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300 lacking HP

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BamaDude
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300 lacking HP

Post #1 by BamaDude » Sun Apr 21, 2019 9:36 pm

Y'all have great insight and knowledge of this motor, and I can use some help.

I am running a '94 300 block with a '72 240 head. The crank and pistons are stock, the cam is a Crane 252H-10, tri-y headers, offy dual plane intake with a holley 600 with vacuum secondaries. (I know the carb is a bit big.) Pertronix ignition in the dizzy. It is hooked to a C4. It has 6000 miles on the rebuild.

I put it on a dyno, and got this:
98 HP at 2800 and was 'curve' was flat, 245 torque at 1750 and went down from there, as expected. If I remember, the crank gear/cam gear was installed with the factory keyway, neither advanced or retarded. Does that cam have advance or retard ground in?

Question of the day is, how can I get some more HP out of this motor without losing too much torque? I would like to pull a car trailer but right now, I don't think it has the ponies to do that very well.

Thanks,
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

pmuller9
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Re: 300 lacking HP

Post #2 by pmuller9 » Sun Apr 21, 2019 11:01 pm

Welcome to the forum.

Do you mean a Comp 252H cam instead of a Crane cam?
You can do a quick check to see where the cam timing is if you are willing to remove the valve cover?

BamaDude
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Re: 300 lacking HP

Post #3 by BamaDude » Sun Apr 21, 2019 11:52 pm

Yes, Comp cam.

I'll check anything at this point. How can I check it by removing the valve cover?
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

pmuller9
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Re: 300 lacking HP

Post #4 by pmuller9 » Mon Apr 22, 2019 12:12 am

Since it is the Comp Cam.
Rotate the crank clockwise until the #1 exhaust valve opens and continue till it is almost closed.
Just before it closes the #1 intake valve will begin to open.
When both exhaust and intake valves are at the same height, check the timing mark on the balancer against the timing tab and see how close the crank is to TDC.
You can lay a short straight edge on both valve retainers to see if they are even.

The crank timing is the same as the cam timing at that point.
If the crank is at TDC then the cam is straight up.
If the crank is at 4 degrees ATDC then the cam is 4 degrees retarded and so on..

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Re: 300 lacking HP

Post #5 by BamaDude » Mon Apr 22, 2019 11:50 pm

Thanks for the tip, but can you really tell a 4 degree difference using that method? The valves hardly budge during a 4 degree move. I'll try it though.
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

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Re: 300 lacking HP

Post #6 by pmuller9 » Tue Apr 23, 2019 11:41 am

BamaDude wrote:Thanks for the tip, but can you really tell a 4 degree difference using that method? The valves hardly budge during a 4 degree move. I'll try it though.

I've been able to get within 1 degrees with larger cams.
If you lay a straight edge across the top of the two valve retainers you should be able to tell when they are at the same height.

You should turn the crank over by hand a few times to make sure both lifters are bled down.

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Re: 300 lacking HP

Post #7 by BamaDude » Tue Apr 23, 2019 8:16 pm

OK, near as I can tell, the valves heights are equal and the timing is at 4-5 degress ATDC. I was pretty darn sure that the marks were lined up when the gears were put on after the rebuild. Guess not.

I read that by retarding the cam timing, making both marks line up, will decrease torque but improve HP. Is this the case? How many teeth equals how many degrees?
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

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Re: 300 lacking HP

Post #8 by pmuller9 » Tue Apr 23, 2019 9:31 pm

Good Job!
Each crank tooth is 12.4 degrees.
The cam is installed correctly and is 4 degrees retarded just like the stock cam.
The retarded position does help horsepower and also makes the engine less prone to detonation.

Last time I installed an aftermarket cam with the stock timing gears and cam key it was 3 degrees retarded so I use an off set key to advance it 4 degrees.
It was a much bigger cam than the 252 (It was a 288) and I didn't need it to be retarded.

Now you know the cam installation is not the problem.

I would look at using the 1.75 ratio Chevy straight six rockers to get more valve lift.
The 240 head really shrouds the valves up to .350" valve lift.

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Re: 300 lacking HP

Post #9 by BamaDude » Wed Apr 24, 2019 12:11 am

Awesome, thanks for the help. :D With the engine only having 6000 miles on it, I'm thinking I can just swap out the rocker arms and nothing else and be fine.

What kind of HP gains could I expect from the rocker swap?
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

BamaDude
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Re: 300 lacking HP

Post #10 by BamaDude » Wed Apr 24, 2019 12:14 am

I would look at using the 1.75 ratio Chevy straight six rockers to get more valve lift.


For the rocker arms, is there a certain year range I should get?
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

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Re: 300 lacking HP

Post #11 by pmuller9 » Wed Apr 24, 2019 12:44 am

They are usually listed as Chevy 230/250/292 L6 rockers.
https://www.summitracing.com/parts/cca- ... /chevrolet
No particular year.

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Re: 300 lacking HP

Post #12 by BamaDude » Sun Apr 28, 2019 5:07 pm

OK, so I got those rocker arms and installed them. But now I am getting a weird reading. Using a gauge on the manifold vacuum, I am getting a fast fluctuation from 16 - 19 in/hg that smooths out at higher rpms, which could indicate worn valve guides, but they were fine before the swap. Also, I am getting an occasional popping sound from the exhaust. Timing is set around 16 BTDC cause that's where she likes it. At 6 BTDC she was really shaking. I checked and do not have a bad plug wire, everything seems to be firing.

What could be the cause of that vacuum reading?
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

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Re: 300 lacking HP

Post #13 by pmuller9 » Sun Apr 28, 2019 5:15 pm

How did you adjust the rocker arms for lifter preload?

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Re: 300 lacking HP

Post #14 by BamaDude » Sun Apr 28, 2019 5:22 pm

I tightened all the rocker arms about halfway, then I rotated the crank until the exhaust valve started back up, then adjusted the intake rocker, then as the intake valve started back up, I did the exhaust rocker.
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

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Re: 300 lacking HP

Post #15 by pmuller9 » Sun Apr 28, 2019 5:40 pm

Yes you adjust the intake valve just as the exhaust valve begins to open BUT you adjust the exhaust valve just as the intake valve CLOSES not opens.

How far are you turning the adjuster nut once the pushrod has no lash?

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Re: 300 lacking HP

Post #16 by BamaDude » Mon Apr 29, 2019 11:31 am

pmuller9 wrote:Yes you adjust the intake valve just as the exhaust valve begins to open BUT you adjust the exhaust valve just as the intake valve CLOSES not opens.

How far are you turning the adjuster nut once the pushrod has no lash?


I did a 1/2 turn after the pushrod couldn't be turned. I will redo the process for the exhaust valves.
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

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Re: 300 lacking HP

Post #17 by Max_Effort » Mon Apr 29, 2019 11:50 am

BamaDude wrote:
pmuller9 wrote:Yes you adjust the intake valve just as the exhaust valve begins to open BUT you adjust the exhaust valve just as the intake valve CLOSES not opens.

How far are you turning the adjuster nut once the pushrod has no lash?


I did a 1/2 turn after the pushrod couldn't be turned. I will redo the process for the exhaust valves.

Just a light touch on the pushrod. Shake it gently while tightening the nut, once the wiggle/looseness is taken up, then 1/2 to 3/4 turn.

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Re: 300 lacking HP

Post #18 by pmuller9 » Mon Apr 29, 2019 6:51 pm

Redo all 12 with what Max_Effort is describing for adjustment.
The problem at idle would be from having too much lifter preload and not allowing the valve to close fully on the valve seat.

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Re: 300 lacking HP

Post #19 by BamaDude » Wed May 01, 2019 3:23 pm

So using Max_Effort's process, the motor is running good. :thumbup: Took the vacuum gauge and tuned the timing and carb, gauge is reading a steady 21 in/hg. The motor sounds better and is starting better, but it does not seem like the power improved much.

I know the 600 cfm carb is too big, but I thought it might be OK with vacuum secondaries. I probably should be running a 390 or 450 cfm. How do you think that may be affecting the HP? Are there any tricks to try with the 600, like smaller jets? Or is it all about the airflow?
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

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Re: 300 lacking HP

Post #20 by THE FRENCHTOWN FLYER » Wed May 01, 2019 4:24 pm

While I prefer a 390 or 450 for the 300 a 600 should perform well. The secondaries will probably never open fully because of the lack of demand. If they do start to open it will be at a high load / High RPM at the upper limit of the usable RPM range.

I'd leave the main jetting alone - its probably close. Some 4Vs are calibrated to run on the lean side on the primary side and to compensate for that the secondary side is a bit too rich so that at max airflow the overall A/F ratio is close to optimum.
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

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Re: 300 lacking HP

Post #21 by pmuller9 » Wed May 01, 2019 7:31 pm

What is the initial ignition timing with the vacuum advance disconnected and what the final timing at 3000 rpm also with the vacuum advance disconnected?

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Re: 300 lacking HP

Post #22 by Max_Effort » Wed May 01, 2019 7:36 pm

I have to wonder if
1) The DP manifold is choking the engine
Or
2) You're getting into detonation with the high compression and short cam.
The horsepower curve will stop (level) when you get into detonation .
Have you done some plug tests , readings? Looked at the plugs under magnification and see if there are aluminum specs on the porcelain?

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Re: 300 lacking HP

Post #23 by guhfluh » Thu May 02, 2019 1:28 pm

Do you have a picture of the dyno graph? What type of dyno? Also, what 600 Holley do you have?

There's a good amount that's different from my build that will effect the rear wheel power numbers, but you're down quite a bit it seems to me.

I ran a new Holley 600 vacuum secondary I bought from the parts store and went through it tuning with a wideband. It drove great right out of the box and ratios were spot on for wide open throttle. I played with secondary springs, and concluded the stock spring was about the best, maybe one step down. If I went any lower, it lean bogged when they opened. As FTF said, they'll barely open and only above 3000rpm or so. The only big thing I changed was restricting the idle circuit to lean out the transition slot fueling for mileage, so I could cruise a little leaner at real small throttle, BUT that made tuning the accell pump cam and squirter for drivability tricky, because it likes the extra fuel in the transition.

What distributor? I'm guessing it's a converted points style like mine. I had real good seat of the pants gains from dialing in my timing curve and trying to get as much timing in as possible as soon as possible. I used a Mr Gasket light spring and 32-34* max is what people say it should take above 3000rpm.

The Chevy 1.7 rockers give a little boost in power, but not much as you noticed. They do make a little more difference with bigger cams, because they're a multiplier, but it's still not too big a difference. I can notice that without them my power falls off right at 4700rpm and with them, it carries closer to 5000rpm, but it does lose some for me below 2000rpm. It does lope more at idle with them :)
1967 F-250 Crew Cab 2wd, 300 6cyl, T-170/RTS/TOD 4-speed overdrive
240 head, Offy C, EFI exhaust manifolds, Comp 268H, mandrel 2.5-3" exhaust, Edelbrock 500, Pertronix ignitor and coil, recurved dizzy. 200whp/300wtq

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Re: 300 lacking HP

Post #24 by BamaDude » Thu May 02, 2019 11:02 pm

Here is the dyno results:

img/_data/i/upload/2019/05/02/20190502225642-61f6d09b-th.jpg

The first pull I gave up a little early, as you can see. Didn't matter, the second pull was almost identical. All the numbers are at the rear wheels through the C4.

I will have to check on the timing at 3000 some time tomorrow. Basically a stock dizzy with the pertronix. Didn't adjust any of the springs.
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1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

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Re: 300 lacking HP

Post #25 by pmuller9 » Fri May 03, 2019 12:03 am

Thanks for posting the Dyno runs.

The stock cam produces peak torque at 1700-1800 rpm.
The actual torque peak on your engine may be bellow 1700 rpm but the converter stall rpm won't let you test any lower.
The Comp 252 cam would normally move the torque peak over 2000 rpm so something is choking the airflow.

The Offy DP primary runner (Lower section) has about 1/3 the Cross Sectional Area of the intake port in the head and relies on the secondary to supply airflow to make upper rpm power.
If the secondary on the carb isn't opening then the airflow is restricted.
I'm assuming the Carb is mounted correctly with the primary side facing the valve cover.

As a TEMPORARY test you could put an open spacer under the carb giving the primary access to both upper and lower sections of the intake manifold.

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Re: 300 lacking HP

Post #26 by Backwoodswalker375 » Fri May 03, 2019 7:38 am

My 2 pennies. You have to figure in the "parasitic loss" using a chassis dyno. So torque in my book is not too far off. I have a feeling your secondaries are not opening, hurting power. I don't have the specs for a 252 cam in front of me. But I think it's "smaller" than stock cam. Definitely not a hi performance cam. Not trying to start a argument but, ditch the intake. I tried 2 builds using that manifold and was not happy with either. Offy C is way to go. I have had good results with bigger motorcraft 2 barrels on top. My personal best has been a edelbrock 500cfm. Took quite a bit of tuning but was worth it. I never really understood the thinking behind the 6019 manifold. When running on "primary" side it flows less than factory log we all hate. So If secondaries don't open, flow is way way down. Reading here, I see others get it to work with small 4 barrel. So I know it can work. Just have to get everything "working together". Sorry for long post. Coffee is working this morning, steve

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Re: 300 lacking HP

Post #27 by THE FRENCHTOWN FLYER » Fri May 03, 2019 9:44 am

X2 on the above posts. Also, what kind of exhaust system are you using? Low restriction? It might be interesting to disconnect it downstream of the Tri-Y headers and do a pull with open exhaust to see how much you are losing to the exhaust system.
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

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Re: 300 lacking HP

Post #28 by guhfluh » Fri May 03, 2019 12:32 pm

I mostly agree with the above posts as well.

Your secondaries probably aren't opening at all. With the big carb, it may not be able to get them open soon enough and maintain a good fuel ratio during the transition though, but it will take trial and error tuning. A quick check is a zip tie(not too tight) or paper clip on the diaphragm rod and go for a run up to x rpm and stop. Look to see if it has pushed the clip down. Run it a little higher, stop and check again, etc. If you're not running it over 3000rpm, you may be better with a much smaller 4bbl that will open the secondaries much sooner, or a big 2bbl.

I also agree with the intake. It's not the best for power. It restricts total runner area. Id think it can work okay for low end power with a smaller 4bbl, but most seem to have more luck with the C series.

I also am curious of the exhaust after the headers. I made sure to have a nice mandrel bent and free flowing exhaust on mine.
1967 F-250 Crew Cab 2wd, 300 6cyl, T-170/RTS/TOD 4-speed overdrive
240 head, Offy C, EFI exhaust manifolds, Comp 268H, mandrel 2.5-3" exhaust, Edelbrock 500, Pertronix ignitor and coil, recurved dizzy. 200whp/300wtq

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Re: 300 lacking HP

Post #29 by guhfluh » Fri May 03, 2019 12:43 pm

pmuller9 wrote:Thanks for posting the Dyno runs.

The stock cam produces peak torque at 1700-1800 rpm.
The actual torque peak on your engine may be bellow 1700 rpm but the converter stall rpm won't let you test any lower.
The Comp 252 cam would normally move the torque peak over 2000 rpm so something is choking the airflow.

The Offy DP primary runner (Lower section) has about 1/3 the Cross Sectional Area of the intake port in the head and relies on the secondary to supply airflow to make upper rpm power.
If the secondary on the carb isn't opening then the airflow is restricted.
I'm assuming the Carb is mounted correctly with the primary side facing the valve cover.

As a TEMPORARY test you could put an open spacer under the carb giving the primary access to both upper and lower sections of the intake manifold.


My truck doesn't seem to make peak torque any higher than 1800ish. It does maintain torque up until above 3k, but peak is still around 1800.
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1967 F-250 Crew Cab 2wd, 300 6cyl, T-170/RTS/TOD 4-speed overdrive
240 head, Offy C, EFI exhaust manifolds, Comp 268H, mandrel 2.5-3" exhaust, Edelbrock 500, Pertronix ignitor and coil, recurved dizzy. 200whp/300wtq

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Re: 300 lacking HP

Post #30 by MechRick » Fri May 03, 2019 1:35 pm

How does that engine push your 3/4 ton around? Those are some great numbers.
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Re: 300 lacking HP

Post #31 by pmuller9 » Fri May 03, 2019 2:01 pm

guhfluh wrote:My truck doesn't seem to make peak torque any higher than 1800ish. It does maintain torque up until above 3k, but peak is still around 1800.

Kinda, but the torque at 3000 to 3200 isn't any lower than the torque at 2000 rpm. That is a great power band.

As you pointed out the torque curve here is falling off way to soon and that is the problem.

I'm glad you posted your dyno session. It demonstrates that a larger cam not only has better low end torque but provides a much wider power band than the smaller cams.
I've been pushing for new engine builds to use cams with around a 220* .050" duration for almost all naturally aspirated mild street applications.

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Re: 300 lacking HP

Post #32 by guhfluh » Fri May 03, 2019 2:21 pm

MechRick wrote:How does that engine push your 3/4 ton around? Those are some great numbers.

It does okay because it's light for what it is and a 3.73 rear gear. 4650lbs without me and with a full tank. It was a lot lighter without 200lbs of deadener, without A/C, power brakes, stereo, etc. 1st and second gear are great. 3rd is a horrible split in the Trans ratios. 4th is good for cruising. It would be real fun with a good trans, like a M5R2, TKO, T56 or even a 6R80. M5R2 or 6R80 is what I plan when this one dies.

I've found it is very susceptible to intake air temperature and headwinds. It looses a lot of power on high heat days and doesn't like high winds on the interstate. It'll do 80mph in OD, but if it's hot and there's a headwind, it won't like it. I've run it up to 100+mph just to see, but it's most comfortable below 70mph with the wind.

It still doesn't feel like there's enough power for me to be comfortable with passing at times, but that may also be because it needs a gear between 2nd and 3rd. There's always room for more power though. ;)

I also don't have a great fuel ratio curve, as you can see in the graph. It's a compromise of not too lean at low rpm for a stumble and not too rich at high rpm for a miss. It's a headache I tried to tune the best I could with PLENTY of mods, but without a new carb I don't think it'll change. It drives better than the Holley 600 though, and with a better curve it should pick up some power in certain areas.
1967 F-250 Crew Cab 2wd, 300 6cyl, T-170/RTS/TOD 4-speed overdrive
240 head, Offy C, EFI exhaust manifolds, Comp 268H, mandrel 2.5-3" exhaust, Edelbrock 500, Pertronix ignitor and coil, recurved dizzy. 200whp/300wtq

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Re: 300 lacking HP

Post #33 by guhfluh » Fri May 03, 2019 2:33 pm

pmuller9 wrote:
guhfluh wrote:My truck doesn't seem to make peak torque any higher than 1800ish. It does maintain torque up until above 3k, but peak is still around 1800.

Kinda, but the torque at 3000 to 3200 isn't any lower than the torque at 2000 rpm. That is a great power band.

As you pointed out the torque curve here is falling off way to soon and that is the problem.

I'm glad you posted your dyno session. It demonstrates that a larger cam not only has better low end torque but provides a much wider power band than the smaller cams.
I've been pushing for new engine builds to use cams with around a 220* .050" duration for almost all naturally aspirated mild street applications.

I've seen your recommendations and would really like to try the custom cam you spec'd around 230* at .050", but I'm torn between more changes for N/A power or focusing my efforts more towards a turbo addition. I've posted my dynos here before in their own threads, but they didn't gather much attention.
1967 F-250 Crew Cab 2wd, 300 6cyl, T-170/RTS/TOD 4-speed overdrive
240 head, Offy C, EFI exhaust manifolds, Comp 268H, mandrel 2.5-3" exhaust, Edelbrock 500, Pertronix ignitor and coil, recurved dizzy. 200whp/300wtq

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Re: 300 lacking HP

Post #34 by pmuller9 » Fri May 03, 2019 9:01 pm

guhfluh wrote:I've seen your recommendations and would really like to try the custom cam you spec'd around 230* at .050", but I'm torn between more changes for N/A power or focusing my efforts more towards a turbo addition. I've posted my dynos here before in their own threads, but they didn't gather much attention.

You can make a few more improvements as a N/A engine but it still will not be enough.
Focus on a turbocharged combination.
You would need to rebuild the old 1985 bottom with at least Hypereutectic pistons.
Do you have the 1985 head stored away somewhere?
I don't want to hijack this thread any further so can you resume this discussion on one of your old threads?

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Re: 300 lacking HP

Post #35 by BamaDude » Sun May 05, 2019 10:05 pm

pmuller9 wrote:What is the initial ignition timing with the vacuum advance disconnected and what the final timing at 3000 rpm also with the vacuum advance disconnected?

It's at 18 degrees at idle and I got 26 +- degrees at 2000 rpm. I did not have any one around to help and my old dwell meter/tach box only went to 2000 rpm, so I'll have to get a 3000 rpm reading in a couple days.

I did notice, however, that one bracket on the accelerator cable was skooched closer to the carb thereby shortening the travel of the pedal. Readjusting that got the butterfies to open properly and the power followed.

Also, I do not have the front of the carb facing the valve cover, it is facing outward. Didn't think that would matter. I do have a 1" phenolic spacer installed, but it is not the open design.
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

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Re: 300 lacking HP

Post #36 by pmuller9 » Sun May 05, 2019 10:31 pm

The two reasons for having the primaries facing the engine is:
The lower runners on the manifold get heated by the heat coming off the exhaust manifold and they are smaller than the upper runners for high velocity so it is better suited for the primary side of the carburetor.
Don't bother changing the carb orientation since it is working OK.

Going to the open plenum "C" manifold is going to give you the most power.

Instead of 3000 rpm just rev the engine till the mechanical advance quits advancing the timing to see what the total timing is.

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Re: 300 lacking HP

Post #37 by BamaDude » Tue May 07, 2019 10:38 pm

So I check the timing again, and with vac line plugged, I'm at 14 BTDC. Revving the motor, the mechanical timing went to 26 BTDC. With the vac line put back on, it is still 26 BTDC, so that can lose me some HP.

The vac advance line (ported) is pulling around 15 in but for some reason that is not affecting the timing. I will pull out the dizzy soon and check all the pieces in it.
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

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THE FRENCHTOWN FLYER
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Re: 300 lacking HP

Post #38 by THE FRENCHTOWN FLYER » Wed May 08, 2019 7:27 am

Put a hose on the vac can and suck on it with a vacuum pump to see if it changes timing. To service the vac can you do not have to remove the dist.
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guhfluh
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Re: 300 lacking HP

Post #39 by guhfluh » Wed May 08, 2019 3:40 pm

I like using manifold vacuum better for most applications. I only run ported vacuum on my truck for the cool lope at idle with the cam.

I'm not sure what application has only a 12* mechanical advance? My "68 F100 300" distributor has 26* mechanical advance on top of the 12* base timing, for a total of 38* maxed out. That would be a 13L slot on the weight in the distributor for me.

Are you using an adjustable timing light or still the old dwell meter? Just curious if you're getting an accurate reading.
1967 F-250 Crew Cab 2wd, 300 6cyl, T-170/RTS/TOD 4-speed overdrive
240 head, Offy C, EFI exhaust manifolds, Comp 268H, mandrel 2.5-3" exhaust, Edelbrock 500, Pertronix ignitor and coil, recurved dizzy. 200whp/300wtq

BamaDude
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Re: 300 lacking HP

Post #40 by BamaDude » Mon May 27, 2019 12:24 am

THE FRENCHTOWN FLYER wrote:X2 on the above posts. Also, what kind of exhaust system are you using? Low restriction? It might be interesting to disconnect it downstream of the Tri-Y headers and do a pull with open exhaust to see how much you are losing to the exhaust system.


I am running the 2 pipes to a dynomax ultra flow welded x muffler. It has 2 inputs, an x inside then 2 pipes out. I pulled it out and ran down the street and had the same performance. I looked in the muffler and it is not restricted.
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

BamaDude
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Re: 300 lacking HP

Post #41 by BamaDude » Mon May 27, 2019 12:25 am

pmuller9 wrote:Thanks for posting the Dyno runs.

The stock cam produces peak torque at 1700-1800 rpm.
The actual torque peak on your engine may be bellow 1700 rpm but the converter stall rpm won't let you test any lower.
The Comp 252 cam would normally move the torque peak over 2000 rpm so something is choking the airflow.

The Offy DP primary runner (Lower section) has about 1/3 the Cross Sectional Area of the intake port in the head and relies on the secondary to supply airflow to make upper rpm power.
If the secondary on the carb isn't opening then the airflow is restricted.
I'm assuming the Carb is mounted correctly with the primary side facing the valve cover.

As a TEMPORARY test you could put an open spacer under the carb giving the primary access to both upper and lower sections of the intake manifold.


If the open spacer helps the power, why would it be temporary? Could I just leave it on?
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

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Re: 300 lacking HP

Post #42 by BamaDude » Mon May 27, 2019 12:35 am

As a follow up, I am replacing the dizzy because the vacuum advance is not working properly. It has a spring in the vac canister with a white 'plug' and I realize it is not the right spring. I found a replacement spring and tried to tune it by using a small washer on the end where the cap unscrews, with no luck. But also replacing because the vac arm that attaches to the plate inside the dizzy was hanging up on something. So that's why my mechanical and vac advance numbers were jacked.

It was a cheap reman some years ago, so I decided to get a whole new one. Will report again when it is installed.
1972 Ford F100 shortbed, 300 ci, C4
2007 Mustang GT Roush blown 4.6

Max_Effort
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Re: 300 lacking HP

Post #43 by Max_Effort » Mon May 27, 2019 8:38 am

BamaDude wrote:
pmuller9 wrote:Thanks for posting the Dyno runs.

The stock cam produces peak torque at 1700-1800 rpm.
The actual torque peak on your engine may be bellow 1700 rpm but the converter stall rpm won't let you test any lower.
The Comp 252 cam would normally move the torque peak over 2000 rpm so something is choking the airflow.

The Offy DP primary runner (Lower section) has about 1/3 the Cross Sectional Area of the intake port in the head and relies on the secondary to supply airflow to make upper rpm power.
If the secondary on the carb isn't opening then the airflow is restricted.
I'm assuming the Carb is mounted correctly with the primary side facing the valve cover.

As a TEMPORARY test you could put an open spacer under the carb giving the primary access to both upper and lower sections of the intake manifold.


If the open spacer helps the power, why would it be temporary? Could I just leave it on?


You can leave the spacer in. Those style split runner manifolds were made for a number of different engines, they were terrible IMHO.

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Re: 300 lacking HP

Post #44 by sandboxer » Mon May 27, 2019 9:05 am

Just a few guesses...
It is my understanding that the lower runners have a weaker signal than the upper runners, so you might have to jet them differently for optimal power. You also might be getting fuel separation in the upper runners as well because of the abrupt turn. The spacer not only helps to identify an issue, but could also help alleviate some flow efficiency issues beyond the diagnostics.

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