70cuttlassvert

I am newer to this site and wanted to ask about how i can get the 350 to 400hp. I have a 1970 cutlass supreme convertible. I have a 10 bolt posi rear end don't know the gears, th400 trans, stock cam and heads, 4 barrel holley 650, edlebrock intake, long tube headers dual exhaust, ..... Any suggestions on what else I can do to get to 400 HP. I bought the car this way FYI only owned it for 1 1/2 years. I put a post on the newbie section with photo too. Thanks in advance and y'all rock ive uses this sit to fix gas gauge, rebuild my suspension and other things.

olds 307 and 403

You need either worked iron heads with 2.07"/1.625" valves or BBO iron or aluminum heads, 9.5 to 1 compression, a rpm intake and something like the Lunati 221/230 cam with matching springs. 80rocket did a 350 with cam and 9 to 1, dynoed just under 350 HP and more importantly nearly 375 ft/lbs of torque. You will also need a 2200+ stall converter and either 3.42 or 3.90 gears and posi, the only new gear ratios available to replace your current 2.56 or 2.78 gears more than likely anyways.

cutlassefi

Do you want 350 or 400?

coppercutlass

I have a 355 that i built with #6 iron heads with just big valves. 10 to 1 compression , lunati voodoo cam 522/539 lift 233/241 duration @ .050 roller rockers , RPM intake holley 750 double pumper , th350 with a 3000 stall that stalls around 2800 and 3.90 gears wheighing in at 3400 lbs runs 12.45 @ 106.6 mph. Im leaving some HP on the table with a fuel pump that looses pressure on the big end and cuts back how high i can spin the engines and a converter thats too tight but off current numbers its about 350 ish but i think 370 is realisitic considering i have spent no real time tuning. Everything is pretty much box stock. someone with more talent could surely get more hp from my combo.

I may add its a street car that gets driven alot and driven to the track and back (120 mile round trip)

Edit: had to re check my numbers and found that i was making 332 rwp based of wheight and mph thats rwp i belive and when converted at a 20 percent loss it comes out to 394 hp

oldsmobiledave

10 bolt rear end = not original
T400 = not original

Better option buy a used 68-72 455 and install it and forget about it. A reliable 400 hp 350 can be built but it will hurt your wallet. It will also mandate a gear swap in your rear end where as the 455 won't

coppercutlass

Idk if my calculator figures are right but my 350 is pretty reliable. Nothing fancy by all means but it runs great and i drive it everywhere.

olds 307 and 403

Definitely makes a difference, 350 HP is relatively easy, 400 HP not so much and as said more dollars. If you are wanting close to 400 HP, a 350 stroker is also an option and will be more street able. The stock rear would be the 12 bolt 8.5" type O, if there is 10 bolts, assuming a corporate 8.5".

70cuttlassvert

Thank All for your input. I'd like to stay with my small block 350. 400hp I just came up with as a figure. I just want as much power as I can out of my motor.

80 Rocket

I don't think it is 394hp but I would bet it is all of 370hp. And I wouldn't sell yourself short on tuning, you know a lot more than you give yourself credit for. Your build proves you don't need to be a professional to build a car that can run mid 12s......with a small (355 cubes) small block.

The reason why your car keeps improving is because of your dedication to learning. Keep it up, I want to see that car go 11s soon.

70cuttlassvert

Here is pic of my beauty I had to have her repainted due to some hail damage I am in the process of putting her back together.

coppercutlass

Im not disagreeing with you don ., but by weight of the car and the hp number after the conversion., the e/t is very close. But I know the calculators are a far cry from sophistication so I'm not holding my breath. I'm not worried about the hp numbers I was just messing around with the calculators to make sure i wasn't bs ing and realized the weight and mph calculator is factored for rwp not fwp . Any who thanks for the compliment I don't consider my self a tuner as I have never made a jet change or even bothered finding out where my total timing falls in. I know how much advance my dist has but where it falls idk. I feel like this are tuning essentials I kinda skipped. Why I don't know.

80 Rocket

BBO heads would be way too much for a 350 unless you are looking for a high RPM screamer which is unnecessary for a street engine.

The 350 that you mentioned was a completely stock bottom end with a Performer intake. Give it a decent short block with good pistons, a Performer RPM intake, and more compression and you can get your 400hp there. The #7 heads will support over 400hp (2.00"/1.62" valves).

I did another 350 (.030 over 355) with speed pro pistons (yuck) that made 432hp @ 6200rpms and 404lb/ft torque @ 4600. That was with #5 heads, 241/249 voodoo cam, 10:1 compression, street dominator intake. The heads had been worked over and flowed 268cfm, which isn't bad for small block irons (and flows more than stock first generation Edelbrock castings).

However, when you start making that kind of hp with limited cubes, you do need at least a 3000 stall converter

80 Rocket

Yah, at the end of the day it don't matter because the drag strip is the ultimate test. Dyno numbers can be fudged, ETs don't lie.

olds 307 and 403

Both these builds are impressive for what they are. I plan on copying the first build with a slightly smaller cam. Don, keep an eye out for when I pull a couple of valves on my #6 heads. I am making sure the center exhaust valves acceptable clearance. I ordered snap gauges and a 0-1" micrometer. I also want to see if the valve job and guide work was done right. Also curious if the intake bowls were opened up for the 2.07" intake valves.

firefrost gold

copper didn't you have some port work done on the heads ?

coppercutlass

Not these. The ones that got ported where for the 355 that's on the stand. Never made the swap.

80 Rocket

Yes, the first build should have had a smaller cam, but the person wanted to use his Performer intake instead of buying an RPM so we ended up being a bit mismatched in that regard. A little more compression would have been nice as well.

BlackGold

ETs do lie, because ET is affected so much by traction. Trap speed is a much better indicator of horsepower-to-weight ratio.

80 Rocket

I meant the ET slip. Kind of a figure of speech I guess. Did you know when you lose traction that trap speed will usually be faster?

My point is that an ET slip will let you know if your dyno numbers are suspect. If you dyno at 500hp, yet your 3600lb car runs 13.03 @ 107mph, something is not right for sure. If you improve your traction to reflect a 107mph run you are still not anywhere near what the engine dynoed at.

BlackGold

Yeah, I knew what you meant; just wanted to make sure everyone else did, too.

If you pick up trap speed when you spin, that's a sign you could use a looser torque converter -- or you need to tune your carb and/or ignition to better handle the transition from line RPM to full throttle. A loose converter or some wheel spin can hide a multitude of tuning sins.

mr.rocket

mr.rocket

ericsolds

I have a 1970 350 Olds engine with the stock #6 heads. Are the #7 heads better ? if so, please tell me why.

coppercutlass

This thread is old lol. My junk ran a best of 12.29 and on tjmhe quest to an 11.99 we found traction issues . Sold the engine. But 5,6,7 heads ate all about the same. All will need the same work to work well in mild applications. Yes some do have 2.in valves but that would be 5's and 6's and not readily available.