Questions concerning lack of power after 4K

[GRM-REPR]

I haven't been on this site for almost 1 year due to certain peoples b.s, and decided to try to find help here once again. I would appreciate intelligent repsonses on this thread and nothing else which doesn't pertain to its relevance.

It's a Chevy 355, 10:1 compression, 10 deg of timming, Holley 650 double pumper, Moderate cam (I don't remember the specs), Vac advance dist, Perfomer RPM Q-Jet intake (will be replacing soon) and all high performance ignition with an MSD control module.

It has a TH-400 with 3.42 gears in the diff. I'm not sure what type of torque converter is in it either. No line lock or trans brake.

The car doesn't pull for crap over 4k. When I leave the line under soft acell and throttle the engine, it just feels powerless, it won't even spin the tires. This engine is by no means a beast but it should certainly get up and go, which it doesn't.

This problem has existed since I've owned the car. I feel as though maybe the torque converter is wrong for the cam. The cam is lopey but not huge by any means. Possibly not enough carb? It almost feels like it's starving for fuel?

Converter? Carb? (which was tuned well by Prince Valiant last summer), Q-Jet intake?

I'm out of ideas, any suggestions on where to start would be appreciated. If anymore info is needed, let me know and I can update the thread.

Thanks, Jon

[Reverend Cooper]

i doubt the converter is a issue,i would go threw the basics,check and make sure cam timing and dist. timing are correct, if so check for fuel issues a bad accelerator pump in the carb could cause an issue like this or maybe the jetting in the carb is too small. pretty open question,fuel filter getting plugged

[wrath]

It's probably fuel related. If you mash the throttle it should spin the tires. It should at least spin the tires 1-2 seconds after you hit the throttle then stop spinning as soon as it's rolling 10mph.

I'd check:

Accelerator pump. It should leave a puddle in the intake. Move it slowly, you need about 20cc of gas being squirted out over the full sweep of the throttle blades. Quadrajets usually have "quadrabog" because of a crappy accelerator pump. I'm a Quadrajet guy, I'm sure there is a Ford guy around here that knows Holley.

The timing. You'd find that it probably wants base timing around 13°. As long as it advances at least 10° you should still have plenty of power. Having the right distributor can make a big difference also. If you've mixed a smog distributor (ESC/electronic spark control... most had centrifugal advance between 25-30°) with a non-smog ICM and vacuum advance you can end up with a real mess. You want 30-38° total advance. The wrong combo can get you 30°+ more advance on top of your base advance. I like to check ideal base timing in gear using a vacuum gauge and a dwell/tach meter (more sensitive than a regular tach). You want peak STABLE vacuum at the lowest RPM. I then usually back it off a degree.

Air leaks. Windshield washer fluid in a squirt bottle works pretty good to spray around gasket areas. Air leaks can introduce a wicked stumble. Windshield washer fluid doesn't provide the incredibly noticeable RPM change as WD40, carburetor cleaner, brake cleaner, et cetera... but it also doesn't make a mess.

Spark plugs for lean condition. Get it hot, run it at WOT up a long hill and as soon as you get to the top let off, put it in neutral, and turn the key off. Pull a couple spark plugs (not #1 or #2). They should be chocolate colored, not white. Kind of a hillbilly method but it works.

[Prince Valiant]

Hey Jon,

Good to see you back....

A couple of questions:

I recall that we basically did two things...set the base timing for around 13-16 degrees, and set the carb for a "lean-best" idle and then slightly richened by 1/4 turn, and that was pretty much it. I can't recall if that improved at least some of your complaints...I know not all though; Did it?

Also, I seem to recall that your ignition wouldn't advance very far over the base setting...is that correct? Did you have a different distributer last year? I do recall you having some pretty quality pieces though.

IIRC, you were generating b/w 15-17" of vacuum on the gauge...do you recall if that's correct?

[GRM-REPR]

I appreciate all the responses.

Chris, to answer your questions, I had replaced the distributer with a vac advance model, with an MSD control module. The carb is still the same Holley 650 DP, with the the same adjustments we made to it last summer.

Since I had replaced the distributer, I had to turn down the base timming, roughly to 10 degrees. Your adjustments last year by the way, had solved all the odd misses and idiling issues. However, since I rarely ever "beat on the engine" the times I have, I've noticed it just doesn't pull at all over 4K.

I agree with Wrath 100% on the basis of wheel spin on soft acell, and mashing the gas pedal, it does no such thing, feels like it's in second gear when I try it (which it isn't).

Yes, the vacuum was roughly about 16'', a good mild/moderate cam too.

I dread to think I may have put the new distributer (installed after you were here) a bit off but it runs too smooth in my opinion for such a chance like this.

Thanks again for the replies.

[GRM-REPR]

Spark plugs for lean condition. Get it hot, run it at WOT up a long hill and as soon as you get to the top let off, put it in neutral, and turn the key off. Pull a couple spark plugs (not #1 or #2). They should be chocolate colored, not white. Kind of a hillbilly method but it works.[/QUOTE]

Thanks for the reply, I had just replaced the plugs before the Automotion Dells car show this year. If I were to say what color they were, for the most part, white but certainly not black.

[jon_we4]

I'm only mentioning this because it was not mentioned before.

If you've checked everything. Fuel, Spark - everything is right. I would consider doing valve springs. They are a wearable item and if they have had a hard life, or the cam is large for the spring selection - they might not last forever.

But I would put it on a chassis dyno. It will really help with trouble shooting and add the ability to show the real gains/losses involved with the things you try. That along with a wideband reading can be useful with fueling as well.

I'm sure it could be anything, I'm just trying to add another perspective.

[GRM-REPR]

I'm only mentioning this because it was not mentioned before.

If you've checked everything. Fuel, Spark - everything is right. I would consider doing valve springs. They are a wearable item and if they have had a hard life, or the cam is large for the spring selection - they might not last forever.

But I would put it on a chassis dyno. It will really help with trouble shooting and add the ability to show the real gains/losses involved with the things you try. That along with a wideband reading can be useful with fueling as well.

I'm sure it could be anything, I'm just trying to add another perspective.

Valve springs would be a good idea, however, I failed to mention the engine was rebuilt in 04' and has only roughly 3,500 miles on it.

Thanks for the suggestion.

[WickedSix]

do you have hydraulic lifters in the engine? when improperly adjusted they can float the valves prematurely.

do you have the right length pushrods? are they screw in rocker studs? or press in?

have you degreed in the camshaft?

to me it sound like your cam in substantially off which will cause the timing to have anomalies as well

[forest]

But I would put it on a chassis dyno. It will really help with trouble shooting and add the ability to show the real gains/losses involved with the things you try.

it does make things go a LOT faster, and with more accurate information, you can make the right changes, once, and be done with it. 80.00 for 1 hour with A/F if you need it.

[GRM-REPR]

do you have hydraulic lifters in the engine? when improperly adjusted they can float the valves prematurely.

do you have the right length pushrods? are they screw in rocker studs? or press in?

have you degreed in the camshaft?

to me it sound like your cam in substantially off which will cause the timing to have anomalies as well

Good points, the entire engine was rebuilt and set up at Engine Rebuilders in 04'. I'd like to think they know what they were doing there (I would never go back for personal reasons).

I know the lifters are hydraulic with roller rockers.

In all honesty, another angle to address the concern is this: It feels like it's totally revved out at about 4,200 rpm's, a "falling on its face feeling." When I had it at the track last year, I thought my tach was off (which it's not). It does this throughout all gears.

[juicedimpss]

falling off after 4 is going to be a fule pump/filter or valve springs,maybe a coil.

if the plugs are WHITE it is starving for fuel.

[GRM-REPR]

Juiced, good point, SUPPOSEDLY Engine Rebuilders "rebuilt" the fuel pump in 04' during the rebuild. When I brought it out this year, there was a lot of wetness around it as well. I've looked since and there is none. Fuel filter is replaced every year so I know it's not an issue. Coil is brand new as well.

What tool do I need to assess the weakness/strength of the valve springs? I can't be sure they've been replaced.:confused

[jon_we4]

Do you know what brand/part # the springs are?

You can test springs with a tester (http://store.summitracing.com/partdetail.asp?part=pro-66774) - I would think a quality engine builder would have one. Compare them to the spring's specs. The springs could still be "good" - they may just be a little on the weak side for your cam.

Again - just throwing out ideas here.

[GRM-REPR]

Do you know what brand/part # the springs are?

You can test springs with a tester (http://store.summitracing.com/partdetail.asp?part=pro-66774) - I would think a quality engine builder would have one. Compare them to the spring's specs. The springs could still be "good" - they may just be a little on the weak side for your cam.

Again - just throwing out ideas here.

Sadly they never gave me a cam card or anything of the like. I have no clue what type of cam/springs or specs available. The person who owned it before I did had too large of a cam in the previous build. I'm unsure of whether or not the springs were ever changed to match the new cam I have in it now. If they were changed out, I doubt it would be the springs due to lack of any mileage or punishment to the engine. I treat it nice.

[jon_we4]

Sadly they never gave me a cam card or anything of the like. I have no clue what type of cam/springs or specs available. The person who owned it before I did had too large of a cam in the previous build. I'm unsure of whether or not the springs were ever changed to match the new cam I have in it now. If they were changed out, I doubt it would be the springs due to lack of any mileage or punishment to the engine. I treat it nice.

Sending the cam out to be cam doctored (or if there are etched #'s on the end of the cam I can see if we can pull the spec's off that) and having one of the springs tested will show right away if your problem is valve train related. Plus it gives you more knowledge on what is in your engine.

[wrath]

Will it even make it to 6k? If it was valvetrain related you'd definitely hear it by then. You can't miss the sound of valves floating.

It's kind of a dumb question, but is the timing fubared? Like, a couple plug wires being reversed or the harmonic damper being spun on the hub?

[GRM-REPR]

Will it even make it to 6k? If it was valvetrain related you'd definitely hear it by then. You can't miss the sound of valves floating.

It's kind of a dumb question, but is the timing fubared? Like, a couple plug wires being reversed or the harmonic damper being spun on the hub?

Nah, no such thing as a dumb question, I appreciate them all.

I don't even bother taking the engine to 5k, it doesn't do anything, it just seems like I'm already at 6k but I'm only at about 4,200!

I put the dist in last summer after Prince Valiant came and tuned my carb. I set the balancer to 0, lined up the rotor with the number 1 cylinder. It was new, so it was kind of tough, I bumped the engine a couple of times to mesh the gears and it dropped in.

Then engine idles great, cruises great and sounds well. I know I have the f.o right because it's always the first thing we check.

[wrath]

I'd still probably focus on seeing if it's running lean.

Do the secondaries ever get a chance to open? They should open briefly when you hold it at WOT. There is no load on the motor so they'll quickly close. I wonder if the reason why it's so wimpy is that it's not getting enough air and fuel. All sorts of crazy crap can keep the secondaries from opening.

I'd probably start with ensuring the harmonic damper hasn't spun on its hub. You can do this by cranking the engine until the distributor rotor is pointed at where #1 plug wire is plugged in and that the #1 cylinder doesn't let air out the intake or exhaust when you put compressed air to it. The timing mark on the harmonic damper should be somewhere close to where you expect it to be.

I'd then check to see that it is advancing. You might have to buy some timing tape if you have a cheap damper like what I run. If it's getting to 30° total advance by 3,000 RPM that's not the problem.


I made this 6 or 7 years ago, I don't know if anyone else might find it helpful:
http://www.wrath.com/sbc/images/ChevyTiming.jpg

[torque.hit]

Do you happen to have a fuel pressure guage before the carb?

[GRM-REPR]

Do you happen to have a fuel pressure guage before the carb?

No, hadn't installed one yet, not a wild set up. I know I need to purchase one though.

I pulled a plug and it's not WHITE but it's not black, the plugs look normal to me.

In connection to what Wrath is stating about the carb getting enough air, I had thought of that last year. The original shaker hood scoop is matted to the hood, so I don't have the original air cleaner assy that drew fresh air from the outside. I had to cave in and put a Ebrock (heart shaped) filter on. I can't run anything bigger than probably 11''. It's awfully tight under the hood.

Could the problem just be the lack of incomming air to the carb? Thanks for all the responses.

[torque.hit]

The plugs could return to a normal color if you let it idle though, you wouldn't know if there was enough fuel above 4k unless you shut it off during a hard run and then checked the plugs.

[GRM-REPR]

The plugs could return to a normal color if you let it idle though, you wouldn't know if there was enough fuel above 4k unless you shut it off during a hard run and then checked the plugs.

Makes sense

[torque.hit]

Depending on the mileage of the rebuild, I'd put my money on fuel delivery or valve springs. Even when my motor had terrible timing it would still rev to 6k, just pinging the whole time.

[DurtyKurty]

I'm gonna guess too much lifter preload.

[GRM-REPR]

Well, my friend has a Holley Blue fuel pump (brand new) going to toss it in and were going to inspect and adjust the valves on Saturday. I will update then.....

[GRM-REPR]

Huhhhh.

Ok, I tossed in a new fuel pump my friend had, turns out the one I had on it had a small crack in it.

So now comes the b.s......

I followed a valve adjustment procedure to the T. I started at number 1 cyl and completed one side of the engine first before moving to the next (per instructions). After finishing, I started it, I could hear some ticking from the valve covers and I could sense a change in the exhaust note (cam didn't lope very strong). So I went back and turned each nut in about a 1/4 turn each.

I started it once again and the engine ran like crap. It sported a "bubbly" feel when I snapped the throttle linkage. So I went back AGAIN and backed each nut off 1/8 of a turn. It seemed to run better and the exhaust note sounded stronger.

However, when I went to take the car home it ran fine but when I got off the freeway, it ran like shit. The engine was somewhat surging, almost like a miss. When I went from stop to start, it felt very sputtery (sorry, best adjective I could think of). So I richend the carb a bit, seemed better but certainly not right still. When the car is cruising it feels fine, stop and start, not fine at all.

WTF did I do or didnt I do right or where do go from here. I'm pretty new to putzing with Chevy engines, especially adjusting valves and tuning carbs. Sorry to sound like an retard but naturally by adjusting valves, it would throw off the tune of the carb? It just feels way wrong.

Any help is appreciated.

Thanks.

[torque.hit]

If you set the rockers too tight, they open the valves off of their seats, killing your cranking compression.

You will probably want to reinstall the rockers. I am having trouble finding the proper procedure for you.

[GRM-REPR]

True, when I crank the engine, it feels "odd". After setting zero lash (spinning and pulling up on push rod while tightening nut), I turned each nut in 3/4's of a turn. After I had done that and started the engine, thats when it didn't sound right out of the exhaust.

This procedure I followed is the same one my friend uses successfully, don't know what I did wrong.

[GRM-REPR]

I went back and started all over again with adjusting the valves. I read two of the same articles and they explained the procedure the way I did it yesterday. I must've messed up on a couple of them because now it's super smooth. In fact the engine was never this smooth before. For all I know Engine Rebuilders didn't take good care of the rebuild because of conflicting interests.

It pulls better but it still comes up somewhat short on the high end. After getting much help here and throwing a fuel pump and valve adjustment at it, I'm really starting to lean toward the carb not getting sufficient airflow, if I didn't know any better, I'm not sure the secondaries are even opening, I never hear them. The scoop when closed over the air cleaner completely seals the air cleaner. Plus with all the engine heat rising to the top, it would almost make sense.

Thanks for all the help.

[WickedSix]

I have been trying to dig up the article from a corvette forum about valve float and hydraulic lifter preload..... but basically it is the same as what you have done but only 1/2 turn after you feel friction in the pushrod. The 3/4 comes from chevrolet and acts as a mechnical rev limiter in a sense due to causing valve float at a lower rpm.

IMHO what you need to do is start adjusting ONE thing at a time if you keep throwing a couple things at it and you fix it you'll never learn what actually fixed it.

Start by setting one of the variable ... like say timing....and then adjusting the carb until you get the best results. The leave the carb alone and adjust the timing until you get the best results..... basically you are trying to weed out what does and does not affect your problem on your engine. By being methodical you will have more insight into diagnosis for the next time.

[forest]

I went back and started all over again with adjusting the valves. I read two of the same articles and they explained the procedure the way I did it yesterday. I must've messed up on a couple of them because now it's super smooth. In fact the engine was never this smooth before. For all I know Engine Rebuilders didn't take good care of the rebuild because of conflicting interests.

It pulls better but it still comes up somewhat short on the high end. After getting much help here and throwing a fuel pump and valve adjustment at it, I'm really starting to lean toward the carb not getting sufficient airflow, if I didn't know any better, I'm not sure the secondaries are even opening, I never hear them. The scoop when closed over the air cleaner completely seals the air cleaner. Plus with all the engine heat rising to the top, it would almost make sense.

Thanks for all the help.

I would be surprized if Donny didn't do somthing right on the motor because of problems between you two. He would do the job right, just to tell you never to come back in again, he doesn't need problems that can easily be avoided. But on the other hand, everyone makes mistakes, and it would be possible that somthing got overlooked. Try adjusting the valves while it is running, and you will have GREAT results with the valve adjust, just a lil bit oily haha. :thumbsup:

[slow90z]

If the carb is a double pumper, why not have someone floor it with it not running, and look down the carb n make sure the secondarys open all the way...
Otherwise, by how you're describing it, it really sounds like valve float to me. And i know it isn't the distributor you got from me, because i was doing 7000+ rpm with that same hei, so that can't be it...