Stevolwevol

iTrader: (1)

My 86 IROC "yellow lines" when I shift from 1-2 at WOT. At WOT it will not matter whether I shift it manually or let it shift by its self. It will go to about 4700 before it shifts.. It seems to handle it fine, but I am concerned it is too close to the redline.

RedHawkLB9

factory shift points are at 5000

AlkyIROC

The factory "red lines" are usually where the engine makes peaks power. Going above that with a stock engine doesn't usually hurt anything unless you really go above it. Going above that with a stock engine means you're HP curve is dropping off and you need to shift to get the rpms back into the power curve.

Where the engine makes peak power depends on the engine. Yank out the 305 and put in a well built 350 and you could go to 6500 with no problems.

I shift my engine at 7400 rpm. My rev limiter kicks in at 7800. Tachs with an adjustable red line pointer should be set at the shift point which is just before where the HP curve drops off. Technically, the engines real red line is just before the valves start to float. With weak valve springs, that number can be very low.

Stock tachometers are known to be highly inaccurate.

Stevolwevol

iTrader: (1)

So if I redline just past 5000 rpm before shifting, I am not risking engine damage? BTW, I really like my 305's LOL

AlkyIROC

If your valve springs are weak, you could float the valves and cause damage.

It's not like you're going to throw a rod or something by taking the rpm a little higher. As I mentioned, going higher than the peak HP loses power and you won't go any faster.

Stekman

If they're the stock springs, you'll bounce the valves before hurting the bottom end.

Stevolwevol

iTrader: (1)

It seemed to be running strong at 5000 + revs. I'm not sure what to look for when it comes to valve floating, and bouncing. How would I know if my valves were floating, or bouncing??

Stekman

As Stephen noted, it's a noticeable loss in power. If it's bad enough, you'll start hearing interference noises. That's the valve bouncing off the seat.

I've also heard more of a buzzing/quick tapping noise, which was caused by the open pressure of the springs not being strong enough and the rate of acceleration of the lifter causes it to leave the surface of the cam, over the nose. The buzzing being the return of the lifter to the cam. This is more of an issue with aggressive cams, and springs not adequate for the job, though.

Stevolwevol

iTrader: (1)

I do not know what the history of this engine is. It could be bone stock, or it may have a better cam than stock. Maybe the springs have been replaced.. I did not hear any unusual noises or a lack of power, I just noticed I passed the redline. It sounded pretty sweet. I just don't wanna push a 23 year old engine too hard. I want my mother to stay active, but I wouldn't want to make her run around the block ten times though..

AlkyIROC

Valve springs don't last forever. Even factory springs wear out. A typical factory valve spring should have around 80 pounds on the seat. I've seen some that were so weak, you could easily push open the valve with your thumb.

You'll know when you have valve float. It will happen at lower rpms as a lack of power. You'll lose a lot of low end power because as the valve is being slammed closed by the spring, if the spring isn't strong enough, the valve will bounce on the seat and vent off cylinder pressure.

As for your shifting at 4700, without a reprogram kit in the tranny, it won't matter if you let the transmission shift by itself or manually shift it, the max shift point will be the same. You would need to adjust the transmission governor to raise the automatic shift point. 4700 is fine for your stock engine. It's not designed to make much power above that rpm. 5000 at the most.

Stevolwevol

iTrader: (1)

Thanks for the info Steve,, I just don't wanna blow the engine, or take years away form it's life. It has only 93 k on the engine, so being a bullet proof chevy small block, it should go for a long time yet.

kkingsrulee

Oh this is interesting, so you guys are saying I am more likely to do damage to the valve train than the bottom end (rods, bearings, etc.)? My engine has 220,000 miles on it, (305) and it doesn't make any weird sounds, leak oil, and pulls alright, but I've always been worried about taking it over the redline, I usually never take it over the redline, so where exactly do you guys think it starts losing HP at? Stock L03.

Stekman

I wouldn't say you're more likely to "damage" the valve train, it's just the weaker link when it comes to RPM's. Especially on a stock engine, where clearances between the valve and piston are on the higher side, it would be less likely than say your 8000 RPM race motor, where VP clearance is minimal, at best.

The problem with valve float, the way that Stephen and I are referencing, is the springs seat pressure not being strong enough to control the valve at higher RPM once the valve returns to the seat. The valve will bounce off the seat and *can* hit the top of the piston. That's the interference noise I was talking about.

As long as it pulls well, and you're mindful of RPM's, there really isn't a need to worry. As for when it loses power, it depends - again, talking about bouncing off the seat, it would depend on exactly how weak the valve springs are. If they're only mildly weak, it would be at a higher RPM than say if they're extremely weak, to the point of being able to be compressed with finger pressure. The weaker the seat pressure (the older, more worn out the springs are), the lower the RPM will be at which valve control is no longer possible.

AlkyIROC

My old 383 was well abused. It was in at least 2 other cars before being put into the Camaro so it had high mileage. It had a really good solid cam and the first year I raced it, it struggled to get a 14 second timeslip because of poor heads and converter. Over the winter I changed out the heads to some camel backs with lots of port work, bigger valves and proper springs.

The engine was an old school 383. Stock cast 350 pistons. Factory cast 400 crank. Stock 400 rods and rod bolts.

For 2 years and 200 trips down the track, I spun the engine to 7000 rpm before the engine finally blew up. I don't know what failed first. It was either a thrown rod from a broken rod bolt or a piston disintegrated. There was so much damage, I pulled the heads and intake off and threw the rest into the scrap metal bin.

After taking off the smog heads and installing better heads and taking out the 700R4 to put in a TH350 with a 3800 stall converter, the car went from a 14.0 at the end of the first season to a 12.0 on the first pass of the second season all with 3.27 gears and 26" tall slicks.

After the 383, I went to a BBC and have slowly increased the size to the current 540 after breaking a few BBC engines.

I was spinning that basically stock components 383 to 7000 for 2 years before it failed. I doubt spinning your 305 to 5000 is going to be an issue unless there's already something wrong with it.

kkingsrulee

Alright thanks for clearing that up.

Stevolwevol

iTrader: (1)

I went to your web sight and saw and read about your 87 IROC.. Sure is sweet! Have you ever been to what used to be called Martin Drag Way in Michigan? I'm not too far from there... I did look under the hood and looked at the water pump/ timing cover area, and it looks like it's been removed at one time. Maybe just a chain replacement, or maybe a cam change. I know someone put a shift kit in it, or replaced the tranny w/one. It just seems to take the revs w/o a problem, and I didn't notice a power drop at 5200 revs. It was still climbing nice and fast. I know... It's not a built up 350, but it performs pretty darn good. Especially w/ the 3.42 rear end I put in it.

AlkyIROC

The only US track I've raced at is Yakima back in 2002. I'd like to get to Spokane in the next couple of years.

It sounds like you may have a cam change. Ignore the yellow/red marks on the tach. They mean nothing with aftermarket parts. Shift where it feels good.

Stevolwevol

iTrader: (1)

Do you know if there is a built in rev limiter in any of the 305's? It did feel good to shift past redline. I did not feel any noticable loss of torque. BTW, where is Yakima?

kkingsrulee

No, I'm almost 100% sure no stock 305 came with a rev limiter, they are pretty exclusive even to this day unless you have a high performance car.

They came with governors but no rev limiter.

Stevolwevol

iTrader: (1)

Does the governor control the speed of the car, or rpm?

kkingsrulee

Speed.