Limit of stock parts

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Limit of stock parts

Post by cheaperthantherapy » Sun Nov 30, 2014 4:05 pm

Hi All,

I am working on a low budget performance motor (oxymoron acknowledged).

The plan is for forced induction on an '83 2L with custom injection. I am aiming
a 225 Hp with 200Ftlbs at 6500 rpm.

I plan to use high quality new bearings, rings, enhanced oil pump, oil cooler
with high quality head studs and multi layer head gasket. A performance clutch
is in the works.

Currently I plan to use the low millage factory low compression pistons and rods
with approximately 14Lbs of boost.

The question for you racer types is how strong are the basic stock parts of the
Fiat engine. How far have you taken the crank, rods, rod bolts, valves, valve
springs etc in racing environment.

As I have finally damaged my current engine i have a great excuse to finally
build my engine i have been planning forever.

Any and all experiences much appreciated.

Best regards,

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Re: Limit of stock parts

Post by vandor » Wed Dec 03, 2014 12:27 am


You might get better answers at, but I don't know anyone who has
taken stock pistons and rods to that power level.
I am assuming you will use some non-Fiat drive train? Neither the 124 trans or
rear end will handle that kind of power.

'71 124 Spider, much modified
'67 850 Coupe, gone
'71 124 Spider, much modified
'72 124 Coupe, new project, ex-Pete, ex-Eli, ex-Jack car (all Mira members)
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Re: Limit of stock parts

Post by fp55scca » Wed Dec 03, 2014 8:50 pm

--Jordan, interesting project! What is your plan for head preparation and
configuration? Even with forced induction, the key to Hp and Tq in these
motors is still in the head. Any chance you have access to Guy Croft's book?
He has a pretty good chapter on this, and a lot of recommendations on the
durability of various engine components.

--The crankshaft on the 2L is the best of the TC motors, as they are forged
steel and nitride from the factory. If your crank journals are damaged, don't
regrind, get another 2L crank and just polish the journals. But first, the
crank must be cleaned properly by removing the welch plugs and probing the oil
journals to remove the sludge. After cleaning, tap the plug holes and insert
1/8 NPT plugs with Loctite.

--2L rods are robust, but I wouldn't trust 40 year old rod bolts. The only
failure I ever had on a stock rod (lightened, shot peened and polished)
running routinely to 9000 rpm was a failed rod bolt, and that was an 1800 rod.
2L rod bolts are stronger, but I wouldn't trust them. I replaced stock rod
bolts with ARP bolts for a 351 Cleveland engine, but eventually just bit the
bullet and bought some Crower rods. (which I recommend).

--If running only to 6500 rpm, you could use a cast piston, but can't say I
would for the Hp you intend. A set of forged pistons is recommended.

--I would replace the stock valves with stainless steel valves available
from the vendors. They are more durable, are slightly larger in diameter, and
have a little longer stem to keep valve shim sizes down. Performance valve
springs are recommended. What cams are you planning?

--Stock oil pump is more than sufficient, but if you plan to routinely run
high rpms, you'll need to open the ports on the drainbacks in the camboxes,
usually by drilling a couple of 3/8" holes about 1/2" below the stock
drainback port. Some recommend restricting the oil journals to the head.
I've never done it, nor did John Baucom, a 3 time national SCCA champion.

--Jordan, as Csaba noted, if you achieve the power you are aiming for,
you'll need some significant modifications to the driveline. The bottom line
is I don't think this is a low budget project. My recommendation is to dial
back engine output to about 180Hp to keep project costs down. You'll have
just as much fun and you won't break things.


72 Spider - owned since July '73
74 Spider - CSA project/daily driver
72 Spider - SCCA FP 24
68 Spider - parts car
Jim Scurria
Norfolk, VA

1972 Fiat 124 Spider
1971 Spider - SCCA FP-24
1974 Fiat 124 Spider
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Re: Limit of stock parts

Post by cheaperthantherapy » Fri Dec 05, 2014 1:33 am


Thanks for the thoughts. I can't wait for my box of parts from you guys!

The T124 guys are mostly Ausies and Kiwis so have limited experience with US
spec spiders. Please see drive line notes below.


Thanks! Exactly the kind of information I am after.

Dialing back the target power to 180 may the best scenario as it fits with my
slow evolutionary development path. Current drive line will be stock with a
sympathetic driver. Power used for climbing hills, carving corners and passing
instead of drifting.

Head. Fairly limited development planned at this time. Gasket matched ports, 3
angle grind, bronze guides and silicone seals. I am still trying to figure out
the valves. I will look at the SS valves as you recommend.

Cams. First thought will be standard '81 FI cams with adjustable cam wheels. I
have read that a 1608(?) exhaust cam is a good idea for forced induction. Any
insight into this?

I have NOS oil pump on the way and was going to increase the spring rate to
increase oil pressure. Mostly I am doing this as I will add an oil cooler.
Thoughts appreciated.

I will investigate the drain backs in the cam boxes.

Future me is looking at a narrowed Ford 8" for a rear end created by using two
short side axles from a Ranger. Lots of ratios available and several LSD

Transmission is an unknown as 131 trans are hard to find and the 124 unit has a
reputation for fragility. I have read that a T5 can be made to fit and I will
consider this if required. Worst case I have another 124 transmission in the
garage if I break my current one. It seems that people race with the 124 unit.

Do you have an opinion on the value of adding a cast pan to the 124
transmission? Extra oil capacity, cooling capacity and some structural rigidity
to the case.


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Re: Limit of stock parts

Post by fp55scca » Fri Dec 05, 2014 8:35 pm

Jordan, some thoughts:
--Head- I still believe you would benefit from additional head preparation,
particularly with porting and valve de-shrouding, and of course the larger SS
valves. If you are handy with porting, or know someone who is, you can do a
proper head preparation by carefully following the advice and guidance in Guy
Croft's book. If not, Jon Logan at Midwest 124 Spider does a bang-up job on GC
type head preparation.

--Cams- Volumes have been written on Mirafiori and other web sites
discussing 1608 cams. I believe it is generally agreed that the timing of
these cams (both US and European spec) is 26/66 66/26, but there seems to be a
lot of confusion about the cam profiles. A few guys here at Mirafiori have
measured the US spec 1608 cam lift and profiles, and reported that they are
the same as the US spec 1756cc and 2L cams. I didn't do it myself, so I can
neither confirm nor deny the accuracy. My experience is with much higher lift
and longer duration cams best suited for carbed race engines.

--Oil pump- the stronger spring in an OEM pump is a good choice. Even the
addition of a washer under stock spring is beneficial. Based on your
operational description, an accusump would be a nice addition, but not
essential. I'll try to get you some pics of the drainback modifications.

--Ford 8" rear- Not necessary, unless you are exceeding 180 hp. Some say
150 is the limit, but I disagree, but let me qualify that. My experience with
Hp north of 150 is with the spider gears welded in the diff. In 12 years of
racing, I've broken one differential.

--Transmission- 131 gearboxes are available. You just have to ask around.
Not a difficult addition, but does require a little modification to the
tunnel, and the driveshaft from an automatic Spider. I personally believe the
124 gearbox is very robust if shifted properly, and I can verify that it can
withstand Hp greater than 150 and operate under race conditions. The gearbox
is splash lubricated, so overfilling would not be a benefit. Overheating is
not an issue, so I don't see the value of a cast pan (unless rally racing). I
don't know of any structural issue either, except for the 1438cc belhousing.
One trick for performance is to use the smaller 200mm flywheel with an
enhanced clutch assembly, but this requires the smaller 1438cc bellhousing to
engage the starter. It will break with increased Hp. Don't ask me how I know
this. Whichever setup you use, you will want to install a stronger flex
coupling. Check with Csaba and Ramzi for this.

--Jordan, when you get to the chassis, there are many considerations for
suspension and brakes.

72 Spider - owned since July '73
74 Spider - CSA project/daily driver
72 Spider - SCCA FP 24
68 Spider - parts car
Jim Scurria
Norfolk, VA

1972 Fiat 124 Spider
1971 Spider - SCCA FP-24
1974 Fiat 124 Spider
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Re: Limit of stock parts

Post by cheaperthantherapy » Sat Dec 06, 2014 5:08 pm


First of all. THANK YOU! for the thoughtful and informative responses this is
invaluable to my project planning.

- Head. I have ported a couple of heads but it was really just removing rough
casting and some light polishing. Please see below for my planned steps for head
preparation. I am proceeding under the impression that a Forced induction head
benefits more from heat control and smooth flow that clever shaping intended to
tease the last bit of gas flow out the NA combustion process. i have already
added a couple of steps from your notes. Any additional thoughts are much
appreciated. Question marks denote steps I am still trying to find budget for or
need more information to make an informed choice.

Work to be completed on a NOS '79 2L head.

-New exhaust valves? Larger? SS? which brand?
-single angle valve guide (larger contact area improves cooling?)
-Stock intake valves?
-Silicone valve guide seals
-Bronze valve guides - cut back port?
-2 locating dowels on both intake and exhaust manifold mounting face
-Drain backs enlarged and lowered to minimize storage of oil in the head.
-Oil is fed to the head through six holes. These should be plugged in the head
and redrilled to 1/16" diameter.
-Smooth any sharp edges in combustion chamber.
-Smooth any unused threads in spark plug hole
-Smooth out any rough castings in inlet and outlet ports
-Coatings - exhaust port, exhaust valve face?

-Cams. From your notes and other readings I think I will keep the standard FI
cams and spend the money on the adjustable wheels to adjust timing. Cams can be
changed later in the car if required. Is this a reasonable approach or have I
missed something?

- Oil pump. Washer under the spring it is.

- Rear end. your thoughts and experience are much appreciated. I will run with a
stock rear end until I have a problem and then will have to make a choice. A
well adjusted Spider auto rear end with Phantom Grip would certainly be the
cheapest and easiest if I do break something. In the mean time I will program
down the boost in 1st, 2nd and 3rd and refrain from doing burn outs.

- Transmission. Nice to hear an encouraging word about he 124 box as I truly
enjoy how it feels in the car. Great driving experience. The transmission in my
car appears to have been rebuilt just before it bought it as it was spotless and
had a gleaming new pan on it when I got the car. I will also run this until
crisis. With an empathetic hand i hope it will last a long time. Nice thought on
the stronger guibp. I will reach out to Csaba.

- Chassis. I did some chassis work before chasing power. The car currently has
25m front bar, 15mm rear bar, Koni yellows, IAP red springs, 15" Speedline
wheels, new ball joints, larger disks and Uno turbo calipers. I have an Auto
Power roll bar that I will be installing in the spring as I have heard that they
provide a little rigidity to the body. This winter will also see the replacement
of all front end bushings. Any and all thoughts are much appreciated.

Thanks again and all comments welcome.

Best regards,

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Re: Limit of stock parts

Post by fp55scca » Mon Dec 08, 2014 10:07 am

--Jordan, some additional notes:

--SS exhaust valves: Carried by several of the vendors. Some say they are
custom. I believe they are the same source and quality.

--Single angle valve guide: what is this?

--Silicone valve guide seals: these would be fine. To be honest, I've used
OEM seals without any problems. If you use others, be sure they have a good
tight fit.

--Cut back bronze guides in port: Not recommended. The small benefit to flow
is not worth the rapid wear that the shorter valve guide will yield. GC has
changed his mind on this one as well.

--Restrict oil feeds to head: Not necessary. This was a PBS Engineering
technique many years ago. Not necessary if you drill the drainbacks as I
described above.

--Unused threads in spark plug holes: I don't think there are any? Indexing
the plugs may be a consideration.

--Coatings on exhaust ports and valves: No experience with coating exhaust
ports, but I don't think it's necessary to coat the exhaust valve if you use
the SS valves.

--Cams: see my email.

--Suspension: I would have recommended slightly stronger springs, and delete
the rear swaybar. See my email.

--The Autopower rollbar will add some rigidity to the chassis.

--Depending on your objective for handling and performance, you might consider
poly bushings on the front control arms. The 1" swaybar to the front is the
single best improvement you can make to most Spiders.

72 Spider - owned since July '73
74 Spider - CSA project/daily driver
72 Spider - SCCA FP 24
68 Spider - parts car
Jim Scurria
Norfolk, VA

1972 Fiat 124 Spider
1971 Spider - SCCA FP-24
1974 Fiat 124 Spider
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