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#1
08-27-2019, 09:17 PM
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Engine Vac
Finally got my new 400 engine running. I am using an HC-02 cam I used in an engine in the 80's and 90's. That engine had 9.8 CR. 3310 vac. Holley. Iron heads. I recall, when tuning it, it had around 12" vac. Just can't remember if that was in park at 1k rpm, or 750 rpm in gear. I can't recall anything about timing. When assembling the new engine I found out the cam was installed 4* retarded in the previous engine.
New engine has 10.3 CR and 4779-1 dp Holley. KRE heads. 1.65 rockers instead of 1.5. Cam is degreed. Vac is now 9" either at 850 rpm in park or 750 in gear at 12* initial timing. I even idled the engine down to 550. On the cusp of stalling, but remained running. I have no problem moving the idle and timing around. After reading a bit about idle problems with a vacuum leak I don't think I have one. I would think with a relatively 'mild' cam I should have a bit more vacuum than that. (My other 'new' engine is a 461, 10.6 CR, KRE heads, stump puller roller cam. Vac at 750 in gear is 11.5") Comments?
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Frank M. 75 Firebird 68 Firebird 400 RAIII 66 Chevy II 461 Pontiac in AZ |
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#2
08-27-2019, 10:14 PM
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vid
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Frank M. 75 Firebird 68 Firebird 400 RAIII 66 Chevy II 461 Pontiac in AZ |
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#3
08-28-2019, 05:49 AM
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Did you degree in both Cam's?
Any timing chain I have ever seem gives up atleast 1 to 2 degrees when the motor is running pretty much right off the Bat! The size CC wise of the combustion chamber effects vacuum, IE smaller chamber = more vacuum.
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! Last edited by steve25; 08-28-2019 at 05:55 AM. |
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#4
08-28-2019, 09:55 AM
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Just one cam. Not degreed when in first engine. 4* retarded. That cam is degreed in new engine. Chambers are 74 cc.
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Frank M. 75 Firebird 68 Firebird 400 RAIII 66 Chevy II 461 Pontiac in AZ |
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#5
08-28-2019, 11:57 AM
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The HC-02 is a pretty health cam in a street 400. They had different versions but all were pretty close to a RA-IV duration wise. The HC-02A I had was 231/243 on a 114 LSA and had 7 degrees of advance ground into it (ICL 107).
In a 400 with regular lifters the idle was pretty rough and it didn't have alot of low end power or response. It worked much better in a 455, especially with Rhodes lifters.
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68 GTO,3860# Stock Original 400/M-20 Muncie,3.55’s 13.86 @ 100 Old combo: 462 10.75 CR,,SD 330CFM Round Port E's,Old Faithful cam,Jim Hand Continental,3.42's. 1968 Pontiac GTO : 11.114 @ 120.130 MPH New combo: 517 MR-1,10.8 CR,SD 350CFM E's,QFT 950/Northwind,246/252 HR,9.5” 4000 stall,3.42's 636HP/654TQ 1.452 10.603 @ 125.09 http://www.dragtimes.com/Pontiac-GTO...lip-31594.html |
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