young olds

we all know the limit of an unsupported 455, seen the carnage too, but what about a small block? ive never seen a sbo with the bottom end blown out or even heard reference to the limit. im going to have a new build finished soon, hopefully, that should be at the "safe" limit of an unsupported big block. i actually dont really care if its breaks but am curious how far i can push it until i can hold my breath waiting for it to break.

BlackGold

I'm surprised no one's responded yet. I'll offer a couple of opinions.

There are SBO racers out there in NHRA Stock class turning 7200 RPM or more. Similar stories surface of W-31s back in the day.

But if you haven't gone through the engine, if you're talking about a SBO (330 or 350) straight from the factory, I'd feel more comfortable setting an upper limit of 6000 RPM.

young olds

me too, i assume that people either run big blocks or diesel and thats why there arent any horror stories of ripping mains out of a sbo.

cutlassefi

Too many variables in your question. Stock N crank? 330 crank? Studded? Strapped? Halo? Full girdle? Bored to the limit?
Like I said, too many variables, you need to be more specific.

70cutty

This is what happened to my stock 350 when pushed past 6k. 39k miles on the car when this happened.

edzolz

And that looks like it is a low compression engine. No pre-ignition? I don't think RPM caused that.

Ryan 1969 Chevelle SS396

Are there reasonably priced supports for 350 bottom end? I plan to use ARP studs.

Ryan

young olds

I mean with an unsupported bottom end i.e. No girdle, straps, studs nothing.

cutlassefi

I'd say 450, 500 would be the max. And that's with a balanced assembly and the right tune. Even stock sbc's won't handle more than that without upgrades.

Fun71

Agreed. I had similar damage to a piston in my engine back in the 80s after winding it up with less-than-optimal gasoline. Detonation took out the side of the piston, very similar to that pic.

67 Cutlass Freak

I think Mark nailed it right here. My SB 350 in Don's '80 Cutlass is puting out close to 450 HP, and he's spinning it up to 7200 RPM. It has light weight pistons, steel crank, Halo, internally balanced, worked over stock rods
As far as the limits of the gas SB, I think Ralleye Bob had the fastest one naturally asperated, running low 10's. He had #5 heads for a while, now he's running Rocket Racing heads. Not sure if he's still running the gas block. You don't really hear about too many guys throwing power adders at the SB. Usually at that level they will step up to the BB or the deisel block. I don't really think the SB gas block is stronger than the BB, it's just not making as much power to push it to the limits.

80 Rocket

I thought Nick Jeffrey was putting out almost 600hp on a gas block. I know he went diesel block because of some issues with twisting the block, which may have had to do with the way it was tied to the chassis. I don't really remember now, it was a long time ago.


I wouldn't be afraid of 500+ on a small block Olds with a front motor plate and a mid plate. My stock block SBC was putting out a fair amount of HP to go mid 8s @ 155mph in my dragster, but that is tied together with a front/mid plate.


I think a SBO gas block is stronger than a BBO block because the mains are beefier. There is more material available since the main journal is only 2.5" diameter compared to 3" on a BBO. Plus, a shorter deck height is less to flex. Couple that with a lighter bobweight than a BBO and we got ourselves a big block slayer.


You boys can have your big blocks, less demand for small blocks makes them cheaper for me.

80 Rocket

I don't believe Bob did that with a gas block. I believe he hit high 10s with a gas block and #6 heads. The D block build used those #6s and went 10.30s and the Rocket heads went 10.0s with the same short block. That is if memory serves me correctly.


I thought Nick J went low 10s (maybe he hit 9s) with a gas block, and Andy Miller claims to have went 9.70s with a gas block.

young olds

This is what I was thinking, looking at a sb and a bb side by side the bottom end looks better, more tied together, than a bbo

Rick Finsta

I'm more worried about the stock rods in mine than I am the block, at between 450-500hp and 6500rpm. Piston to head clearance is tight on mine (0.034") though so I wouldn't spin past that. I've got a 680g piston and pin which I wouldn't exactly call lightweight. I do have main cap straps.

80 Rocket

Mr. Finsta, great to hear from you! Do you remember what Nick Jeffrey was doing with his gas block?


Now that you are here, us small block guys can start rallying and taking over.

83hurstguy

I always thought Nick said his safe limit with the gas block was 550 hp. I remember him saying that a few times... no ideas on the details of the rotating assembly or RPM. It may be a touch conservative, as I can't remember what power level he broke it at.

CutlassRacer on ROP had a pretty aggressive 355 that was seeing some nitrous use too.

Rick Finsta

For some reason its in my head that Nick had water problems with his heads and that's when he pulled everything apart. Someone at R&S in Albert Lea would probably remember. He was going 10.80's I thought at the time? Kevin was into the 10s on nitrous I thought - he was running low 11s on that pump gas 355. No slouch for certain.

Looks like I might be sticking a Jones cam in my junk this summer and sticking a mid plate in so I might have the heads off and poke a stick at the bottom end and such while I'm at it.

wr1970

I just want to say welcome to the site Rick hope you stick around.

madmax442

Gas Blocks big or small are pretty much the same except for the obvious deck height, main and bore sizes, I believe once you are up in the 500+ range it's a crapshoot as to what fails first!

wr1970

I checked the full throttle list for reference! It says that two guys went deep nines on gas 350 engines. Now that info may not be correct if they were using dx blocks.By the info i assume these were gas 350 blocks. I would think above 500 hp also.

young olds

curious what you guys would estimate for hp on this

350 .030 over
9:1 comp
quadrajet with 1" tapered spacer
holley street dominator intake
#7 heads, crossovers filled, pocket ported
.540 lift 227 dur. single pattern on a 114 lobe separation
stock exhaust manifolds

madmax442

325ish.

young olds

No one else would like to chime in with an estimate?

olds 307 and 403

I have heard 900 HP on a boosted gas block but that was way over doing it. BTR says 650 HP and would think that is right. The SBO has A LOT fewer bottom end failures no doubt due to much lighter parts and smaller bearing sizes. You will be closer to 350 HP and 350+ torque. Look at 80 Rocket's mild 350 build. I am thinking 325 HP with a smaller cam for my build. I would think even cheap headers add what 25 HP and 20 ft/lbs of torque? My car all ready has dual exhaust and the manifold capped.

coppercutlass

I feel like thats a bit too much cam IMO.

young olds

Cam seems very mild to me, I've been driving this everyday, mark ground it for me.

coppercutlass

I just figure duration would be in the lower 220's. With that duration i would personally imo want 9.5 to 1 but thats just me.

cutlassefi

It was basically done as a blower cam because that's what he planned to do with it. The wide lobe sep really tames them down.

cutlassefi

young olds

I was getting there, wanted to see opinions on n/a hp first. I've been running between 6-8 psi for almost a year now, adjusting and tuning.

young olds

Idk how much hp 8 psi adds but when we were talking about a cam we were talking 550-600 hp at 10psi

olds 307 and 403

With quality parts, 500 hp should be no problem. Thre 650 hp is probably a full girdle number. I just really like GM's best 350.

young olds

Been tuning the car for a nearly impossible to win race, against a 65 nova, playing with boost and meth. I turned the boost up to far today, hit 19psi and the clutch started slipping, let off as soon as I saw how much boost I had. Shooting for a safe afr at 15psi which should put me around 600-650hp. I'm hoping traction will be on my side since I know the nova doesn't hook and will be playing catch up

young olds

My opponent, my dads 65 nova. A destroked 502(477ci) dart 360 heads with 2.30 intake 1.88 exhaust, massive turbo, th350 transbrake, stock rear suspension, factory rear end( spool, axles and 3.36 gears) on 26x10.5 tires. Last time it was at the 1/4 mile it did a mid 11 at a bit over 130mph. Estimated 1200hp at 20psi
392E0F0B-8AFB-4C6B-937E-280E7C4FEFE3_zpsc6kqivk0.jpg
AFFBAC0B-4649-4183-9993-ECC078457852_zps0ld9iiuq.jpg

Pictures are from when it was still a 502/iron heads. Same turbo setup though

madmax442

No intercooler on that nova! Hope he's got a methanol injection kit to keep the inlet charge somewhat cool!

young olds

Meth kits keep things more than somewhat cool. I've ran my car, at full operating temp, and shut it off pulled over to touch the intake and turbo and you can easily rest your hand anywhere from the compressor housing to the intake runners. But no he doesn't, with as big of a turbo as it is I doubt the temps get very warm at his boost level. Though injection would be a great idea not only for cooling affect but octane boost too

wr1970

Who is sitting in the trunk. Cool stuff you posted on the nova.

young olds

That's my dad, owner of the nova.

Olds468

I ran a 350, with TRW flat top pistons, stock rods, cast crank, W31 cam, larger valves in the heads ported the heads both intake and exhaust, Holley dominator intake. Ran this for 4 yrs up to 7200 rpm and did not have any problems. Was not pushing any huge Hp, but internals were heavy as hell. With light weight pistons, rods and a steel crank, I could see that you could push close to 700Hp and not have too much of a problem.
Put a halo on it for extra security. Also the weight of the car and if you use a transbrake for racing play into the longevity of the bottom end.