[tininjun67]

I ran a 406 with an almost identical cam as yours. victor intake with stock edelbrocks, 9:1 compression and a 930 cfm carb. jetting was in the 90's, 36 degrees timing. car ran 11.40 @ 117 weighing 3420 with driver. I don't think you're over cammed, will probably see improvements on the intake swap. good luck, gorgeous car and engine bay!

[ho428]

I got the intake swapped, intalled a 3/4" 4 hole spacer, cut the air bleeds down to .023's and jetted the Carb 80 square. I can got up from there, but based on my old 365 that should be a good start. Wish I had an 850 to take with me.

Patrick @ Pro Carbs said to keep it square since they built it with power valves front and rear. Not sure exactly why PV's front and rear, but it is a Road Race engine.

[johnta1]

What's the power valve rating?

Maybe they're not opening up at full throttle?

[ho428]

Originally Posted by johnta1

What's the power valve rating?

Maybe they're not opening up at full throttle?

6.5 PV

[BruceWilkie]

1/2 of idle vacuum isnt a bad place to start and usually no more than 3/4 my vacuum at steady state "cruise" vacuum. Too low on pv number often affects response to light part throttle application acting somewhat like insufficient accelerator pump. Too high on the pv number mostly sucks more fuel than you need for the load.

IMO pv on both ends is a good idea on a road race application as there could be times where you may not have the secondary fully open and dont need full enrichment.

[ho428]

Went back to the dyno Saturday, went from bad to worse.
Had another engine guy stop by and his assesment is the intake valve is open way to long, giving up compression.

Compression test showed only around 135 lbs using a good Snap On tester at WOT. Leak down showed very low leakage.
Where should the Compression be?

407 cu in. Should be around 11.5:1 static.
KRE 290 Heads, Machined chamber, milled to 65 cc 2.07 int 1.66 exh
3.75 stroke
4.16 bore
Icon 4.5cc FT Pistons .006 in the hole
.036 Cometic gasket
Tried the Northwind and T2, Northwind actually dyno’d better.
Pro Systems 750 DP, .023 bleeds, 80 jets, PV’s front and rear. Ran a little fat with the T2, little lean with the Northwind.
RobbMac pump, -8 lines.
Headman 1.78 Primary, 2.5 exhaust, H pipe side exit.

Best dyno run was 301 hp with NW, with T2 it dropped to 278
This engine should be putting down about 380-400 min at the rear wheels.

Attached is the cam card. Cam is installed straight up based on the Roller Master sprocket card. 1.65 rockers.

I pulled the front down yesterday to verify everything, having a tough time trying to re-index it in the car though.

I'm stumped.

[Half-Inch Stud]

248 & 254 @ .050" lift is...a big cam. YET should idle & off-idle rhomp extremely well.

Don't blame the Big cam yet. Don't blame the Big Plenum. See MY 11.0 & 12.0 Signature details for confidence.

Keep looking for problem.
=================================
I'd like to get sassy & say "trow a Q-JET on and see if the trouble clears up"
BUT,--> talk about the Ignition system (& IGN history in that car) (& Alternoator healthy (battery ever drain down when sitting?) & Total ADV ( & method of measuring ADV)

[ho428]

I was reading the Comp Cams general info, it says they grind most all their cams +4, if you notice the cam card it says 110+4
Make me wonder if it's actually +8

I have a call into Comp, waiting on a reply. Hope to verify 106 ICL tonight. Degreeing it in the car sucks.

[J.C.you]

try a 1.5 exhaust rocker.

[JY455V4-Z]

generally speaking a 750 carb(even up to say 1.400" venturi) should be no where near an 80 jet with power valves on both sides. that's ridicoulus. i can't believe patrick james gets away with this stuff.

[firechickenman]

Cam is installed straight up based on the Roller Master sprocket card

Does this mean the cam wasn't degreed when installed? When I installed my Comp Cams cam with a Rollmaster timing set, it was off 9 degrees! I can't remember if it was advanced or retarded though. The cam is very similar to your grind and I installed it at 106 ICL. Glad I checked it!

[Half-Inch Stud]

...yea you noticed my 11.0 & 12.0 ET Cams were Advanced +4 Degree.

+4 & +4 would suck, but would ALSO yield higher Compression readings huh. Just doing the Columbo thing.

Keep looking for the Problem (do the Monk hand thing on your engine area, or if too far away; do the Psych thing from the PC).

[WARPed]

Have you checked fuel pressure at the carb at speed/WOT ? Just trying to rule out variables.

[ho428]

generally speaking a 750 carb(even up to say 1.400" venturi) should be no where near an 80 jet with power valves on both sides. that's ridicoulus. i can't believe patrick james gets away with this stuff.

Patrick said I shouldn't need that much jet either but it needed it based on the O2 and plugs, he jetted it 73 sq to start but it was so lean I melted a plug. I went to .023 bleeds and 80's this last run to fatten it up, based on what we've seen on the dyno I could probably go to 76-78 jets once I get it making some power.

Does this mean the cam wasn't degreed when installed? When I installed my Comp Cams cam with a Rollmaster timing set, it was off 9 degrees! Glad I checked it!

Unfortunately yes, installed it straight up. One of those "install and I'll check it later", week or so later I buttoned it up and had the OS moment. after the engine was in.

Was hoping since it was straight up I'd be ok. Last one was spot on.
Gets back to my other post about the best way to degree it in the car. I'm paying for my oversight now.

[Skip Fix]

Even with a big cam 135 is pretty low. My 9.0 low compression 400 was in the 160-170 range. My firends 10.7:1 428(#48s on a 428) with an UD 288/296 hydarulic was 215 and blowing head gaskets as he was running pump gas with just a spot of race gas added. (But I couldnt hear any detonation!).

You can still check the degree the cam with the engine in the car. The Comp crank socket that takes a degree wheel is almost the exact diameter as a balancer and will slide in the timng cover so you can check it with out pulling the cover. You can use a valve cover bolt or a rocker stud to anchor the dial indicator and use an extension to locate it on the edge of a lifter-or less accurate but close on the pushrod. If it's way off then pull the cover and use the sporcket or a offset key way. I never get the spocket to give the exact change I want so I always use an offset key.

[goatasaurus rex]

what were your driving impressions this weekend after degreeing the cam?

[ponjohn]

Interesting read. Good luck.

[ho428]

Originally Posted by goatasaurus rex

what were your driving impressions this weekend after degreeing the cam?

Beat my personal best Road Atlanta lap time by 3.5 seconds.
Car lauched off the corners like shot out of a cannon. Got it sideways a couple of times by getting on it to soon.
Had a bad vibration all weekend though and had to baby the downshifts. Pulled it apart last night, trans case broke... again. Time for a Jerico.

Still set a new PB.

Forgot one thing.
I'm able to pump the carb dry on the long back stretch. RobMac 550 pump, -8 lines from fuel cell to pump to carb. Only did it once though, I raised the level a little, it's mid sight glass now. Plugs look to still be a tad lean, .023 bleeds, 80 jets, need to get it back on the dyno for an O2 reading.

[johnta1]

Congrats on the PB!



If the carb is running dry, it'll show lean even if the AFR is right?

Do you run a return line?

I'd look for a restriction/problem?

Also, fuel cell or gas tank?

[ponjohn]

So degreeing the cam was the fix?