Inliners International Forums General Discussion Engines 250 'somewhat' stock maximum safe rpm range

I'm looking for what would be the safe maximum (red line) rpm. I've built a 250 that was the stock block in a '67 C20 bored .030. I used stock bearings, oil pump, rod and main bolts, rods, pistons, rockers and push rods. I've put a comp cam 252 duration cam with recommended the comp cam springs and lifters. Opened the valves to 1.84 intake and 1.60 exhaust and mildly ported (basically smootherd all surfaces and cleaned off the rough surfaces on the valve guides), and installed bolt in lumps from Tom Lowe. I had the block decked to zero clearance (cut .032) and cut the head .020 on the deck surface. I have Langdon cast iron headers and an Offenhauser 4 barrel intake with a 450 Holley. It also has HEI from a '76 250. It seems to run with the most power between 3000 and 4000 rpm's, but I'm a little nervous to take it much over 4300. My bearing clearances and crank journals measured in spec according to the numbers in my '67 engine manual. I think it should take 5000 rpm's with no problem, but I'm not sure.
Also, what components(s) are keeping me from running more rpm's?
p.s. - your posts have been extremely helpful and value your opinions!

Hi Jim, most times it isn't practical to rev or turn an engine above the point it quits making power. I would look at the RPM range on the cam, and use that as a reference for how hard you need to turn your engine.

Looks like a good combo you got there.

It's also nice to see some people take advise of what I always suggest(zero deck).

Also w/the 1.84 intake,,,,,why loose some bottom end & mileage w/the 1.94 especially w/the combo you have there.

Your cam only has 206 duration @ .050,so pushing it to 5000 RPM will be out of the cams power range,it could go to 5K,but probably not make peak power there.

Comp says 1000 - 4200 max RPM.

The main thing that holds back the 250 from reving freely & smoother is the stock damper,,,,by installing a good aftermarket damper,or a stock SBC 300 Horse 350 CI 8" damper will be much better.

What kind of compression are you running?

It's been so long since I had a stock 250 running,but IIRC,they would rev to 4800 RPM,would not make much power there,but that's what I remember shifting to 4800 in my Moms 73 4 dr Nova 250 w/a PG.

If you want to turn to 5000 RPM,the next size cam would be better ,the 260H cam has 6 more degrees duration than your current cam.


MBHD

Jim,
With that cam, you should be able to see 5k rpm. It may start dropping power output by then. One thing to consider, The lower end will take 5K rpm no problem. I would be more worried about valve float if it were a v8. But one unique thing with the chevy chamber shape will allow valve float without damage, to a point. The valves sit almost 1/2" above the edge of head in the chamber, very hard to hit a valve.

The 292 dyno mule revved to 5400 rpm with no complaints and that was with a duration of 214 @.050. So the little 250 should also easily see 5K rpm comfortably.

Get some videos of it. How does it idle?
What is the WOT timing set at? Tom

The angle of the valves makes it so it's not close to hitting the pistons.

MBHD

With that cam the power should be dropping off after 4500 RPM, there would be no reason to turn it any faster than that. The lower end of a 250 will take as much as 7000 RPM with lots of cam and carburetion so there would never be any problem at 4500.

I would be concerned with the stock 11/32 rod bolts if you are going to wind a 250 up in rpm. In fact, I would be concerned about the stock bolts in a grocery-getter too.

If using stock rods, I recommend ARP rod bolts. Use bolts for early small journal small block (283 v8) application. Make, buy, or borrow a stretch gage. I've used a micrometer to measure stretch but a dedicated gage is much easier.

Recondition rods (resize big end) is recommended after bolt installation. However, I've run rods with new bolts without resizing and not had a problem other than asymmetric witness marks on the bearings upon teardown. Not ideal but better than a rod through the side of your block. Make sure the underhead and under nut seats are smooth and there is adequate clearance for underhead radius.

holds back the 250 from reving freely & smoother is the stock damper

Do the 194/230 use the same dampers as the 250?

Tom,
I haven't checked compression since it has been rebuilt and I also have not checked the timing advance since prior to the rebuild, but the timing was advanced about 26 degrees at max rpm prior to the rebuild. I will definitely recheck both this weekend (it is currently cold in my unheated garage!). I'll get some photos this weekend and attach-hopefully. It idles a little rough, my wife calls it the popcorn popper until it gets some throttle. I think it's the dual Cherry Bombs that create most of the idle noise.
Hank & Panic
I regret that I didn't drill the crank to accept a SBC dampener, but instead installed a new stock (6.75") dampener. I didn't drill it because this is going to be daily driver, for my son, and I assumed a stock dampener would be fine. (FYI - My son and I read Leo Santucci's manual from front to back before starting this project, but I guess I didn't pay enough attention to the dampener section) But if the crank ever gets removed or changed, my son or I will get it done.
My cam card range power range is 800-4800 rpms, hence, my rpm range concern. Maybe someday my son go for the bigger cam.
Strokersix
I forgot to mention that I had to have the rods refitted for stock bearings and I had new, stock rod bolts and nuts installed.
Thanks for all the input - will supply requested info soon.
Does anyone know what kind of compression, in psi, I should expect? And is the stock fuel pump adequate?

I believe the stock 194 damper is a single groove.

Not too sure about the 230's,but I think depends on what year the 230 is for t to be single or dual??? Anyone care to chime in?

The problem w/the SBC dampers, is ,they require relocation of your water pump pulley,alternator,power steering brackets.

Or @ the very least you could run a SBC 6.750" damper @ have the "V" grooves machined into it. That would be fine for a daily driver.

What type of pistons did you install in your rebuild?
Dished w/a big chamfer on the top sides of the pistons?
Or dished & the rest is a flat top?

26 degrees of total timing is a bit low by about 8 - 10 degrees.

As far as drilling the crank for damper retaining,if you have room for a drill,you can drill it on the car. They are not hard to drill.

Stock fuel pump should be OK,but I think for an upgrade you ca use a 292 pump,they sometimes have a 3/8ths outlet instead of 5/16ths? But ask here from the BB for a more definate answer.
MBHD

The wide open throttle timing (checked in neutral @ around 3500-4K rpm) should be around 36 degrees. I would not worry about the compression since it all together and running good. I bet it is below 9.0 to 1.
Fixing the timing will certainly help it. Tom

Get some video and post it up. Sure sounds like a fun project for you and the son. Tom

Hank,
My pistons are the dished & the rest is a flat top.

Regarding the dampener, I do have enough room to access the crank to drill for a bolt, BUT, after I thought about this, I was wondering how much much affect my 11" flywheel and clutch have on engine vibration/performance (the 11" clutch is listed as the heavy duty option for my truck). Basically, do you think that I'll see a benefit from SBC dampener in a sub 5000-5200 rpm situation with this clutch and flywheel or am I looking at this incorrectly?

In regards to the distributor, I've read that the weights and springs in a SBC are same parts that are in an inline. Is this accurate? By the way, you and Tom were right, my distributor is not working properly. I'm working on correcting it.
Thanks.

I'm still working on gettin' some video and pics posted. I'm looking for some advice on how to post a video.

I would not worry about putting a SBC damper on a 5000-5200 rpm engine. It is not a bad idea to put the bolt in for the balancer though.

Upload the video to Youtube or to one of the many pic/ vid sites ( like imageshack). A newer digital camera can shoot nice videos.

Get that timing fixed with some newer V8 tuning parts and then see how it behaves. Tom

I ran an 11" clutch before & worked fine,they are (0)/neutral balanced.

As far as the damper goes,,yes you will see & feel the improvement.

I ran for many years stock dampers(because I did not know better)
until I switched to a SBC 8" damper,,,,,WHAT A DIFFERENCE!
My engine would run smoother everywhere. From idle to high RPM.

I would highly recommend it.

Is it absolutlety necessary in your application,,,,no,,,but like I stated earlier,your engine will run smoother & not make the flywheel or flexplate or torque converter bolts to loosen up as they do much more so w/a stock damper.

For your distributer timing,,,,run as much initial timing as the engine can stand(w/out detonation), example 15-20 degress initial & 20-15 mechanical,,,(thats just an example3)& then the rest can be mechanical advance along w/your vacuum canister advance.

With your zero deck & having a better squish band,,your engine should be able to handle more agressive timing.

Hope this helps.


MBHD

Never mind, someone will just tell me I'm wrong.

Just post away,we are all learning here.


MBHD

I've repaired the distributor, but haven't gotten to the test drive yet, but I recently discovered that I might have the wrong carb adapter plate (1 11/16" bore) installed for the Offy 5416 intake. I'm hoping that one of you guys can tell me what the 5416 bore size is, so that I don't have to pullit back apart to check.. I assumed that the bores on the carb adpater were the same as the carb and intake. But, as sometimes happens, I might get some practing R&I 'ing, and also be reminded of the true definition of assume.

Hank,
You and others have mentioned squish / squish band. What does this mean? I have an idea that it relates to compression rate based on cam timing in relation to RPM rates and rates of change, but I'm not sure.

Tom,
I think I figured out the pic posting process. We'll see how well it works.

Thanks for all the help

http://yfrog.com/4v1002419jx

http://img175.imageshack.us/g/1002419.jpg/

Jim,
x2 on the other posts, great build.
I've run my home grown computer the Gonkulator on Tom Lowe's 292 dyno tests, so here is what I compute for your build. My main caveat to these numbers is that I have no dyno data yet with Langdon's cast headers, Tom Lowe plans to get some during his next dyno series. So for your engine I calculate:
Torq 258 at 3500
Powr 226 at 5000

Since you describe the engine fading after about 4300 I think something is wrong with its tune. I like about 36 total advance, 26 seems way too low. Or, another easy thing to check - here is the Gonkulator if the secondaries don't open on your Holley:
Torq 248 at 3200
Powr 203 at 4700
If this is happening, and advance is too low as well, that could explain what you're feeling. Put a paper clip on the secondary diaphragm rod, slide it up against the housing. Then, go out and floor it thru a couple gears. When you get home, you should see where the paper clip had to slide down on the housing IF the secondaries opened.

Right now I am running a stock, tired 250 with a Clifford 4v intake and various 4v carbs (Holley and Autolite). The mismatched engine feels like a sick dog until about 3500 and then it feels like you flipped the "NOSS" button. I have to watch the tach to keep it BELOW 4800. So I think yours should be pulling to 5000 if everything is tuned right.
Again, great combination of parts.

Sounds like you have the Clifford intake no low end Blues.

Have you tried a Offy intake?

When you run the Offy intake, the carbs will get a much stronger signal also.


MBHD

Hank,
Thanks for the tip and I agree -
I don't have an Offy intake but no worries, I plan to "Grow" the engine into the Clifford, first a 292 will replace the 250, then a few parts added to that. So I am following T Lowe's dyno tests fairly closely to see how the two compare.

The Clifford intake is surprisingly driveable, this is a stock 3-on-the-tree car and I can just let the clutch out slowly and it will take off with the throttle closed and run. I was surprised it was that well behaved once I got a good carb on top and all the vac leaks sealed. But to the floor, you can tell, the intake is too big up to about 3500, and at that point the stock cam and exhaust are too small so everything is fighting itself. I knew this, I just threw it on the stock 250 to see how bad it would be. It does misbehave in "cold" weather, ie below 50F or so. So I would not suggest it as a winter intake for areas that have real winter like New York or Michigan. Some of those nights in DEtroit would get so cold you had to pull the battery out and bring it inside at nite so the car would start the next morning at -20F. Zings right over then.

Finally,
I've had the time to get all of my dilemmas taken care of. My timing is right and my carb is working properly (tuned). I thought it was running good after I put the lump head on, but I was able to get the carb operating at 100%, it is truly surprising how it runs!

I want to thank everyone that sent me in the right direction - T Lowe, Panic, CNC, MBHD, Beater and everyone else. This forum is an excellent resource for those of us that are new to inlines - sincerely - THANKS!

I ran into only one snag and it was related to the distributor. When I freed up the shaft and installed new springs I also shimmed the end play to .010". After installing it and running it for 10 or so miles I found an oil leak at the base of distributor due to the shims took too much space and didn't allow the distributor to set on the block properly (I didn't notice it when I originally installed it.) I was a tad befuddled by this, so I busted out Leo's book and reread the timing section. I noticed in one of the captions it said that shimming was not that critical due to the gear direction actually pulls the shaft toward the oil pan. I removed .041" of shims and rechecked. It didn't affect nmy timing and it eliminated the oil leak. I guess that is what I get for reading a forum on HEI repairs for bent engines - you know - the one that are like cow pies.

I still have to mess the with throttle linkage some. I made a temporary homemade setup that I don't care for the appearance of.

p.s. - if anyone didn't chuckle at Frenchtown Flyer's post on the "SBC or Inline" thread, then you need to get a better sense of humor because that was FUNNY!

One last question,
With an HEI on my engine, what should the gap on the plugs be set at?

I currently have them at .035" as that was the gap GM recommended for the car that the distributor came from. I'm asking due to I pulled the plugs to inspect and they appeared to be running cold. I have Autolite AP26 plugs.

.035 should be fine, the HEI shouldn't care.

Close it up a tad if you feel the need.

If the plugs are indeed running cold, I would step the heat range to the next step hotter that your parts store has on the shelf (as long as that isn't WAY hotter).