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Title: Noise Under Load Post by: dive!dive! on March 18, 2014, 20:25:59 pm Folks
Been scratching my head with this. Asked the question elsewhere but not got to the bottom of it yet. I did some mods over the winter to the valve train as I was getting some float - changed springs, used ti retainers and lightweight Al pushrods. Very pleased with the results as the motor now revs cleanly to 6500-7000. Managed to drive the car for the first time last week and noticed a noise I don't recall hearing before. It occurs at 3200-3500 ish Rpm under load and is best described as a 'blatting' noise - over an above the normal induction noise. Putting the engine under load (full throttle , uphill) above 3600rpm I get nothing apart from the normal induction roar right up to the redline. The same rpm at standstill is fine. Other than this the car runs very well indeed, so its annoying me. Spec is 1776, c/w crank all balanced, bugpack 4062-10 with scat 1.25 rockers, 044 ported 40*35.5, twin DRLA40 on CSP manifolds, Mallory CDI/Unilite with vac ignition. Exhaust is a turbo Thomas 1.5inch. I've checked the valve clearances,and timing and done a compression test on the engine (all fine at 140psi+/-5psi), tried different manifolds , tried upping the main jets, with / without filters and trumpets. Tried a different muffler but that just changed the tone marginally. I (and another local VW guy) are both convinced its not bearing noise. Any input is appreciated! Cheers Steve Title: Re: Noise Under Load Post by: Jim Ratto on March 18, 2014, 22:00:25 pm I had a combination which had a weird sonic rap up through intake, FK45 cam advanced 4 degrees. Under wide throttle at similar rpm, I would get a pronounced "wopwopwopwopwopwop" through intake as revs went over 3800 or so, it went away. Not sure what caused it, other than overlap of cam and cylinder pressure/exhaust pulse getting back up intake @ that rpm.
Title: Re: Noise Under Load Post by: Phil West on March 19, 2014, 13:13:16 pm Folks Been scratching my head with this. Asked the question elsewhere but not got to the bottom of it yet. I did some mods over the winter to the valve train as I was getting some float - changed springs, used ti retainers and lightweight Al pushrods. Very pleased with the results as the motor now revs cleanly to 6500-7000. Managed to drive the car for the first time last week and noticed a noise I don't recall hearing before. It occurs at 3200-3500 ish Rpm under load and is best described as a 'blatting' noise - over an above the normal induction noise. Putting the engine under load (full throttle , uphill) above 3600rpm I get nothing apart from the normal induction roar right up to the redline. The same rpm at standstill is fine. Other than this the car runs very well indeed, so its annoying me. Spec is 1776, c/w crank all balanced, bugpack 4062-10 with scat 1.25 rockers, 044 ported 40*35.5, twin DRLA40 on CSP manifolds, Mallory CDI/Unilite with vac ignition. Exhaust is a turbo Thomas 1.5inch. I've checked the valve clearances,and timing and done a compression test on the engine (all fine at 140psi+/-5psi), tried different manifolds , tried upping the main jets, with / without filters and trumpets. Tried a different muffler but that just changed the tone marginally. I (and another local VW guy) are both convinced its not bearing noise. Any input is appreciated! I had that type of noise in that RPM band on my old 1776 in my van - turned out to be chuffing, the head studs needed retorquing and it went away. I found tell tale blowby marks on one cylinder head. May not be that on yours but worth checking. Cheers Phil Cheers Steve Title: Re: Noise Under Load Post by: dive!dive! on March 19, 2014, 14:52:12 pm Cheers guys.
It's reassuring that this is not a unique problem.... I'll re-torque the heads. What torque are people generally using ? Stock or a little more ? Steve Title: Re: Noise Under Load Post by: Phil West on March 19, 2014, 15:06:22 pm Is it a mag case with 8mm studs and case savers? Good quality studs, etc. what's the compression cheers
Title: Re: Noise Under Load Post by: dive!dive! on March 19, 2014, 15:21:16 pm New autolinea case, 500miles on it only, 9.0:1
Thanks Title: Re: Noise Under Load Post by: Phil West on March 20, 2014, 09:35:57 am With an ally case and 10mm studs with case savers you should be able to torque to 25ftlbs+ so definitely more than stock. Cheers
Title: Re: Noise Under Load Post by: dive!dive! on March 29, 2014, 20:41:36 pm Well I managed a day playing on the car today. I haven't torqued the heads yet as I didn't have time to drop the engine and strip the tinware.
What I did do was a proper leak down test - got 1-3% leakage on a cold engine, which I understand to be excellent. I don't know if the potential chuffing if the heads need torqueing would have been revealed by this test or not. Out of curiosity, I also changed the vents in the dells from 32's to 34's. Made no difference to the noise, and surprisingly not much difference to the driveability either. Still scratching my head... Steve |