What am I doing wrong to get decent power out of a 350?
 

I've spent countless hours researching online over the past year and several thousands on parts and my car is still kind of sluggish IMO.

I have a hard time seeing my 350 producing much more than 300 horsepower. The below is what is on it:

• original stock block with 65,000 miles
• Crower 60916 camshaft with hydraulic lifters
• Kaufmann KRE 65 cc D-port heads- they are supposed to be milled down further to get compression around 10.1-10.5 but I never confirmed it was actually done. Valves are 2.00/1.66
  
• 1.65 roller rockers
• Edelbrock RPM Performer intake manifold
• Hooker headers with 2.5" Pypes exhaust system
• 600 cfm double barrel Holley carb (I tried putting a 750 double pumper and it was bogging down the engine)

Any idea of what I can look at that may be wrong with this set up? Or what upgrade I should do to get this thing to over 350 horsepower?

I was expecting some decent power but boy this thing is kind of a dog. I have a hard time seeing it do less than 15 seconds in the quarter mile but I haven't tested yet. When I asked Kaufmann what kind of power he thinks it can produce, he said I may be around 375-400 hp.

Glad to see you are giving it a run. You have a build that on paper sounds similar but better than mine.

Cam: your 60916 is just a couple more degrees more than my 10510702 Voodoo cam, same LSA. The lift is slightly less than mine, but very close.

Heads: your KRE d ports undoubtedly flow better than my 2.11/177 mildly ported #12 iron heads.

I run FiTech for fuel system. It's likely not faster than a Holley, but might be easier to tune.

What is your ignition setup and timing curve?

My best et was 14.04 with awful air and embarrassing 60 foot times. I think mph was something in the 100 ballpark. This was during my last track trip years ago, where I had just got into data logging my runs and adjusting afr settings for best et/mph. I have no problem admitting I suck as a driver. But I have no doubt I could've had 13's.

The rest of the package was th350, 2000 stall converter (more stall would've helped), and 3.73 in a 1st gen. Stall and gears with a cammed up 350 really helps. The power band really comes in above 2000 rpm.


As a point of reference, I broke out of the 15's with a 69 350, stock 47 heads, Summit 2800 cam, same trans/2k converter, and 3.23 gears. I can't remember if I was running a qjet or Holley then.

The point of telling you what I ran is not to peacock on my setup, but that I think you are selling yourself short, or something is off in your tune. I am really not that good at this compared to many people.

Dare to be different! Btw, welcome, congrats on post #1.

Have you done a cranking compression test? If so what are see seeing.

Stan

As was mentioned above, steeper rear gear and some stall will allow the engine to perform in its power band. Start with ignition curve and timing. Most aftermarket camshafts require 16 to 18 degrees initial as a starting point. Then knowing your timing advances coming all in at specific RPM allows for fine tuning. Example: 36 total all in by 2,800 RPMS……

Several things are wrong with your combo!
1)
The larger port volume of those aftermarket heads or any of the available aftermarket heads only serves to harm throttle response and torque in your CID motor below 4000 rpm.

2)
You want more then 300 hp you say, well stock heads are more then capable of producing that along as a stated above. Producing superior throttle response.
You only need 175 cfm@28” to make over 350 hp.

Good port velocity in the motors average rpm range is just as important or more then cfm if the motor will not run above 5500 rpm.

3) your choice of intake manifold is harming the motors power production just like your choice of heads is.

4) if your cam is not producing at least 175 to 180 psi of cranking compression then that’s a issue also and a big issue at that!

In short and in my opinion everything you have bolted on above the deck of the block is fully counter productive to your stated goals.

I agree do this. Engine should work pretty well. What gearing convertor and weight of car?

Cliff always said that the Crower cams always need 4 to 6 degrees advance to get to correct 108 or 109 centerline. If its retarded it will be sluggish.https://forums.maxperformanceinc.com...ighlight=60916

HP is in the heads,start there.Tom

In the Nov 2000 issue of muscle car review a stock rebuilt RA3 400 fitted with long branch Firebird exhaust manifolds and the 068 cam was dyno tuned on race fuel ( just to be safe ) to 368 hp @4700 rpm and 448 ft @ 3500 rpm.

So you should have no problem making 350 hp with stock heads with your 354 cid motor if your cylinder pressure is up where it should be.

Which 600 and 750 Holley’s were you running? We have had a lot of trouble with new Holley stuff make decent power without an extraordinarily amount of tuning. OTB they have been 50 HP short of a well prepped carb. I can’t imagine a newer 600 DP running well at all on that combo without and insane amount of tuning. The bogging on the 750 DP is easily fixable. It could also be a sign you have some issues with the timing and carb tuning.

This….the 2802 cam dirt motor 350 took 8* to get it to a 108-109.

The smaller the cubic inch in any engine brand the more you have to rely on the RPM factor to make HP / Speed ... The 350 Pontiac spent most of its life in fuel mileage and emissions era... So they were paired with bad rear gear ratios, low compression and old school transmission tech a;; of which are counter productive to fun..

I always find it funny how every Pontiac guy will admit our stock head flow suxx but the minute you bolt on a flowing head OMG that's not the way to go

To have fun with a smaller N/A engine you have to make it easy and in a short time to get from idle to a productive torque output

A 462 engine is a no brainer with its almost linear torque curve

That cam isn't really that big but in a 350 it will noticeably soften the off idle response and while the engine is loafing around trying to get out if its way the clock is ticking

I will try to check that this week and report back

I've adjusted the timing probably several dozen times by testing and never really seen a huge difference in performance with adjustments. Right now I believe I set it around 15 degrees initial and around 32-36 full around 3,000 rpm.

The 600 is a Holley Model 4160 vac secondary. The carb was rebuilt because it was dumping fuel in it and running rich. I put a lighter vac spring and really doesnt seem much faster.

This is very helpful. It was installed dot to dot. I am not an advanced engine builder and really only know the very basics. I believe I can take the timing cover off with the engine block in the car and check this

The gearing is 3.55 in a 68 firebird which I believe is around 3,300 lbs. It has a 200-4r transmission. I had a TCI saturday night special convertor (1,600-2,000 Stall) but just changed it to a TSI Race convertor (2,800-3,200) this weekend. It performs a little better but still not an impressive improvement for the time put into it.

I could be selling myself short and plan on seeing what the 1/4 mile time will be at the track this summer. This is very helpful and gives me a reference to see if I am matching up. Part of me wonders if I am just use to the low end torque when I built a 302 67 mercury cougar- that seemed to perform a lot better than this 350 engine which has a mid to upper power band camshaft. However, I've read that pontiac 350s are suppose to have a lot of torque so that has me scratching my head.

What transmission, torque converter and rear gears does it have?

Interesting. I appreciate the numbers for me to check. I was wondering if I should change out the intake manifold from the RPM Performer to the standard Performer. I read that somewhere online and then another place said to go with the RPM :confused:

The heads were a little bit of an investment so I would like to see if I can get those to work. I thought about taking them off to port them but you're suggesting I should definitely not do that?

I kinda get the impression that the engine isn't really flowing well. I did recently stumble on the suggestion of checking the pushrod length and that if they are too short, the valves won't open to its full potential. I do not believe I checked that and hope to get to that today.

200-4r with TSI race 2,800-3,200 stall. Correct me if I am wrong- I believe that means small blocks like mine would stall around the lower end of 2,800.

Rear gears are 3.55

The standard performer can make well over 400 hp with superior drivability up to 5500.

Here are Edekbrocks own recommendations for there intakes and as you can see the performer rpm has a power band of 4500 to 6000 rpm.

If your motor is not Camed and you do not have a converter to flash up to 4000 rpm then you have simply put yourself behind the 8 ball.

Don’t advance the cam until you have done an across the board compression test so you have a base line to refer to .

To save yourself a mess jack up the ass end of the car after you have drained the rad and before you pull off the lower hose.
This will get the water level in the block below the water pump holes and keep coolant out of the nose of the pan.

This is easier then removing the 1/8” pipe plugs each lower side of the block when you have headers.

The motor has the same stroke as a 400 and is only a mire 13% less in total CID.
I had a 350 in a 4 door Tempest with a 2 speed trans.and 2.93 gears.

Once I put on a stock 70 intake and carb , stuffed in a used 067 Cam and swapped out the Super Turbin 300 for a TB 350 I was very pleased with what it had for low speed power and mid range power up to 4000 rpm.

Basically your motor is suffering from too little power in too narrow of a rpm band.

That all sounds great! Who assembled the top end, installed/degreed cam, determined pushrod length, etc? As mentioned already, hopefully a compression test (engine hot) will shed some light on dynamic compression. No sense in pulling anything apart until you've done some testing. A factory 68-72 iron intake should be better than the RPM in your combination, but even so, at high RPMs that engine should be screaming. What does the fuel system consist of? fuel line size, mechanical pump, etc?

Here’s another opinion but since you’ve asked for things to check….
Personally I’ve never ever owned or seen a vacuum secondary Holley carb that would fully open on at WOT. Put a small screw and nut in the slotted secondary linkage and go drive it. I didn’t realize the cam specs until I looked it up. The cam, heads, and intake would work well on a 400. It’s just too much for a street 350.

I say take it to a chassis dyno and see what its doing.Power time it and check AFRs.They will tell you if the carb is getting full throttle.Tom

It is asking a lot out of a untuned 600 DP 4160 Holley to make much more than 320HP.

This may be a good application for a Q-jet. The small primaries will give the low RPM venturi velocity required to be responsive and meter fuel properly until the airflow demands increase to open the secondaries.

My first pontiac was a 60 over 350 with 670 heads, '68 iron intake, late 70s olds Q-jet, XE256 cam. Super comp headers and 3" exhaust. Stock converter, TH350 with redneck shift kit, 3.23 gears in a '67 Lemans. It would run low 14s. Wasn't a world beater but was fun for what it was. Would easily do the dairy queen burnout with 235/70-15 Firestones. Was a bit soft below 2200 RPM and had a slight lope. Maybe 8.9 compression with 76CC heads.

Late one night my GF at the time and her girlfriend "borrowed" the car and went terrorizing the good people of Jackson MS. I didn't wake up until I heard it chip 2nd down the street.
Another time I barely lost a top end run against a early '60 thunderbird. Car developed a vibration about 115 and I got out of it.

Good times.

The power band of an Edelbrock RPM is 1500-6500, and is fine for your application. People run them on SBCs all day long and do fine.

Your cam makes power to around 4800, beyond that it flattens out. You should be doing pretty good up to that 4800 though.

**I think the combo of not having the cam degreed and the small carb are the areas to focus on. You should have at least a 670 on there. A 700 or maybe 750 dialed in would be best.**

Usually, smaller displacement engines like more gear, but 355s should work 'good', and your stall should be fine too.

You could be suffering from lack of fuel, you should check your delivery, and fuel psi.

Your SCR may be lower than you think, but even so, it's not going to make a huge difference unless it's really low. CR test is in order.

Have someone who knows how to degree a cam help you, and same with your 750 carb if you still have it. Check your fuel system. Think that is the best approach for now.

EDIT: There's time to get it ready for summer if you get to it.


.

If it has a throttle cable on it.
I was driving my LS Sonoma to work and it lost power. On the way home I wrung it out really good (been trying to blow it for bout 7 years). Got it home and thought, yep, she's done...:first:
On a hunch I popped the hood jammed a broom on the peddle and the throttle barley moved, and the cable coiled up like a spring.:huh:

The power band for the 60916 is listed as 2000-4800 but its listed for 326-455. I can only assume it’s closer to 52-5500 in a 350, depending on how it’s degreed.

Check your pushrod length before doing anything else. They wont be the right length if the heads were swapped on and the original pushrods were used. Who assembled it?

PRIMARY problem is that you started with a 350 when there's no penalty for going 400+ cubes. On a mild engine, every cubic inch is one horsepower and 1 1/4 ft/lbs of torque. ~50 cubes = more better. 100+ cubes = happiness.

Secondary problems:
600 cfm DOUBLE BARREL Holley carb??? Apparently with no tuning

Cam installed "dot-to-dot" when there's a half-dozen things that all are needed to be precisely machined for that to be accurate--and "accurate" may still not be "optimum".

No mention of timing advance tuning

No mention of piston design/quench distance/ring package/block honing


As said--compression test needed. Fuel pressure test needed, with engine at WFO and max RPM. Verify throttle plates open fully, and the trans TV cable and shift-points match the torque curve.

Kauffman sold us the completed heads with new everything of course. I just installed it with my father a very long time ago but just got it on the road the past year and trying to figure it out. If I recall, we didnt degreed it but lined it up dot to dot with the original timing chain. I believe we were told the original pushrods should work but will double check the geometry this week.

Fuel system- original mechanical pump and

So here are the numbers. Oddly the cylinders on the passenger side were similar and the cylinders on the driver size were similar but the 2 heads were drastically different.

Driver side head

• # 1: 160 psi
• # 3: 165 psi
• # 5: 160 psi
• # 7: 163 psi

Passenger side head

• # 2: 192 psi
• # 4: 188 psi
• # 5: 190 psi
• # 8: 185 psi

Searching online, I am reading that may indicate one side needs a new head gasket. I do recall taking the passenger side head off so may have used a different head gasket- would that be the reason for the large difference? Any ideas?

Yes, a 400 would be great. If I can get this 350 to produce 375 horsepower with some adjustments, I would be happy though since I am not into competitive racing. Just want a high performance street vehicle to take racing a few times for fun.

opps, I meant to type 600 cfm four barrel holley carb. It actually has a vac secondary. The other one I tried was a 750 double pumper but sold it since it was too much carb

That engine should be strong for a 350.


I would re check my head bolt torque and my valve adjustments. Are those stock head bolts? Valve train geometry correct?

A 600 vaccuum secondary is more of a 250 or 300 HP carb, that is not even worth tuning. I wouldn’t go wild changing anything until you switch carbs to something that matches your expected power levels. The 750 DP is a much better choice for tuning efforts.

Have you tried running more timing with the allum-heads and only
around 10:1 compression I would try 38-40 degrees of timing, it
should like it, don't hurt to try and don't cost nothing. If you put a
different thickness head gasket on one side that would make a differance
in compression from side to side.

GT

Something is by far not right with those cranking compression differences from bank to bank and a different head gasket that might have been used unless crazy thick would not make for those psi differences.

You need to do a leak down test and if that checks out pull both heads and CC them .

Did this motor by chance start out life as a 2BBl ?

The higher compression numbers on one side can be a few things:

Battery going dead during testing. The faster the engine cranks, the higher the numbers. Did you test the passenger side first? Did the battery get weak or did you boost it at any point during the test?

Valvetrain adjustment or geometry. If the intake valve closes earlier for any reason, the cranking compression will be higher. Rocker adjustment, valvetrain geometry, lifters not pumped up prior to test, etc will result in higher numbers. In my case, I found that one intake lifter that did not pump up gave 185 PSI when all the other cylinders pumped 165.

Odd airflow or intake issue. A restriction in the intake system can cause low numbers, but not very common. Same for exhaust restriction, stuck heat riser, etc.

Smaller combustion space: One head could have smaller chambers than the other (did you CC both heads?) Or the wrong head gasket or strange deck height issue.

I don't know why the difference from side to side, but that is like the difference in 1 point of CR or about 10 cc's difference in total volume from side to side.

Stan

I did the driver side first but then hooked the battery charger up before doing the passenger side. The starter while turning the passenger side may have even turned slightly slower but not much.

Appreciate all the suggestions. Yes, I am thinking of doing the following in order:
1. Check valve geometry, adjustments and head bolt torque
2. Leak down test
3. if is okay, I will take the heads off to cc- mill them evenly if needed and install new head gaskets

The head bolts are the new ARP brand.

I think I have gotten it up to 40 degrees in the past when I tested various timing adjustments and never saw significant performance improvement. With everyone's help in brainstorming potential issues, I am thinking I need to focus on the heads whether it is a leak, valve geometry or heads being milled differently. The timing adjustments and carb changes never improved much.

I personally would run down why the compression is so different ... .. . I don't know KRE heads do they have a part number that's visible under the valve cover? Might have two different chamber sizes or maybe one head got milled twice

I would expect putting a battery charge on between banks would effect the result on a pump test. At very least you need to do it again before make any conclusions.

I had a Pontiac that the factory deck machining height was off .018” between banks.

60916 >>> INT/EXH - Dur @ .050” Lift: 221°/229° RR: 1.5/1.5 Gross Lift: .455”/.470” LSA: 112°

I agree with others, advance the cam to 108/109 centerline. try a smaller intake like the performer to increase port velocity.

you need to make sure the torque convert and gear is correct for the setup. that engine should want to rev.

You will go crazy with a stock 600 vac looking for power making engine changes. Out of the box they are only jetted for about 275 HP. That is the power level that has worked best for us with those carbs.

So you did a cranking compression test with all the other plugs in?

If so then now you have to do that test again or make a leak down test before you say that removing the heads is needed.

Be sure to kill the power to the HEI before making these test.

Once you get the compression sorted you should definitely get that cam advanced. The 60916 needs to be advanced most likely 4 deg to a 108 intake centerline for best performance.

This engine, its kinda like he has different thickness head gaskets on each bank or something. The difference is strange.
600 Holley I would not waste my time with it.
A 3310 750 could be made to work well. At least you could tune it and the secondaries could be set up to come in as needed and not bog.
Or a real Holley 650 DP would be sweet too. I think I have one that somebody overtightened a base bolt with a thick gasket and snapped the ear off. Needs a new baseplate.
You do not see them a lot anymore. But, back when all us kids Hot Rodded everything we drove (the good ole days !) All the young guys with their 350s in their Camero's wanted one.

Yep. A buddy of mine has a’68 dart with a 340. 230/236 cam. I have tried 3 Holley carbs on it. 650 dp, 700dp and 3310. It likes and starts better the best with the 650. It’s a Dodge, but…

Call me nuts, but I fail to see correlation as to how a certain size / cfm carb will start an engine better cold then another size carb if there both set up right .

You’re not. These were out of the box. The 650 had the best factory idle circuit for this motor. :)

340 is a pretty small engine with a short stroke. Its going to move air faster though a smaller venturi like the 650 DP has.

I can attest to the smaller carbs having better idle and off-idle drivability. Cold warm-up too.

On my Olds 350, the 670 avenger was great, but it flattened out around 45-4800 RPM.

I switched to a 770 and it pulled past 6000, but idle and drivability suffered.

There was really no in-between, and with the 670, as I would go into higher altitudes, it would lean out and overheat.

So I switched to a Holley Terminator throttle body setup. Problem solved. I'm sure timing control had some to do with it too.



.

So I adjusted the valves again just to get the hydraulic lifters to zero lash, then tightened 3/4 turn. Then tested the compression a 2nd time with the below. Took all the spark plugs out and the engine warm. Overall, the readings seems to be similar +/- 5 psi. (not sure how precise my old gauge is)

Driver side head
# 1: 155 psi
# 3: 160 psi
# 5: 155 psi
# 7: 158 psi


Passenger side head
# 2: 195 psi
# 4: 194 psi
# 5: 200 psi
# 8: 187 psi

I am ordering a leak down tester to see if there is leakage in that driver side head. Hopefully I should get that complete early next week.

The next thing I realized, is the pushrods are indeed a little too short. See the test I did in the attached photos

Passenger Side
https://www.hyperleadit.com/wp-conte...enger-side.jpg

Driver Side
https://www.hyperleadit.com/wp-conte...river-side.jpg