MelWff

If no other changes have been made to improve the valve train or bottom end, I think it would be unwise to go beyond 6,500.

gkull

Overall this is a worthless post. When I was younger and bought stock motored cars I used to get so sick of how most models had such a lack of HP. So I would build a hopped up version and just take the old motor out for a last ride before retiring them.

I found that stock Chevy's with a bunch of miles and years could not spin their self fast enough to blow up. I would drive with my foot on the floor in first gear and try and pop the motor.

It is a combination of poor flowing intake track, small valves, small CFM of flow, weak springs with heavy rotator cups, and a Cam without enough lift or duration. It makes for a motor if dynoed, would have peak power at a relatively low rpm and drop off to hardly any power above that. It is a self limiting max rpm and it has little if any power at higher rpm. So it can't blow up.

Now with big flow intakes, heads, cams they are making high HP at high rpm and that is when you are going to fail the weakest link. I have personally broken crank shafts. (nice forged aftermarket) Valve train failure with AFR heads.

If you own a stock type motor it is out of power below the listed red line. so a smarter person shifts

vince vette 2

So true. When I bought L82 in 1980 I regularly ran it to 6,000 RPM in first figuring that the 5,200 RPM redlinie was just GM being conservative. Then saw a spec saying I should be able to run run 0 to 60 in about 7 seconds. So of course I had to check that out. Well, running up to to 6,000 RPM before the shift to 2nd got me about 11. 5 seconds. So then I just opted to put it drive, stand on the brakes, run it up to about 2k and release and, sure enough, a tad under 7 seconds. I learned a lot that day and through later reading about peak torque, peak hp, etc. etc. On the plus side, I did prove that an L82 could be run up to 6k rpm repeatedly without apparent harm. Of course, how repeatedly is an open question. But at least as often as a 21 year old might do it until he decides to learn something.

As for a stock 400 since this was never a high output engine I assume it was never cammed to shift the power band up, so as someone else pointed out, beyond low to mid 4000's rpm, nothing is gained. e.g. L81 which was the standard engine in 1980, peaked out at 4,200 rpm.

Averystingray75

It’s not a totally stock motor just BOTTOM end
Top is VORTEC heads, nice intake carb and exhaust

And I started this post to settle a pretty heated argument so it’s not worthless to me

calwldlife

in stock form a 327 will spin higher safer than a 383.
as stated earlier, weight of rotating parts.

even say a sbc 427 with hardened assembly can spin higher than i would ever
reach.

as far as floating before exploding, i have heard that
idea.

tough call.

F4Gary

Why not just present the argument for us to help you win? That way it makes you look a lot less incompetent.

Big2Bird

You might as well argue "How long is a piece of string?"

You could play GM, build two, and let one grenade. Even then the other might grenade lower or higher due to production differences.

BLUE1972

I thought of a funny thing I overheard as a kid in a speed shop, frustrated the engine builder said: keep revving the engine slowly until it blows, right down the RPM and then set the rev limiter 300 - 500 below that. Rebuild the engine with the same parts and you should be good. (1968ish)

The owner had said he did not want to leave and HP on the table.

The engine builder had told the guy to set the rev limiter at 6000 rpm on his 67 - 327 corvette, I almost peed my self.

gkull

Which Vortec heads do you have? Vortec heads introduced several years ago (PN #12558060)1.94-inch intake valves, and 1.50-inch exhaust or "small-port" (PN# 25534421) 2.00/1.55 valves, which are better 185 cc

The vortec heads from everything I can find are worth 25- 40 HP over older heads which is really nothing when held back by a stock low performance 400 h-flat cam and some low compression dished stock pistons.

Rpm + HP can break the bottom end, but if you are past peak power a TQ things drop off pretty fast especially the more CI you are feeding.

400's were never hot rods because of the cam and compression. so GM never put good internal parts in them

I'm not sure how you can have a heated argument over a motor that generally came in 1500 pickup trucks. your changes make for some more TQ than a 350 just be happy

Averystingray75

Here’s the argument in a nutshell:
I said if i went out to my car right now and with engine warmed up held the throttle to the floor and never let up ...
- my prediction rpm will continue to increase but slow down higher in the rpm range probably around 6-7k and after a few minuets something in the bottom end will break, rod cap bolts, piston to rod connectors but with way a rod will go through the block.

- his prediction: the rpm will stop pretty low and the valves will “float” and rpm will not increase past that point the heads valves or etc will either fail or sit there and nothing else will happen eventuallly the engine will overheat or oil flow will case some an issue at that point but effectively I could hold the gas pedal down for quite some time and the heads will limit the bottom end from exploding.

So who’s right?

Averystingray75

To respond to gkull:

My vortec heads casting number 10239906,
Came off ‘95 Chevy k1500

What heads are you talking about?!
Only “vortec” heads I know of to fit this gen sbc ends in ‘906 or ‘062

Knerf

the 100% way to end this argument is just go do it.

let us know how it turns out.

Averystingray75

It got to that point honestly he said he would replace the engine $
But it’s a ‘509 block and really hard to get these days
And I’m Worried about my front clip aftermarket C3 Vette Ecklers body kits discontinued the fiberglass work to fix a scar is more than the engine is worth

I’m super confident a rod will puncture the engine block but I don’t think my friend has the $$$ to back up the disagreement considering if I’m
Right it would be thousands of dollars of damage

That’s why I’m consulting you guys to get some positive real world feedback because at the end of the day... I’m not gonna take this bet and potentially ruin thousands of dollars of car parts

Big2Bird

That's the correct answer.

Knerf

knowledge is the true prize in this bet, i say go for it.

Big2Bird

We could all chip in $20 for the video clip. Have the Road Kill crew do it.

derekderek

Too bad myth busters is no longer running...

L88Plus

Grew up poor, had no idea what a torque wrench was. I was rebuilding a V-6 in the 70's and asked my Dad how tight to get the head bolts.
"Tighten one until it snaps, then replace that one and don't tighten the others quite that tight". Of course he was joking but had the same message.

lionelhutz

You claim you've spun the engine to 6000rpm so how can any claim that the rpm will stop climbing at some low value have any merit? You would definitely be running it over 6000rpm if you did the test.

So, the engine WILL be over 6000rpm. At that point, a rod might let go, the crank might break or a piston might fail. But, the bottom end might also stay together just fine until you decide to lift or the valvetrain fails.

You can't know unless you do it.

cv67

valve float can happen before you hear it, if you dont have an "ear" for it get a rev limiter
I wouldnt run a stock 400 bottom end over 5500. No reason to with a tiny head anyway

If your engine is nosing over at 4500 for instance theres no point in