502 won't rev

[Ken_Parkman]

We are trying to understand why my friends 502 crate engine will not rev above 5500 - it falls on its face. The engine is stock with 2 exceptions - he put a Comp XR 288 hr cam, 236/242 with .521/.540 lift, and to fit the air filter below the stock hood on a 71 Camaro he installed an Edelbrock low rise dual quad with matching 750 carbs.

He has been swapping ignition components with no difference. The carbs have been jetted all around, it was initially stupid rich, currently it is not quite so rich, all with no difference.

I'm suspicious of the stock hydraulic roller lifters collapsing being the problem, but had been under the impression they were good to over 6000 rpm. The car has 10-30 conventional oil, would changing to a synthetic 15-50 help?

Any suggestions?

Thanks in advance
Ken

[bmftech]

With only 236 duration @ 50 it is done at 5500. There is nothing wrong with it. My 502 has a 254 @ 50 solid flat tappet and it is done at about 6000-6100. It has oval port heads.

[Troy Patterson]

That cam is very small for that displacement, but you can have other issues that are preventing it from reving.

What's he doing for air cleaner and air filter? How tall is the element and how much space is there over the carbs choke towers?? What's he doing for fuel delivery in terms of pump, lines, filters, etc.?

Troy Patterson TMPCarbs.net TMP Carbs

[67RS502]

it should pull to over 6000 with that cam.
my 502 with a 252/263 HR oval ports, single plane pulled to 6700
I think with a decent dual plane like an rpm or stealth and 1000cfm carb it would rev there.
It may be a valvetrain issue, how much spring pressure is on it, does it break up above 5500?

[Abbottracingheads]

Probably not enough valve spring.

[bigjoe1]

I remember that I put some of the very first Beehive springs on an engine like that, and it would rev up 1000 RPM higher and also picked up around 60 more horsepower.


JOE SHERMAN RACING ENGINES

[Ken_Parkman]

Thanks for the replys

A bit more data:

The air filter is constructed from a mopar 6 pack filter assembly, with a acccel element. He made fiberglass bellmouths and glassed them into the fiberglass 6 pack base, then properly finished everything. It looks and fits quite profesional, but is still only the stock Mopar size. We realize it should be bigger, but it does fit below the flat hood. The lid is approximately 1 1/2" above the choke horn. The fuel pump is the GM recomended pn 12355614, listed as 100 gph, a canister fuel filter, and all lines are 3/8". I have a picture of the filter, I'll try to post it this evening. I do not believe this to be a fuel delivery problem as the issue is rpm related, and load or gear does not seem to have much effect.

The springs are the stock GM dual, 140 lbs on the seat 325 rate. They are more load than the Comp recomendations.

It does not really break up, but the engine note changes, and it stops making any power. Almost like a rev limiter, but it does continue to rev higher, just very slowly. I've got no exerience with hydraulic lifter float or collapse, but am thinking that is what it is. Just seems that the rpm should be higher. The car is a stick, so a 5500 rpm shift point will happen real fast.

Does anyone think a different oil will help?

[Troy Patterson]

Okay, moving on to the exhaust system, what's there?

I'll leave Joe and the others to comment on the springs and so forth.

Troy Patterson TMPCarbs.net TMP Carbs

[Ken_Parkman]

The headers are the Hooker 2", 3 1/2 collector. The exhaust has a collector extension (sized by pipemax) with a flat plat blockoff at the end, arranged for removal at the track. Partway down the collector extension a 2 1/2" pipe is welded on about a 45 degree angle and connects with the original small block exhaust, which is 2 1/2" with hooker aerochamber mufflers. Running so far has been with the caps installed, trying to get is close before taking it to the track.

[Troy Patterson]

I'd expect some sizable differences going open exhaust compared to whatever the small block exhaust system is. It'll be interesting to see what happens and how it affects things when the exhaust is uncapped.

If the small block exhaust system is real restrictive for this motor, it'll definitely extend the rpm range a bit I'd expect, but then again it'll depend on how it affects air / fuel ratios and scavenging and so forth.

Troy Patterson TMPCarbs.net TMP Carbs

[F-BIRD'88]

Did you verify the actual installed and open spring pressures? Nothing like having the correct springs for the job.

The factory gm crate motor springs are very light as the stock GM cam action is mild moderate for a hyd roller.
The agressive fast action XE HR cam needs a much more aggressive spring. Especially on a BBC.
if the lifters are "collapsing" preset the lifter plunger at or very near bottomed out.
If the lifters are floating/pumping up at rpm set the lifter preload at the top against the retaining clip or with .001-.002" lash. (and get better springs)
Call or email Comp Cams cam help and get past the tier 1 tech level guy and get the right new premium valve spring for this combo.

The air cleaner lid may be too close to the carb choke horm. If you have 1/2" to spare between the (custom mopar tripower) air cleaner lid and the camaro hood
raise the air cleaner assembly up using edelbrock 1/2" air cleaner spacer rings.

The BBC low rise dual quad manifold restricts the top end power of this motor a lot. A new Performer Rpm hi rise Dual quad manifold (and carb spacers) will make this motor into a whole new beast. But will poke thru the stock hood for sure.

The way you plumbed the exhaust system with cutouts is very restrictive. Get rid of the Cutouts. This motor will function fine when capped up thru a full 2.5" dual exhaust system with 2.5" muffles and full tailpipes ... And uncapped ... The cut outs add unnecessary weight, complexity and rob power.

For a Big block 1971 Camaro I recommend a custom 2.5" dual system but with a Magnaflow dual 2.5" in-- dual out 2.5" muffler mounted transversely behind the rear axle just like stock.
Ground clearance and interior sound resonance will be much better with the Magnaflow transverse muffler.


http://www.magnaflow.com Find the correct 2.5" dual in dual out transverse mounted Magnaflow muffler for this car, here. And rethink the exhaust system.
When you do the exhaust system right you won't need to uncap it for the track.

Re: fuel pump:
The mechanical fuel pump has enough flow capacity in of itself to feed this motor BUT With the under hood heat of this
engine /chassis combo the pump will falter when ever things get hot and overheat the pump/fuel lines and carbs.
reroute the fuel lines away from heat.

Get a Carter #P4594 or # P4070 (pusher pump) rear mounted electric pump added to this system.
The Pusher pump will pressurize the fuel feed line from tank to mech pump eliminating vapour lock.
No regulator is required. Rubber mount the eelctric pusher pump near the gas tank. If the gas tank has the OEM fuel pick up tube with sock get rid of the sock and flair/bell mouth or slash cut the end of the fuel pick up tube. Replace the in tank pick up tube if nessessary.
Get a mech fuel pump heat isolator mounting gasket kit www.sealsit.com
Install edelbrock wood carb heat spacers and block off the manifold heat riser passages. (cooler carbs)
If using the edelbrock banjo style fuel inlet fittings make sure they are "clocked" so that the internal passages are aligned for best fuel flow into the carbs.
Take the banjo fittings apart and have a look see.

I been there done that with this BBC motor/ car chassis combo.

[JoePorting]

The spring pressure sounds low. I associate hydraulic rollers as needing 170 on the seat and 450 open. I looked up in the Comp catalog to see what they recommend. As you stated, the Comp catalog recommends the #924 spring which is 112 on the seat and 300 open. That sounds rediculously low. For the red "Premium Choice", they recommend the #26120 spring which is 148 on the seat and 350 pounds open. Sounds better, but makes me wonder why the recommended Comp pressures are so different. Going from 112 to 148 on the seat is quite a bit. I would use the #26120 spring or shim up your existing springs to the 160 seat, 400 open area. Hopefully your old springs are tall enough for the shims if you go that way. Since your lift is kind of low for a BBC, I'd think you wouldn't have any coil bind problems with shimming your existing springs. I'd think a .060" shim would work. But double check everything to make sure it fits.

[GTACamaro]

Thanks, I've read a lot of interesting thoughts on my "5700rpm multi cylinder miss". Feels like a cheapo rev limiter. It is independant of coolant temp, oil temp, acceleration rate, and is always at 5700 and up. It is still there at 6000, so it isnt a "critical speed" type of problem (although I havent ruled out a standing wave exhaust resonsnce due to my odd exhaust setup..but I think, considering the symptoms it is a bit of a long shot). Have had 2 unilites in the car this week, 2 coils, re-checked the valve lash, ran it on 1 carb, then both, then one again, WOT AFR is too rich (mid to high 11's). I am going to chassis dyno it next week, try with open exhaust, no air filter etc etc.

I havent 100% ruled out the 6AL, but it worked fine into the mid 6000's with my small block.

Does anybody know of any issues or what the limitations are with the stock GM hydraulic lifters in the ZZ502's? If it is a lifter collapse issue, could I test for it by using 15W-50 to see if the RPM where the issue is shifts to the right, or is this just a waste of time and oil?

Re: Underhood temps..Yes it does get pretty hot, after the first hot summer day, I found several issues with the fuel system, and I've insulated the fuel (and brake) lines..I would love carb spacers/insulaters but as it is, my stock hood only just closes (I prefer the flat hood)

BTW calling the GM performance parts phone number is practically usless as the best they could do is refer me to a dealership when what I wanted is to talk to an engineer who knows something about their lifters.

[Wolfplace]

Regardless of what Comp "says" or "recommends" in the catalog,,,,
300lbs of spring is not going to control a hyd roller valve train with a 10 pound intake valve

My vote would be at least another 50-60lbs open at a bare minimum & with standard dual springs I would prefer more with most hyd rollers.

The 26120 spring Joe listed is a Beehive & as such will sometimes work with less pressure
This spring should work very well with a cam that mild

[levisnteeshirt]

how are you setting the valves ??

fuel ,,, umm ,, if its not pulling over this rpm in first gear ,, then i'd take a look at the fuel needs ,,, its not under full load in 1st gear ,,, IMO , fuel problems show up more in higher gears

i would try a HD 30 type oil, but thats what i like ,,