Hey guys, hope everyone had a very nice Christmas and all is well.

I have been VERY busy working on the vette the last week or so, I was able to get the body off the frame, also got the motor and transmission pulled out of the frame. then decided to take the motor down to see what I am working with, the block is in great shape (just crudded up)

I am planning on rebuilding it and would like to make more H.P. with this motor. I have an estimated budget of around $1500.oo to work with, do you think I can make somewhere around 400 hp. within this budget??
I will have to have the machine shop clean and check the block for oval'd cylinders and or cracks.

I am a fairly good mechanic but am not real familiar with putting together the best combination of cam/heads/pistons/intake.

anyone have a good recipe for a budget 400 hp small block please share.

by the way, I have 462 heads (the worst from what I read) so I'm fairly sure I'll need new heads too. unless you think I can use these without any trouble.

thanks, Jig.....

 

the 1500 is in addition to the short block work?

 

For a total rebuild where you're talking about new heads, cam, pistons and intake, you will need alot more than $1500. You'll have almost that in a good set of aftermarket aluminum heads alone.

 

 

if the block really is in great shape avoid the machine shop and re-ring it. Not a high class solution, but a low $$$ deal, then a mild cam and aluminum Dart SHP heads $900 and it is under budget. (by 11 cents)

 

thanks guys, I figured that budget was a little out of line but it's been a long time since I messed with anything like this.

so lets go at it like this, I am looking for the most RELIABLE and STREETABLE horse power I can make using most of the parts I have already. I plan on keeping the block (standard bore and stroke), the intake (factory) and the carb (factory). I know the heads I have are pretty junky so I'm not opposed to getting others (either new or used). If getting a new intake will help significantly I will get one as they are not too pricey, but the fewer parts I have to buy the better. also, I plan on having the transmission rebuilt, the guy I'm using builds drag trannys all the time and I'll get him to "beef" it up a bit while he's in there. I don't plan on changing the torque converter or the rear end gearing so whatever I do to the engine will have to match those things. I'm not sure what gears I have yet as I can find the tag on the rear end (will have to do it "old school" and count the turns). I'm assuming 3.73:1 but I'm not sure of that.

so, all that said, and bearing in mind the above, what kind of numbers can I get if I upgrade the cam, heads and intake? and what parts should I look at?

thanks a ton "the newbie"

 

does it have dish or flat tops?
headers? true dual ex?

 

OOPs, sorry----

the pistons have a slight dish in them but I can do flat tops if that makes a big difference, also, I plan on using the factory manifolds and factory exhaust with new mufflers (maybe flowmasters), I also plan on gutting the cat at the same time.

thanks,

P.S. don't get me wrong here, I want to do it the right way and will do whatever it takes but I don't believe in throwing money away just to have a ton of power that I won't use, that said, I would like more power than what the factor put in it. this motor work is just a small piece of a $10,000 rebuild so I don't want to waste money on it and take it away from the hundreds of other parts I have to get for this project.

 

without headers ($100) dreams of 400 hp just vanished. i'd sooner use the dish p, than give up headers.
carcraft got 419 hp w/Dart SHP heads. w/headers.
.
SHP 900
weiand 8150 $140
cam/lifters 100/170
headers 100
~400 hp doable with headers.

 

thanks, the headers are not out of the question but I'll have to see if I can find a set that has the emissions tubes on them, we don't have a "sniffer test" here but they do check to see if the proper components are there and hooked up at inspection. it's a pain because I know that kills some power.

can you elaborate on the cam and head specs some? I'd like to be keeping my eye out for sales and specials while I'm working on the rest of the car.

thanks for all your help with this, I know these things have to work in unisson with each other to be the most efficient, I just don't know the things I should know to make the right choices, I know just enough to make me look stupid.

 

Exhaust manifolds are a real HP killer. It would be kinda of pointless to install some decent aftermarket heads and choke them with manifolds.

Also............It would really surprise me if it has 3.73 gears. I'd bet high 2.xx's or low 3.xx's for rear gearing.

 

it may be geared that way, I will have to go out and count the turns because I don't see a tag on the rear end. I'll do the headers, just have to find some that will work for the inspectors around here too.

thanks,

 

i'm in FL.
no tests here.
hopefully others will chime in
good luck!

 

engine back to reliability stock+used blower

 

OK, went out and did the 'ol count the turns technique, got 2 3/4 turn on the drive shaft for 1 turn on the rear wheels. so I'm guessing 2.73: 1 ratio. does that sound right ??

'81 coupe, sbc 350, automatic

 

 

That sounds about right. So, with $1500, upgrading some of the engine components will not do a lot of good, if you keep the 2.73 rear gear. Now, the '81 trans is a THM-350C, which has a lockup clutch built into it (first year for that feature in a Corvette). It does not have overdrive, so the 2.73 rear end is a benefit for highway comfort and efficiency. If you just want a "cruiser", keep the trans/diffy combination you have and UP the horsepower some with some mild engine changes. Keep the carb, replace the manifold with one that breathes better [but still can work with the Q-Jet and the existing hood], change cam, put on some used Vortec heads that you have refurbed by your engine builder, and install true 2-1/2" dual exhausts with a small CAT in each. Will the exhaust manifolds be a restriction? Yes, but not so bad with the larger dual exhaust system.

You also need to rebuild your existing carb (unless already done recently) and recurve your distributor for better performance. Those two things alone may account for 1/3 of added power you get from cam, heads, and intake. If you have enough money, put better flat-top pistons in it; if not, have block rebored and re-ring the pistons you have. The recess in your existing pistons will lower the CR about 0.5 from what flat-tops would provide. And, you won't have to pay for premium fuel with that lower CR.

Good luck with your overhaul.

 

you can get most after market heads with 64 or 72 cc combustion chambers .depending on which pistons you have and what compression you want.you can find dart iron heads for $850 and less.consider a comp cam extreme hydraulic cam,the xe 268 mite make 400 hp with good flowing heads,and headers..a newer dual pane intake will help also,consider a edlerbrock rpm performer .competition products is a good place to start.can you fab your own exhaust ?

 

Everyone looks at the big pieces, like heads, block rotating assembly and it comes out looking pretty inexpensive, it's all the other stuff that doubles your est. My shaft rockers were $1500, if you think you can do a body off restoration and a 400hp motor for $10,000 ask a few guys who have done it

 

stock 1981 with auto should be 2.87 rear gears.

Are you using the stock ECM and distributor still? you mention wanting to use the stock carb. If you are 400hp might be a lot for the stock computer system to handle unless you are going to go to a roller cam conversion.

If using the stock '81 Block, pistons ,carb, distributor, ECM and intake
You might be better off shooting for 300hp. I would look for low mileage used ZZ4 heads. You can get them for around $600 usually. Then find a cam that will work. I think around a 262 might keep the stock MAP sensor happy at idle.
You can go with the Summit Headers like I did, around $120. You should really get a Dual 2.5" exhaust installed also.
add a bearing and gasket kit, double roller timing chain and whatever you need to do to clean up the block, you MIGHT make it in your budget depending what the exhaust cost.