I have a been working on a 1975 Ford Classic Bronco for some time now. I have built a 302 engine which I tought would perfrom better than it does.
I had a solid lift cam built. I told them all the variables of my engine and they built me a cam to match. so I fugured all was good, but I am not impressed at all. I do have a few issues that I know I need to correct, but here is the question.
The cam I had built has a 351W fireing order, so looke up the correct firing order for a 351w and used that. But I did buy a MSD Dist. for a 302 if i remeber right
The cam specs and ignition timing specs will help, but it's a very good chance you need more initial timing. Take a look at the info here on timing. Even though the page was originally written about the GM HEI, the timing section still applies to you.
The problem w/not using enough timing is caused by the overlap, reversion and late intake closing point that gives a high performance cammed engine that sound we all know and love. The fuel/air charge is diluted and very lean. This means the ignition timing needs a lot more advance than a stock cam to get that lean charge lit soon enough that it is mostly burned while it can still do work inside the cylinders.
Other things that could be a problem is if the engine wasn't built w/enough compression for the cam, or a too-tight torque converter, or too high rear gears. Carb tuning can cause problems, fuel delivery has to be adequate, even something as simple as a bad plug or plug wire, or a carbon tracked or cracked distributor cap can cause problems like you have. And on and on. But for now I'll see what you can add to help diagnose this.
I do have the wiring correct for a 351W. And the engine does run good, i am proberly just had my hopes up to much, and exspecting a big block perfromance out of little 302. I do agree with your statement about the gear ratio. I have 350 grears in it, I though I had 4.11's and I did mess up am put 38" tires on it which killed me even more. I have listed all of the copmpnets of my moter below. Tell what you think and what I could do to get more power. when i was builing the moter, I was trying to find a happy medium between low end tourqu and a high reving moter such a dragster you could say. I really built this moter around a 125 hp Noz kit i have and that I did plan on installing. But I never did get try it yet and just might not worry about it.
I do have a question though. I have noticed that my engine loves a lot of timing I think i have the initial timming set at 22 - 25 right now and I couls still go more unitl it bites the starter. you know what i mean. so how do you where to set the timing at?? I think with noz you cant go above 32 degs toal timing right. I tryed several things like locking out the Dist,, changing springs ect. but nothing make a real diffance.
Oh and I have the world product Jr's and I did not port or gasket match. Soi know that one week area I have. I read that once you port these heads it really wakes them up. what i really want is some alum. heads I hear trick flow is right up there with best perfomance.
302 BORDED 60 OVER WITH 1975 STOCK ENGINE BLOCK
CAM SHAFT BUILT BY CAM MOTIONS IN BATON ROUGE LA - GRIND# S2361-2401-12 - CORE 149002 (351 FIRING ORDER)
LOBE SIZE - (2) : 2
CAM SHAFT DATA = 4 CRNK DEG
DURATION @ .05 IN
INTAKE - ROCKER RATIO = 1.6. LASH IN 23-24-25-0
EXHAUST- ROCKER RATIO = .06 LASH IN 23-24-25-0
INSTALL CAM : CYL 1#
LOBE SEPERATION = 112 CAM DEG
VALVE OVERLAP = 13.5 CRANK DEG
VALVE OPEN = 9.9 BTDC
CENTER LINE --- 108 ATDC
VALVE CLOSE = 46.2 ABDC
DURATION ----- 236.1 CRANK DEG
LOBE LIFT = .32268 IN
VALVE LIFT ---- .51628 IN
LOBE AREA = 27.04 IN *DEG
VALVE OPEN = 50 BTDC
CENTER LINE --- 116 BTDC
VALVE CLOSE = 3.6 ATDC
DURATION ----- 239.6 CRANK DEG
LOBE LIFT = .33677 IN
VALVE LIFT ---- .53883 IN
LOBE AREA = 27.08 IN *DEG
VALVE LASH SET TO 24
WORLD PRODUCT / WINDSOR JR. LITE CYLINDER HEADS
VAVLE INT = 1.94 IN
VALVE EXH. = 1.60 IN
COMBUSTION CHAMBER VOLUME = 58 CC
INTAKE RUNNER = 180 CC RUNNER VOLUME (PORT DIMENTION 2.00 X 1.12)
EXHAUST RUNNER = 64 CC RUNER VOLUME (PORT DIMENTION 1.300 X 1.22)
HEAD BOLTS 7/16 THREAD BOLT
HEAD GASKETS - FEL PRO 1250 OR FEL PRO 1011-2
INTAKE GASKET - FEL PRO 1415 OR EQUIVALENT
SPARK PLUGS - USE 5/8 REACH - ACCEL 278
VALVE SPRING SEAT PRESSURE - 190 TO 200 IT HINK THIS CORRECT
HEAD BOLT TORQUE (MOTER 302) UPPER ROW 80FT/LBS; LOWER ROW 70 FT LBS
ROCKER ARM STUDS 55 FT/LBS ( I USED A FIXED SETTING / VALVE LASH)
WHEN I BROKE THE CAM SHAFT IN I REMOVED THE CENTER VALVE SPRINGS
JEGS ROLLER ROCKERS 1.6 RATIO
PUSH RODS USE
PRE - 1982 (302)
WHAT I DID (351 FIRING ORDER) 1-3-7-2-6-5-4-8 I THIN K I USED THIS ONE
KEITH BLACK HYPEREUTCTIC PERFORMANCE PISTIONS
GROUND THE RING GAP TO .0025” TO .0035
SET AT FACTORY SETTING (TIMMING MARK)
USED A ADJUSTABLE CHECKING PUSH RODS 5/16 DIA. 6.125” TO 7.500” LENTH
USED EAGLE FORGED RODS
WELAND 7515 SINGLE PLANE
DIST. MDS - WITH MDS SPARK BOX
oh yea one more thing when I put that big cam in I had to use a adjustable push rod to get a measurment for my new push rods, so when i order the push rod I gave them the leanght that I measured, they did not send me the excact leanth I ordered but it was real close. but i did not degree the cam. so that sould make a differance as well right?
I really want to thank you for your help, I have learned so much sence this project began I will send you a pic if can figure out how lol I think you will love it..
Overall, it sounds pretty well thought out. I'm guessing the single plane intake was more for the nitrous than torque off the spray, because that's costing you some torque down low.
The timing can be as high as the engine likes it as long as you keep it from detonating, of course. I always try to use an advance curve (initial plus mechanical). That always seems to work better on the street, unless the cam is just too radical. But my first impression is that the cam isn't too big to use a curve. But it would be a short curve, the mechanical advance might end up being less than 10 degrees, and that's close to the point where locking it full is a viable option. I would let the way it runs locked at full timing be the deciding factor.
I also like to use a vacuum advance, even though this flies in the face of tradition according to some. When using a lot of initial or locked timing it needs to be connected to ported vacuum. It also needs to be adjusted to give about 10 degrees advance at a high enough vacuum level that it doesn't cause any detonation when the engine is under any real load.
When using nitrous, the timing has to be retarded from max naturally aspirated power timing. This is best done w/an ignition box like the MSD 7531 or something similar. That way you can run max timing under all conditions.
If it gets hard to start you can use an ignition interrupter that lets you spin the engine over w/the starter first, THEN when you let go of the switch the ignition is hot. That prevents the starter from kicking back.
You already know the gears are hurting you. What kind of weight are we talking about here? If you are using an automatic trans, the stall speed needs to be at least 3500 rpm and a higher stall will accelerate better.
Do you know the actual (not theoretical) compression ratio?
This is just the tip of the iceberg. Others here will likely chime in and I will give this whole thing some more thought and get back to you.:thumbup:
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