[DeTomaso] Converting 358 Cup motor to lower compression

[Arjun Ghosh-Dastidar]

Ron McCall lowered the compression on my '72 wide body car.

The motor started it's life as a 358 cast in 2002 for the Winston Cup
series. After the 2002 series, the engine sat at Roush Yates for 7 years
before being converted from a Cup spec Roush Yates D3 head to a C3 head to
run in the ARCA series in 2010. Luckily for me, the buyer of the engine
backed out of the deal with Roush Yates when his sponsorship fell through
and I bought the engine in 2011.

The engine had a 13:1 compression, ran on 110 octane race gas and put down
730hp at 7,900rpm and 530lb ft. at 6,700rpm on the engine dyno. I got tired of
the hassle of procuring race gas (the closest place was 30 minutes away and
would not allow direct fill to the car since race gas is for "off-road" use
only), so we switched out the pistons for a set of lower compression JE
pistons and less aggressive cams.

The engine now has a 10.39:1 compression and makes 500hp at 7,000rpm and 407lb
ft. at 5,400rpm at the wheels on 93 octane pump gas.

I was a little taken aback by the transmission losses - around 24% (Ron had
an identical motor in his GT40 that put down 660hp on an engine dyno using
the same pistons and cams, so we arrived at the 24% transmission loss
figure based on that). Ron said that this common for the ZF transmission
and that the big wheels probably ate up around 20 whp. A 20+% transmission
loss is high compared to the 10 - 15% loss of Ferrari and Porsche
transmissions. Guess the ZF is starting to show it's age.

All in all, I think this was a good conversion and I would do it again.
What the motor lost in it's manic rush in the top end, it picked up more
and then some in the bottom end. The car is completely tractable at 2,000
rpm whereas previously it would bog and chunter at anything less than 4,000
rpm.

Pic of dyno run attached.
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   Ron McCall lowered the compression on my '72 wide body car.
   The motor started it's life as a 358 cast in 2002 for the Winston Cup
   series. After the 2002 series, the engine sat at Roush Yates for 7
   years before being converted from a Cup spec Roush Yates D3 head to a
   C3 head to run in the ARCA series in 2010. Luckily for me, the buyer of
   the engine backed out of the deal with Roush Yates when his sponsorship
   fell through and I bought the engine in 2011.
   The engine had a 13:1 compression, ran on 110 octane race gas and put
   down 730hp at 7,900rpm and 530lb ft. at 6,700rpm on the engine dyno. I got
   tired of the hassle of procuring race gas (the closest place was 30
   minutes away and would not allow direct fill to the car since race gas
   is for "off-road" use only), so we switched out the pistons for a set
   of lower compression JE pistons and less aggressive cams.
   The engine now has a 10.39:1 compression and makes 500hp at 7,000rpm and
   407lb ft. at 5,400rpm at the wheels on 93 octane pump gas.A
   I was a little taken aback by the transmission losses - around 24% (Ron
   had an identical motor in his GT40 that put down 660hp on an engine
   dyno using the same pistons and cams, so we arrived at the 24%
   transmission loss figure based on that). Ron said that this common for
   the ZF transmission and that the big wheels probably ate up around 20
   whp. A 20+% transmission loss is high compared to the 10 - 15% loss of
   Ferrari and Porsche transmissions. Guess the ZF is starting to show
   it's age.
   All in all, I think this was a good conversion and I would do it again.
   What the motor lost in it's manic rush in the top end, it picked up
   more and then some in the bottom end. The car is completely tractable
   at 2,000 rpm whereas previously it would bog and chunter at anything
   less than 4,000 rpm.
   Pic of dyno run attached.
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