How much fuel will a ZZ4 with a Holley 750 and MSD use if I break in at 2500 RPM for two hours? I am building a break in stand, I have a 2.5 gal tank and am wondering if it's enough.

Calculate your displacement, VE and air/fuel ratio over time.
I'd do it for you but I've had too many beers. :disco:

Probably easier to have a spare jerry-can and funnel and just keep an eye on your tank.

Calculate your displacement, VE and air/fuel ratio over time.
I'd do it for you but I've had too many beers. :disco:

Probably easier to have a spare jerry-can and funnel and just keep an eye on your tank.

An honest man..

Why would you want to run it for 2 hrs on a stand? Normal cam break-in is typically 15-30 minutes. Isn't a ZZ4 a roller cam engine? If so there is no cam break-in required...

I have a sbc on a test stand now. I am using a 2.5 gal tank and it was adequate for the 20 min break in and then some. However, I’ve managed to run a total of 7 gallons through it since it was first started. Tuning, just letting it run to look for leaks, a few revs and a good bit of idling to admire the lope of the Voodoo 104 cam burns up the fuel pretty quick.

....to admire the lope of the Voodoo 104 cam burns up the fuel pretty quick.

Hey Robert, I've been contemplating the Comp 280H and the 104. How does the lope of the voodoo 104 compare to the 280H your running in the 355?

Jon, I think the Voodoo 104 has a bit more lope to it than the 280H but as you know that can change with different engines and different tunes. It's supposed to be more aggressive and just running it on the stand it seems that way. Can't wait to get it in the '67. You can't go wrong with the 280H either, you'll need some stall and gear which ever choice.

Most cars run highway speed around 2500rpm. (+/-) 60miles/hr..

If this is for a cam breakin, you'll run it steady for 20 mins.
(no secondaries)
I'm guessing with that setup, you'll get about 10-15mpg, until you get the carb tuned just right.

2hr @ 2500rpm = 120m \ 15mpg = 8gal

Also remember that when testing on an engine stand you need to move the heat away from your headers or they will dis-color.
A professional engine builder has a room with lots of air moving.
I've had a pro do 3 different cam break-in for me and I watched the temps hit from 1200*-1400*
Mrs. Doug Thorley says their headers risk color damage between 1400*-1500*

Thanks Tony that is the answer I was looking for. Thanks everyone for your responses. This helps alot

Not trying to dispute Tony at all.. (great ball-park though :) )

But you will use much less fuel because you will have next to no load on a free-reving engine, so you're throttle position will be much less in order to maintain your 2500rpm.

In other words, your VE will be less. (Higher manifold vacuum)

I bought a new zz4 with a roller cam from Pace Performance. It didn't come with any docs. What break in procedure is used for a brand new engine. I don't plan on racing more than once or twice a year at Grudge Wednesdays just for fun. Mostly cruising on the weekends. What I was going to do is run for 2 hrs at 2500 rpm, repair any leaks, drain oil, retorque main caps, connecting rods and head bolts change oil filter and run again for about 1/2 an hour. If everything is okay drop the engine. Does this sound right?

Like I said a couple days ago, no break-in per say with a roller cam'd engine.

Wouldn't hurt to run it a bit to check for leaks if you're already setup for it, but not for 2hrs. Maybe run it through a couple of heat cycles. But as Dennis suggests it's not necessary.

with a roller cam, no break in is necessary. but you might need to load the engine a bit to get the rings to seal- but that can be accomplished with a couple of good 10 mile cruises on roads that require you to vary your speed a bit. you aren't ever going to put any sort of a load on an engine on a test stand, unless that test stand is hooked to a water brake like they use on engine dynos.

you must crank your engine as often as possible for the following reasons, may need to change stuff, call fellow gear head and let him hear it on phone, bust it off to celebrate coming home from work, heat her up one more time at 11 pm to get your fix to last till tomorrow. if you crank it often enough you should be able to tell friends within 2-5 secs when it will run out of fuel. when the wife says "are the hamburgers ready to take off the grill ?" you reply "when the motor quits they will be perfect" good soundin cam can heal the sick , free the soul and piss off that neighbor that dont have a life. crank it up man we all want to hear it. the neighbors dont know she's a roller so tell em it will take a long time to break her in.

Bubba I like the way you think.

Engines deserve to run.


motto for the day " If you don't have a runnin stand, get one".


But seriouslier, no break in on rollers. And most rings seat fast depending on fit and finish. I typically hear mine seat at idle on good engines in 10 to 30 minutes. Old truck engines it sometimes takes an hour, and you can feel them seat going down the road. The engine I'm building now I figger will seat the rings in about a minute or less, as soon as they see a smidge of pressure.

Idunno why y'all are giving him grief for wanting to run his engine 2 1/2 hours. I've been trying to destroy a perfectly innocent cam for about 30+ hours now in the 283.I guess I shoulda started a fuel/time log for it. But I don't care about that kinda crap:).


2500 rpm ain't bad, your hand is gonna get tired after 2 1/2 hours though. I have an electromagnet I've been gonna hook up to my 283 throttle on it's runnin stand so I can goose it from across the garage. You may want to look into something like that or some baling wire. I guess you could do it the old fashion way with the idle screw, but that is quite boring to me.:D Gimme a contraption anyday.

I just had another stupid idea, I'll rig up a microswitch on a relay to my electromagnet at the foot of my stool in the garage and when I wanna goose the damthing, oops need a footpedal, OK the 66 doesn't need it's pedal this year yet hehe.

Have fun dude

if you can get it in the house and rig some exhaust up in the fireplace, u can crank it up during comercials ,thats living. have wife check gauges and dipstick.

There is more chance to damage a new engine on a stand or even installed under a hood just running for long periods of time. At best you won't break something but are probably shortening the engines life by doing so. With modern honing the rings are likely seated during cam degreeing and valve adjustment. Roller cams don't require break-in and flat tapet need no more than about 20 min (follow the cam manufactures recomendations). By then you should have found any leaks and the best thing after cam break-in is to start driving the car. It's all about respect for the machine and your hard earned money and labor that went into building a nice mill.

I am building my engine test stand and should be ready to do my break in runs next weekend. Thanks for everyone's help.

If you're not breaking in the cam because it's a roller, what are you breaking in?

if its a zz4 its already been run with propane at GM. Put it in the intended vehicle and run the crap out of it with straight 30 wt. Any leaks will be your doing and will be easily detected.

I wasn't aware of any break in by Pace Performance or GM. How reliable is it? I don't want to drop the engine in and find leaks or other problems. What is the consensus on the break in additive from GM? What I want to do is run it retorque main, connecting and heads, run again and then drop it in. Am I being paranoid? Is this overkill?

yes, it's overkill.
GM builds them just like they build production engines that are going into any one of the millions of cars and trucks they build every year, and none of them need anything retorqued after they leave the dealer. granted, they might have a few failures from human error on the line, but that's why they run them on propane for a while before shipping them out. if it's a leaker, smoker, or knocker, it doesn't make it out of the building. as already said, if it leaks after putting it in your car, then you screwed something up.
just drop it in, get it running, set the timing and idle screws, and go for a drive. change the oil after a little bit- say, 100 miles- and don't worry about it.

u r in good company man, the ones that test stuff that others don't, learn what they wanted to know. and u got a test stand for the next test, run em all, it's the smartest thing u can do, if you enjoy it, it's well worth the labor.

I'm putting in the engine this weekend. I bought a cherry picker from Kragen's that I found on line for $23. At first I thought, 'Cool, I got a cherry picker for $23' then a second later I thought, 'Man I hope it isn't worth $23 when it's over my painted front end'.

Well your thinking is in line with good common sense. Test that picker out!!!. Hang the engine barely off the ground for awhile. Wiggle, nudge, maybe even give it decent little kick before taking it on its journey to its new home.

please find another engine to put on the run in stand just to fire up at will. i think this will add 10 years to your life.