Vacuum.....It really sucks!
Thread Starter
Instructor
Joined: Mar 2002
Posts: 110
Likes: 1
From: Botkins Ohio
Vacuum.....It really sucks!
I am looking at purchasing a crate engine for my 68, but I am concerned that the cam it uses is to large to produce the necessary vacuum to open my headlights/wiperdoor properly. The engine is the GM performance Fastburn 385, with the LT4 hot cam/1.6 rockers etc.
Advertised Cam Specs
Duration @ .050" I/E: 218/228
Lift I/E: .525"/.525"
I called the GMPP dealer to ask about this, and they couldn't give me a definite yes or no if this would provide adequate vacuum. Their comment was that other people have put this engine in vettes, and they have not had any complaints yet. They couldn't produce any numbers for what kind of vacuum this engine combo produced to compare it to what my engine has now. I searched through some of my corvette material last night, and I could not find what the vacuum reading should have been on a factory engine to compare to either.
I have seen other ZZ4 engine swaps on this forum, but I have not seen anyone with this cam combination.
If anyone can provide some insight on this or any other aspect of this swap to consider, it would be greatly appreciated.
Thanks in advance
Advertised Cam Specs
Duration @ .050" I/E: 218/228
Lift I/E: .525"/.525"
I called the GMPP dealer to ask about this, and they couldn't give me a definite yes or no if this would provide adequate vacuum. Their comment was that other people have put this engine in vettes, and they have not had any complaints yet. They couldn't produce any numbers for what kind of vacuum this engine combo produced to compare it to what my engine has now. I searched through some of my corvette material last night, and I could not find what the vacuum reading should have been on a factory engine to compare to either.
I have seen other ZZ4 engine swaps on this forum, but I have not seen anyone with this cam combination.
If anyone can provide some insight on this or any other aspect of this swap to consider, it would be greatly appreciated.
Thanks in advance
Burning Brakes
Joined: Aug 2002
Posts: 1,146
Likes: 10
From: Scottsboro Alabama
Re: Vacuum.....It really sucks! (mpettus)
The engine you're speaking of is a ZZ430 clone, I have one in my 81. Every vacuum operated item works fine in mine. I have never checked the vacuum numbers but I do recall the guy that's working on my transmission telling me he checked it last week. I'll see him tomorrow and ask him. The hot cam isn't a radical cam. Mine has a moderate lope at about 675 rpm. I think there is two or three other guys here that has this same engine one of which is spokewrench. It's a good choice of engine, you'll like it.
Pro
Joined: Apr 2004
Posts: 687
Likes: 0
From: Atascadero Ca
Re: Vacuum.....It really sucks! (Older Than Dirt)
i'm curious on this subject as well. I"ve got a comp cams solid roller cam in a 355 inch motor running 10.5:1 compression, dual plane weiand intake, demon 650, ported and polished dart heads, triple valve springs, headers, etc. I'll have to dig around for the cam specs but if i remember correctly the duration is in teh 290's. I'm making over 460 rear wheel hp in a 355, so its a big cam. This motor ran great in my 71 el camino with manual brakes, but i'm now transplanting it into the '73 vette. Do you think i'm going to have any problems with power brakes and getting the headlights to rise?
Melting Slicks
Joined: Dec 2001
Posts: 2,025
Likes: 1
From: Billings MT
Re: Vacuum.....It really sucks! (mpettus)
I am running a Comp XR280R Solid Roller (242/248 @ .050; .570/.576").
With a proper tune (or at least as close as I can get) I pull 14" of vacuum and have no problems with headlights.
I have had as little as 8" of vacuum with a previous motor and my headlights still worked fine, they were however a little slow.
Don't worry about it. ;)
With a proper tune (or at least as close as I can get) I pull 14" of vacuum and have no problems with headlights.
I have had as little as 8" of vacuum with a previous motor and my headlights still worked fine, they were however a little slow.
Don't worry about it. ;)
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Re: Vacuum.....It really sucks! (VETDRMS)
The amount of vacuum that it takes to operate the wiper/headlight doors and HVAC is pretty minimal. With an empty sytem, they may take a few seconds longer to operate but once there is some vacuum in the reserve tank, they'll work as advertised.
I think you're confusing this with the vacuum requirements for a vacuum booster for power brakes. You would have issues with that since the booster has to be pumped down every time you use your brakes -a good reason to go hydroboost.
I think you're confusing this with the vacuum requirements for a vacuum booster for power brakes. You would have issues with that since the booster has to be pumped down every time you use your brakes -a good reason to go hydroboost.
Pro
Joined: Sep 2002
Posts: 690
Likes: 1
From: near Memphis TN
Re: Vacuum.....It really sucks! (mpettus)
I don't think you will have a problem. I have 230 duration @.050 with a comp cams 280, very lumpy idle. Many here have larger cams. I get 12" of vacuum at idle and have no problems with lights. I think problems begin at less than 8" of vacuum. Come to think of it, with all the guys here with huge cams I can't remember seeing one post with people complaining of low vacuum problems not working brakes, lights, wipers, etc. This may just be one of those overexaggerated, overused warnings like "your call will detonate to death with anything over 9.5 compression". Don't worry about it.
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Re: Vacuum.....It really sucks! (mpettus)
At the Dyno Shop, we had a cust come in one day with a black 68. He had just installed the HOT ZZ4 and wanted it dyno tuned .... he had a vacuum pump mounted on the frame, and plumbed into the under hood system.
I asked him about that and he said that the dealer who sold him the engine told him it would not produce enough vacuum. So he took it upon himself to wire in the pump. When we checked vac on the motor though, it was not more than a couple of points lower than normal. I think it produced 15 inches of vacuum which should have no problem powering a vacuum circuit ... as long as the system is good and has no leaks.
:flag
I asked him about that and he said that the dealer who sold him the engine told him it would not produce enough vacuum. So he took it upon himself to wire in the pump. When we checked vac on the motor though, it was not more than a couple of points lower than normal. I think it produced 15 inches of vacuum which should have no problem powering a vacuum circuit ... as long as the system is good and has no leaks.
:flag
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Re: Vacuum.....It really sucks! (mpettus)
Spend a couple more bucks and step up the ZZ383. I have run the same cam that is in the ZZ383 in a low comp 350 and it pulled 14 to 16 at 900 rpm idle so it should pull even more in a higher comp 383.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Re: Vacuum.....It really sucks! (SpyderD)
...I can't remember seeing one post with people complaining of low vacuum problems not working brakes, lights, wipers, etc. This may just be one of those overexaggerated, overused warnings like "your call will detonate to death with anything over 9.5 compression". Don't worry about it.
I'm installing an electric vacuum pump on my '67 Fairlane this weekend because my brakes flat suck. My engine does 14" of vacuum at 800rpm with as much initial as I can run. Brakes, mechanically, are more than up to snuff. SSBC Force 10 calipers, good pads, new lines, solid vacuum booster. I can get one good application and after that it feels like I'm stepping on a brick. No fun at all.
I have no doubt that the things other than the brakes will be fine with a much lower vacuum signal but I'd seriously question the brakes if there is a vacuum assist once you get on the short side of 16". They may work "okay" but there's every reason to think they would not be up to spec.
Thread Starter
Instructor
Joined: Mar 2002
Posts: 110
Likes: 1
From: Botkins Ohio
Re: Vacuum.....It really sucks! (gerry72)
Thanks for your help!! I am not running power brakes, so it sounds as if I shouldn't have any problems. I just wanted to see how many people have done this and what their comments were.
Now to order the engine!
Thanks again :D
[Modified by mpettus, 10:45 PM 5/6/2004]
[Modified by mpettus, 10:45 PM 5/6/2004]
Now to order the engine!
Thanks again :D
[Modified by mpettus, 10:45 PM 5/6/2004]
[Modified by mpettus, 10:45 PM 5/6/2004]
