Best 1/4 mile ET 13.2. Based on trap speed and weight of the car, my current combo is 350 fwhp. Based on similar combos, I should have got 370-430 fwhp:
http://www.compcams.com/v002/Pages/396/XR276HR-10.aspx
http://www.airflowresearch.com/dyno.php

Any ideas what is limiting power in such amount in the engine? Specs of the current combo:
355cid ('88 350 block, .03" over)
Holley 3310 (model 80508S, choke deleted, original jets)
Edelbrock RPM intake
AFR 190 heads (out of box, no mods), specs: http://www.eecis.udel.edu/~davis/z28...s/chev190.html
1.52:1 ratio CC roller tip rockers
CC XR276HR cam, specs: http://www.compcams.com/Company/CC/c...?csid=188&sb=2
MSD distributor + plug wires + programmable box
Total timing 36* (at WOT)
1 5/8 Hedman shorties
Single 3" catback with two Hooker Aerochamber mufflers in line

Idle needs alot of advance to operate (50*).
Timing chain/gears are in 0 position.

Any thoughts and ideas are very appreciated, thanks!

 

That doesnt seem right for that combo although those heads typically like alot of advance

I would check that carb and see what the air fuel ratio is. Verify distributor is working and matches timing at the balancer

Could make improvement with better exhaust/headers. Also 1.6 rocker on intake valves could help.
What valvesprings? Make sure its not floating

 

Thank you very much for your ideas!

Yes, idle is weird and I counn't figure it out - tried adjusting mixture, different vacuum wiring etc.

Advance is checked many times at the balancer. I ran 13.2 with cheap Mallory HEI distributor, so distributor is changed and no effect (exept little bit better idling).

Rebuilded carb this winter - no effect, tried bigger jets - no effect, tried double bumber with bigger jets - no effect. According to the O2 (not wideband), mixture at WOT is rich enough.

Valvesprings are original AFR-s. With heavy ARFs valves, they should be OK til 5700-5800, in sense of valvefloat, according to AFR.

Edit: it has good power and torgue in 2000-4000 rpm, but it revs not so good past 4k ...at least it seams so. I have rev limiter set on 5k and it rarerly touches it when driven aggresively.

 

That could be an issue to look at. It should pull to 5500 very strong.

Could be fuel mix and maybe some valvefloat but hard to say

 

Start w valve springs.

AFR has used some kinda crappy ones over the years; K-Motion for example. Put known good ones in it. That should solve the lack of RPM problem.

Next, your timing is obviously wrong. If you need 50 degrees of advance to get it to idle right then something is wrong with either your light or your measurement technique. Put down the light and set the timing to where THE ENGINE runs the best. Start by advancing until it pings then back off slowly til it quits. Somewhere near there is where THE ENGINE wants it. THE ENGINE knows ahelluvalot better where it needs to be than the light does.

 

Possibility of the carb being oversized, leading to inadequate atomization of the fuel. I know everyone likes to throw the biggest carb they can on there, but there is a science to proper sizing. Your setup should require a 600-650 cfm at most. There are calculators available online, or just do google searches for 355 sbc carb size, see what setups others are using and their results.

 

The carb is fine.

The same carb was used on motors as small as the 302.

Might not be "optimum", but as far as being catastrophically wrong, it's not.

In fact, the symptom about no high RPM performance, is THE EXACT OPPOSITE of what "too much carb" will do. "Too much carb" produces a motor that has any number of street (or pit) driveability problems and falls on its face at low RPMs, but comes on like gangbusters once the air gets to flowing. Since that isn't the symptom at hand, then that isn't the cause at hand, either.

See my signature for the logical process: if a proposed "explanation" of observations fails to account for any of them, let alone is in DIRECT OPPOSITION to the observations, then it's probably not the right one.

In point of fact, a 750 is about right for a 350 with a dual-plane intake. Since the engine takes air in in pulses rather than in a steady stream, and the air intake of a 350 peaks somewhere in the 650 range LONG-TERM AVERAGE, the pulses that must be handled gracefully by the carb are clearly SUBSTANTIALLY LARGER THAN a 650 CFM average flow. a 750 or 830 is a better match, depending on the desired RPM range.

Bottom line: leave the carb alone until you fix the high-RPM problem.

 

Thanks guys! I really, very appreciate it.

Forgot to mention previously, compression ratio is 9.8:1 and I'm using 1" carb spacer.

Selection of parts was mainly based on dynoed combos (Comp Cams and AFR, linked in the first post).

Tried different strobos and mechanics and the result was the same. As I said, the more advance in idle (in gear) the best. It was also so with the previous mechanical distributor that was initially set between terminals 1 and 8 (about 22,5* base timing) and then tuned with strobo to 12*.

With current programmable MSD box I'm able to customize retard curve, so distributor is set to 50* advance and in idle retard is 0*. Depending on MAP and RPMs, retard during driving is 5-20*, 14* at WOT.

OK, I will order new valve springs and replace them, this is easy to do. AFR is using "1.450" OD Hydraulic Valve Spring, 120 lbs. on seat, .550" maximum lift, AFR #8020".
Good replacement seems to be:
http://www.summitracing.com/int/part...6-16/overview/
or stronger;
http://www.summitracing.com/int/part...7-16/overview/

Next step is to go on dyno and try to play with mixture using WBO2 and timing.

Thanks, guys!

 

986 is the better choice for this situation IMO. (has a damper)


I'd worry less about what "number" your "light" says your timing is, and worry more about what YOUR ENGINE thinks when you make changes to it.

 

More info about AFR valve springs. According to their catalog, they are for "Hydraulic Flat Tappet": https://www.airflowresearch.com/valve_spec.php
From the same place, hyd roller springs are much stronger.
COMP Cams 986
Seat load: 132lbs @1.750''
Open load: 293lbs @1.250''
Coil bind: 1.150''
Rate: 322lbs/in

COMP Cams 987
Seat load: 121lbs @1.800''
Open load: 343lbs @1.200''
Coil bind: 1.150''
Rate: 370lbs/in

AFR 8020 (current springs) Hydraulic Flat Tappet
125lbs @1.800
304lbs @ 1.250
Coil bind: 1.090''
320lbs/in

AFR 8017 Hydraulic Roller (used on 190cc SBC "Eliminator" Vortec 23° Street Heads)
140lbs @ 1.810
356lbs @ 1.210
1.000
360

According to that, might be the 987s more safe bet?

 

I used the 8020's to 5600 rpm with a 280xfi cam before severe float happened. Thats a much more aggressive cam than yours. Not sure why you would see float but if you are i would def go afr 8017 springs and retainers

You need more seat preasure and alittle more open pressure.

 

I have better access to Comp Cams products, so I'll go with 985 instead?

COMP Cams 985
Dual Valve Springs
I.D. of Outer Dia.: 1.070"
I.D. of Inner Dia.: .700"
Seat load: 165lbs @1.750''
Open load: 346lbs @1.250''
Coil bind: 1.150''
Rate: 366lbs/in
With damper
http://www.jegs.com/i/COMP-Cams/249/985-16/10002/-1

My AFRs are about 10 years old, but springs are original. So change of them couldn't hurt and one potential bottleneck will be eliminated.

 

Are you sure your balancer/timing pointer is telling you the truth? 50* advance at idle and the motor probably wouldn't even want to run. And it goes HIGHER as you rev it, I assume?

Something's off and it's gotta start with your timing. I don't think your TDC mark is actually TDC at the piston.

Yes, valve springs, yes, yes, yes.... but you have to figure out the timing first. Have you changed the balancer? Where is your timing tab located? The middle of the face of the timing chain cover or over to the driver's side in about the 1:30 position?

 

50* advance at idle and the motor idles OK, but when I retard it 10* (base 50* advance on distributor + 10* retard with MSD box = 40* advance), then idle becomes crappy. At 1k+ rpm engine runs good and is starting to fade past 4k. Tried today: floored it while standing, tires started to spin insta but didn't hit the rev limiter, because power started to fade past 4k rpm.

Checked timing many times, with and without strobo, with different distributors, with and without MSD box.

Checked also TDC mark both times rebuilding engine: piston #1 is in the top position and mark on the balancer is at 0* on the timing tab.

Balancer is original (from '88 TPI engine). Timing tab is located on the driver's side in about the 1:30 position.

 

Whats the spark plugs look like at idle? Make sure the fuel curve is right. Sounds like it may be rich and using timing to stabilize

Comp 987's could work shimmed slightly, maybe .030 if you can get away with it.
Check current install height. It should be nearer 1.800" but if its near 1.78" or tighter then dont shim. You should have enough seat pressure. I'd like to get nearer 130-135 lbs seat pressure.

 

Idle mixture screws are about 1.5 turns out from totally closed position (definitely not more than 2 turns) and they are set at minimum what is needed for normal operation at idle. If I'll turn them another 0,5 turns in, engine dies (in gear, at idle). Regular O2 shows little bit on the rich side at idle. Some smell of fuel, but nothing terrible.

Haven't checked spark plugs lately, will do that.

 

Use the 986.


Ignore the timing "numbers" you think you have generated. Adjust your timing to where it runs the best. That means, adjust it from wherever it is; evaluate, better or worse; if better, adjust in the same direction some more; worse, go back where you were, plus a bit more. Repeat until no further improvement is possible.


Did I mention, ignore your "light" and "mark" until you've found the point the engine runs the best.


"If it RUNS good, it IS good".


Don't outsmart youself over something that simple.

 

Max, you got a weird one here. If that's the timing it WANTS to work, it just points me to something else that isn't right in the engine somewhere. With those heads and that cam, it should pull like a mule well past 5000 RPMs. I have the EXACT same heads on my mild 383 blower motor, smaller cam and a super-inefficient old-school Weiand 142 blower whose techology was invented around the time of the steam engine. It does NOT liked the be revved because the blower's efficiency drops like a stone in the upper RPMs. I still shift around 5800-6000.

So, I've got two off-the-wall ideas here:

1. Cam is off by 1 tooth at the chain. I know you put it dot-to-dot but it's easy to be off by one tooth if they weren't lined up in EXACTLY the 6 o'clock position. I have also (one time) encountered a chain where the dot on the top gear was stamped in the wrong position. Have you done a cranking compression test on the motor? It would be a good diagnostic step to give a maybe/maybe not indication. For instance, if you're only huffing up 130 PSI you KNOW something isn't right (my 8.0:1 blower motor makes 135).

2. Secondaries on the carb aren't opening up. Lots of reasons why that could be. I know it's a new carb, but one small vacuum leak at the secondary vacuum chamber and you're running effectively a 2bbl carb on your engine. And that's not the only thing that could go wrong.

Oh, by the way.... does your throttle cable FULLY open the throttle arm on the carb? You wouldn't be the first person tripped up by a cable that's mis-adjusted or a floor mat that keeps you from getting the pedal all the way to the floor.

Those are my two best shots, given you've crawled all over the ignition side of the engine.

 

1. This is highly unlikely that cam is off. I have Cloyes double roller and I have installed it carefully twice. Both times bought a new set.
2. Yes, it feels like something is restring the engine. I have also bone stock '99 Z28 LS1 A4 with 2.53 rear and it pulls better than my 3rd gen. I performed "paper-clip test" on secondaries some time ago and tried 750cfm double-pumper with no luck. Will check secondaries again.

Throttle cable checked many times.

My plans for next 1-2 weeks:
1) To check spark plug after idling
2) To check spark plug after WOT
3) To check secondaries with paper clip
4) To record a video while driving from my computer screen and MSD box software running (I'll get rpms, vacuum, retard, sounds)
5) Ordered CC 987 springs, will try them (or will order also 986)
6) To go on dyno

Thoughts that are flown through my head so far:
1. Faulty cam? Haven't degree it. My friend (engine builder and mechanic) said that CC is trustworthy brand and you should worry about that. (sorry, talked to the mechanic and he degree it, so I'll opt that out...)
2. Too hot air and intake? I have RPM intake (actually AFR's analogue for RPM) and it doesn't have air-gap. Plus I don't have CAI, so maybe air gets too hot before combustion chamber?
3. Original hydraulic roller lifters can't handle the valve spring pressure?

 

Checked idle mixture and timing today.
* After idling in gear about 5 mins, pulled one spark plug and it was OK.
* Tried retard the idle timing by 10* (from 48* to 38* advance): idle was little bit worse, but it was still idling OK. Vacuum dropped by 0,5 psiA: from 8,5 psiA to 9 psiA (vacuum readings from MSD 6AL-2 box that is getting data from MAP, where reading vary from 0 (max vacuum) to 15 psiA (no vacuum, WOT). Not sure at the moment, how to convert it to the vacuum gauge readings.
* Idle mixture screws were 1 1/4 turns out and another 1/4 turn in killed the engine
* another retard by 10* made idle horrible (total 28* advance at idle)
* engine idles in gear at 700-750 rpm

Performed also paper clip test with secondaries and they had been open olny 1/4 of what they could be at max load. Problem might was that I couldn't apply max load to the engine during the test, becouse it vas little raining and the car was most of the time sideways, around the small block. Left the paper clip attached, we'll see soon.

Spark plugs were OK after that agressive lap around the block. Definitely not too rich.

Throttle cable and pedal were OK: throttle blades opened fully when pedal was pushed to the floor.

IIRC, with the initial ignitios system (Mallory HEI and spark plug wires), vacuum readings were quite low. Thought that it was because of agressive cam. No vacuum leaks were found. Haven't measured vacuum with gauge with MSD ignition system. Could be converted fron MAP readings I think...

 

After 5 mins of idle in gear





Engine bay, right side





Engine bay, left side





After agressive driving around the block

 

How'd it go after changing the valve springs?

 

I'm going to bypass your timing issue. Like was said earlier, unless the cam is off a tooth, just give it what it wants and ignore the number.
Is there something possibly blocking exhaust flow? I assume you're not running a cat converter. Are those in-line AeroChambers a full 3" thru? Any chance you could disconnect the exhaust after the Y-pipe and try it?
What kind of hat/aircleaner on the carb? I've seen one of those flat "elbows" show similar symptoms.
What kind of intake gaskets (manifold to heads) ? Did you make sure during the assembly that they're not hanging down into the ports? This was an error my builder buddy found on an engine brought to him; he corrected it and picked up 80 rwhp.

 

1. Intake gaskets are OK, I've checked them many times on the manifold and heads during the assembly. Gaskets were FelPro's 1205, IIRC.
2. Air cleaner is Summit's drop base 14x3" with a paper fllter: http://www.summitracing.com/int/part...3001/overview/
Lower part (base) looks like this:
http://www.ebay.com/itm/Chrome-Steel-14-Deep-Recessed-Holley-Air-Cleaner-Base-Fits-Chevy-Ford-Mopar-V8-/400874234582?hash=item5d55f762d6&vxp=mtr3. Exhaust has been redone this year: no sharp turns, 3" everywhere, AeroChambers are 3" center in/out straight thru, no cats:
http://www.summitracing.com/int/part...6hkr/overview/
Hedman 1 5/8" shorties doesn't fit in ideal way (had to trim inlets in corners), but visually there's no significant restrictions (please check also pics above). Yes, I can unbolt the catback and try then, but I quite sure that it isn't restricting so much. Hopefully on dyno next time.

 

What effect did changing the valve springs have on it?

 

Out of springs, out of spark or out of fuel. Those are your options.

Springs you're either doing or did.

Spark I'm gonna say you've crawled over that enough (unless the MSD is mysteriously yanking timing in the upper RPMs for who-knows-what reason)

That leaves fuel. You have a fuel pressure gauge you can actually read while driving? Idle readings are meaningless. If you're outrunning the fuel system it will happen at WOT at the top of each gear. Especially in 1st and 2nd when acceleration is strongest.

 

Back from dyno:
1) Secondaries are opening max 2/3 way, no more
2) Didn't get valve springs yet, still waiting for them.
3) Got best results with 38* timing at WOT (on dyno)
4) Installed WBO2 gauge and mixture is OK
5) Tried Holley 650cfm double pumper (4777-2) in place of my Holley 750cfm vac sec (3310 (80508S)) and picked up 20 rwhp (see the graph)

Overall results are little disappointing, because power and torque are way far behind what it should/might be with that combo, after adjusting optimal timing and mixture.

Next time on dyno:
1) Will change valve springs
2) Will try 1.6:1 full roller rockers (in place of my 1.52:1 roller tips), first on the intake side and then also on exhaust side.

Dyno graph: best run with 750cfm Holley vac sec carb (80508S) vs best run with Holley 650cfm double pumper (4777-2): 650cfm wins (rwhp, rwtq):


Couple more things:
* Double pumper runs very rich at idle and I can't get it leaner without stalling the engine.
* AFR is about 12 at WOT and it won't get leaner during acceleration, so fuel pressure shouldn't be the issue.
* Tried also AFR 13 at WOT on dyno, but results were worse than with 12.

If you have any thoughts, plaese let me know, I'll very appreciate it. Thanks!

 

Running through an automatic trans and assuming 20% driveline loss that would be about 377 HP at the crank. In the realm of sanity, but on the lower end.

While you're waiting for valve springs, why don't you run a cranking compression test on all 8 cylinders (Sears has a perfectly serviceable compression gauge with a flexible hose you can snake around the headers for not a lot of money). I know you said your compression is around 9.8:1, so let's make sure the compression test agrees with you. I'd guess you should be around 170 PSI cranking compression. CHECK ALL EIGHT OF THEM.

Oh, and I can't believe I missed this before, but could you explain this a little further:

"Single 3" catback with two Hooker Aerochamber mufflers in line"

Since my last suggestion was going to be "have you checked to see if somebody shoved a banana up the tailpipe?", maybe this could be a cause of some of your problems. IN LINE? As in the exhaust goes through two mufflers in a row? I have to be reading that wrong.

 

Will do the compression test. Actually done it 2-3 years ago and it was OK: all eight were the same and around 180-190 psi. I think the new test will be with the same results, because "butt-dyno" tells me that the engine pulls like when I performed the test for the first time.

Sorry about my english. Yes, I have 2 mufflers in a row. Exhaust looks like this: 1 5/8 Hedman shorties with 3" collectors, custom 3" Y-pipe, 3" mandrel bent pipe, 3" center in/out straight thru AeroChamber (in place of catalytic convertor), 3" mandrel bent pipe over the rear axle, 3" center in/out straight thru AeroChamber, 3" mandrel bent pipe.

I have 200R4 with Edge 3000-stall converter.

 

That exhaust is killing you a good bit but it is quiet

 

Will try it on dyno next time: unbolt catback from Y-pipe or even from headers. Depends on how I'll be able to unbolt it.

Actually I installed the second muffler lately, because noise was too loud for me. Didn't feel the difference. 13.2 on strip was with 1 muffler and old carb.

 

Change the parts you need to change; don't go changing other stuff if it's not needed (like your rocker arms). In this regard you can effectively see what your changes do without essentially just guessing at your problems.

 

It'll be interesting to see if this guy ever FIXES HIS DAMN CAR instead of just posting incessantly on the Internet about it.

 

Exhaust can make a big difference on some cars. Had a big cammed ls3 car come thru friends shop that picked up 38 whp when exhaust was dropped

 

Exactly. That's why I suggested above that he drop the exhaust and try it.
My 500+ hp LT1 loses at least 40 hp with the exhaust on it. And it's what would appear to be a decent exhaust - mandrel bent 2.5" dual with x-pipe.

 

A dyno sheet is a good tuning aid.
BUT not every dyno operator is a competent tuner.

An actual pass down the track will trump any dyno sheet, because a time sheet will give you vastly more information on actual performance than a dyno sheet ever will.

by looking at your 60', 330' ,1/8, 1000, and 1/4 data A timeslip will tell you how the car leaves, how it accelerates ,and how much power it really makes.

 

At the track you want to tune for best MPH because this is your HP.

There are too many variables tuning for best ET, but if you tune for best MPH,
your ET should improve.

3 basic things to improve MPH

Carb Jetting / Injector volume
Timing
Shift point

SBC with 23 degree heads; 38 degrees of total timing sounds about right for a hot day.

on a hot day or high DA you want a bit less jetting, and bit more timing ( but usually no more than 38 )

on a cool day or low DA you want a bit more jetting and bit less timing (but usually no less than 32 )