Rusty's Second Dyno Test

[Gregski]

In Rusty's Baseline Dyno Test over a year ago, my 1974 350 SBC pulled almost 190 horse power at the rear wheels and almost 270 foot pounds of torque @ 3000 RPM. That was in stock form (points distributor, Quadrajet carb, exhaust manifolds, etc.) with only LMC Truck's dual turbo muffler exhaust system on it.

The ultimate goal is 1 hp per cubic inch, so 350 hp, however we want this to be a daily driver with decent idle. So after doing a top end upgrade here are the new numbers:

225 HP and 270 TQ at 4500 RPM

The carburetor appears to be the main limiting factor.

Current Specs:

GM H.E.I. Distributor P/N 93440806
- 10° Initial Timing
- 32° Total Timing
- no vacuum advance

Holley 4160 Vaccum Secondary 600 CFM Carburetor P/N 0-80457SA
- 65 Primary Metering Jet (need to double check this)
- 65 Primary Power Valve
- 0.031 Pump Discharge Nozzle

GM Dual Plane Intake Manifold P/N 12366573

Vortec Cylinder Heads (off of a 1999 Chevrolet Suburban)
- 1.94" Intake / 1.50" Exhaust Valves
- 64cc Chambers

Chevrolet Performance Hydraulic Flat tappet Camshaft P/N 24502476
- 212° / 222° @.050" Duration
- .435" / .460" Valve Lift
- 112° Lobe Separation

Note: we had to go to a new shop to get this test done since the first shop closed down.

[MikeB]

I'm not sure of the conversion factor, but isn't flywheel HP gonna be around 20% more than rear wheel HP?

Nice flat torque curve you have there. Did the engine just hit a wall above 4600 RPM? With that cam, I'd expect to see it rev to 5500 or so, with peak HP in the 5000-5200 RPM vicinity. Heck, I once had a base Goodwrench engine with a 204/214 cam that would make power to 5,000 RPM with a small 4-bbl and headers.

35 total advance should be good. In fact, Vortecs do well at around 32 total.

I don't think your carb is the limiting factor; 600 CFM is certainly not too small.

Just noticed your A/F ratio is VERY lean! Maybe that cam wants bigger jets. What do your plugs look like after running the engine under load above 2500 RPM?

I also gotta wonder how many RPM those stock Vortec valve springs are good for, although GM claims to use them in the RamJet 350. In fact, I just ordered a set of LS6 beehive springs and the proper Comp Cams retainers and locks for my stock Vortec heads, just to see what if any difference they make with my RamJet roller cam.

[Gregski]

Thanks Mike for your reply you raise a number of good points so let me address them one at a time

Originally Posted by MikeB

I'm not sure of the conversion factor, but isn't flywheel HP gonna be around 20% more than rear wheel HP?

That's cool so I am looking at 270 HP at the crank. Online I see there are different numbers for manual transmissions vs automatics, but this is ball park.

[Gregski]

Originally Posted by MikeB

Nice flat torque curve you have there. Did the engine just hit a wall above 4600 RPM? With that cam, I'd expect to see it rev to 5500 or so, with peak HP in the 5000-5200 RPM vicinity. Heck, I once had a base Goodwrench engine with a 204/214 cam that would make power to 5,000 RPM with a small 4-bbl and headers.

I agree with you I was looking forward to reving it up to 5500 RPM too, Tony the guy who ran the dyno said that when he sees a dip in horse power he lets off of it, so he must have seen something. The last place I went they reved it up to 5500.

Here is a graph for the Chevrolet Performance 350 HO Turn Key engine I was emulating when I built mine P/N 19210009.

333 hp @ 5100 RPM (that's at the crank so 277 at the rear wheels approximately)

[Gregski]

Originally Posted by MikeB

35 total advance should be good. In fact, Vortecs do well at around 32 total.

that's what I thought that's why I left it on 10° initial so that when the 22° mechanical kicked in it gave me a total of 32°

the dyno guy recommended a billet MSD with a setting of 15° initial and 36° total (no vacuum)

I did have a nick in one of my spark plug wires that we could see and maybe there are some others, although the wires are brand new but they are the cheap AutoZone kind, I will be replacing/upgrading them to see if that will make a difference

I think there is nothing wrong with the GM H.E.I. distributors and they should be more than adequate for 300 HP. Do you all agree?

[Gregski]

Originally Posted by MikeB

I don't think your carb is the limiting factor; 600 CFM is certainly not too small.

I also agree with you, I think the dyno guy recommended one that is more tunable and just mentioned a 650 CFM kind. He did not like the metering plate for the secondaries nor the vacuum secondaries.

I was already planning on getting a 4150 model instead of my 4160, I had my eyes on the 650 CFM Classic Holley PART# 0-80783C which comes with an electric choke and vacuum secondaries, but now I am thinking of going with mechanical secondaries so I am thinking of getting the 650 CFM Double Pumper with manual choke PART# 0-4777C

Thoughts?

[MikeB]

Originally Posted by Gregski

I was already planning on getting a 4150 model instead of my 4160, I had my eyes on the 650 CFM Classic Holley PART# 0-80783C which comes with an electric choke and vacuum secondaries, but now I am thinking of going with mechanical secondaries so I am thinking of getting the 650 CFM Double Pumper with manual choke PART# 0-4777C

Thoughts?

I'd stay away from a DP, unless you have a low axle ratio (like 3.73) and high-stall T/C or manual trans. And if you do go that way, a 600 will be enough to handle the engine's air requirements, and will keep throttle response crisp (smaller primaries).

The 80783C is a great carb -- one of my favorites -- but it's a lot of money just to get a secondary metering block. Here's a kit with the parts you'd need to convert your 4160 to a 4150 style: https://www.summitracing.com/parts/h...STKBoCh2rw_wcB
All you'll have to do is add jets. Your current carb should have a 134-39 metering plate, with orifice sizes comparable to #69 jets, so that's where I'd start.

http://www.superchevy.com/how-to/148...et-conversion/

Finally, have you monitored your fuel pressure? The A/F ratio is a lot lower than what I'd expect to see with jets that are a little too small. I think something else is going on.

How about float settings? And have you checked the float bowls and needle seats for debris?

[Gregski]

Originally Posted by MikeB

I also gotta wonder how many RPM those stock Vortec valve springs are good for, although GM claims to use them in the RamJet 350. In fact, I just ordered a set of LS6 beehive springs and the proper Comp Cams retainers and locks for my stock Vortec heads, just to see what if any difference they make with my RamJet roller cam.

Mike and all have you seen Hog's post on the TriFive.com website titled ID please - 350 Vortec L31??? he seems very passionate about the Vortec engines and goes into great detail about them I learned a lot from it myself

[Gregski]

Originally Posted by MikeB

Just noticed your A/F ratio is VERY lean! Maybe that cam wants bigger jets. What do your plugs look like after running the engine under load above 2500 RPM?

I just replaced my 65 jets with some 72 ones I know that is a big jump the the truck seems to like them. I think my PCV was too loose in the rubber grommet in the cylinder head and maybe that was causing the lean condition, I have replaced the brand new loose rubber grommet with the old one from my old non Vortec cylinder head and the PCV fits nice and tight now.

... and I will read the plugs next as you have suggested

[MikeB]

That's a big jump in jet size. But, hey, why be timid?

Good find on the PCV valve grommet leak.

Keep us updated.

[MikeB]

Here's are the parts I have coming from Summit Racing:

NAL-12499224 LS6 VALVE SPRING SET
$62.97
CCA-648-16 VALVE LOCKS
$28.97
CCA-787-16 16PC RETAINER SET
$51.97

Also bought this tach, so need to get it installed in place of my monster OEM fuel gauge to learn at what RPM my stock Vortec springs give up. Would rather tear into an engine than the instrument cluster. What a PITA it is in these trucks compared to 67-72 trucks.

http://gmsports.com/content/new-tach...and-gmc-trucks

[Hewfil1]

Originally Posted by Gregski

I also agree with you, I think the dyno guy recommended one that is more tunable and just mentioned a 650 CFM kind. He did not like the metering plate for the secondaries nor the vacuum secondaries.

I was already planning on getting a 4150 model instead of my 4160, I had my eyes on the 650 CFM Classic Holley PART# 0-80783C which comes with an electric choke and vacuum secondaries, but now I am thinking of going with mechanical secondaries so I am thinking of getting the 650 CFM Double Pumper with manual choke PART# 0-4777C

Thoughts?

Me and most of my friends run 750cfm carbs and have no issues with them. But for a daily, I do believe a good 650cfm will do you well.

[Gregski]

Originally Posted by Hewfil1

Me and most of my friends run 750cfm carbs and have no issues with them. But for a daily, I do believe a good 650cfm will do you well.

Thanks for your feedback, I have always heard that the 750 is too big for a SBC and when my buddy Mike offered to loan me his 750 Tony the dyno guy said the same thing, something to do with the hole being too big therefor you dont get the pressure that you would want / need, aka the optimal flow

[ptc]

The AF ratio looks all wacko to me.... that SBC should easily rev 5200-5500... almost every engine has the HP/TQ crossover at about 4800 rpm.... if your not getting that far then you have something setup wrong along the way. a good all adjustable 4150 carb can only make things better.

A chassis dyno is for "final tuning"... Check everything and start with new stuff and LOG it all:
plugs - check gaps
wires - if think they are bad
cap and rotor
valve lash- check and set all the same
even tire air pressures can make a difference


good luck! --- Im gonna check these guys out for my exhaust/header build and my final dyno....

[enaberif]

I wouldn't be happy in any bit with those results and let me explain why..

Here are the two results..
190 hp
270 tq
@ 3000 rpm

225 hp
270 tq
@ 4500 rpm

So your first run you made 190/270 @ 3000 and then in your second run you did 225/270 @ 4500 rpm.

The reason why this isn't impressive for is because you made the same amount of torque but it took a lot longer to get there. You made a difference of 35hp but again you are running that truck a lot higher in the rpm range to get there which could be where that difference comes from.

For a big heavy truck like yours I'd much rather see a higher torque number down low to get that thing moving and worry less about hp.

[Gregski]

Originally Posted by enaberif

I wouldn't be happy in any bit with those results and let me explain why..

Here are the two results..
190 hp
270 tq
@ 3000 rpm

225 hp
270 tq
@ 4500 rpm

So your first run you made 190/270 @ 3000 and then in your second run you did 225/270 @ 4500 rpm.

The reason why this isn't impressive for is because you made the same amount of torque but it took a lot longer to get there. You made a difference of 35hp but again you are running that truck a lot higher in the rpm range to get there which could be where that difference comes from.

For a big heavy truck like yours I'd much rather see a higher torque number down low to get that thing moving and worry less about hp.

you are spot on, I thought the same thing when I compared the tests, I was like wait a second the torque kicked in much sooner the first time around

to be honest with you all I was not too impressed with the second dyno place so I already found a third place and it's right by my house and cheaper too, ha ha, so hoping to touch up a few things and take it in to this place and see what the results are

again I liked the first place but they closed the shop, so I am not just jumping around for the heck of it

[RDrancher]

I can't help you out with anything, but I'm in to learn.

[Gregski]

Originally Posted by RDrancher

I can't help you out with anything, but I'm in to learn.

Awesome, so am I, lol

[Gregski]

gosh darn it, four of the 8 spark plug wires was bad, or at least had nicks and cracks in them, man these wires are less than a year old and have less than 1,000 miles on them

yes Duralast from AutoZone but hey they was Made in the U.S. of A and I liked them cause you could mix and match the set with matching individual ones, that was nice if you like me have long tube headers [pronounced] P.I.A ha ha

gonna try some AC Delco ones next

[MikeB]

Originally Posted by ptc

Check everything and start with new stuff and LOG it all:
plugs - check gaps
wires - if think they are bad
cap and rotor
valve lash- check and set all the same
even tire air pressures can make a difference
.

Yeah, did you adjust the valves with 1/2 turn preload? It can be very tricky to find the "zero lash" spot, and not unusual to go too far. Anything past 1 turn could possibly keep valves from fully seating.

[MikeB]

Originally Posted by Gregski

gosh darn it, four of the 8 spark plug wires was bad, or at least had nicks and cracks in them, man these wires are less than a year old and have less than 1,000 miles on them

yes Duralast from AutoZone but hey they was Made in the U.S. of A and I liked them cause you could mix and match the set with matching individual ones, that was nice if you like me have long tube headers [pronounced] P.I.A ha ha

gonna try some AC Delco ones next

Bet it looked like 4th of July under the hood at night!

I've had really good service from Taylor Spiro Pro and MSD Helicore wires with silicon jackets. I get the cut-to-fit models, because the pre-cut sets always seem to have at least one wire that's too tight, and one that's waaaay long. The cutting and assembling takes a little time, but not too bad once you do a couple. And you only have to do it on the distributor cap ends.

Also, the conductor is spiral wound metal wire, not carbon like OEM type plug wires use.

[Gregski]

Originally Posted by MikeB

Yeah, did you adjust the valves with 1/2 turn preload? It can be very tricky to find the "zero lash" spot, and not unusual to go too far. Anything past 1 turn could possibly keep valves from fully seating.

valves have been adjusted recently when I thought I had valve ticking noise which turned out to be an exhaust leak, so valve lash is spot on, the exhaust leak was fixed also

[Gregski]

Originally Posted by MikeB

... and MSD Helicore wires with silicon jackets. I get the cut-to-fit models, because the pre-cut sets always seem to have at least one wire that's too tight, and one that's waaaay long. The cutting and assembling takes a little time, but not too bad once you do a couple. And you only have to do it on the distributor cap ends.

Also, the conductor is spiral wound metal wire, not carbon like OEM type plug wires use.

This box seemed to have all the right buzz words you mentioned, so I decided to put my Big Boy Pants on and make my first set of custom wires

for more details please visit my Restoring Rusty thread

[Hewfil1]

Originally Posted by Gregski

Thanks for your feedback, I have always heard that the 750 is too big for a SBC and when my buddy Mike offered to loan me his 750 Tony the dyno guy said the same thing, something to do with the hole being too big therefor you dont get the pressure that you would want / need, aka the optimal flow

Yeah, but most of us run with far from stock internals and obviously swapped out heads, so in the end it works for us. I'm running 14:1 compression, which I doubt Rusty is.

[MikeB]

Originally Posted by Gregski

I have always heard that the 750 is too big for a SBC and when my buddy Mike offered to loan me his 750 Tony the dyno guy said the same thing, something to do with the hole being too big therefor you dont get the pressure that you would want / need, aka the optimal flow

Very true. Using a square bore carb larger than 600-650 on virtually ANY 350 engine gains NOTHING at WOT, but it does hurt throttle response. Why? Because the 750's larger primary bores reduce the airflow velocity past the idle transition slots and boosters. However, if a 350 revs to 7,000 RPM and has 100% volumetric efficiency (as in a race engine), a 750 would be appropriate to feed the beast at very high RPM. Not my opinion, but simple math.

If you're looking at a square bore carb like a Holley, the best fit for a 5,000-6,000 RPM street 350 is 500-650. And those who downsize from a 750 will immediately notice snappier response when they step on the gas pedal. As a bonus, gas mileage is better. Been there, done that with a couple 350s over the years. One went from Edelbrock 750 to Edelbrock 600, the other from Holley 750 to Holley 600.

Of course, a 750 Q-jet with its small primaries would work well on a variety of engine sizes.

An interesting note: The baddest solid lifter 396 Chevy ever made used a 780 cfm Holley vacuum secondary carb. And the popular, high-revving 350hp/327 used a 585, which would equate to 625 on a comparable 350.