Well as the title says i have a 383 stroker i just got done building. I came up with the engine combination with the idea of making 475-500 @ the flywheel. This is my first performance old school SBC build for my 87 GEN3 firebird. I could have done a LS1 but they seemed over played and i wanted to due a carbureted engine. Not sure its perfect but its the combination i came up with reading and talking to different people and experience I've had with new style ls1 engines. The original engine was a 305 and the car had a 700R automatic. I did a swap to a T5 manual trans and a 4 bolt main 350 out of a donor car.

Heres my engine combination

383 Stroker Spec's

Eagle Billet stroker crank
Arp main studs
Eagle H-beam rods with ARP bolts
Machine Work: 350 machined 4 bolt main block .30 over balanced and blueprinted
Forged Diamond Pistons with custom thick ring glands for large nitrous shot in the future
compression ratio 10.8 to 1
clevite bearings throughout
Melling high flow oil pump
Lunati 1.7 to 1 billet rocker arms

Lunati Voodoo Cam
Cam Spec's:
Advertised Duration 294/302
duration 243/251 @ .50
.560/565 lift
LSA 110/106

195 AFR eliminator heads
ARP head Bolts
Edelbrock single plane Air gap RPM performer Intake
Quick Fuel HR-780-VS Carb
High Flow edelbrock fuel pump and regulator set to 6.5 PSI
MSD Billet Distributer 85551
MSD 6AL Ignition
NGK Plugs one plug cooler then stock have to look up the number.


So now where I'm at and what i have done. The first problem i had was the aftermarket pointer was no where close to TDC. So i found TDC and made a mark on the balancer and worked with that.

I set the initial timing at 10 BTDC 850 RPM and i get my total timing around 3800 RPM of 32 BTDC. The MSD 8551 mechanical Distributer is set up stock i haven't touched the timing curve which appears to be 22 degrees advance. Full advance @ 3800 unless I'm looking at the chart wrong. So with my initial timing at 10 BTDC I am at 32 BTDC degrees total @ 3800 rpm. Im sure this is very mild for this motor, I have not heard any type of audible pinging.

Engine runing at Idle only makes about 7.5 In vac and at about 2500-3000 no load i get around 10-13 in

The only adjustments i have done to the carb is the idle mixture screws on the carb. At the suggestion of a local shop i changed the power valve from the 6.5 that was in it to a 3.5 which they recommended for the vac the engine currently has at idle. All changing the power valve seemed to do was lower the upper end of the stumbling issue from 3000 RPM down to 2500 and it seemed to make the idle air mixture screws work better.

I pulled the one plug yesterday to see what them look like and the plug looked brownish black more brown then black. So A/F docent appear to be that bad overall.

Engine wants to idle around 950-1000 but diesels when shut down, but i managed to get it down to idle around 800-850 after changing the power valve and re-adjusting the idle mixture screws the dieseling affect not nearly as bad almost gone.

One issue id like to eliminate is the engine dieseling from time to time. I assume this is because the cam profile, and having the idle circuit open too far causing too much left over gas at shut down. An idea i had was to add a little more initial timing, many bump it to 13-14 degrees to make the compensate fro the big cam and bump the idle up a little more, then adjust the idle back down with the idle screw hopefully closing the butterfly enough to just be in the idle circuit. Then re adjust the advance stop to 18 degrees advance so my total would still only be around 32 degrees at full advance.

Second issue is the engine stumbles and does not run well tell 2500 RPM up. From 3000 up the car is almost underivable, the power comes in and you can physically feel the car twist and the rear end of the sink deep into the springs almost like to wants to lift the front end......, tires light up etc....to be expected with stock tires on the open dif. Cruising is poor the car runs real rich bumping the throttle lightly even causes a little visual brown/black smoke. Milage is currently extremely poor honestly less then 5 MPG

I spoke to quick fuel today and they recommended adjusting the primary to secondary progression which is a small allen located under the vacum secondary adjustment module on the passenger side of the carb.

I am going to try that adjustment but i am curious if my timing advance curve is also contributing to this issue, would i be better to adjust my timing curve first so that my total advance came in at say 2500- instead of 3800 where it currently comes in?

I plan to get a A/F gauge in the car just haven't tuned a performance carb engine before and want to take it slow as i figure it out, have plenty experience in EFI LS1 engines. Looking for suggestions on tuning this carb as I'm not familiar with and there are no local shops in the Vegas area id trust to tune it considering the investment i have in the engine.

Also would like to know your thoughts Good or negative on the engine set-up and my HP goals i have. I'm open for all feed back at this point, thanks

 

Nice engine combo! That is ALOT of cam.

For good street manners, you need much more timing. You will want total around 34-36* but intial will need to be in the 16-20* range, so you will need to limit the mech advance to 16 or so.

You will want to change the advance springs out too to get total advance all in around 3200 rpm. Going down to 2500 or so will cause pinging.

By increasing your timing, you will also speed up your idle, letting you close the idle valve down and covering the transition slot more and stop the dieseling. Dieseling happens alot due to the carb butterfly being open too far and letting just enough air to enter after your shut it down tp keep it running sort of. This can be cause you had to crack the idle speed way up to get it to idle, or throttle return spring is loose and not holding throttle closed good enough, etc

Put a 3.5" HG power valve in the carb

Do not expect too much low rpm (off idle to 2000 rpm) torque with that big of cam

 

Oh BTW do not expect that T5 too last very long behind that powerhouse engine

 

I actually already changed the power valve to a 3.5, only noticed a difference in the quality of idle and the idle mixture screws seems more responsive.

The drivability concern seems to be in the primary circuit but i want to make sure i have a solid base adjustment before i start attempting to changes any jets. The tech line at quick fuel seemed to think the secondary;s where coming in to soon cruising which is why they suggested adjusting the progression back a little which would lean out the cruising no load A/F according to them. Does that sound right?The engine seems very rich trying to cruising 35-40 mph on flat ground no load, crusing at 3000 and above the engine runs well at no load but from about 2500 and under it seems to run rich and bogs/hesitates when to stomp on it. IF you stomp on it at 3000 or higher the response is almost instant night and day different.

So it looks like the the lowest advance block i can install is 18 degrees advance, so i could run 16 degrees initial and that would give me about 34 total. Based on your input it appears the chart B would be the best curve. I was actually considering the C curve but i will try the B curve first.

I am running 100 octane fuel just as an additional safety tell i get tuned but i planed to run 91 if possible , but the more i read i might be stuck running 100. Do you think i will be able to run 91? If I'm stuck running 100 i may consider switching to E85.

 

I am looking to change the rear gears to 3.73 due you think that will help the T5 live a little longer. I went with a stage 2 clutch rated at 425 HP to hopefully act as a buffer to the trans tell i can put the bigger T56 trans in, its a similar trick we use in offroad racing to help the trans live in hash environments. The T56 was tapping the budget to get the engine done.

I plan to eventually build a sub-frame connector, install ford 9" rear end or a 3.73 posi out of a gen 4 with disc brakes but what i have will have to work tell budget allows the final upgrades.

 

Is not really the rear gears as much as it is the case and internals for the t5. It wont handle the torque and will basically just twist and flex till it cracks and goes boom. On another hand, I have heard and seen people with a t5 with that much hp and it still works. Don't do hard launching or slicks on the back. A friend has a mustard stain that is built with a t5 and he loves it... But i keep telling him, someday.... Also, with those forged pistons, the piston to block clearances are more than a hypurtetic/aluminum piston that will cause piston slap. Make sure that motor is good and warmed up before ******* on her. The machine shop knew you were using forged pistons right?

 

I'll give a quick chime in here since I have a minute. I am running the same cam in a similar combo, we have my base timing set at 14° right now, and idle at 32° and WOT is 36°. Still got a lot of tuning to play with however.

 

Update,


SO i finally got the limiting bushings from FBO. I went with the 14 degree bushing. I set my initial timing at 22 and my total is now 35 degrees. I change the springs in the distributer swell. The total timing comes in at 3000 about a 1000 less then it did before. I also install a A/F gauge so i could start tuning the carb.

Thank you for all the suggestions, the car runs completely different, will easily break the tires loose at 60mph causing instead of just laboring so i think i am on the right track.

The car runs well under full throttle but was extremely rich causing at 3000 rpm no load. AT idle i am @ 12.0-12.5 A/R

Cruising i am extremely rich at 3000 RPM no load the gauge is buried at 10.0 A/F

Under hard Acceleration 6000 RPM i am at 12.3-12.5 A/F


So what i have done was started with the vacuum secondary adjustment which did not help. I then re-jetted the the main jet and the secondary mains.

I went from a 72 on the primary to a 68 and on the secondary i went from 83 to 87

I adjust the A/F at idle to 13.5-14 A/F

Cruising at no load 3000 rpm I'm at 14.3 to 15 A/F

Moderate acceleration still goes rich to 10.0 A/f ( I think this issue is because the power valve is opening to soon currently at a 3.5 gonna drop it to a 2.5)

Hard Acceleration is now 12.8 to 13.2 A/F

On decel i am around 13.8-14.5 A/F

Engine runs strong. here is what the plugs look like. I am thinking it needs a little more fuel and maybe a little less timing. Maybe put the primary back to a 70, leave the secondary alone and maybe pull timing back to 34. I am also on the fence of dropping to one colder plug. What do y'all think.

 

Cool deal! I'm glad you got it running better. IMHO 1st thing I would do is throw those bosch plugs as far as I could and put Auto lite, AC delco, or NGK V power plugs in it. I have never had good results with bosch plugs. I seen a .2 second slower ET at track with bosch vs auto lite plugs in my own car.

Based on your plug coloring you need more timing. Look at the ground strap where it welds to the base ring threads. Perfect timing would have the carbon mark flush with threads. Higher up the strap = Timing too retarded for engine combo.
Too hard to judge small size from a picture but here's the info.
about 1/16" movement of carbon mark = 1 degree of timing.
So measure from the top of carbon mark on bottom of ground strap to the base thread .. Adjust timing (advance it) based on the 1/16" = 1*

I can not see the top of ground strap too well but it looks like you are getting a color change right in the middle of the bend. If so then plug heat rage is correct.

If color changes closer to the tip end of strap, plug is too cold, if color change closer to the welded on part , plug is too hot.

And jetting is read from the soot on the base ring. 1 full round of light soot would be perfect. It looks like you are too rich for sure

 

My 383 ran great for 12 years on 93 octane pump gas.. about the same compression as yours. I had a little less because I used Dart (cast iron) Eagle heads. 10:1

You will need to convert the carb to E85. QFT can do it if you send them your carb. Your fuel system will need to be able to flow 30% more fuel and must be E85 compatible. (pump, lines, etc.)

OR just use the highest octane pump gas you can buy and spike it with a little bit of 100.

11 gallons of 91 and 4 gallons of 100 will give you 93.4
10 and 5 94
7.5 & 7.5 95.5

You will get better MPG on gasoline too so that would help offset the cost.

 

A/F numbers look good.. rather than the power valve opening too soon on moderate acceleration I would consider adjusting the vacuum secondaries (maybe they are opening too soon as well)

you want the PV to open on moderate acceleration as you transition to the secondaries to WOT if the secondaries open too soon that could be your rich spot.

I would trust the A/F gage, especially if it's a wideband.

remember with a power valve the primary jets should be at least 10-12 jet sizes smaller than the secondaries. try a 66 or 64 jet before going fat on the primary side.

 

throw a fresh set of plugs in there, those tell me you are pig rich at idle based on all the soot at the base (did you replace the plugs after you adjusted the carb)

to check WOT you want to look for the fuel ring (at the base of the plug's porcelain inside the plug you need a spark plug scope or ear scope to look inside there.

BUT you have a A/F gage I would not bother reading the plugs for fuel.

for a SBC 36 degrees total mechanical advance is about right 99.99 % of the time.

 

I don't have a A/F gage ( yet ) no time to look at it when you are going down the track.

I have rely on reading the spark plugs/timeslips and watch video playback.

 

Those heads shouldnt need more than 34-36 deg timing