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Cylinder head/Cam max lift?

15K views 94 replies 10 participants last post by  jokerZ71 
#1 ·
Okay I have been having nothing but problems with my SBC 355 vortec motor. First its in a TBI truck, I do have TBI mods that should support the build. Anyway I ordered some ProMaxx Vortec heads and on summit's website it says it has a max valve lift of .575. Well I was looking at a spec sheet I got with the heads (That I didnt notice at first) and it says it has a max lift of .500 with a hyd. roller cam. My problem is the cam I have is a ZZ4 cam with a lift of .474 intake and .510 exhaust. What kind of problems would that extra .010 cause?
I talked to summit and they said "it is probably coil binding the exhaust springs and causing valves to float off the seat." Could that be true?
The motor is reading around 120 compression which most people I've talked to said is low. Also the vacuum drifts between about 14-15. Could that lift problem cause that?
Thanks for any help!
 
#2 · (Edited)
There should be a safety margin of .040" to .060".Measure the total seal to retainer clearance to see how much you have,then subtract .050" from that measurement.This will be your max safe lift.With the valve fully open,you should have a minimum of .060" between the spring coils.What springs are on the heads?Does the spec sheet list coil bind?
 
#3 ·
There should be a safety margin of .040" to .060".Measure the total seal to retainer clearance to see how much you have,then subtract .050" from that measurement.This will be your max safe lift.What springs are on the heads?Does the spec sheet list coil bind?
Im not sure what springs are on the heads they came assembled. It is a dual spring with dampener though. The spec sheet doesnt say anything about coil bind.
 
#4 ·
Low vacuum readings with low cylinder pressure sounds like cam timing is off. How's the engine itself run? Coil bind and valve float are two different things and don't run with each other. Google valve float and then Google coil bind. Either way all this should've been checked before engine assembly.

You never said what the engine is doing or not doing.

Was ignition timing set with the ecm control for the distributor unplugged? Firing order verified to be correct? Timing marks are true to tdc? Engine well grounded, engine to battery, battery to frame, frame to body, body to engine? Valves properly adjusted?
 
#15 ·
The engine lacks power. When its not in gear it will rev up and sound great but when you put it under a load it wants to bog down some. It seems above 3000 rpms it wants to wake up a little. Yes it was timed with the ecm control unplugged. Timing marks are correct we've also set the timing at different degrees and 4 degrees adv. seemed to run the best (as it should). Yes everything is grounded and the valves have been set multiple times and they are set correctly.


. As was asked above, what's your running problem?


. .575 may be max lift for a flat tappet cam, but the valve spring pressure may only be enough to handle about .500" lift of a roller cam which is harder to control... as was said, doubt the .010" over is hurting anything... prolly don't even see that .010" except at higher RPMs... the lifter prolly settles that much at lower RPMs...


. Is the 120 compression on just one cylinder or all of them?

. Was the compression test done at WOT and the engine spun over 5 cycles (10 crank rotations) with the starter to get max pressure?

. That 208/221 cam will have a slight lopiness at idle and thus the vacuum will vary slightly... what idle RPMs are you reading vacuum at?

. How thick is your head gasket? Do you know the compression height on your pistons used for the rebuild? The cc's of the head chambers?
.
The compression is about 120 on all of the cylinders
It was done with WOT and turned over atleast 5 cycles.
I check the vacuum around 600 rpms.
Also has new knock sensor and a 180 thermostat as requested by brian harris who made the custom chip for me.
 
#8 · (Edited)
max valve lift of .575. max lift of .500 with a hyd. roller cam. My problem is the cam I have is a ZZ4 cam with a lift of .474 intake and .510 exhaust. reading around 120 compression which most people I've talked to said is low. Also the vacuum drifts between about 14-15.

. As was asked above, what's your running problem?


. .575 may be max lift for a flat tappet cam, but the valve spring pressure may only be enough to handle about .500" lift of a roller cam which is harder to control... as was said, doubt the .010" over is hurting anything... prolly don't even see that .010" except at higher RPMs... the lifter prolly settles that much at lower RPMs...


. Is the 120 compression on just one cylinder or all of them?


. Was the compression test done at WOT and the engine spun over 5 cycles (10 crank rotations) with the starter to get max pressure?


. That 208/221 cam will have a slight lopiness at idle and thus the vacuum will vary slightly... what idle RPMs are you reading vacuum at?


. How thick is your head gasket? Do you know the compression height on your pistons used for the rebuild? The cc's of the head chambers?
.
 
#9 ·
Something is smelly with this. The heads are setup with a max valve lift number that is irrelevant to type of cam. The spring type changes based on type of cam, (i.e. hyd flat tappet, hyd roller, solid roller), sometimes lifter type, and lift requirements. What is the part number of the heads?

Also, what you said you were told by the Summit rep is not accurate. He should have consulted someone else before laying out the pile of poop he gave to you. Coil bind is going to cause a whole slew of issues of which none are low cranking compression.

I'd recommend a leak down test to see where your compression is going. If it passes a leakdown test, then you have a cam timing issue in my opinion.

Regarding your 'kinda' low vacuum readings, I'd like to know what others are coming up with for vacuum readings with similar builds before I would get to concerned. Your cam has a long ramp and quite a bit of duration from seat to seat which could be causing the lowish vacuum reading. Other than that, I'd be concerned of a vacuum leak or your aftermarket chip not controlling (closing) the IAC. Some datalogging on a dyno or while driving might pick up some issues or confirm that there are none.

Lastly, how does it run? Is the short block stock other than the .030" overbore? Is the valvetrain stock (including the pushrods)?

I feel your pain in that you're end result appears not to be what you expected - we've all been there and done that. Hashing out the aftermath of a build can be discouraging - keep your head up and answer everyone's questions. That are a bunch of guys on here that'll get motor straightened out.

Best of luck - Jim
 
#16 ·
These are the heads - http://www.summitracing.com/parts/pmx-2151
We set the timing marks on the timing chain and gears twice and they are perfectly lined up. Enless TBI and Votec timing chain and gears are marked different because I had to use a vortec gear set because of the bolt pattern on flat tappet cams vs roller cams are wider apart but I dont think they changed it.
That cam should be closer to 18" of vacuum.
The short block has new valve train went from flat tappet to roller setup measured the pushrod length and ordered accordingly. It feels as its lacking power.
 
#11 ·
Jim, IIRC this is the OP's 2nd shortblock,2nd short block/build.Both with identical problems.Low cylinder psi,no power'varying low vacum.That cam shouldn't have any lope to it.Tho it is about as large as he should go with the TBI setp,it is a tunable combo that will run well.Bryan Harris(tuned the chip).He has probably tuned 100's or possibly 1000's of these combos with this cam with great results.This cam works better if installed 4* advanced in a stockish motor.It can be a little weak on the bottom end if not.Never had any vacum problems with this cam.Usually in the 16 to 18 range.
 
#12 · (Edited)
. OP's earlier thread:


http://www.hotrodders.com/forum/355-sbc-vortec-problems-355746.html


. ~ .040" head gasket, Summit 4-eyebrow flat tops claiming 1.560" compression height, 64cc ProMaxx iron heads...


. Some people have returned other pistons to Summit because compression height wasn't as listed... if not here, quench distance may be .080"-.090" total... giving low compression pressures and a tendency toward pinging... however, engine should run well, otherwise... unless knock sensor activating... or wrong temp. thermostat used...


http://www.crankshaftcoalition.com/wiki/Quench
.
 
#14 ·
I once had the zz4 roller cam for a short time and I had almost 19 inches of vacuum at the most with around 16 degrees of initial timing and a idle rpm of about 800 rpm in park. I swapped it out for a slightly better lunati voodoo hydraulic roller cam which specs at 219/227 @ 50 with a 112 lobe separation and I have almost reached 19 inches of vacuum on my gauge depending on my carb adjustment. My needle does fluctuate a little since there is a slight amount of overlap and a very faint lope at idle but nothing choppy. Valve adjustment and other factors involved can affect your reading as well.
 
#19 ·
The timing advances more when i rev the truck up. The rear end ratio should be 3.73s and stock stall is 1400 on these trucks. It will do a brake stand (only 1 tire though haha)

This is going to end up being a duplicate thread to your other one, I'm still stuck on the cam timing being off. With all cylinders being equally low on the compression test and the engine lacking power it leads right to cam timing.

Besides lacking power how does it run? Does it pop and backfire?
It runs pretty good besides lacking power it does not pop or backfire except when its really cold sometimes it will feel like its going to stall if I give it to much gas. I still dont see how it could be cam timing I did not put it a tooth off and its a brand new gear set no way it jumped a tooth either..
 
#18 ·
This is going to end up being a duplicate thread to your other one, I'm still stuck on the cam timing being off. With all cylinders being equally low on the compression test and the engine lacking power it leads right to cam timing.

Besides lacking power how does it run? Does it pop and backfire?
 
#20 · (Edited)
. Not interested in should be, need to put rear end on jackstands and rotate the driveshaft and find real rear end ratio... I thought they were more like 2.73, not 3.73... and how tall are rear tires?


. Not interested in stall specs, what stall RPMs does your engine actually achieve? If don't have a tach, may need to borrow one and run temporary 3 wires to make it work...


. The ZZ2 - ZZ5 cam is ground on 112 degree intake centerline with no hidden advance ground in... GM designed it for a 10:1 compression ratio engine (like yours should be now)... to bleed off a little compression at low RPMs... so, installed straight up, it may be slightly lower than expected on cranking compression psi... I don't have any problem with that, except as pertains to quench distance of the long block... GM expected it to punch hard from 1500-5500 RPMs... make 345-355 HP in a stock ZZx engine... 375+ HP @ 6,000 RPMs in a well built engine... like yours should be... that's what we're aiming for...


. You will need to be running premium gas plus possibly some octane booster to keep pinging at bay, otherwise your ECM cuts back on ignition timing/power... especially below 3500 RPMs... you won't hear the pinging if knock sensor doing it's job... the extra MPG from a high compression engine more than makes up for the few cents more per gallon for premium gas... you may be at 10:1 - 10.5:1 compression ratio now... I'd suggest running for a few days with premium gas, highest octane available in your area, plus one ounce of kerosene for each 10 gallons of gas and see how it reacts to that...

. Like Russell said above, we don't want this thread to end up failed like your last one was...
.
 
#21 ·
Well my dad has 2 of the same trucks and they both have 3.73s according to the codes in the glovebox and mine has the same size tires and runs the same speed at the same rpms so thats how i got the 3.73s. The tires are 265/50r20 which should be about 30.5 in tall
The truck should have 9.7:1 compression ratio.
I do run 91 octane in the truck only which is the highest we have in town. Also what the custom chip called for.

I'm going to take a piston out of the first shortblock I put in the truck which is the same pistons that is in the current motor just not .030 pistons. I will find the stall not sure how accurate it will be because the tranny is starting to slip.
 
#22 ·
. OK, 9.71:1 looks about right for ~.065" quench distance... rather horrible quench distance... in the old days, the auto manufacturers would prolly call it 10:1... and they did... I suspect the ECM is pulling back ignition timing because this engine would ping itself to death otherwise... the fuel mix I gave above, might get it to start running right, and will need to be used from now on... should have been built with a .015" shim head gasket...


http://www.crankshaftcoalition.com/wiki/Quench


. My main interest in the stall RPMs was to see just exactly how weak this engine is at low RPMs... a weak engine won't make it to expected stall RPMs...
.
 
#26 ·
. Yes, it causes all kinds of minor problems... hopefully, that fuel mix makes the ECM re-adjust and be happy in a day or two... if not, try 2 ounces of kerosene...


. Do you have a big enough TBI/intake to support 375 HP? Headers? Singles/dual exhaust? Have you regulated fuel pressure above stock level?
.
 
#28 ·
I believe your expecting too much with only 120psi on a compression test. If your certain that the compression ratio is at least 9.7:1, then the cam needs to be advanced a minimum of 4 degrees IMHO. At least it will be a good start to diagnosing what the engine needs to get to the power level you think it should have. The compression test should increase an appreciable amount, but I couldn’t give you a number. Even if the springs don’t have the rate that a roller cam requires you should still be ok at lower rpms as the lifters won’t have enough speed to float the valves, or the valves have enough speed to cause them to bounce off the seat, again IMHO. I know it’s a lot of pia work to just to swap a timing chain, but if your certain that the ignition timing is optimized, it will be a good troubleshooting step that should give you a better picture of whats going on and what direction to proceed.
Don’t expect a lot of power increase at higher rpms as advancing the cam is more of a low rpm torque boosting mod/tuning experiment. If your springs are not what the roller cam needs for valve control it will be more evident at higher rpm. You need to get the specs for the springs and find out if they are suitable for your cam. Of course you need to find out what the spring requirements are for the cam first.
Still, like many others have indicated, 120psi is low. I’ve seen many stock 8.5:1CR engines make more psi than that. I know that a timing set isn’t exactly cheap. Perhaps you can just get the crank gear with multiple keyways that will match your current chain.
FWIW
ssmonty
 
#31 · (Edited)
So the plot thickens - stock converter on a slipping trans, check engine light is on and haven't resolved the issue, guessing at rear end ratio, you've set the base timing ahead of what the chip programmer intended with an expectation of an increase in performance.

If this was my engine the first thing I would do is verify why the crankng compression is low.
Step 1 would be to confirm my gauge is reading accurately - I'd hook up my compression tester gauge to my air compressor and compare gauges.

Step 2 would be a leakdown test to confirm proper valve and ring seal with one of these :

Amazon.com: OTC 5609 Cylinder Leakage Tester Kit: Automotive

Step 3 - MAKE SURE my balancer is at #1 TDC via whatever method I'm most comfortable with. I use a dial indicator on #1 piston prior to installing the driver side head. But there are other methods that will work with the heads on that are cheap and accurate.

Step 4 is it advance the cam with one of these :

http://www.summitracing.com/parts/hrs-94505/overview/

I would do it in this order because if your leakdown rate is high, then anything else that you attempt in an effort to resolve your low cranking compression will be fruitless. A leakdwon test will confirm that all of your parts are sound and your assembling went as planned.

Once I resolved the cranking compression issue I would now find out why the check engine light is on and resolve the issue. Then resolve the slipping transmission issue and find out exactly what gears are in the rearend.

These steps don't necessarily have to be completed in the order that I would do them in, but you need to start finding answers and stop the guessing. I much prefer to spend a few bucks on a tool or two to identify a problem and spend my money on fixing the issue. The best part is that you'll have the tool to use again - the money won't be wasted.

Regarding ignition timing, if you set the timing advanced or retarded on a computer controlled motor, then remember that the ECM doesn't know that. It, the ECM, is making fuel trim adjustments and timing changes based on the assumption that base timing is correct. Speak to whomever you purchased your chip from and they should be able to explain it fully. Look at it this way, if you advance the base setting 4 degrees and the programmer designed the timing to advance to 38 degrees, then when the ECM is commanding 38 degrees your timing will actually be at 42 degrees and if it begins to detonate then the knock sensor will retard the timing by however much the programmer set it to retard timing which might be 8-10 degrees. This can create a situation where you think you advanced it 4 degrees but the engine might actually be running at 4-6 degrees retarded due to the knock sensor. You'll think the engine is running poorly, which it is, and you created the issue.

Regarding your heads, according to ProMaxx's site those heads are sold with .575 lift capability. If you have a sheet that came with the heads that identifies something different, then I'd call Promaxx to clear up the issue. I would guess that they are setup for a roller as all Vortec heads were orginallt designed on roller motors. But again, I'd eliminate the guessing and contact Promaxx.

Is this process going to take some time - yes. Are you going to have to learn a bunch of information - yes. Are you going to be better for it - yes.

Good luck.
 
#33 ·
Just a question, Was the same timing chain set used on both engines, just swapped to the new build??

I'm asking because just lining up the dots doesn't mean it actually is correct, could be a manufacturing defect in the dot or keyway position.....I've seen it happen before......that's why you see cam degree'ing mentioned in so many posts on this site. If you don't degree it, you really have no actual proof of where the cam timing is....
 
#35 ·
At 9.7:1 & a quench of .065",you very well could be getting some detonation,causing the timing to be pulled by the ECM.You would be better off at 10.2:1 & a quench of .040 than what you have now.All of this can easily be checked tho by seeing where the timing is at different RPM ranges,preferably by a scanner, data logging,or,at the very least,with a timing light.I still don't think this is causing cylinder psi to be this low.We usually install the ZZ4 4* advanced in stockish 350 motors with 9.5:1 or less,but,it shouldn't be needed in your case.This is not some "monster race cam"that should be giving you the problems you're having if installed/timed correctly.It's a very mild GM performance cam.
 
#38 ·
This motor should be seeing somewhere in the 170 to 190 psi,if everything is sealing.(rings,valves).A stock ZZ4 sees 180 to 195 psi.Even if slightly retarded,I can't see 120 psi.Something is wrong.He either has a mechanical issue or a bad compression tester,or,not performing the test correctly.
 
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