Fiat 124AC Race engine prep

[Melvin]

I am preparing an early 124AC (1438cc engine) for the UK HSCC Historic Road Sports series.

Regs as follows:
Block - standard, main caps std but can uprate bolts.
Crank and rods - to original design, size, weight, configuration of plane and same number and position of balance weights. Rod section as original design, can uprate rod bolts. Stone polishing and balancing permitted - no titanium or other exotic materials.
The engine must be the original make, type, material, stroke and bore (80mm x 71.5mm) (allowed 0.040" oversize) and date from period.
Ignition - as original including distributor.
Lubrication - as original but can fit oil cooler.
Cooling - as original but can increase rad core capacity (not alloy rad).
Induction - as original (Weber 26/34 DHSA) jet and needle sizes free.
Cams free, valves free but material as available in period.
Exhaust free (inc tubular manifold) but must be road legal.

Having done a couple of races with the standard untouched engine it is distinctly lacking in power (85 bhp on the dyno - the book figures for the std 124AC are 96BHP and 82.5 ft/lb). It also runs out of steam at about 5,800 and won't rev much over 6,200.

The target is to have a free reving engine (up to 7,500?) with around 120-125 bhp with the following mods. Fully balanced, ARP rod bolts, head bolts, big-end bolts etc. 10.5:1 pistons?, block relinered (bad scoring so it needs to be done), Total Seal rings, poss larger valves?, race profile cams, head ported/flowed, inlet manifold worked and port matched, 4-1 exhaust manifold, uprated oil pump? lightened flywheel, clutch etc.

Has anyone worked a 1438cc 142AC engine within these parameters and can you offer any advice / shopping list.
Many thanks

[Guy Croft]

Hullo Melvin, thanks for joining and posting as we discussed.

I have indicated below what I would do with the 124 AC 1438 within those regs. Based on my ideas the power it gives will depend on the cams and exhaust - all things being equal, but your target is not unrealistic.
The only thing I'd say in respect of your plans is ARP rod bolts (if aval) are not needed, the old rod bolts are not highly stressed in an ex-road unit, if they torque up on rebuild they will not likely break anywhere in the rpm range you're going to be using (say to 7500 to 8000).

SINGLE CARB SPEC 124 SPORT AC 1438 RACE UNIT

NEW COOLANT GALLERY CORE PLUGS
BLOCK REFACE
REBORE/SLEEVE AND MICRO-HONE TO FORGED PISTONS 9.8/1 APPR
FORGED PISTONS PRESS-FIT TO 80.40MM BORE
CRANK POLISH OR GRIND DEPENDENING ON CONDITION
CRANK GALLERIES CLEAN TAP, PLUG
MODIFY CRANK OILWAYS
RODS RESIZE IF OUT OF ROUND ONLY, DRESS TO REFIT
REFACE AND LIGHTEN FLYWHEEL
BALANCE CRANK FW
BEARINGS MAIN
BEARINGS ROD
BEARING THRUST
UPRATED ORGANIC COMPETITION CLUTCH
HEAD REFACE
ALLOY-BRONZE RACE VALVE GUIDES
VALVE SEAT S REGRIND TO RACE SPEC
FULL GAS-FLOW HEAD AND INLET MANIFOLD
REJET CARB, FIT RADIUSED RAMPIPES WITH K&N RACE FILTER AND FULLY ENCLOSED INTAKE DUCT (TO CAR FRONT)
IN VALVES REGRIND AND MODIFY IF FIT FOR OVERHAUL
EX VALVES RENEW OE SPEC
RACE VALVE SPRINGS
‚¾ PAT CAMBELT
ADJUSTABLE CAMWHEELS
COMPETITION BILLET CAMS AROUND 10-10.5MM LIFT
OIL PUMP OVERHAUL AND REBUILD
NEW WATER PUMP
KENLOWE RADIATOR FAN (GET RID OF ELECTROMAG VERSION IF FITTED)
BAFFLE SUMP - OR USE ACCUMULATOR WITH REMOTE FILTER, COOLER
FULL ENG GASKETS/SEALS
HEAD BOLTS RACE
FW BOLTS OE 10MM
74 DEG IN-HEAD STAT
NEW CRANK END BRG
NEW BELT TENSIONER BEARING

I hope this is useful in the first instance, sorry for delay, feeling a bit 'under the weather' today, a cold still trying to get me I think.

GC

[Melvin]

Guy
Many thanks for that - all really useful advice. We're used to working on the Jaguar XK engines here with most of the same basic principals but it is interesting to see the differences - lower compression ratio than I'd expect and the inherent quality of the Fiat OE parts that we would normally expect to upgrade on a Jaguar Race engine.
When the engine is fully washed off and cheked over I'll get back to you with my 'wish' list.
Best regards

[vandor]

Melvin,

Your car must be a US spec car if it uses a Weber 26/34 DHSA.
In 1990 the Italian car magazine Quattroruote profiled the 124 'AS' Spider as a "Future Classic". In the specification they listed the carb as a 34DFH3. I assume the Euro model coupe would have had the same carb (usually with Fiat 'Sports' models the Spiders and Coupes have the same engines).
If you can find proof of this then you could use a 34/34 carb, which I'm sure would help power.
Good luck,

Csaba

[Melvin]

Hi Guy

An update on the 124AC 1438 engine build as discussed.

Basic spec as follows:
Head - GC flowed and reworked
Standard size valves (GC worked)
Uprated vernier cam gears and belt (GC)
GC design forged pistons, rods, cams etc.
Block - bored, decked and line checked (Chesman Engineering)
Crank - reground & balanced (Chesman), oilways keyholed (GC tech tip)
Sump - boxed and baffled (in-house based on GC tech tip)
Oil pump rebuilt (GC)
Standard steel radiator and water pump
Mocal oil cooler
Flywheel lightened (Chesman)
Helix clutch
Weber downdraft carburettor on standard 124 inlet manifold (GC flowed but surprisingly good flow characteristics from std factory finish)
Matched length tubular exhaust manifold with straight through system and single silencer box.

The engine was blue printed and built in-house by our mechanic (Barry Burgess). It was completed and fitted at the end of March, run in on the road for 500 miles and dyno¢ž¢d in time for track testing and the first race in April. The exhaust manifold was fitted after the first race and the car re-dyno¢ž¢d (another 6bhp). Attached results are the final figures.
140bhp @ 7,340
120ft/lb @ 5,500
We have had pretty consistent results from this rolling road with engines dyno¢ž¢d elsewhere, fitted and then retested here with very similar figures - I don¢ž¢t think we¢ž¢re being too optimistic with the results!
The engine revs freely to 8,000 (probably nearer to 8,500 when the red mist comes down as I haven¢ž¢t yet fitted an accurate rev-counter - next job?)

I have now completed the first 4 races of the season (HSCC - Historic Road Sports) and also a couple of our track days at Goodwood for my own practice.
Donnington - 19/27 (3rd in class)
Cadwell - 12/17 (3rd in class)
Silverstone - 20/29 (1st in class)
Snetterton - 16/27 (2nd in class)
I am in the steel bodied 2ltr class, up against the 2ltr Porsches and 1750 Alfas so not too bad results for a little 1438cc Sports Coupe.

On-going development included suspension tweaks and driver bravery, I don¢ž¢t think there is too much more to come from the engine without making it unreliable.
I will post some pics of the engine bay shortly and try to find some of the engine build.
Best regards and very many thanks for all your help Guy
Melvin

[sumplug]

Excellent, well done.
Iam wondering if you could stroke the engine out to 1608cc to improve torque. You could class your car as a 124 1600? I think then, you would have class wins much easier!
Amazing, that the twin cam is still Giant Killing after all these years!!

Andy.

[FIAT125T]

Do you have any pics of this wee beastie? The AC is such a nice looking car. Also just a query, what compression pistons did you end up using? The end figure of 140hp is a really great result especially on the standard carb set up. well done.

[Melvin]

Hi Guy
Sorry I haven¢ž¢t posted the pics of the car or engine bay yet (it really does exist‚¦. honest!).
Just to update you.
We took the car to the Spa Six Hour meeting last weekend - fantastic event for those motorsport enthusiasts. I raced it in the 2 x ‚½ hour HSCC races and the 1 hour Bitish Sports, GT and Saloon Challenge. Total of 4 hours race driving with the free practice and qualifying.

I managed a best time of 3:25 with consistent 3:27/28¢ž¢s - as long as you weren¢ž¢t baulked at Eau Rouge you could just about take it flat which would slingshot you up the top straight to the heady terminal speed of 160K (100+mph) - it really feels uphill in the Fiat. By then most of the rest of the cars have gone past but you get your own back down the hill (Chris who co-drove me (best time 3:27 in the Fiat, 3:15 in a Jaguar XK) came in grinning after his session in the Fiat saying he¢ž¢d just overtaken a Chevron round Pouhon).

Great weekend and met a couple of Fiat enthusiasts. Last race is the Championship finals 20th October at Silverstone - currently lying 3rd in class and 9th overall in the championship.

I¢ž¢ll make sure the pics get posted as soon as I get some spare time.
Best regards
Melvin