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post #1 of 11 (permalink) Old 11-24-2015, 10:06 PM Thread Starter
 
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setting Rev limiter/redline

Ok 1st the shop that built my engine doesn't do many pontiacs, and the ones they do do are typically standard rebuild. That being said we went for dyno tune today going to set the Rev limiter and figure out redline. The theory we were going by was we would start at 5500 go up by 200 rpm and till we saw a power drop. At 7300 she was still pulling. I told them to stop. 4.5 stroke on factory block I started sweating it a bit. Gotta take it back next week to finish but still. Should I be happy she wants to keep on pulling or do pontiacs typically pull tell they die? Just curious, I know I'll be pushing it at the track but I was planning on about a 6k shift point now from the test I am looking at substantially higher. Just nervousness I guess.
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post #2 of 11 (permalink) Old 11-25-2015, 07:59 PM
 
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Originally Posted by maktope View Post
Ok 1st the shop that built my engine doesn't do many pontiacs, and the ones they do do are typically standard rebuild. That being said we went for dyno tune today going to set the Rev limiter and figure out redline. The theory we were going by was we would start at 5500 go up by 200 rpm and till we saw a power drop. At 7300 she was still pulling. I told them to stop. 4.5 stroke on factory block I started sweating it a bit. Gotta take it back next week to finish but still. Should I be happy she wants to keep on pulling or do pontiacs typically pull tell they die? Just curious, I know I'll be pushing it at the track but I was planning on about a 6k shift point now from the test I am looking at substantially higher. Just nervousness I guess.


Glad you told them to stop - I hope no damage has been done. With that said, there are many factors that determine the RPM limits of an engine. Waiting for the power to drop is the most absurd thing I have ever heard UNLESS they have already calculated a few formulas that determine max RPM's of an engine assembly and were observing power drop off based on head flow or carb flow(?). If you put a 2 Bbl carb on your engine and the power dropped off at 4,000 RPM's, would your machine shop guys figure that was it and set the redline for your engine at 4,000? On the other hand, if you had 2 Holley Dominators on the engine and it would allow the engine to rev to 10,000 RPM's, would your machine shop guys buy you a new engine when it blew up at 8,000 RPM's as they were looking for the "drop" on the dyno? Sounds scary to me, BUT, I am not an expert on this subject by any means. The 409CI I had would never quit pulling and kept on making power past 6,500 RPM's. I learned that the limiting factor was the factory outer spring which would break at 6,500 RPM's or so. The inner spring kept the valve from dropping and damaging the engine. Finally figured this out after the 3rd broken spring - 6,400 RPM was max in an all out drag blast. So what factors determine an engines redline?

There are many factors that come into play in determining your max RPM for any given engine. Most widely used is the piston speed in feet per minute based on the piston material/pin and its total weight. Other considerations are head flow CFM's, fuel flow, carb size, cam, valve springs, crank journal size, bearing speeds, oil pressure, side loads, the rod to cylinder bore angle, and other info that needs to be calculated via known formulas that will determine your engine's RPM limit - not trial and error. Perhaps your engine builder already calculated these numbers for you and knew these before doing what he was doing to determine engine RPM's in 200 RPM increments? I know my 455CI build will be limited by the factory iron heads and not any of the engine internals.

Here is a neat read that gives you some idea about the piston speeds. There is a section on "Calculating RPM Limits." Understanding Piston Speed in High-Performance Engines

Although this is about Ford engines, it gives you a good explanation and some comparisons within the Ford engine family plus recommended piston fpm speeds and a simple formula at the bottom to determine an engines max RPM.
http://www.mustangsandmore.com/ubb/S...stonspeed.html

Hope this helps with your question.
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post #3 of 11 (permalink) Old 11-25-2015, 09:32 PM
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4.5" stroke... large journal (428/455) or small journal (400) block? --- Also, what kind of rods, and are you running a forged or cast crank? What kind of valve train?

If it's a large journal block, cast crank - even with very good rods I'd be very hesitant to spin it much past 6000 with that much stroke.

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post #4 of 11 (permalink) Old 11-26-2015, 10:41 AM Thread Starter
 
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Large journal block, probe pistons forged h beam rods forge crank, not sure on the valve train that was decided between Kauffman and my builder.
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post #5 of 11 (permalink) Old 12-05-2015, 04:57 PM
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To answer your question, yes, a Pontiac will rev until it explodes or spins a bearing very easily, especially if it has good valve springs. With a big journal block, I'd be leery of anything over about 5800 RPM.....never mind having a stroker crank. That would make it more of an issue, IMO. Way back when, I ran my stock rod, stock piston 428 up to 7000 RPM...and it cost me the crank and bearings. They will do it, but it's not a good thing. Best to cam the engine to make all its power lower down on the RPM scale. I have shifted the 389 in my '65 and the 400 in my '67 at valve float in the past, not a good thing, but heat-of-the-moment and no damage done. But these are small journal short stroke engines. Still, very easy to grenade if not careful. I don't do any of that nonsense these days, that's for sure.....
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post #6 of 11 (permalink) Old 12-05-2015, 06:14 PM
 
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My engine guy built a 4.5 stroke engine. It made 755hp @ 5900 rpm, if I remember correctly. Also made 700+ ft lbs of torque. There is absolutely no need to wind a 4.5 stroke engine passed about 6000rpm IMO. Gear it to use the torque, instead.

BTW--That engine had a small journal block, port matched KRE High Port heads, a solid roller, and a 1050 carb on E-85.

Here's some more details and the dyno sheet. As you can see, the power went down, after 6000 RPM--not up.

http://forums.maxperformanceinc.com/...61&postcount=1

Last edited by oldskool; 12-05-2015 at 06:31 PM.
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post #7 of 11 (permalink) Old 12-06-2015, 11:37 AM
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I'm no expert on dyno testing, etc, but I do know that if an engine is making more power at 7300 RPM than 6000 RPM, that it is breathing really well and designed for high rpm: large ports, HUGE valves, heads would be flowing 300+ CFM, a lot of cam, A great roller valvetrain, great exhaust scavenging, etc. In other words, it would be spec'd like an old NASCAR engine, where the power was all up high and meant to be driven in the high RPM range at all times, at peak HP levels. For a street engine, I would want just the opposite: Max HP and torque down low, where I could use it to pull a tall rear gear and move out with ease. An engine that makes it's power at 7000+ RPM is going to be a saggy, soft, sluggish performer on the street 99% of the time.
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post #8 of 11 (permalink) Old 12-06-2015, 01:29 PM
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Step 1
Build engine.
Step 2
Increase RPM until it grenades.
Step 3
Rebuild engine to same specs.
Step 4
Set rev limiter 500 RPM below grenade point.
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post #9 of 11 (permalink) Old 12-06-2015, 06:44 PM Thread Starter
 
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Oh my I just reread my post. 6300. It was still pulling at 6300. Builder wanted to take it up to 7k or until power drop. Geetee. I think I have 2.11 1.62 valves. Had heads ported to flow 340 intake matched. When we ran them here they flowed just over 360. I was just under the impression I would get about 500 more rpm 6k redline. I got scared lot of ot went into paying for this thing.
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post #10 of 11 (permalink) Old 12-07-2015, 04:17 PM
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Any chance you can post the dyno sheets and some more specs on the engine?
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