 - 09:41

Bright work is bright again for 6653

image.jpg

#259 SJ Lambert

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Posted 21 December 2014 - 10:17

A close inspection of 6653's steering rack reveals it to be a "quick rack", we'd assumed it was a standard one as it's in a steel body, it's insides contain the magnesium bearings & all the good stuff. Most of the quick racks were in magnesium bodies.

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#260 Ray Bell

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Posted 21 December 2014 - 12:03

The prototype, perhaps?

Or was Garrie on an economy drive?

#261 SJ Lambert

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Posted 21 December 2014 - 17:36

Likely a prototype, the first magnesium body was made from " bar stock", then after that they were cast off a pattern.

#262 GMACKIE

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Posted 21 December 2014 - 20:50

Bright work is bright again for 6653

image.jpg

Hope it has all been heat-treated....don't want any 'hydrogen embrittlement'.



#263 SJ Lambert

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Posted 21 December 2014 - 23:13

That would be a disaster! Fingers crossed that it's been done right!!!!

#264 SJ Lambert

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Posted 31 December 2014 - 12:24

Early shot of Bob Jane at The Farm

 

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#265 SJ Lambert

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Posted 31 December 2014 - 12:30

Ian Smith's shot of Jack Humnam at Winton in 68. 

 

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#266 SJ Lambert

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Posted 08 January 2015 - 19:51

Finished sealing the tub on 6653 yesterday, next job will be engine assembly.


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#267 SJ Lambert

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Posted 11 January 2015 - 20:50

Here's a clip of the slosh sealing process

https://m.youtube.co...eature=youtu.be

#268 SJ Lambert

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Posted 19 January 2015 - 12:51

The pistons for the purpose built motor have had a shave, I've pipetted everything in sight & come up with the following -

with combustion chamber at 40.5, above ring volume 0.63, volume above piston deck @tdc 0.15 a head gasket at 1.5mm compressed by 30% giving 5.68 and intruder volume of 14.6 I get clearance volume (46.96 - 14.6) of 32.36.

So with swept volume 379.52 I get compression ratio of 12.73!

It appears as though I'm 0.6cc away from a 12.5 : 1 ratio.

#269 SJ Lambert

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Posted 19 January 2015 - 13:00

My Twin Cam guru has advised me to check the valve to piston clearances on overlap before taking anything more off just in case I may need to deepen the pockets a little.

image.jpg

Edited by SJ Lambert, 19 January 2015 - 13:04.


#270 Bandola

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Posted 19 January 2015 - 19:54

Where did you get the pistons, James? Just had the frost plug come out of the twincam in my Lotus 41 resulting in a cooked engine so might need some new pistons.



#271 SJ Lambert

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Posted 19 January 2015 - 22:31

image.jpg


Pistons are CP, rods are Carrillo. Hope the 41's have survived intact.

#272 Ray Bell

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Posted 19 January 2015 - 22:41

Yes, James, with those engines clearances get really tight...

Watch how close your valve clearances are (valve head to valve head) as they pass each other too.

#273 Bandola

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Posted 20 January 2015 - 00:25

Thanks James. Have taken the head off and the head gasket is well and truly destroyed but pistons/head/block look OK. Will strip the engine down completely to check that there is no damage lower down.

Looking at your pistons and with the clearances you quote it would need some serious cam lift at TDC for the pockets to need deepening. My cam lifts .200+ inch at TDC with plenty clearance but found pocket width to be more of an issue.Good luck with it.



#274 SJ Lambert

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Posted 20 January 2015 - 03:18

I'm putting Omnitech 510 & 480 cams into one of John McCoy's stage 4 heads. I reckon it'll go together well, but I'm gonna check everything!

#275 Paul Hamilton

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Posted 20 January 2015 - 23:31

The pistons for the purpose built motor have had a shave, I've pipetted everything in sight & come up with the following -

with combustion chamber at 40.5, above ring volume 0.63, volume above piston deck @tdc 0.15 a head gasket at 1.5mm compressed by 30% giving 5.68 and intruder volume of 14.6 I get clearance volume (46.96 - 14.6) of 32.36.

So with swept volume 379.52 I get compression ratio of 12.73!

It appears as though I'm 0.6cc away from a 12.5 : 1 ratio.

 

That looks about right, James.

 

My no.1 engine is running a 12.8:1 comp ratio with a smaller intruder on the piston and a chamber volume of 38.6ml.  My valve sizes are 42.14 inlet and 39.56 exhaust and I am using Wade 160 B and C cams in that engine which are claimed to be Hart equivalents.  The performance both on the dyno and in the car is pretty much on par with my old Hart engine which is now the spare after a very long and active life. 

 

The secret to top twin cam performance is all in the cylinder head!!  Valve timing, valve sizes, comp ratio, combustion chamber  and porting.  Its a tricky combination to get right as there are clearance problems to address when you stretch it at the margins and some compromises to accept.



#276 SJ Lambert

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Posted 21 January 2015 - 09:26

The head I'm using started life as a Stromberg one, it's been attacked fairly vigorously by a milling machine, so I'll start my checks by establishing that the cams spin freely in new bearings before I do a clearance check.

 image.jpgimage.jpg



I haven't done any comparitive calculations (based on a hypothetical larger displacement) (I don't want to confuse myself!!!) to determine why my intruder is seemingly on the high side, but I presume that as my cylinder head supplier has optimised his ports/chambers/cams for 1600 cc (& bigger) engines, mine running as an ANF1.5 (1518cc) does have a bit of a hole to fill to get the compression ratio back up.

There may be precedent for Elfins running Carrillo rods too, Al Bartz put Fred's rods into his good Chevy motors, so there's every chance the ME5 ran them


Edited by SJ Lambert, 21 January 2015 - 09:34.


#277 Ray Bell

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Posted 21 January 2015 - 10:00

And the 400 before it, most likely...

Possibly even with the 5.0 Olds in it.

#278 SJ Lambert

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Posted 22 January 2015 - 09:07

Even Tony Ingram (Ginetta, Lotus 7 & Twin Cam man in So Cal) commented on the size of my intruder! So I've weakened and if I redo the sums based on a larger swept volume without altering anything else then the intruder as it is on a 1600 cc engine would give a compression ratio of 13.36 and same set up on a 1650cc engine would give 13.75 : 1 compression ratio. Feel free ( anyone !) to correct me if I'm barking up the wrong tree / barking down the wrong cylinders!!

#279 SJ Lambert

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Posted 22 January 2015 - 13:29

P1100135.jpg
 

 

I reckon this head's running smaller exhaust valves than yours Paul - I think John McCoy looks to deliberately choke the 'em on the way out - I don't know what your Wade cams are doing either - John's are relatively short on duration compared to the Hart ones - I suspect these ones have every bit as much lift as any though - the springs that are available today make the job easier.



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#280 Ray Bell

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Posted 22 January 2015 - 14:27

Your figures look fine, James...

And the head modifications, too.