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new build feels under powered

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355 chevy
13K views 66 replies 15 participants last post by  Project89 
#1 ·
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
 
#9 ·
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
 
#11 ·
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?
 
#12 ·
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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#21 ·
been searching around trying to find a set of suitable heads and im thinking maybe instead of using a 76cc i could running a smaller more abundantly available size cc head and run a thicker cooper head gasket (.093 compressed thickness) i think a 64cc head is widely available and cheaper and the titan copper head gaskets seem to be a good choice as far as increase my cr in order to run more boost and to seem the boost better what-da-ya think?
 
#23 ·
ive been on the turbo forums either no one repsond to ur thread or u get a jerk repsonding whole just wants to talk crap... nonetheless im looking for advice as to ideas on why this motor feels lacking not so much on the turbo theres no debate on if an aftermarket set of heads is better than stock i plan to change it would u agree the lower the compression a bit in order to run more boost is a good idea? what do u thiink about copper head gaskets for a boosted motor
 
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#50 · (Edited)
I bet that 9sec firebird is using a efficient air to water intercooler, cooling down the charge air temp
to BELOW AMBIENT temp.

You say you can show it. Post a link where it is discussed in a forum or other web site BY THE OWNER OF THE CAR.
I know its possible and I know what it takes to achieve that level of performance.

Yup the twin Buick GM turbos work very well. (TWIN being the key word.)
sorry i never even saw this reply
heads have 1.72 intake valves
The block and heads came out of a 80 chev pickup(not original motor) and near as we can tell, it has 150k on it. Has dogcrap 991 small valve truck heads with 76cc chambers and 1.72 intake and 1.5 exh. valves. Should be 8.6 to 1 with 4 valve relief flat tops that are .022 in the hole and a .038 gasket.
no water to air cooler here here is the thread
http://www.theturboforums.com/smf/t...ever-did!-go-figure-)-grenade-part-2-to-come/

and if u dont want to take 3 years to read all couple hundred pages or so

For those of you who dont want to go blind reading all this, the old used up motor was pulled out intact and running perfectly after going 9.37@150! Best power number was 738 whp @ 25 psi and a 75 shot of NOS. Ring gap ended being .090 on the top ring when i finally pulled a piston out of the hole. Yikes! :doh:
 
#24 ·
Inside I all the nonsensical bickering I'm hearig to change the head... I looked at the world s/r torquer heads I believe they are 195cc int runners with 76cc chambers going back to my questio would u suggest using a thicker head gasket maybe copper in order to lower compression ratio so I can crank up the boost
 
#30 ·
engine will not spin above approx 4000rpm

hey guys i need a little help for the last couplke weeks ive been trying to get my nova to perform ... its a sbc 355 with a stock small block cam stock heads single plane intake manifold powerjection 3 efi msd e curve distributor and a gt45 turbo... since i got it on the road i feel its been way down on power...i was hoping for AT LEAST 500 hp it makes some torque not what i would expect but i was expecting a lot more up top and going down the road ive been pretty scatterbrained trying to check everything out at the same and im fried... my lastest discovery is that with my foot to the floor the car other reaches 4000 rpm it shoots a little above probably because of the inertia of the rotating assembly... obviously something is dropping out... any help is apprecciated
 
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