Rayhill
08-17-2002, 05:10 AM
Can anyone give me a good recipe for a Twin Turbo 350 chevy. I melted #6 piston and am ready to rebuild. Would like to compare ideas before I get into it.
Spec's on current engine are as follows:
Heads are new World Products 67cc heads (standard
small valve versions with as measured 69cc combustion
chambers - chambers were close to 70cc when received
but I had to slightly mill them in order to true them
up and then I equalized the chambers @ 69cc). Valve
seats were multi-angled cut, and valves were "back
cut" and radiused/polished for increased flow. Valve
bowls were "ported/radiused". Valve size is 1.94"
intakes and 1.5" exhausts. Total calculated
compression ratio is 8.05:1. This is using head vol.
of 69cc, deck hgt. of +.008" (total quench hgt. is
.047" - .045" is considered minimum perfect for turbo
engines), gasket vol. of 9cc (Fel-Pro #1014 .039"
thick head gaskets), TRW forged pistons #L2441F with a
as measured dish vol. of -23.5cc (suppose to be
-21.1cc dish but measured -23.5cc). Bore is 4.030"
diameter and stroke is stock 3.48" = 355cid.
Rings are Childs & Albert Moly High Strength Plasma
coated (dutile iron) with wider 1st & 2nd ring end
gaps for turbo usage (.019" gap).
Complete engine rotating assembly was balanced.
Exhaust manifold gaskets are Fel-Pro with steel core.
Cam is Crane Energizer #10003 (204 deg. duration @
.050" tappet lift & with .427" valve lift. and 110
deg. lobe separation). Cam is normally installed
straight up with 5 deg. advance built in. This cam is
retarded via 8 deg. offset bushing in cam timing chain
sprocket for a total retard of 3 deg. (5 deg. advanced
-8 deg. bushing = 3 deg. retard). Timing chain is a
Cloyes Tru-Roller.
Rockers are 1.52:1 Competition Cams roller tip
rockers.
Ignition timing is 8 deg. initial advance with an
additional 24 degrees in the dist., all in by 2800 RPM
(max. advance is 32 degrees total). Initial timing
can be reduced to 6 deg. initial, but recommend not
going below that. Contrary to popular belief,
retarded timing (for long durations) does reduce
knock, but then it increases combustion chamber temps.
as well which then causes knock to return with a
vengence).
Note my thinking when building up this engine
initially was to increase low end torque (for better
hole shot), and use the turbo's to increase top end.
I know that I overdid this on the low end and this
caused the top end to suffer somewhat, and I told you
about retarding the cam (8 degree retard bushing) to
get back some of the top end. The new cam was the
next step (according to my discussions with the
experts- Gale Banks & Engle Cams), but I never
installed it. It depends upon how you are going to
use the boat (everything is a compromise). If you are
going to ski, tube, etc. and bottom end is more
important, then return the cam timing back to it's
initial setting of 5 deg. advanced (replace the cam
sprocket offset bushing with a "zero" bushing). If
top end speed and high speed cruising is where it will
be operated at, then leave it as is, or replace the
cam with the new one (your choice either way).
Frankly, as it is, I think it is a good compromise
with great performance in all catagories (but we
always want more).
New Engle cam spec is as follows:
#1002H (grind # TCS-2HYD). Duration @ .050" tappet
lift is 216 deg. intake & 210 deg. exhaust. Valve
lift is .458" intake & .440" exhaust. Lobe center is
116 deg. Description per Engle: Turbocharger Hyd.
Camshaft designed for modified engines with 8:1
compression ratio. Power band 2800 to 6000 RPM. This
cam will definately be weaker on the bottom end, but
would wake up the top end considerably!
[ August 17, 2002, 06:30 AM: Message edited by: Rayhill ]
Spec's on current engine are as follows:
Heads are new World Products 67cc heads (standard
small valve versions with as measured 69cc combustion
chambers - chambers were close to 70cc when received
but I had to slightly mill them in order to true them
up and then I equalized the chambers @ 69cc). Valve
seats were multi-angled cut, and valves were "back
cut" and radiused/polished for increased flow. Valve
bowls were "ported/radiused". Valve size is 1.94"
intakes and 1.5" exhausts. Total calculated
compression ratio is 8.05:1. This is using head vol.
of 69cc, deck hgt. of +.008" (total quench hgt. is
.047" - .045" is considered minimum perfect for turbo
engines), gasket vol. of 9cc (Fel-Pro #1014 .039"
thick head gaskets), TRW forged pistons #L2441F with a
as measured dish vol. of -23.5cc (suppose to be
-21.1cc dish but measured -23.5cc). Bore is 4.030"
diameter and stroke is stock 3.48" = 355cid.
Rings are Childs & Albert Moly High Strength Plasma
coated (dutile iron) with wider 1st & 2nd ring end
gaps for turbo usage (.019" gap).
Complete engine rotating assembly was balanced.
Exhaust manifold gaskets are Fel-Pro with steel core.
Cam is Crane Energizer #10003 (204 deg. duration @
.050" tappet lift & with .427" valve lift. and 110
deg. lobe separation). Cam is normally installed
straight up with 5 deg. advance built in. This cam is
retarded via 8 deg. offset bushing in cam timing chain
sprocket for a total retard of 3 deg. (5 deg. advanced
-8 deg. bushing = 3 deg. retard). Timing chain is a
Cloyes Tru-Roller.
Rockers are 1.52:1 Competition Cams roller tip
rockers.
Ignition timing is 8 deg. initial advance with an
additional 24 degrees in the dist., all in by 2800 RPM
(max. advance is 32 degrees total). Initial timing
can be reduced to 6 deg. initial, but recommend not
going below that. Contrary to popular belief,
retarded timing (for long durations) does reduce
knock, but then it increases combustion chamber temps.
as well which then causes knock to return with a
vengence).
Note my thinking when building up this engine
initially was to increase low end torque (for better
hole shot), and use the turbo's to increase top end.
I know that I overdid this on the low end and this
caused the top end to suffer somewhat, and I told you
about retarding the cam (8 degree retard bushing) to
get back some of the top end. The new cam was the
next step (according to my discussions with the
experts- Gale Banks & Engle Cams), but I never
installed it. It depends upon how you are going to
use the boat (everything is a compromise). If you are
going to ski, tube, etc. and bottom end is more
important, then return the cam timing back to it's
initial setting of 5 deg. advanced (replace the cam
sprocket offset bushing with a "zero" bushing). If
top end speed and high speed cruising is where it will
be operated at, then leave it as is, or replace the
cam with the new one (your choice either way).
Frankly, as it is, I think it is a good compromise
with great performance in all catagories (but we
always want more).
New Engle cam spec is as follows:
#1002H (grind # TCS-2HYD). Duration @ .050" tappet
lift is 216 deg. intake & 210 deg. exhaust. Valve
lift is .458" intake & .440" exhaust. Lobe center is
116 deg. Description per Engle: Turbocharger Hyd.
Camshaft designed for modified engines with 8:1
compression ratio. Power band 2800 to 6000 RPM. This
cam will definately be weaker on the bottom end, but
would wake up the top end considerably!
[ August 17, 2002, 06:30 AM: Message edited by: Rayhill ]