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Discussion Starter #1 (Edited)
Ok guys what i currently have is as follows

The car is a 1970 chevy impala its been lightened and weights just around 3780 without me in it. It has a fully built th350, PTC 3000 stall and 3.55 gears, posi, and moser axles. The car is a daily driver and i use it often mostly for spirited driving and it does see the track here and there for fun.

Current set up has only 4500 miles on it runs very well, no smoke, no leaks, and pulls hard but just had a couple things happen that lets me maybe change a few things. I have a buyer for my current short block for 1500.00 and I had a lil money come avaliable so thought bout the engine I had and wanted, and thought should I do this??

I came across a good deal on a cost is less than 3000 for all of it and I would get 1500 back from my short block

Fully machined, decked, honed, SHP dart block tht has all the provisions for factory roller cam setups
Set of forged Probe dished pistons with hastings plasma ring set
Set of forged Scat extreme duty I-beam rods with ARP 8740 cap screws
Complete set king bearings and a Scat 3.75 stroke crank
Pro street balancer and matching flexplate its all been balanced and just needs to be assembled.

Its all done cleaned, bored honed, balanced, etc etc and will end up being a 406 when done.

What i currently have is

2002 vortec block thats been decked, honed, bored 30 over, and in it is,

Mahle forged flat top pistons with total seal rings has 9.8 to 1 comp with a 8.19 DCR

Stock machined rods with arp throughout the lower end

King coated bearings throughout Mellings pump all new

Top end consists of AFR 195 eliminator competition heads set up for hyd roller with 7/16s rocker studs

Edelbrock rpm air gap with an HVH 1 inch spacer its been port matched to the heads

Comp ultra magnum roller rockers 1.6 ratio on both exhaust and intake with smith bros .080 5/16s +100 pushrods

Quickfuel 680 vacuum secondary carb tht has been tuned to the engine

MSD billet HEI with msd wires NGK plugs with 18 degree bushing installed and 18 degrees of initial using the 2 blue springs.

Mike Jones custom speced hyd roller cam tht was installed with a lunati cam degree wheel. Specs are 230/230 360in (576 with 1.6) 340ex (544 with 1.6) 108 lobe sep on a 105 icl. using LS7 roller lifters and roller cam guides and hold down. Has a Rollmaster billet matched single roller timing chain

Breaths out 1 5/8s hedman headers with dual 2.5 exhaust with a x-pipe and magnaflow mufflers.

Right now i have enough money to get the above mentioned kit which should yield round 10.5 CR with the 65cc heads being Im at 4500 ft above sealevel should be fine on premium pumpgas. I would be reusing my heads, intake, cam, lifters, timing chain, dist, headers, exhaust, basically just switching short blocks. I knwo the engine could use a bigger cam but its not in the budget at the moment and I can always get another later if I dont like this combo. But feel like the cam i have is decent sized for a 355 right now my current rwhpo according to the local dynojet is 401rwhp and 398 rwtq. Like I said just want to know if its worth changing over and roughly the differences would be thanks all
 

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Sure, would be a step in the right direction. But IMO why not just go a little further. 410-421ci The heads(Induction) would be the limiting factor.
Just the Cubic inch isn't going to make a "Ton" of difference by it self. I would look at your goals and go from there. See what all is needed to get to your goals and then some.
 

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So changing to the 406 over the 355 short block wont get me much of a difference?
It will, but how much Tq/Hp?

The RPM at witch it will occur will change but actual Tq/Hp might not vary much.
If I were to make this move and spend $3000+/- I would make it a good change.

I think for about the same money you could gain 60-100hp rather than 20-40hp

IMO, just dont think going to 406 will help a whole lot. A little, but not a bunch.


At your weight the cubes will help, but you have to feed them! With those small heads and Induction I dont think it will benefit much.

Bigger head or (Total Induction) and cubes will gain a bunch!
 

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I like the 3.75 stoke myself, and feel that you would never go back to a 3.48 if you try it. If you run the same heads your hp may not go up much, but the torque WILL increase a lot, and help get your heavy car moving easier (lower et's).
 

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those heads will run fine on a 406. a 800 cfm carb would be better.there is a guy that posted ln the mickey Thompson site here that runs mid 11 sec. quarter mile times with a 57 chevy that weighs more then the OP's car.195,s flow over 300 out of the box.how fast does he need to go?
 

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he is running same cubes and similar cam specs.dont know how serious you are about going that fast, but you can see the point iam trying to make.bigger stall and 410's or 430's out back would help.
 

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Discussion Starter #10
Id be happy with 11s but have to stick with the 3.55s being I have to remain a daily driver and the car does see some highway not alot but some haha. I can get a new carb just have to sell the current carb for a decent price or i hve a friend tht will trade me straight across a 780 cfm quickfuel for my 680 cfm quick fuel.
 

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with that shortblock and those heads and cam,you'll love the difference.lotsa torque to move that Impala.sounds like a fun ride.
 

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In my experience just changing the bore and stroke from a 355 to 406 with no other changes usually had about the same output but at a slightly lower rpm. You current engine is screaming for a 750 double pumper or larger. Just the carb alone should pick it up more those 50 cubes with the small carb.

I would do the 406 and then build it up as the budget allows. Some better aluminum heads and intake sized appropriately for the 406 and then a .625 lift solid roller would really wake it all up.
 

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Go with the 406. You can't beat that extra 1/8" on each cylinder...I had a 383 last year and built a 406 for this year. So far the 406 has been 3 tenths and 4 mph faster...it also had valve spring issues and major hooking problems. Alot left in her....Should of built a 406 years ago. Good luck with your build!
 

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It will, but how much Tq/Hp?

The RPM at witch it will occur will change but actual Tq/Hp might not vary much.
If I were to make this move and spend $3000+/- I would make it a good change.

I think for about the same money you could gain 60-100hp rather than 20-40hp

IMO, just dont think going to 406 will help a whole lot. A little, but not a bunch.


At your weight the cubes will help, but you have to feed them! With those small heads and Induction I dont think it will benefit much.

Bigger head or (Total Induction) and cubes will gain a bunch!
Looking at his rpm range (currently 3000 converter), do you think his average gains would be considerable in his rpm range?

Regardless of the peak hp gains, whats going to happen throughout the range?
 

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Anybody that doesn't think you'll see much gain going from a 3.480 stroke and a 4.030 bore to a 3.750 stroke and a 4.155 bore is just Naïve........ you ill seem a BIG difference in power... it will be earlier in the power band
but it will make more average power, more HP and a lot more torgue........ Cam it accordingly and it will move your Tank much faster...... 195 AFR head is kind of small for a 406, but they are Damn good heads and will be Explosive off the line and get you moving......

Do it....... you won't regret it......... and then you 'll have the platform then for bigger heads and MORE power
down the road....
 
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