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Old 07-19-2012, 09:30 PM
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new build feels under powered

hey guys just got my nova road worthy however im not too happy about it while driving it for the first real drive i feel it is massively under powered for what it is...which is...
sbc 355
all forged rotating assembly 9:1 cr
stock gm heads
cam is .488 lift
summit high rise single plane intake manifold
full roller rockers 1.5 ratio
msd ecurve dizzy 15deg intial 30 total
profesional products throttle body efi 750 cfm
and a gt45 single turbo on top

the car take s little while to start i think may be due to the time it takes to build initial fuel preesure at start up
it idles at 15 inhg smoothly and it doesnt seem to miss at all on the road

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Old 07-19-2012, 09:31 PM
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im stumped after all the time i spent on the car im fried and need another brain to help figure it out thanks in advance for the help
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Old 07-19-2012, 10:06 PM
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First thing you need to do is give it more total timing. Adjust your curve to have about 16 - 18 static, vac adv plugged, with 36 to 38 total, and bring it all in by around 3000 rpm.
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Old 07-20-2012, 04:50 AM
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currently i have it all in by 2500 is that too early i have it set for only 15 degrees in the advance sweep should i increase the amount in the advance sweep or just add more timing? there is no vacuum is just similuated vac adv since its all digital
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Old 07-20-2012, 06:30 AM
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Quote:
Originally Posted by Pupsvette76 View Post
hey guys just got my nova road worthy however im not too happy about it while driving it for the first real drive i feel it is massively under powered for what it is...which is...
sbc 355
all forged rotating assembly 9:1 cr
stock gm heads
cam is .488 lift
summit high rise single plane intake manifold
full roller rockers 1.5 ratio
msd ecurve dizzy 15deg intial 30 total
profesional products throttle body efi 750 cfm
and a gt45 single turbo on top

the car take s little while to start i think may be due to the time it takes to build initial fuel preesure at start up
it idles at 15 inhg smoothly and it doesnt seem to miss at all on the road
What are you tuning it with? What heads, cam? What boost pressure? If its slapped together junk you may not be over 400hp.
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Old 07-20-2012, 06:36 AM
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Also, there's a lot more to the equation than just engine...gears, tranny, convertor, exhaust, etc. Make sure you've got all that right too.
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Old 07-20-2012, 09:07 AM
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I'd like to know more specs on the cam beyond .488 lift. What duration, and LSA? Might be the cam is too big to respond well at lower rpm's.
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Old 07-20-2012, 02:34 PM
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Sorry for leaving so much info out Stock heads cam is .488 lift 292 duration at .050 i believe 114 lsa boost is 5 psi gears are 4.88 on a spool 3000 stall converter in a turbo 350 the efi is self tuning
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Old 07-20-2012, 03:16 PM
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What stock heads? Casting number. Your .488" cam is not 292@.050".

Most likely 234@.050". You should be using a 3500++stall converter so you leave under full turbo boost. You will need a lot more boost to get any power , working with crappy stock heads.

start tuning with 110+ octane gas. 10-12 psi boost and 30-36deg timing.

Pump gas will require less ignition timing. 26 to 33deg. and will limit the amount of turbo boost you can run without detonation. 6 to 8psi.

start by simply locking out the distributor advance and start tuning around 28deg .

Make sure the carbor EFI is plenty rich @ WOT. 11:1 AFR @WOT (rich is safer)

Stock crappy restrictrive heads EG: 882-624 castings etc will cost you 100++ hp compared to good hi flow high prf heads.

You lack of detail and accuracy in detailing the engine combo probaily says it all.
A equal lack of engine build details is really going to limit the power made.

again start tuning using high octane 110+ gas. (so you can use boost and timing to make power with crap heads without melting pistons)

Then detune ( less timing less boost) for pump gas.

stock heads are really going to limit power.

I would have used a 224deg cam on 114 and a dual plane hi rise RPM manifold.
( a 234deg cam and single plane manifold may need up to a 5000 stall to get any real turbo boost
at launch, depending on the turbo used. The turbo AR ratio needs to be correctly matched to get a good boost response curve.

You are not going to make any real power with 5psi boost and crap stock heads.

Get some real heads for it.

Last edited by F-BIRD'88; 07-20-2012 at 03:24 PM.
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Old 07-20-2012, 05:42 PM
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in order to keep the cr low i need a large cc in the head theres not too many options out there for a 76cc head or larger (76cc give me a 9:1 cr) im not sure what STOCK heads they are ...i obviously dont have as much experience as u do as im only 23 yrs old so bare with me do u have any suggestions on heads that have a larger chamber i have thought about running a thicker head gasket but dont like the idea of that i need this car to be a pump gas car due to price and availability of race fuel
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Old 07-20-2012, 05:44 PM
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i do have a manual boost controller that i will hook up to enable more boost
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Old 07-20-2012, 06:03 PM
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How about some pics.

Did you make the turbo system, what does it consist off.(Headers, custom made manifolds, stock manifolds?)

Sounds like you expect the motor to really rpm(4.88 gears), but youve choked off the air flow with a non modified head.

There are plenty of 76cc aluminum heads available with better flow and bigger valves.

Do you know what your fuel ratio is currently?
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Old 07-20-2012, 07:52 PM
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a/f ratio is controlled by the efi system it idles at stoich 14.7 wot richens up to around 11.5 with a boost referenced fuel press reg rises 1 to 1 with boost not my first choise on gears but when i bought the car thats what it had have gotten around to changing them out i will prob go with a 3.55 or something close
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Old 07-21-2012, 01:38 PM
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Take it to the track and get some time slips on it.
The MPH from the time slips tells you how much horsepower you are making.
Once you know the weight of the car+driver.

The casting number for the heads is under the valve cover.
Some of the 76cc heads are very restrictive. ( really restict the engine power)
The rest are lame in stock form but improve with porting.
Think of it likened to blowing air thru a straw.
Lots of back pressure, not much flow.

Turbo boost on the gauge is a measurement of back pressire.
What is not getting into the motor.
With a restrictive head you don;t get much (power increase) from
a indicated 5psi boost.

A restrictive exhaust system (stock ex manifolds, small exhaust, stock muffler) will really
restrict the torbo response and restrict engine power too.
A turbo motor needs free exhaust flow. A turbo does 4/8ths the job of a muffler in quieting the exhaust .
Often a turbo motor can run on the street with no muffler and be relatively quiet.
if the muffler is restrictive is will sure like the flow increase.

How would you rate the turbo's boost response time?
"turbo lag"

Last edited by F-BIRD'88; 07-21-2012 at 01:47 PM.
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Old 07-21-2012, 01:44 PM
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I see so actually a restrictive head will cause more boost pressure even though it's not causing an increase in power
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