Tuning my 400 with 915 heads and Hughes cam

[mopar400]

Hi all mopar freaks,
I need help on tuning my newbuild engine, (1973, 400BB, 4bbl thermoquad, edel RPM intake)

Basicly I need to know where to start!
Do U start with setting the initial timing or do u
strart with the mixture/idle screws om the carb?
I get a bit confused cos: if change the timing the idle changes...

Where I´m at:
about 20degrees in timing
6-7 inch hg vacuum (moves around a bit) feels a bit low huh
Mixture screws out about 5 turns! (its a thermoquad carb btv)

I use a vacuum gaguge, a tac and a timing light to tune it.
Please let me know if i´m missing something

/Linus

[elacruze]

Need to know;
Pistons
Cam specs
ignition type/vacuum source

If you have stock pistons and big cam, the low vacuum signal will demand a very rich carb setting and lots of initial timing.

[mopar400]

ok i will try and give all the nessesary info:
Pistons are stock.
Cam specs:
Its a hughes,  HUG HMC2942BL-7
.518 lift int, exh
229 int dur
242 exh dur
I use ported vacuum, elektonic ignition, stock.

The mixture screws on my carn are out about 5turns but it dosen´t seem to have any effect
turning them..

/Linus

[elacruze]

Seems like your vacuum should be higher, yes.

Set your idle speed
Set your timing with the vacuum disconnected and plugged off
Reset idle speed
Set idle mixture screws
Reset idle speed
Reset idle screws
Reset timing
Repeat until best idle/vacuum is achieved. If you have an auto trans, the carb will want to be richer/advanced in gear.

If your block/head/main caps have been machined, this can affect pushrod preload and cam timing. Consider the possibility that your lifters are too tight which can affect idle vacuum in a big way. Your timing chain should have no slack in it. Was the cam degreed during install, and if so to what spec?

[greenpigs]

  I would think it should have more vacuum than that, have you checked for leaks around the intake/carb? Something like 14 inches at least sounds more feasible. If adjusting the mixture screws doesn't do anything do you have a Holley or something you can switch on it. I don't know how much the thermoquad can be tweaked but Holleys have a lot of room for adjustments.

[elacruze]

 

I assumed you've made sure you have no vacuum leaks or unplugged sources?

[firefighter3931]

ok i will try and give all the nessesary info:
Pistons are stock.
Cam specs:
Its a hughes,  HUG HMC2942BL-7
.518 lift int, exh
229 int dur
242 exh dur
I use ported vacuum, elektonic ignition, stock.

The mixture screws on my carn are out about 5turns but it dosen´t seem to have any effect
turning them..

/Linus

That's a BIG cam for a low compression 400 and will be difficult to tune. It's going to want lots of initial timing to idle somewhat descent. Try 25* at idle but you're going to have to limit your mechanical advance. Ditch the vacuum advance and tune without it. 

The carb is going to be wrong....stock carbs are calibrated for engines with a strong vacuum signal ; which you don't have. If the idle circuit is un responsive then you're idleing too high and using the main circuit rendering the mixture screws non functional.


Ron

[greenpigs]

 

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HUG HMC2942BL-7

383/400 MUSCLE GRIND CAMSHAFT

WHIPLASH SERIES FLAT TAPPET HYDRAULIC CAMSHAFT

$160.00





Whiplash Series Flat Tappet Hydraulic Camshaft Drop in Muscle Car Cams. Want that mean 60's & 70's muscle car lope without doing a complete rebuild? You need one of our muscle car cam.

No machine work, leave the heads on, raises cylinder pressure. Ground on true .904" cam lobes. This gives you max area under the curve. Has low lift to clear guides.
  SHAKE, RATTLE & RUN!!!!

You can feel your car transforming!!!



These HMC cams have bad-to-the-bone idle, very quick stop light to stoplight acceleration! Idles like a funny car but smooths out above 1600-1800 RPM.

These cams are designed to drive better than the sound would imply. These are killer cruising cams made for low compression (8:1-8.75:1) engines and  are designed so the cylinder pressure will not be reduced (Torque Killer!) like other cams of this size or type.


Camshaft Technical Details
Intake Valve Lift 1.5
Exhaust Valve Lift 1.5 .518"
.518"

Intake Valve Lift 1.6
Exhaust Valve Lift 1.6 .552"
.552"

Intake Duration at .050"
Exhaust Duration at .050" 229°
242°

Lobe Separation Angle 107º

Intake Opening at .050"
Exhaust Opening at .050" 10.5° BTC
51° BBC

Intake Closing at .050"
Exhaust Closing at .050" 38.5° ABC
11° ATC

Min. Suggested Cylinder PSI  

Sweet Spot RPM 1800-5200





Home

Dunno, this is over my head as it is a big cam duration but suposed to be ideal for low CR motors. Is it the 107 deg lobe seperation that is what saves the cylinder pressure?  

[mopar400]

thanks for the reply guys!
I´ll try the method described by elacruze
and i´ll look for vacuum leaks sap!
I´m gonna take your advice to FF3931 and advance the timing to about 25*

Also the vacuum was fine before the "changes" about 13inch and I´ve done nothing I can think of to
get any leaks..but ofcourse allways check first!(manifold, carb base, breake vacuum aso)


/Linus

[firefighter3931]

These cams are designed to drive better than the sound would imply. These are killer cruising cams made for low compression (8:1-8.75:1) engines and  are designed so the cylinder pressure will not be reduced (Torque Killer!) like other cams of this size or type.


Camshaft Technical Details
Intake Valve Lift 1.5
Exhaust Valve Lift 1.5 .518"
.518"

Intake Valve Lift 1.6
Exhaust Valve Lift 1.6 .552"
.552"

Intake Duration at .050"
Exhaust Duration at .050" 229°
242°

Lobe Separation Angle 107º

Intake Opening at .050"
Exhaust Opening at .050" 10.5° BTC
51° BBC

Intake Closing at .050"
Exhaust Closing at .050" 38.5° ABC
11° ATC

Min. Suggested Cylinder PSI  

Sweet Spot RPM 1800-5200


Home

Dunno, this is over my head as it is a big cam duration but suposed to be ideal for low CR motors. Is it the 107 deg lobe seperation that is what saves the cylinder pressure?  

The tighter LSA will spike the torque peak but it also reduces idle quality (bigger overlap)...hence the low idle vacuum and tuning issues.

If i was picking a cam for that type of build it would have less duration at .050 and be specced on a wider LSA (110*) A 229 @.050 grind in a low comp 400 is too big, inmo. If i had to work with it and wanted to improve performance i'd be looking to advance the cam timing and degree it in at least 4* advanced or maybe more....to help build cylinder pressure.

Was the cam degreed in ? If so, what was the installed intake centerline ?



Ron

[mopar400]

No did not degree it, was installed with no advance!

[BSB67]

Ron, the cam has 3 degrees of advanced ground in, so it designed to go in at 104.  I'm guessing that Dave is trying to do two typically opposing things with the Whiplash design.  Kinda having your cake and eating it too.  It helps make a relatively low performance/compression engine run decent, while making it sound like its got a big ole cam in it.  It hangs the exhaust valve open a long time with its relatively long duration and has quite a bit of overlap with the 107 LSA to give it the rumpity rump,  but probably closes the intake valve sooner than a stock cam so its got some cylinder pressure.  I bet the advertised duration on the intake is in the high 260's, maybe 270.  270 adv. dur. installed on a 104 closes the door pretty early.  Others that like the big cam sound in a mild application have stated that they like these cams.  Obviously it wont have a bunch of idle vacuum.

[firefighter3931]

Ron, the cam has 3 degrees of advanced ground in, so it designed to go in at 104.  I'm guessing that Dave is trying to do two typically opposing things with the Whiplash design.  Kinda having your cake and eating it too.  It helps make a relatively low performance/compression engine run decent, while making it sound like its got a big ole cam in it.  It hangs the exhaust valve open a long time with its relatively long duration and has quite a bit of overlap with the 107 LSA to give it the rumpity rump,  but probably closes the intake valve sooner than a stock cam so its got some cylinder pressure.  I bet the advertised duration on the intake is in the high 260's, maybe 270.  270 adv. dur. installed on a 104 closes the door pretty early.  Others that like the big cam sound in a mild application have stated that they like these cams.  Obviously it wont have a bunch of idle vacuum.

Yep, i'm aware of that but it's just not my cup of tea. I'd still want to know what the intstalled intake centerline was just to make sure it's where it's supposed to be 

It's possible that the timing chain marks are off and the cam is installed in a retarded position.

No did not degree it, was installed with no advance!

Can you do a cranking compression test Mopar400 ? I'd like to see how much cylinder pressure is being generated.



Ron

[mopar400]

Sure vill do! sap

[mopar400]

That's a BIG cam for a low compression 400 and will be difficult to tune. It's going to want lots of initial timing to idle somewhat descent. Try 25* at idle but you're going to have to limit your mechanical advance. Ditch the vacuum advance and tune without it. 

The carb is going to be wrong....stock carbs are calibrated for engines with a strong vacuum signal ; which you don't have. If the idle circuit is un responsive then you're idleing too high and using the main circuit rendering the mixture screws non functional.


Ron
[/quote]

Ron would you please tell me how to limit the mechanical advance?
Is it complicated, any special skills?
/Linus

[greenpigs]

Try this - http://www.dodgecharger.com/forum/index.php/topic,62311.msg695241.html#msg695241


I bought a copy and it was well worth the $30. To limit the mechanical advance you need to put a spot of weld in the slot(not sure which side)and grind away at the new weld. It is trail and error but the video explains it MUCH better and Wayne has some tricks to help this process along. I always recommend the Lunati Voodo 301 for low CR motors linky - http://www.summitracing.com/parts/LUN-60301/.

[RD]

he does has 915 heads on there, so his engine is not a 8.2-1 motor anymore.. more like 9.2-1.  this would be more conducive to his current cam choice correct?

[Nacho-RT74]

that was what I was to say... beside the Cam manufacturer STATES SPECIFICALLY the low comp use... sooo, aren't you trusting on the manufacturer specs use ?

on Moparts there are several guys using that one ( on BB and SB ) and it looks all of them are happy with it.

[BSB67]

"Yep, i'm aware of that but it's just not my cup of tea."

Amen.



Shoot for slots about 0.340" and that will give a total mech. advance about 12 degrees

[firefighter3931]

he does has 915 heads on there, so his engine is not a 8.2-1 motor anymore.. more like 9.2-1.  this would be more conducive to his current cam choice correct?

Jamey....without knowing the actual piston to deck measurement it's a guess at best. Even with closed chamber heads i'd be willing to bet it's in the 8.5:1 range. If the engine had more displacement ; say a 440 instead of a 400 the cam in question would be a better fit. 

Ron would you please tell me how to limit the mechanical advance?
Is it complicated, any special skills?
/Linus

Linus, to limit mechanical advance you need to weld up the advance plate as shown above by BSB67. The newer MP distributors have adjustable stops to limit mechanical advance.



Ron

[RD]

CC heads bump up the compression more than just .3 pts dont they?  I mean going from a 88-92cc head to a 78cc head has to do something for the engine.

on average, do CC heads only bump up the compression .3?  curious is all.

[firefighter3931]

CC heads bump up the compression more than just .3 pts dont they?  I mean going from a 88-92cc head to a 78cc head has to do something for the engine.

on average, do CC heads only bump up the compression .3?  curious is all.

It depends 

Actual compression on those smogger 400's was closer to 7.8:1 and if the OP used felpro .040 head gaskets instead of a factory style steel shim (.020) then the head swap isn't worth much in the "real world". 

A closed chamber is usually good for half a point increase all things being equal.



Ron

[greenpigs]

I have heard that the smaller valves negate most of the HP you get from the cr increase.

[RD]

A closed chamber is usually good for half a point increase all things being equal.

Ron

ty!

[mopar400]

I used the steel shim gaskets on this engine
and  the Heads are fitted with 2,14 int valve and 1,81 exh valve, ferrea.
/Linus

[firefighter3931]

I used the steel shim gaskets on this engine
and  the Heads are fitted with 2,14 int valve and 1,81 exh valve, ferrea.
/Linus

That's encouraging news.  

Where is the initial timing set ? A low compression build with lots of cam is going to want lots of initial timing....probably 25+ at idle if not more.  

What i would do is adjust the base timing for max vacuum at idle and see what you've got....then modify the advance plate to limit mechanical advance. 



Ron

[mopar400]

Thanx Ron, The timing is now set at aprox 25*, I havent got a timin tape on yet but as soon as I do
I will be able to set the timing more accurately, and check total timing.
And I can try to use manifold vacuum ibstead of ported, and maybe play around with the mechanical advance..

Havent got around to do a comp test yet
but i dont think is is the problem, I leak tested the manifold
and carb and vacuum hoses with some start gas, no leaks found.
Its wacation time for me so I wont be able to work on the car for a week or so,
I´ll be updating the thread when I´ve know moore..

/Linus

[mopar400]

ok some update..
I did some tuning today on my "former smog engine"..
I did as U told Ron, set the timing for highest vacuum, this occured
at about 30* (its a little difficult to se cos the timing tab is in the way! so the tape isnt so much help anyway
but about 30*, the vacuum reading then was 10 mm hg

and then I tested total advance at app 2500-3000rpm it
read about 35-40*..
(maybe some of the figures arnt excact, little hard to read...)

I then took it for a drive and it behaved GOOD!
Takes of and runs strong through the whole range!

BUT I have one concern!
And I think its carb related.
When I take of the power dosnt come until I'm doing about 50-60 mph
Its like turning on a tap first slowly, slowly then Ka boom
its wide open and just takes of!
I figured its the secondaries on my thermoquad that needs to be adjusted
I´ve heard that u can set them to open soner, (the preload of the venturies or something)
Any ideas!

/Linus

[Nacho-RT74]

I figured its the secondaries on my thermoquad that needs to be adjusted
I´ve heard that u can set them to open soner, (the preload of the venturies or something)
Any ideas!

there is a link between both throttles shafts that can be bended to any custom setup.

[firefighter3931]

ok some update..
I did some tuning today on my "former smog engine"..
I did as U told Ron, set the timing for highest vacuum, this occured
at about 30* (its a little difficult to se cos the timing tab is in the way! so the tape isnt so much help anyway
but about 30*, the vacuum reading then was 10 mm hg

and then I tested total advance at app 2500-3000rpm it
read about 35-40*..
(maybe some of the figures arnt excact, little hard to read...)

I then took it for a drive and it behaved GOOD!
Takes of and runs strong through the whole range!

BUT I have one concern!
And I think its carb related.
When I take of the power dosnt come until I'm doing about 50-60 mph
Its like turning on a tap first slowly, slowly then Ka boom
its wide open and just takes of!
I figured its the secondaries on my thermoquad that needs to be adjusted
I´ve heard that u can set them to open soner, (the preload of the venturies or something)
Any ideas!

/Linus

That sounds much better....you're giving the engine what it's asking for with the increased base timing. The fact that the idle vacuum picked up 3in hg is a proof that you're headed in the right direction. 

I use Holley carbs exclusively and prefer double pumpers with mechanical secondaries. There is no question as to when they are opening. 


Ron

[Challenger340]

Dunno what you were looking for in the way of power ?
but,
IMO,
Ya get the Timing/Fuel/And Tune figured out,
Your gonna have a powerhouse on your hands !

I've used that Cam from Hughes a coupla times, (at the Customers supply/request), more just for the "Musclecar sound" THEY wanted, and I was PLENTY surprised at the output !
even at relatively lower CR's, 9.0:1 ?

I'm with Ron, in that "on paper" that Cam seems wrong for the Application ?
I'd have never "picked it" myself, good thing, I would have been wrong !
That Said,
I suspect Hughes are doing something goofy with the closing ramps, although, I've never V-Blocked & Plotted one to know for sure,
because,
the thing pulls Freight Trains for Power !

Just IMO
Bob out.

[mopar400]

there is a link between both throttles shafts that can be bended to any custom setup.

[/quote]

ok Nacho, si it the one going from the choke valve to the air valve?
How do you do it, do u just bend it..how much?

/Linus

[Nacho-RT74]

http://imperialclub.com/Repair/Lit/Master/290/index.htm

[mopar400]

HI there
Is it bad i any way to set the timing to high? I set it at 35* today (initial)
and it drove good, vacuum inreased, 
shouldn´t it detonate at those numbers?
Everyone says to me "dont push the ini timing to high or it will detonate
but i´ve had no such problems...yet
Is it cause my relativly low compression, i believe I´ve got "dished" pistons (I believe its called that)
/Linus

[firefighter3931]

HI there
Is it bad i any way to set the timing to high? I set it at 35* today (initial)
and it drove good, vacuum inreased, 
shouldn´t it detonate at those numbers?
Everyone says to me "dont push the ini timing to high or it will detonate
but i´ve had no such problems...yet
Is it cause my relativly low compression, i believe I´ve got "dished" pistons (I believe its called that)
/Linus

How does the engine restart when warm ? Does it start easy ?

Fwiw i had mine at 35* at idle...that's where it ran best !

Have a look at the plugs for signs of detonation (small black/silver specs on the porcelin) and if you don't see any leave it alone. Big cams + low compression like LOTS of timing....as you've found out 


Ron 

[mopar400]

ok thanks Ron
it seemed a litle harder to crank than usual so maybe
I´ll back it of just a bit..
and I look for black spots on he plugs to!
/Linus

[greenpigs]

Yep check the plugs and if good back off the timing a little. It should start easy and if not you might want to pull timing out.