[C2] In praise of the 250hp 327
12-12-2018, 02:19 PM
#61
Race Director
12-12-2018, 02:58 PM
#62
Drifting
For the 1965 model year they also used the same -461 heads, so the only real difference that year was carb and intake manifold. I don't know about the exhaust manifolds used on the 327/250 Corvette, but on the full-size cars like mine they used the 2" outlet manifolds (with single exhaust pipes standard and duals optional).
Verne
12-12-2018, 03:02 PM
#63
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12-12-2018, 03:03 PM
#64
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C1 of Year Finalist (performance mods) 2019
You are likely confusing many people here with passenger car specifications. ALL Corvettes from day one have had dual exhaust standard.
12-12-2018, 03:08 PM
#65
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Yes and some of the other posts that followed that as well. However, I am speaking to the entire thread and the fact that this is a Corvette forum and that people come here to educate themselves about Corvettes. It is too easy for someone to become confused trying to educate themselves when we are discussing passenger car specs and not distinguishing that.
12-12-2018, 03:48 PM
#66
Burning Brakes
http://stlouisncrs.org/news_files/Ta...shaftsRev1.pdf
Last edited by AmericanPie; 12-12-2018 at 07:49 PM. Reason: Changed name of camshaft
12-12-2018, 07:20 PM
#68
Team Owner
My 63 car came to me with an AFB 3721S carb and an Edelbrock 3CBX intake manifold - a nice combo - but, without a head change, there was no "seat of the pants" change over what I felt when I dropped back to the original WCFB and cast iron manifold...
12-12-2018, 11:25 PM
#69
Drifting
12-13-2018, 06:32 AM
#70
Instructor
It is also worth noting: the 250 HP rating is GROSS. By NET-HP standards, it would likely come in @ 190-200HP, tops.
Last edited by Jonz79; 12-19-2018 at 09:27 AM.
12-13-2018, 10:52 AM
#71
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Thanks for chiming in, Duke. Yes, it does have the double-hump, -461 heads. The cam I had in mind is one of several "RV" type hydraulic grinds with ~205-210 degrees duration @ .050" lift. But I'm sure any of them would still move the torque curve up slightly from stock, which would compromise some low-end power. I've never really heard anything bad about the stock -929 cam, so maybe I'll just stick with it.
I'm assuming that the only noticeable difference between driving a 327/250 and a 327/300 is that the 300 HP pulls a few hundred rpm higher.
I'm curious what a "McCaw Special" cam is; I've been out of this for awhile and have never heard of it.
I'm assuming that the only noticeable difference between driving a 327/250 and a 327/300 is that the 300 HP pulls a few hundred rpm higher.
I'm curious what a "McCaw Special" cam is; I've been out of this for awhile and have never heard of it.
Don't drink the "RV cam" Kool-aid. Their duration a bit more than OE base engine cams, and they have more overlap, which roughens the idle and hurts low end torque and fuel economy. If you want stump pulling low end torque you can't beat the ....929 with stock heads and the McCagh Special with massaged heads. The ...929 is available from Federal Mogul, CS-274 and costs about fifty bucks. The McCagh Special is a custom grind that Crane can make and costs about 250 buck and REQUIRES massaged heads.
Since your 327/250 has big port heads, all you need is a big port manifold and AFB to have a 327/300. My experience with the 327/250 is that they don't make useable power above about 4500 and 5000 for the 327/300. The McCagh Special with massaged heads makes about the same low end torque and 327/350 type top end power with useable revs to about 6500 in a 327. The complete story is posted on this forum in a thread started by me - "A Tale of Two Camshafts", so it's an easy search, and you may find some other useful articles in threads started by me like the compression ratio article and tuning seminar.
Duke
12-13-2018, 11:06 AM
#72
Race Director
Interesting. When you say low end torque, what is your RPM staring baseline? Same as the 300/327 or 300/350? How would this cam be with an auto trans with stock converter?
Doug
Since your 327/250 has big port heads, all you need is a big port manifold and AFB to have a 327/300. My experience with the 327/250 is that they don't make useable power above about 4500 and 5000 for the 327/300. The McCagh Special with massaged heads makes about the same low end torque and 327/350 type top end power with useable revs to about 6500 in a 327. The complete story is posted on this forum in a thread started by me - "A Tale of Two Camshafts", so it's an easy search, and you may find some other useful articles in threads started by me like the compression ratio article and tuning seminar.
Duke
Doug
Since your 327/250 has big port heads, all you need is a big port manifold and AFB to have a 327/300. My experience with the 327/250 is that they don't make useable power above about 4500 and 5000 for the 327/300. The McCagh Special with massaged heads makes about the same low end torque and 327/350 type top end power with useable revs to about 6500 in a 327. The complete story is posted on this forum in a thread started by me - "A Tale of Two Camshafts", so it's an easy search, and you may find some other useful articles in threads started by me like the compression ratio article and tuning seminar.
Duke
12-13-2018, 11:54 AM
#73
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One of my basic engine system engineering requirements for a high performance road engine coupled to a manual transmission is that it produce at least 80 percent of peak torque at 2000 revs. With an automatic transmission my requirement is 90 percent at 2000, and typical OE converter stall speed is about 1800-2000.
I always request that dyno pulls start at 1000-1500 revs with an owner specified reline, but getting dyno operators to do this is like pulling teeth. I did get a chassis dyno operator to run my Cosworth Vega from 1000-7000, but it took a lot of effort on my part to get him to agree. In Mike's lab dyno test of his "cheater motor" the test starts at 3000 and terminated at 5000, when power was still climbing slightly, but Mike said he didn't plan to rev it over 5000. From the extremely flat torque curve I believe that it made the 90 percent peak torque at 2000 criterion.
I talked to Mike at last July's NCRS national convention in Las Vegas. He brought a stunning '57 airbox car that achieved a Duntov award - black with red interior, widebase wheels with blackwalls and dog dish hub caps... and absolute knockout! I asked Mike about the performance characteristics of the "airbox" car that has a "stock" 283/283FI engine versus the "Powerglide" car (Duntov award about ten years ago), which is the one with the McCagh Special camshaft 283 stroker "cheater motor" that's a subject of the "Tale of Two Camshafts" article. Mike replied that "the Powerglide car runs circles around the airbox car". I asked if he was serious or just stroking my ego. He said he was dead serious!
Duke
I always request that dyno pulls start at 1000-1500 revs with an owner specified reline, but getting dyno operators to do this is like pulling teeth. I did get a chassis dyno operator to run my Cosworth Vega from 1000-7000, but it took a lot of effort on my part to get him to agree. In Mike's lab dyno test of his "cheater motor" the test starts at 3000 and terminated at 5000, when power was still climbing slightly, but Mike said he didn't plan to rev it over 5000. From the extremely flat torque curve I believe that it made the 90 percent peak torque at 2000 criterion.
I talked to Mike at last July's NCRS national convention in Las Vegas. He brought a stunning '57 airbox car that achieved a Duntov award - black with red interior, widebase wheels with blackwalls and dog dish hub caps... and absolute knockout! I asked Mike about the performance characteristics of the "airbox" car that has a "stock" 283/283FI engine versus the "Powerglide" car (Duntov award about ten years ago), which is the one with the McCagh Special camshaft 283 stroker "cheater motor" that's a subject of the "Tale of Two Camshafts" article. Mike replied that "the Powerglide car runs circles around the airbox car". I asked if he was serious or just stroking my ego. He said he was dead serious!
Duke
Last edited by SWCDuke; 12-13-2018 at 12:05 PM.
12-13-2018, 12:55 PM
#74
Race Director
One of my basic engine system engineering requirements for a high performance road engine coupled to a manual transmission is that it produce at least 80 percent of peak torque at 2000 revs. With an automatic transmission my requirement is 90 percent at 2000, and typical OE converter stall speed is about 1800-2000.
I always request that dyno pulls start at 1000-1500 revs with an owner specified reline, but getting dyno operators to do this is like pulling teeth.
Duke
I always request that dyno pulls start at 1000-1500 revs with an owner specified reline, but getting dyno operators to do this is like pulling teeth.
Duke
That is one of my pet peeves when i see dyno pulls start at 2500 or 3000 RPM. You have no idea what the motor will do, or if it will even run well enough to accelerate, at 1500 RPM.
Doug
12-14-2018, 09:40 AM
#75
Instructor
Thread Starter
Thanks for suggestions
First off just want to clarify that in relating how much I like my 250hp base engine I did not mean to take anything away from the optional powerplants, Just thoroughly enjoy the characteristics for the way I drive this car which means 99% of the time I am below 2500 rpm.
That FI is absolutely beautiful without question!.
As suggested I am now in the process of installing a dual master cylinder so thanks for that.
Other very useful comment concerned playing with the conservative ignition timing. We have 93 octane here so that should help make it a safe exercise.
Finally, someone mentioned the base engine makes the car harder to sell, I will disagree with that, and in fact often get unsolicited offers on my car for 3X what I paid for it 20 years ago. What is obviously true is that the higher hp options and of course especially an FI will bring more money. I think all owners of nice C1 or C2 will agree they are a very easy car to sell at a solid and realistic price. As prices exceed $70k though the number of qualified buyers are fewer no doubt.
Cheers .
That FI is absolutely beautiful without question!.
As suggested I am now in the process of installing a dual master cylinder so thanks for that.
Other very useful comment concerned playing with the conservative ignition timing. We have 93 octane here so that should help make it a safe exercise.
Finally, someone mentioned the base engine makes the car harder to sell, I will disagree with that, and in fact often get unsolicited offers on my car for 3X what I paid for it 20 years ago. What is obviously true is that the higher hp options and of course especially an FI will bring more money. I think all owners of nice C1 or C2 will agree they are a very easy car to sell at a solid and realistic price. As prices exceed $70k though the number of qualified buyers are fewer no doubt.
Cheers .
12-14-2018, 12:47 PM
#76
First off just want to clarify that in relating how much I like my 250hp base engine I did not mean to take anything away from the optional powerplants, Just thoroughly enjoy the characteristics for the way I drive this car which means 99% of the time I am below 2500 rpm.
That FI is absolutely beautiful without question!.
As suggested I am now in the process of installing a dual master cylinder so thanks for that.
Other very useful comment concerned playing with the conservative ignition timing. We have 93 octane here so that should help make it a safe exercise.
Finally, someone mentioned the base engine makes the car harder to sell, I will disagree with that, and in fact often get unsolicited offers on my car for 3X what I paid for it 20 years ago. What is obviously true is that the higher hp options and of course especially an FI will bring more money. I think all owners of nice C1 or C2 will agree they are a very easy car to sell at a solid and realistic price. As prices exceed $70k though the number of qualified buyers are fewer no doubt.
Cheers .
That FI is absolutely beautiful without question!.
As suggested I am now in the process of installing a dual master cylinder so thanks for that.
Other very useful comment concerned playing with the conservative ignition timing. We have 93 octane here so that should help make it a safe exercise.
Finally, someone mentioned the base engine makes the car harder to sell, I will disagree with that, and in fact often get unsolicited offers on my car for 3X what I paid for it 20 years ago. What is obviously true is that the higher hp options and of course especially an FI will bring more money. I think all owners of nice C1 or C2 will agree they are a very easy car to sell at a solid and realistic price. As prices exceed $70k though the number of qualified buyers are fewer no doubt.
Cheers .