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Old 04-20-2012, 07:02 AM
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SBC 388 S/C Weiand 177 Help in Tuning

Hello, I'M Mauricio from chile and i have problems tuning my engine, ok let's describe engine:

Chevrolet 388, 3.75 Stroke, 6" Rod, Je Pistons -28cc dished 0.60 , Edelbrock Performance cylinder head 70cc (i will check it), Clevite 77 tri metal bearings, Weiando 177 at 5psi, 3" free Exhaust per head, Holley Avenger EFI TBI 900cfm,
Crane Cams CRN-119661 camshaft, Mechanical advance distributor with MSD 6AL, i spin it at 6000rpm redline, i have wideband and pyrometer but doesn't get it right tuning because my EGT get very high over 1500 °F, i use 10:1 A/Fr (Maybe too rich?, but i melt pistons couple of time and i don't want it to happend again), timing 32-34° at 2600rpm (maybe too much?), i have a Water Methanol kit controlled by the Holley Avenger but i don't know how much % of Meth/wather against fuel i must throw inside.

Any tips will be apreciated

pd: Sorry for English

edit: i have like 7.9 8.0 compression ratio, maybe it's to low for 5psi?, i dont want more than 5psi, also all my rotating assembly is Forged, and i'm attatched to a th400

Mauricio

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Old 04-20-2012, 09:30 AM
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You should not be burning up the motor at 5 psi and 8:1 cr.

The real cr may be higher than you think.
I get 8.5 to 8.8 w a 0 dech height depending on the head volume.

If the pump gas you are using is low octane less than 92 R+M/2 or 98 RON
"premimum unleaded" ( European rated), that is going to be an issue.
I would start by locking the timing at 28deg BTDC
Lock the timing so there is no advance 28deg BTDC full time.
after verifying chamber volume and true TDC.

I cannot help you with tuning the EFI fuel curve.
I'm a carb guy.

The water methanol can be up to 30 % of the total fuel volume at WOT
use a 50-50 mix water to methanol.

The afr meter may be reading wrong.
The EFI may be fuel limited at high rpm
(pump, lines filter, reguator. injectors toped out.)

I would get the thing to run correctly on high octane 110 unleaded, then retune for pump gas and water methanol injection.

Again 5psi should not be hurting parts. Something is not right.
I suspect its a fuel octane issue. And the cr is higher than 8:1. (64ish CC cylinder heads and or pistons are not -28cc dish)

If the real cr is more than 8:1 you must use less spark advance
to avoid detonation (28deg BTDC)
If the fuel is less than 92 octane (R+M/2) it ain;t going to work

Get some good high octane race gas and try it.

Why are you not using a carb? much simpler.

Last edited by F-BIRD'88; 04-20-2012 at 09:37 AM.
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Old 04-20-2012, 09:37 AM
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i have 97 octanes RON, i know how to tune the efi, im running 10:1 10.5:1 intentionally, is too much?, im worry about the HIGH EGT issue, i will try the 28° , i dont use a carb because is an engine for hillclimb and a carb quench

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Old 04-20-2012, 09:43 AM
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Quote:
Originally Posted by TJ555
i have 97 octanes RON, i know how to tune the efi, im running 10:1 10.5:1 intentionally, is too much?, im worry about the HIGH EGT issue, i will try the 28° , i dont use a carb because is an engine for hillclimb and a carb quench

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10:1 afr is more than the motor needs but you must give it all the fuel it wants to stay cool under boost.

if that is the true AFR, its plenty rich.
I would check the real fuel octane quality and real cr.
Is the cam over advanced in the motor?
Pistons and or heads are not to spec.
The exhaust temps are going to be high(er) with a over rich or over lean AFR
(It does put stress on the exhaust valves under extended WOT under boost.
How long is the motor working at WOT high boost? ( up the hill)

Why not just run the whole thing on methanol or ethanol?

Last edited by F-BIRD'88; 04-20-2012 at 09:50 AM.
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Old 04-20-2012, 09:49 AM
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Fuel is 97 OCT, i will cubicate cylinder heads cc, the cam isn't advanced (should I?, i have the timing set that allows it, but is at 0°), the engine works almost always at heavy load, there are long hills like, longest maybe 2-3 minutes WOT Full Load
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Old 04-20-2012, 10:00 AM
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The cam should be installed normally, without you having to move it.
It should check to the crane cam card specs +/- 1°

112 LSA 108 in C/L 116 ex C/L is normal for this cam.

That cam: the intake closing point checked @.050" should be 42°ABDC +/- 1°.

Everything looks like crap gas and or higher cr.

With a true 8:1 cr and good gas and water methanol you should be able to run 10psi boost easily. (2.38:1 blower drive ratio) all day long.

what is the blower pulley drive ratio?
This engine should not even be breaking a sweat @ 5PSI.

Last edited by F-BIRD'88; 04-20-2012 at 10:17 AM.
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Old 04-20-2012, 10:23 AM
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i think i run 2.33, but my boost gauge read 5-5.5 at full load,
cam sheet http://www.cranecams.com/product/car...detail&p=24188, i will check real CR
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Old 04-20-2012, 10:39 AM
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Quote:
Originally Posted by TJ555
i think i run 2.33, but my boost gauge read 5-5.5 at full load,
cam sheet http://www.cranecams.com/product/car...detail&p=24188, i will check real CR
At 2.33:1 drive ratio on the 177 blower you should be getting 9 to 11PSI boost

AT 2.33 drive ratio the real cr must be 8:1 or less
especially for extended WOT running under boost.
(or run race gas)

You are driving the motor pretty hard with a 2.33:1 ratio.
It will need much better than 92 octane fuel @34deg timing

Your boost gauge is wacked if the drive ratio is 2.33:1.

Either reduce the pulley drive ratio or run better gas
or reduce the true spark advance (28deg) locked.

Did you degree the cam? The indicated boost (5psi) is much less than what you should get with that cam in that motor with that blower @2.33:1 drive ratio.

The motor should be making a ton of horsepower @ 2.33:1.
Is it making any power?

Get some better gas.
If you want to run it that hard , for that LONG @ WOT (2.33:1 driver ratio) you need to find the true tuneup using high octane gas and then change fuel take the timing out of it, add the water methanol injection and pump gas and then sneek back up on the spark advance to find the happy spot.

You will not find the tuneup or get the water injection right, while raceing up a hill. you need a chassis dyno to dial it all in.
Much cheaper than burning up pistons.

I would just race it on methanol. It will be cheaper and go faster/ farther for less net cost. Roots blower motors love methanol fuel.

Last edited by F-BIRD'88; 04-20-2012 at 10:59 AM.
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Old 04-20-2012, 10:45 AM
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i got like 7-8 psi when it's 350cid, now at 383 it makes 5psi, i will check my gauge also, it use to make good power, i compare it to a 350hp 350Ci i have and it's moves really better than it, im now waiting to get some new pistons cause piston melt, but im from CHILE, so i have to buy it in U.S.A. and wait them to get to my hands, i dont know if im 2.33 or 2.10, i will check all, i dont degree camshaft, i just put them at the timing set mark with no advance
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Old 04-20-2012, 11:08 AM
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verify all the real specs of what you got there.
The stock default blower drive pulley ratio is 1.71:1.

6" crank pulley 3.5" blower pulley.

and should create +/- 5psi at WOT at high rpm.
Go back to this 1.71:1 drive ratio and sneek up on the tune up starting at 28deg timing.
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Old 04-20-2012, 11:16 AM
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If you are rebuilding this motor. and want to run it @ a 2.10-2.33 drive ratio on pump gas up a hill,, build it with a true verified 7.5:1 compression ratio. OR LESS

Now you know what the result is when you just throw it together and wing it.
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Old 04-20-2012, 11:20 AM
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Quote:
Originally Posted by F-BIRD'88
If you are rebuilding this motor. build it with a true verified 7.5:1 compression ratio. OR LESS

Now you know what the result is when you just throw it together and wing it.
im sure that the heads are 76cc stock, but last time i have to rectify them so i dont really know how cc them have now, btw i dont found piston with more tan -28cc dish, for 1.125 pin diameter and 4.060bore 6" rod
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Old 04-20-2012, 11:33 AM
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What is controling the spark advance?
What is the spark advance curve?

What happens to the spark advance curve at part throttle cruise?
Any all pressure sensors (MAP , vacuum, etc) that are above the supercharger
like attached to the TBI it self.

that sense vacuum or manifold abolute pressure (MAP)
to adjust the spark advance (like old school vacuum advance does) must be disabled or moved to below the supercharger.


Or just disable all spark advance and run locked fixed timing
(28deg for pump gas and high boost)
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Old 04-20-2012, 11:38 AM
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spark advance is only mechanical, not vacuum advance, i got all advance at 2500-2800rpm like 32°, al sensor are above supercharger
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Old 04-20-2012, 11:39 AM
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Edelbrock does not sell a stock 76cc SBC performer or performer RPM cylinder head.
Their heads are either 64 or 70cc.

you need to start actually measuring the stuff.
You must measure your parts. Do not assume the part is the spec on the box or in the catalog. including the piston dish volume and true deck clearance.

Its a lot easier to build a 355 to the desired true low 7.5:1 cr than a 383-388 using available parts.
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