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post #1 of 8 (permalink) Old 07-27-2014, 10:02 AM Thread Starter
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351C results - jumpy curve

Hi guys!
I tested my 351C on a chassisdyno yesterday at a muscle car meet, just for kicks. Engine is "garage-tuned" by myself, and i am an amateur. We did 5 runs, no changes between runs.

All pulls showed a wobbly curve and dip @ 5100 and then picked up [email protected] 5700 and down again. The dynoguy said it was probably timing related. Have a Mallory Unilite with a Mallory Promaster coil. 8mm ford Racing wires and autolite 25 plugs.

You guys have any input on this, and my results over-all? I havent got any reference and dont know what to expect.

Dynoresults attached as file.

Engine data:
351C 4V CC
Comp: 10.88:1
Cam: Crane H-288-2
Intake: Air-gap RPM
Carb: Holley 650 DP
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post #2 of 8 (permalink) Old 07-27-2014, 10:10 AM Thread Starter
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Re: 351C results - jumpy curve

Other side also shows lambda curve, isnt the lambda curve very low?
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post #3 of 8 (permalink) Old 07-27-2014, 01:37 PM
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Re: 351C results - jumpy curve

The biggest issue with giving advice on a single dyno sheet, is that no changes were made, which would have helped to indicate what was causing the anomaly. I realize you only did it for fun, but numbers from a dyno are not worth much unless they are used for comparison to each other with changes. It is quite dangerous to make a suggestion without more info, but my first hunch is over-advanced ignition.

I say this because your AFRs are quite rich from 3700 to 3900 rpm, yet the engine likes the extra fuel. It should not, and should have lost power (assuming the AFR sensor was properly calibrated). However, richer mixtures burn slower. Because it liked the extra fuel, this may be a clue that the engine could be over-advanced, and the extra fuel caused a retard effect. This retard effect could then increase power. Coupled with the momentary power drops (bucking) increasing from 5100 rpm and higher - this is my first guess.

Again, without comparative information, this is just a hunch. You can try driving the car, reducing your base timing 5° to feel if there is an improvement at higher rpm, confirming over-advance or not. Second is your fuel curve, which you want relatively flat, and at the AFR that the engine makes best torque (with correct timing). It would appear your carb needs a change of jets and probably PVCR tuning. If you experiment with changes, let us know what single changes help and what does not, and in what rpm ranges. Only change one thing at a time, or the information becomes confusing.

David

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Last edited by PSIG; 07-27-2014 at 01:39 PM.
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post #4 of 8 (permalink) Old 07-27-2014, 01:44 PM
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Re: 351C results - jumpy curve

Quote:
Originally Posted by 70_mach1 View Post
Hi guys!
I tested my 351C on a chassisdyno yesterday at a muscle car meet, just for kicks. Engine is "garage-tuned" by myself, and i am an amateur. We did 5 runs, no changes between runs.

All pulls showed a wobbly curve and dip @ 5100 and then picked up [email protected] 5700 and down again. The dynoguy said it was probably timing related. Have a Mallory Unilite with a Mallory Promaster coil. 8mm ford Racing wires and autolite 25 plugs.

You guys have any input on this, and my results over-all? I havent got any reference and dont know what to expect.

Dynoresults attached as file.

Engine data:
351C 4V CC
Comp: 10.88:1
Cam: Crane H-288-2
Intake: Air-gap RPM
Carb: Holley 650 DP
hello;

ok i must not be awake. you have only 280 hp but you have over 500 lb of torque?

do you have an old style msd box?

if it was timing it typically would not dip then come back up again. i have never seen timing cause this its nearly impossible. you are talking about a 30 hp dip. thats massive. you should EASILY be able to feel this. it kinda looks like a bog when the secondaries come in but thats way late for them to kick in. the advance is mechanical it has no ability to advance then retard then advance under increasing acceleration. it simply can not do that. also, you should have full advance by 3200 rpm at the most. 5400 rpm is way too late for it to be a mechanical advance problem

do you have mechanical or vacuum secondaries?

what jets do you have?

i can't see the afr's.

you should also be spinning more than 5700 rpm with that big cam. crane lists it as 6400 rpm for 350 chev eng. a comp xe274h will spin that thing to exactly 5800 rpm with ease.

also, your carb is too small. needs a 735.

i would also buy higher ratio rockers. that cam only has .480 lift.

if you do these things and jet and time it properly, it will gain around 40 hp. yup!

disconnect the dist vac hose and tell us the following.

timing at idle

timing at 1600 rpm.

total max timing.

rpm where total max timing is reached.l

Last edited by barnett468; 07-27-2014 at 03:18 PM.
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post #5 of 8 (permalink) Old 07-27-2014, 04:19 PM
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Re: 351C results - jumpy curve

Quote:
Originally Posted by barnett468 View Post
ok i must not be awake. you have only 280 hp but you have over 500 lb of torque?
...
i can't see the afr's.
He is probably in Europe, and the dyno sheet is in PS (Pferdestärke) instead of HP, and Nm (Newton-meters) instead of ft/lb or lbf/ft.

The AFR trace is on the second photo.

David

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post #6 of 8 (permalink) Old 07-27-2014, 05:29 PM
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Re: 351C results - jumpy curve

Quote:
Originally Posted by PSIG View Post
He is probably in Europe, and the dyno sheet is in PS (Pferdestärke) instead of HP, and Nm (Newton-meters) instead of ft/lb or lbf/ft.

The AFR trace is on the second photo.

David
Ok thanks - 280 hp = 278 ps . . 500 nm = 368 ft lb tq. Kinda makes more sense now, lol. That’s low for his set up. It certainly needs something. Irregardless of the grand canyon hp dip, I think his timing is probably too low like many other cars. If it was too high it would ping his brains out so he should know somethings wrong. to little would also at least partially explain his low peak rpm unless the dyno guy just stopped it there and it actually revs higher than shown.
.

Out of the box many of these aftermarket distributors are set up to around 15 degrees of mechanical. Many people just assume the advance is correct, drop them in and never check.
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post #7 of 8 (permalink) Old 07-27-2014, 11:04 PM Thread Starter
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Re: 351C results - jumpy curve

Quote:
Originally Posted by barnett468 View Post
Ok thanks - 280 hp = 278 ps . . 500 nm = 368 ft lb tq. Kinda makes more sense now, lol. That’s low for his set up. It certainly needs something. Irregardless of the grand canyon hp dip, I think his timing is probably too low like many other cars. If it was too high it would ping his brains out so he should know somethings wrong. to little would also at least partially explain his low peak rpm unless the dyno guy just stopped it there and it actually revs higher than shown.
.

Out of the box many of these aftermarket distributors are set up to around 15 degrees of mechanical. Many people just assume the advance is correct, drop them in and never check.
Thanks guys, yes its European units. Shouldve told you.

I have set my timing at [email protected] and total [email protected] Will control this again. Have KB177 hypers which says 34 degrees is limit. The unilite is all mevhanical, no vacuum. I have no MSD-style box. Just coil + dist.

The dip occured same place on every run, we did 5.

Carb has mech secondaries, jets are now 71 primary and 73 sec.

I was looking for a 750dp, but the one i borrowed for test was a 650. No choketower, so seller had it wrong.
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post #8 of 8 (permalink) Old 07-29-2014, 02:50 AM
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Re: 351C results - jumpy curve

Quote:
Originally Posted by 70_mach1 View Post
Thanks guys, yes its European units. Shouldve told you.

I have set my timing at [email protected] and total [email protected] Will control this again. Have KB177 hypers which says 34 degrees is limit. The unilite is all mevhanical, no vacuum. I have no MSD-style box. Just coil + dist.

The dip occured same place on every run, we did 5.

Carb has mech secondaries, jets are now 71 primary and 73 sec.

I was looking for a 750dp, but the one i borrowed for test was a 650. No choketower, so seller had it wrong.
HELLO.

I'm stumped unless as i mentioned, it occurs when the secondaries open but that is kinda late to open and kinda small of a carb to cause that.

do you feel that when you drive?

if you cruise along at around 40 us mph and floor it, does it bog for a second then accelerate?

why did you not use the carb you normally have on this engine?.
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