a70oldscutlass

I have a 70 cutlass that i want to build a motor for and i want to drive it and race it so i want the best of both worlds.The car will have a overdrive tranny,3.42 or 3.73 gears,probably exhaust manifolds and i want the hood to be funtional.I read on another post that a guy used a 2in. spacer under his carb and still used his breather so wouldnt a performer work and if so i will use that and if not a cast iron intake.I would like to here from people that have built cars that run hard and still got good gas mileage and have tried keeping there manifolds and cast intake.I have some parts for both bb and sb.I have a lunati bracket master 11 280-290 496 520 and a comp 280 280 480 480,E and 6 heads fully ported and heat risers filled with 2.07 1.71 valves both are about 9to1 comp.I can buy whatever i need but i want to use what i can.

drop top olds

Be prepared to spend $$$. I would say, 350DX block, Edelbrock heads, 200 4R transmission and 3.90 or 4.11 gears would be apretty good start. Build the diesel block to 430 ish displacement. Have a knowledgeable Oldsmobile engine builder pick your cam (roller) and oh yeah headers.

Sell the #6 heads and the cam(s). If you are serious about going racing. Someone else will chime in with their view.

If you are adamant about building a small block you will certainly have to run headers. Any cam above 280 duration sounds way to big for a SBO that will see the street.

380 Racer

I disagree about doing a DX. I would look at what I could afford, in other words do you really want a max effort street engine? That will take some very healthy $$$$ to do with the DX. A 68-72 block will work just fine. Do a 380 build and not have to worry about lifters, spending $$$ to have a 425 crank done. If you have the #6s already done, just use them. A RPM intake works very well with a good carb. Headers required! My 380 produced 518 HP with #7s. A 380 would be awesome on the street and would not break the bank.

Cutlass EFI has done a few SBs with great results. He can recommend pistons, rods & etc. He also has a source for .921 lifters if you do go the DX route. Remember this is supposed to be fun but also affordable.

a70oldscutlass

Wow i thought there would be more people that had tried to build a motor like this.I guess i will have to figure out what it will take through trial and error aproach.thanks

455man

You might take a look at other peoples builds and go from there. Those manifolds are going to hold you back but a good gear w/overdrive tranny will help make it fun.

coppercutlass

My build is I would say similar to what you want. My approach was diffrent but the important part is the combination. Look up swap meet 350 build. so far I have not hit the track. My las combo ran 13.3's with a tight converter and a small carb.

chadman

Build a 455 with 10:1 compression, 230-240 @ .050 hydraulic flat tappet, Torker intake, 850 DP Holley, cheap headers, out of the box Edelbrock heads and run 11's all day and drive anywhere you want.

a70oldscutlass

coppercutlass
i couldnt find your build

chadman
that motor is way to big to get any gas mileage but it would run good

Im sure i can get a motor to get good gas mileage and run hard.

oldcutlass

What kind of gas mileage is considered good?

a70oldscutlass

I have a 70 rallye 350 that im doing a ground up on and everything is going to be new on it.i would like for it to run high 12 low 13 and get atleast 15 mpg.I seen a couple people have done this and i would like to see some more builds to see what i like best.im going to be needing info on the front and rear susp. also.i would like for the car to set a couple in. above the tire in the rear and i dont want to have air shocks and dont want it to drop much under throttle.i want the best susp. for racing i can get without sacrificeing a good ride and handling.i have 15-10 with 5.5 bs and 295-50 tires.

coppercutlass

This is my current engine build. https://classicoldsmobile.com/forums...350-build.html

Previous to that I ran a 350 std. bore with a comp 280h 10 to 1 compression, #6 heads with 2.07 in. and 1.7 ex. valves, roller tip rockers, edelbrock rpm intake, edelbrock 600 cfm carb backed by a 2300 stall converter, th400 and 3.73 gears, running full length headers and an x pipe with hooker aero chamber mufflers dumping at the axle. It's fastest time was 13.3 @ 103 mph. That was with that small carb and tight converter. I really needed a 650 dp or 750 vac. carb I now have both and I needed a 2800 stall for that cam.

The difference between my current build and my old one is the cam and I went with .030 speed pro's and did more machining that my previous frankenstine build. Of course I also have a 650 dp. and a 2800 stall converter.

With the edelbrock I was getting 10-12 mpg on the previous build it's horrible with the 650 dp I plan on going with the 750 vac. secondary holley I have eventually.

a70oldscutlass

Nice.it would defently run better with carb and converter.what kind of mileage did you get?

coppercutlass

On the 350 std. bore it was between 10-12 mpg with the edelbrock but I have a lead foot so I bet if someone drove it much easier it would surpass 15 mpg. With the current build and the holley 650 double pumper im lucky to be getting 10 mpg but I also beat the tar out of it.

a70oldscutlass

what pistons did you have in your 280 comp motor?

coppercutlass

Cast flat tops that where bought used and re used.

a70oldscutlass

So you had about 10 to 1?i cant make up my mind on the 350/403/455 motor but i dont think the 455 will get any mileage.i have it put together on the stand with the lunati 496/520 cam/fully ported c heads and 9to1 comp.i dont have but about $600.00 in it.most of the parts were new that i got in on trades.

coppercutlass

Yes 10 to 1 . 9 to 1. With that lunati might not be enough compression. The bbo can get good mileage with a good tune and a vac. Secondary carb. If you have the bbo almost done I would run it. As much of a small block guy that I am I would go the bbo route I would just go with a better cam. A mild bbo would do low 13's high 12's easily. The 350 would require a more agresive build.

a70oldscutlass

I never have watched the gas mileage on my olds motors before but i think you can build a sb pretty stout and still get better gas mileage than a bb.I have a bb with a mondello jm3-4 and it runs pretty good but the gas mileage sucks.

brddg

N2o

a70oldscutlass

I want the motor to run hard without it but im going to have that for backup.

brddg

If you want 15mpg without it you're really going to have to work at it.

brddg

I had a '70 chevelle with a 350 4 spd and 2:56 gear. With a cast iron intake and adapter plate to a holley 600 and a comp 280 cam it got 17mpg. And it was slow. But it felt fast for what it was. It ran with stock 5.0 Stains back then. I was happy no matter what they said.

oldsmoboogie

I would go with the big block personally. If you have a set et goal then it takes a certain amount of power to get there wether its bbo or sbo you need to make the power and as the sayin goes there is no replacement for displacement. My first bbo was stock bore, stock compression, mild cam, performer intake, quadrajet, hedders, 2.5 inch dual exhaust, 3.73 posi, and a stock th350 and it ran 12.80s on crap gas. I later installed a 2004r trans and a 3000 stall converter and with the same engine got 13 to 16 mpg. I have since built a new motor with more compression, ported heads, and probably more cam than i need with a torker intake and hp 850dp and the milage is horrible but it runs 12.20s and i havent messed with jetting, timing etc. Its very streetable and yes i drive it long distances. Do you have any info on the c heads you have? Ported is a term thrown around by alot of people if the builder of the heads is not familiar with olds you may not have what you think you have. If your heads are good then i would shoot for 9.5 to 1 comp. talk to cutlassefi about a cam, performer intake, hedders and a good exhaust, and a quadrajet. If you play around with timing and advance curve, and getting the qjet dialed in you would be where you want. Put in a 2004r with about a 2200 stall and 3.73 gears. Good luck with whatever you choose and keep us posted.

a70oldscutlass

oldsmoboogie what cam and comp. did your first motor have?My heads have the exhaust ports raised,the guides are teardropped,the undersides of the valves are opened up,the bumpes are removed ,the crossovers are filled,the exhaust dividers are welded up and the crossovers are poured.

oldsmoboogie

I believe it was the the jm 22-20 if i remember i could check to be sure and the compression was around 8 to 1. As for suspension i run a bmr rear sway bar comp engineering 3 way shocks ans drag radials

odddoylerules

i ran the jm 20 22 in a lower compression 455 w g heads, it was great. 2.73 gears, 14.6 et's and almost 20 mpg on the freeway. For a fast street car BB is the way to go. SB is fun, but to go real quick its much much harder.