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Discussion Starter #1 (Edited)
Hi everyone,

I have been reading up on this for a while now and I am just looking for some experienced knowledge on engine setups. I have had my 402 .030 over in my nova for about 5 years now and the original plan was to put a blower on it as this is what it was setup for; however I was hoping to see if there may be a better option for getting up to around the 500+hp/tq naturally aspirated on 91 octane. The reason I am not going with a blower is that I believe with the setup I could only put a small blower on it or a 671 with a small amount of boost which does not seem worth cutting the hood up for or the price. I would really appreciate any suggestions. And maybe it is not something worth trying but I figured I would give it a shot. I attached my full engine spec sheet but see below for a quick rundown.

Specs:

402 .030 over
Heads 102cc
Bore: 4.155
Stroke: 3.766
Edelbrock rpm air gap intake
Holley 750 double pumper carb
Cam comp cams hyd 11-404-4
9:1 compression
 

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402...

It appears you already have the base line blower cam...getting 500hp/tq out of a small rat takes a little bit of effort. Couple of questions:

What heads do you have...?? valve sizes..?? any porting or mods..??

Have you had the current setup on the dyno yet to see what you are starting with..??

Would you be willing to run higher octane fuel..?? my sense is you will need to ramp up the compression to get nearer to the numbers you want.

You might be able to run NO2 and get a quick boost of power when needed...perhaps the tech gurus can comment on this?

eg; a stock L78 in 1965 was rated at 425hp...the next year this motor was rated 375hp at a lower rpm...same engine. Getting to 450hp is not that difficult..500 will require a little more effort. I believe if you increase compression in the range of 10.5 to 11, swap out for a solid lifter cam, have a good set of heads with 2.19/1.88 valves that have some massaging you may be able to get close. Making that kind of power requires the correct combo of parts, excellent machine/assembly work and a well thought out plan. My sense is you will need to spin this motor a little to get the power you want...I can suggest an excellent engine person [well known on the SYC] who could help you with this if you want to explore further.

wilma
 

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Discussion Starter #4
402

My heads are stock iron gm
Valves: Int 2.063 Exh 1.72
pistons TRW L2383

It has not been setup on the dyno, I was really looking for approximate figures
based off of the setup

I would rather run it off of pump gas (91)

I am looking at trying to be decently cost effective and in the end if it just makes sense to run something along the lines of a weiand 177 at low boost than that may be the best route. I am only looking to see what might be possible. If not then i may just need to sell it and go bigger.
 

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what about a turbo or a procharger? That would save the hood for sure...
 

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Aluminum heads will allow a bit more compression on pump gas too.:yes:
 

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Discussion Starter #7
402

I looked into it, it's not a bad idea but it would be a lot of manipulation and cost the same if not more.
 

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402...

My heads are stock iron gm
what casting number are they??

Valves: Int 2.063 Exh 1.72
you will need to go to 2.19/1.88 and do some head work if they are good castings

pistons TRW L2383
these are 10.25 to 1...

It has not been setup on the dyno, I was really looking for approximate figures
based off of the setup
there are calculators for this...details on heads will be a factor

I would rather run it off of pump gas (91)
it will be close...cam choice will be a factor as well as piston setup

I am looking at trying to be decently cost effective and in the end if it just makes sense to run something along the lines of a weiand 177 at low boost than that may be the best route. I am only looking to see what might be possible. If not then i may just need to sell it and go bigger.
I can't comment on the boost...
 

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Discussion Starter #9
402

Heads: 3993820 PASS

How are you coming up with 10.25 to 1 for the Pistons, everywhere I look say right around 9:1 plus my spec sheet has that?

I appreciate the quick response man
 

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402...

from Nastyz28.com
L2383 - .110" dome with 8.65 to 1 CR (based on 109.4 cc)
L2354 - .169" dome with 9.26 to 1 CR (based on 106.9 cc)
L2328 - .319" dome with 10.53 to 1 CR (based 109.4 cc)

You are right, my error. I saw a reference to a L2328F...got the numbers mixed up. So with your 102CC chamber and those small dome pistons the 9/1 ratio is about right.

here is a link about your #820 heads...based on this it appears your heads have been milled a little to get the 102cc volume. They are a good casting for performance...it appears most folks do upgrade the valve size and do some minor upgrades. With your 9 to 1 CR, I'm not sure you can get to the 500hp area...maybe these heads will work with the higher dome pistons?? Those L2328's with the 102cc would be close to 11 to 1...just not sure about piston to valve clearance.


http://www.clubhotrod.com/chevy-big-block/8003-3993820-casting-heads.html
 

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I don't want to hijack this thread but very interested in what it takes to put a small blower on a 402 30 over. currently running 11:1 compression.
 

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Discussion Starter #12
402

I believe you would need to drop the compression to a max of 9:1 and even then you could only run about 4lbs of boost.
 

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Out of the box flow numbers from the Chevelle Forum for 820 heads:
.100"-52/69
.200"-140/114
.300"-208/143
.400"-245/166
.500"-270/180
.600"-280/190
.700"-285/195

Your going to run out of flow after 450HP. Getting to 500HP is WAY easier with a new set of Heads. Just as an example, AFR 315 Heads flow @.500:
0.500 321 intake
0.500 284 exhaust
That is 50HP right there. I guess what I'm saying is boost from a small Super or Turbo (keeping your 820 heads) is the best option but equal work time / cost with a head change. jmo Jack
 
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