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 Post subject: Engine rattles
PostPosted: Sun May 30, 2021 3:01 pm 
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3 Deuce Weber

Joined: Thu Mar 25, 2010 7:04 am
Posts: 87
Location: new orleans
Car Model:
Fresh build slant 6 225 with molner rods and wisco pistons with 10.5/1 650 holley hurricane long intake.
Question: Engine runs good, but when cruising at about 55 and nail it pass traffic, I get a rattle/valve/maybe detination.
If i nail it out the hole it doesnt rattle until it reaches about 3500 rpms. I played with timing until i got tired and no results.
blocked the vacuum advance and still no result. I dont think its an octane issue, running 93/non ethonal with a bottle of lucas octane boost. Could it be valve lash out..engine only has 100 miles on the build. It did this since day one. What are yall thoughts on this.

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 Post subject: Re: Engine rattles
PostPosted: Sun May 30, 2021 5:47 pm 
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EFI Slant 6

Joined: Mon May 26, 2014 4:02 pm
Posts: 414
Location: Vermont
Car Model: Slant Six M37
Many here on the board much more knowledgeable than I am, but I would start with a cranking compression test, and report back..as cylinder pressure can suggest how to tune for a happy engine. also have a look at the spark plugs for proper coloration.

If you are lean, it will rattle.. even if you are using good gas.


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 Post subject: Re: Engine rattles
PostPosted: Sun May 30, 2021 6:05 pm 
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Joined: Tue Oct 29, 2002 8:27 pm
Posts: 9760
Location: Salem, OR
Car Model:
Long ram manifold and 10.5 SCR.... time to break out the vacc gauge and tune the carb and timing....
I tuned the Hyperpak and a 600 cfm Holley using this ball park 65-68 primary jet, and a 73-78 secondary...PV should be
about a 10 to fill the gap that occurs due to the longer runners than stock...I would install the pink cam
in #1 to start and run it with the brown spring, changing to plain once you think everything else is dialed in
... this will be pretty close on a 650.

Next on the list will be to recurve your distributor... at WOT I would not go past 28 deg total mech + base timing...
cruise sounds like it's fine but pending gearing and transmission I would install a VC-185 vacc can on an EI mopar unit
(limiting the full adv- static+mech+vacc to 47 total... if everything was in order, I would prefer the dizzy to be 13-14 static,
16 mechanical and 17 vacc).


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 Post subject: Re: Engine rattles
PostPosted: Sun May 30, 2021 6:06 pm 
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Joined: Tue Oct 29, 2002 8:27 pm
Posts: 9760
Location: Salem, OR
Car Model:
DusterIdiot wrote:
Long ram manifold and 10.5 SCR.... time to break out the vacc gauge and tune the carb and timing....
I tuned the Hyperpak and a 600 cfm Holley using this ball park 65-68 primary jet, and a 73-78 secondary...PV should be
about a 10 to fill the gap that occurs due to the longer runners than stock...I would install the pink cam
in #1 to start and run it with the brown spring, changing to plain once you think everything else is dialed in
... this will be pretty close on a 650.

Next on the list will be to recurve your distributor... at WOT I would not go past 28 deg total mech + base timing...
cruise sounds like it's fine but pending gearing and transmission I would install a VC-185 vacc can on an EI mopar unit
(limiting the full adv- static+mech+vacc to 47 total... if everything was in order, I would prefer the dizzy to be 13-14 static,
16 mechanical and 17 vacc).


Hopefully the cam is at least 270-280 deg adv. duration.


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 Post subject: Re: Engine rattles
PostPosted: Sun May 30, 2021 8:27 pm 
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3 Deuce Weber

Joined: Thu Mar 25, 2010 7:04 am
Posts: 87
Location: new orleans
Car Model:
I am running 78 primary jets, and I changed the vacuum secondary spring to a heavier spring, and put in a 2.5 PV, because I had a bad bog in the engine thinking it was getting to much fuel.. Maybe going back to the 6.5 PV may help some. It may be running to lean. What is the pink cam in #1 not sure what you mean..? Running 904 tranny with 3:23 gears. Running the 270/280 cam.

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Brian Long


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 Post subject: Re: Engine rattles
PostPosted: Mon May 31, 2021 12:19 am 
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Joined: Tue Oct 29, 2002 8:27 pm
Posts: 9760
Location: Salem, OR
Car Model:
Quote:
I am running 78 primary jets, and I changed the vacuum secondary spring to a heavier spring, and put in a 2.5 PV, because I had a bad bog in the engine thinking it was getting to much fuel.. Maybe going back to the 6.5 PV may help some. It may be running to lean. What is the pink cam in #1 not sure what you mean..? Running 904 tranny with 3:23 gears. Running the 270/280 cam.


Your accelerator cam...it provides the shot to blanket the leanout that occurs when you floor that go pedal...usually with a long ram manifold there is a need to have a heavy long acc pump shot (pink will provide gas long after the orange cam stops...) and secondaries with about 2-4 steps in jet size over the primaries... if it's a plate, time to ditch that for a metering block conversion kit and proper jets...6.5 is a bit up there for almost 200hp and the combination you are driving, compromise and run an 8.5 PV...


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 Post subject: Re: Engine rattles
PostPosted: Mon May 31, 2021 5:59 am 
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Joined: Mon Oct 21, 2002 11:08 am
Posts: 16447
Location: Blacksburg, VA
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My guess is the total advance is too high and it is detonating. With factory advance springs, it will not hit max advance until over 3000.

Lou

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 Post subject: Re: Engine rattles
PostPosted: Mon May 31, 2021 6:13 am 
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3 Deuce Weber

Joined: Thu Mar 25, 2010 7:04 am
Posts: 87
Location: new orleans
Car Model:
thanks guys for your input. I will have to play with it more, at least I have some valuable info to get me started in the right direction. Thanks again.. will report back.

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Brian Long


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 Post subject: Re: Engine rattles
PostPosted: Sat Jun 05, 2021 8:46 pm 
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3 Deuce Weber

Joined: Thu Mar 25, 2010 7:04 am
Posts: 87
Location: new orleans
Car Model:
I did some home work on the slant. I installed the green and black springs on the dizzy and changed the vaccuum advance pod to a vc-185 played with the timing. Installed the 10.5 pv on the primary side and left the 78 jets in. Runs good till about 3800 rpms and then it starts to fall and sputter some, almost like its not getting fuel, however the rattleing stopped. Did not put in the secondary metering block. Maybe that will help?..Your thoughts.

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Brian Long


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 Post subject: Re: Engine rattles
PostPosted: Sat Jun 05, 2021 11:01 pm 
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Joined: Thu Oct 17, 2002 7:27 pm
Posts: 14117
Location: Park Forest, Illinoisy
Car Model: 68 Valiant
With 78 jets in it I would guess it's pig rich. I only run between 68 and 72 in my race junk.

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 Post subject: Re: Engine rattles
PostPosted: Sun Jun 06, 2021 9:22 am 
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Joined: Mon Oct 21, 2002 11:08 am
Posts: 16447
Location: Blacksburg, VA
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Agreed.
Lou

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