Calling All Gearheads

[rgtrough]

Hey guys, I need help/ideas. After 2 years of adding and subtracting componets to the engine on my '74 coupe I finally put it on a dyno. Boy, am I depressed.

Max hp 227 max torque 288
air fuel ratio 13-1

383 cu. in. holley 650 double pumper mech secondaries. Holley Street Dominator intake manifold. World Sportsman II heads with 64cc chambers, 202 intake valves/160 exhaust valves. 1 5/8" headers into 2 1/2" true duals. 280h comp cam whose lift and duration I don't have with me . Stock coil and points distributor. 9-1 comp. ratio
The funny thing is that it made 201hp on the primaries alone.
Last week with the bowl levels set wrong and gas pouring in the air horn out of the vent tubes it made 267hp and 324 tq.
I need help. peace Bud :confused

 

[81 Corvette]

if it made more gas with a ill adjusted carb, maybe you adjusted the carb to be iller? I know nothing about carbs, but seems like you need more fuel

 

[tomtom72]

I'm no mechanic, but...

Hi Bud, Consider this a C3 LT-1 motor used a 780 cfm holley, single pump on primaries, vac secondaries & dual feed. Your motor may be under carburated?? Just go look at the specs for an LT-1, with the exception of the cubes the two are similar in alot of ways. Just a suggestion . Tom

 

[Glensgages]

280h comp cam whose lift and duration I don't have with me .

I believe the 280H cam has .480" lift (with 1.5 ratio rockers), and approx 234* at .050" lift.....

fwiw, I ran a 650 (#4777) on a slightly-milder 350" years ago:
I'd think you could handle a 750 just fine.

 

[JohnZ]

What's your timing advance map look like? Initial, centrifugal, and how much total advance are you running? They normally map that on a dyno run - you should be at around 35-37 degrees at WOT/high rpm.

 

[Koop]

Hey guys, I need help/ideas. After 2 years of adding and subtracting componets to the engine on my '74 coupe I finally put it on a dyno. Boy, am I depressed.

Max hp 227 max torque 288
air fuel ratio 13-1

383 cu. in. holley 650 double pumper mech secondaries. Holley Street Dominator intake manifold. World Sportsman II heads with 64cc chambers, 202 intake valves/160 exhaust valves. 1 5/8" headers into 2 1/2" true duals. 280h comp cam whose lift and duration I don't have with me . Stock coil and points distributor. 9-1 comp. ratio
The funny thing is that it made 201hp on the primaries alone.
Last week with the bowl levels set wrong and gas pouring in the air horn out of the vent tubes it made 267hp and 324 tq.
I need help. peace Bud :confused

Geeze, my 383 was down about (not dyno verified) 100 Horsepower because of improper jetting on my stock quadrajet (which can put more fuel in that stroker motor than it can handle) my wiring harness was replaced it didn't match the coil and to top it off some bonehead put a non vented gas cap on the car so it was starving then flooding... (69 has a vented cap, I believe the 74 does not)...Go figure. Now you've made me want to dyno my car to see what it's putting on the ground.

 

[craig32]

Bud,
I haven't built an engine in a quarter century, so I'm completely unfamiliar with a 383, but I can tell you about the 327 I did. I also had 64cc heads, (194 intake, 150 exhaust) 531 lift 290 duration gear driven cam, (roller lifters and rev kit) and an intake off of a '58 Corvette with two 600 Crater four barrels. The coil and distributor are stock, with the exception of the reverse gear to accomodate the gear drive cam. I think the timing was somewhere around 40 degrees. I tried using a single four barrel with no luck. A Holley 750 double pumper barely kept it running. Back to the 2 Carters and it purred (roared) just fine again, really obvious it was under carbureted without the two fours. If you're running a stroked engine with a high lift cam, a 650 Holley does sound overworked. Just my opinion, I could be wrong.
Craig

 

[rgtrough]

Update

Hey guys, thanks for the quick replies. Before buying my new 650cfm mech secondaries carb 3 weeks ago, I called the Holley tech line and asked them what size carb to buy. Giving them the same info I have provided you they recommended the 650cfm. I chose the mech. sec. because of the trouble I had with the old carbs' vacuum ones.
Yesterday I called the Holley techline, looking for suggestions and the first thing they tell me is "THE CARB IS TOO SMALL". Imagine that. I did find out a couple thing though (if I can belive them). You can increase your jets 10 sizes up before you need a bigger carb and you should see an increase in hp of 30 to 40% between primaries and secondaries. This last bit of info he actually put me on hold and asked someone else (probably the guy who recommended the 650).
Hey JohnZ, my intial timing is 10 btdc. all in is 34 at 2200 rpm. I have not seen the curve this is without a load.
I'll keep you informed in case anyone else faces this mess.

peace Bud still :confused

 

[tomtom72]

Hey Bud, I used a comp cams cam in my '88 sb & I called them to get a size on the carb. The cam was a 268HE & they said a 4777/650 DP Holley would work fine. The displacement was stock. Just for fun call comp cams & run down your specs to them & see what they say about what size carb to use. Can't hurt? Tom

 

[rgtrough]

Update #2

Hey guys, it's amazing what you see when you're asleep at the wheel. Still feeling in my gut that I have a air/fuel problem I decided to make sure my valves were adjusted properly. Much to my surprise I found the #8 intake lifter stuck, not letting the valve to open. Things became much worse when I pulled the lifter and saw that it was 1/8" shorter than spec. I installed a new lifter and even though it moved alittle I'm sure my cam is wiped. I have gone from :confused to
:cry in 3.4 seconds. Well at least I have my answer and a good reason for a new XE Comp cam.
Again thanks for being here for guys like me. peace Bud

 

[Jack]

I decided to make sure my valves were adjusted properly. Much to my surprise I found the #8 intake lifter stuck, not letting the valve to open. Things became much worse when I pulled the lifter and saw that it was 1/8" shorter than spec. I installed a new lifter and even though it moved alittle I'm sure my cam is wiped.

I had a sneaking suspicion it was in the valve train http://www.corvetteactioncenter.com/forums/showthread.php?p=530137#post530137 ... sorry for your trouble ... try to find root cause ... check for any coil bind/pushrod binding before you tear it apart ... AND as you install new cam & lifters. Also verify that roller tips are riding correctly on valves. If you're not certain of the procedures, get someone nearby to give you hands-on help.
JACK:gap

 

[rgtrough]

Hey Jack, thanks for the advice. I pulled the cam last night 15 lobes and 1 spacer. What a mess. I'll post the outcome. peace Bud