Hot Rod Forum banner

Dyno'd My First Engine Build

6K views 64 replies 12 participants last post by  OldTech 
#1 ·
Dyno'd my first motor build and numbers are much lower than expected. Need help.

Fresh 350 non roller block
.030 over
flat top hyper pistons
vortec heads 3 angle cut
Complete Comp Cam kit Hydraulic Flat Tappet 262/270, Lift .462/.469 w.springs and lifters
New edlebrock intake
HEI Dist
4 barrel

Did 4 passes on dyno and max power we could get was 240hp 288 torque. Timing set to 14 and water temp 185, air ratio was 14ish.

Do these numbers seem correct?
 

Attachments

See less See more
1
#31 ·
forget timing at idle,,, mark on the balancer where 34º. Rev engine about 3,000 rpm and set timing to 34º. Dont ever say 10-14 degrees again,,,lol. Its 34º while engine is at 3,000 rpm. You do NOT need to worry about advance weights until after the dyno tune is finished. You are working on drive ability issues before you iron out the turtles,,,,lets find the missing 75 horses first!
 
#38 · (Edited)
Rochester QuadraJet:

Picture link had url instead of img...

I guess what everyone is asking is are you aware that the distributor is supposed to be automatically advancing the ignition timing as the RPMs increase? That is, 12 degrees BTDC at idle ----> 34 degrees BTDC (maximum) by about 2500 RPMs... This advancing is easily seen at the balancer using any timing light while gently revving the engine...

Your engine will require Premium gasoline 91 - 94 octane, whatever the highest available locally, to avoid engine damaging pinging at WOT... it may also need a touch of Octane Booster added as well... although keeping max timing at only 34 degrees instead of 36 - 40 degrees will hopefully avoid the need for that... Don't worry about the extra cost of Premium gasoline, the extra MPG of a high compression engine more than makes up for that... Your Vortec heads usually only need 32 - 34 degrees max timing to make max power possible...
 
#37 ·
Is your balancer labelled with timing marks or are you using timing tape or are you using a dial back timing light? It would be great to see what you're ALL IN timing was during the previous pull so as to make a comparison. It looked a little bit rich at sub 12.5, but that means you could try adding some timing to see how it responds as the additional timing will lean it out a tenth or two.

Hopefully you understand what is being asked/instructed about setting the timing. Keep in mind that most every degree of additional all in timing that you can run will be worth another 5hp at a minimum. So if that last run was at 32 and your motor is capable of handling 37 without experiencing any detonation, then you would see another 25-35 hp just in that. Keeping in mind that you might have to put a little more fuel to it.
 
#39 ·
Pic of the old carb. I couldn't get my hands on a 750 cfm today so I settled for a new 670 holley avenger.

Installed carb and used 110 octane fuel this time.

Total timing was 36 at 3300 rpm. Had difficulty holding idle because the dyno was fighting us.

Results were the exact same.

280 hp
340 torque
 

Attachments

#40 · (Edited)
The good news: the torque is now peaking from 2900 - 4100 RPMs !!! About what I expected... Oh wait, that's a big improvement over your first tests, but not as good as your second tests...!!! Maybe old carb. is a 750 !!!

The bad news, torque still weak by 40 - 80 and 80 - 100 HP still missing... 700 RPMs still missing...

Was the choke flapper FULLY open on both carb.s? I assume both are vacuum secondaries. Did the secondaries butterflies and secondaries air door open on both carb.'s? This is all adjustable as needed. Youtube has videos on how to adjust them.

Yep... old carb. looks like a Carter made under license by Weber... looks like a strip of metal was riveted on to hide a name cast into the carb. body... or provide a place for a name... did you get the measurements of the diameters of the butterfly valves/bores on the bottom of that carb.? So we can estimate its CFM flow?

The new Holley 670 sounds about perfect for your engine... I heard that by coincidence the August 2016 issue of Car Craft has a carb. article that will also verify that! Did you check the primaries jets size?
.
 
#41 ·
Choke was zip tied open. Jet sizes are whatever comes stock out of the box. We adjusted the mixtures screws a little bit and adjusted idle. Otherwise bolted up and that's it. wasn't able to look at the butterflies because they have a big intake that sits on top of the carb.
 
#42 ·
wasn't able to look at the butterflies because they have a big intake that sits on top of the carb.
Is that like an air cleaner or air horn... Does it have a lid that sits at least an inch above the carb. top so that air can get in? Do you have to use it?

You'll need to add a piece of white tape or something to the secondaries and air door linkages so that you can easily see if they are moving/opening... I suspect they aren't... because power is missing...
 
#44 ·
Need more fuel and maybe some more spark if it can with stand it. AFR was 13.9 , needs to be in the high 12's to low 13's. You've got more in it kid. Keep going.

It would be best to add 2 jet sizes and see what that does to the AFR. If it drops to 12.4-12.7, then add 2 more degrees of timing. Report back. If not, then add 2 more jet sizes.
 
#49 ·
The secondaries may be set for the higher vacuum levels of a stock engine... the slightly lower vacuum levels of a performance engine may not open them... they are sensitive and adjustable... YouTube has instruction videos...

Holley has a spring kit available with springs of different colors/strengths to use to adjust them... the springs go in the vacuum cannister attached to the secondaries linkage... unless it has an adjustable cannister...
 
#51 ·
NO WAY !!!

Here's a dyno run of your cam in an engine with no where's near the power potential of your engine! It has crap heads and lower compression ratio:

COMP Cams® - Xtreme Energy 262 Hydraulic Flat Tappet Camshaft, Part # 12-238-2 Dyno Sheet

If you look in that Low Power 350 thread I linked to, you'll see everyone here poopooed me when I told the guy right off the bat I was going to knock 15 tenths of his 1/4 mile E.T. time with only some slight changes... but then you'll see later in the thread I did that... and more!
 
#53 ·
Mixture first, go up a couple sizes on the secondaries to get the AFR closer to 12.5-13:1 at WOT.

Carbs are almost never right out of the box unless its a near stock build.

Concentrate on getting the mixture right, then timing. You don't want to detonate lean while playing with timing under full load.
 
  • Like
Reactions: 64nailhead
#55 ·
X2^2!

Without speaking for Chuck, he's describing creeping up on the tune. Always creep up on the tune with it too rich - this is done with the timing safe at something like 32-34 degrees. Once the AFR is just a minor bit too rich, then add timing as described previously. I feel it should be closer to 12.5:1 than 13:1, but anywhere in there should work. Then add timing at 2 degree increments and see what that does to both the AFR and HP/TQ numbers. A couple of different things might happen once you start adding timing, it might make more power and lean out just a little bit. If so, then add another couple degrees as long as the power is increasing. I feel that once it hits 13:1 and the power is still increasing then you need to add more fuel again and retest. If it increases, then try another 2 degrees.

When adding timing, as soon as you see the HP/TQ drop, then you've gone too far and you need to drop it back a degree or two and retest. Creeping up on the tune makes the entire dyno process safe. It will correct any timing TDC issues you might have. If you think about it, let's say your TDC mark is off by 1-2 degrees. It won't matter and it won't hurt anything. If it makes the most power at 32 or 38 degrees and your TDC mark is off by a degree or two, who cares. You'll know where you need to set the timing ON YOUR ENGINE to make power. Of course it would be great to have TDC precisely marked, but at the stage you are at now it isn't a deal breaker for continuing on with the dyno testing. Buzz is correct when he indicates that you should end up at 34-36 degrees, but he's assuming that your TDC mark it spot on (it may not be.)

The same applies with an inaccurate AFR gauge. If the gauge is off by half a point for whatever reason, it doesn't matter. Make your tuning decisions based on HP numbers. The same applies to the HP/TQ numbers. All dynos don't read the same due to calibration factors. IMO it's not important what the numbers are, but rather when they change and what adjustments you made and how they affected the readings.

Give the motor what it wants - more timing and/or more fuel until the power starts to drop.
 
#54 · (Edited)
No more timing... If still at 34 -36 max... and timing tab is accurate at -0- TDC... I guess could try more timing and see if power increases, maybe the timing tab isn't accurate...

What kind of power are you seeing now...? .. What A/F now?

Are you sure those are -062 or -906 castings true Vortec heads from a 350" engine? Or the -059 heads from 305" engines? (Not Vortech Swirl Port head?)

Iron Vortec Head

Check primary jets size...

How far were pistons down in the bores? Flat top pistons? Head gasket thickness?

Will it rev to 6,000 RPMs?
.
 
#57 · (Edited)
The power is so far off, seems like there is a major problem... not just tuning... Can you get the head gasket thickness with a feeler gauge?

Just slapping the carb. on out of the box should have gotten torque in upper 300's and HP in lower to mid 300's with your setup... then we tune a bit higher up from there...

OK, that last pull looks more like it... HP 316... Torque 373...what did you change?

Maybe a compression test on all 8 cylinders to see if some valves got lashed too tight... I'm running out of things to check from here...

Bigger jets needed...
.
 
#59 ·
That last picture looks like it is the "corrected" Hp version. They have a screen that bumps up the numbers if it were adjusted for perfect conditions I was told. 70 degrees, at sea level etc etc. The first 2 are what my motor is actually putting out.
 
#60 ·
Your lean in the midrange where your BSFC is under .500, since it goes above that higher in the rpm it suggest lean primary main jets...not much probably one or at most two jet sizes...at most!

When your dyno tuning just look at torque, thats all that matters. Your pretty close now...maybe 20-30ft/pds away from all your going to get with out component changes and some timing tuning

Don't be tempted into throwing on spacers etc like you see in magazines, all it usually does is move the torque up the rpm band which gives the illusion of more HP.

HP is just a multiplication of torque and rpm remember, torque is all that matters. I predict your going to see about 410-425 ft/pds (corrected) peak and there is nothing wrong with that from a 350sbc.

Pretty nice little street motor if you ask me, would really work well in a truck with stock gearing or heavy car. Should be decent on fuel too considering the limitations of building on a budget.
 
#62 ·
You're lean in the midrange where your BSFC is under .500, since it goes above that higher in the rpm it suggests lean primary main jets...not much (bigger) probably one or at most two jet sizes...at most!
X 2... My assessment also... secondaries are usually shipped rich... current jetting may give good cruising MPG... couple steps richer primary jets give more HP...

Don't know if your carb. came with a secondaries metering plate with fixed jets... or a metering block with removable/swappable jets... but they look OK, anyways... unless wanting to keep the primaries lean for better MPG and going bigger on the secondaries when wanting most power...

Some power prolly also available from a traditional .015" - .020" thick steel shim head gasket for a bump in compression ratio and improvement in engine quench effects...

What elevation are you at? Are you in Denver or somewheres high up?

Did you ever get the measurements of the throttle bores of the first carb.?
.
 
#63 ·
Yes. Customer brought in an old edelbrock to get replaced today and looked the exact same as mine. Found the casting numbers and it is a edelbrock 1400 600 cfm carb.

Tampa Fl, Home is about 5' above sea level :)

Stock jets for new carb are 65 primary/ 68 secondary
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top