When contacting BluePrint about the amount of vacuum their 383 and 400 GM small blocks produce, they claim under 12 inches. They recommend a vacuum pump or canister to get it up to 18 for the brake booster and headlights.

For those of you who have a BluePrint 383 or 400, what are you seeing for vacuum? Did you need to add anything for the brake booster or headlights?

BluePrint doesn't allow for changes to their builds, so I am not able to order an engine with a more mild cam to get better vacuum.

I was considering buying a BluePrint engine, but the low vacuum adds to the list of downsides to the point where I may no longer consider a BluePrint. I do not want to add a vacuum pump or canister.

Smeding has a 383 with decent vacuum and they allow for more customization, so I am highly considering going with them. But I could also likely get a 400 from BluePrint for the same price as a 383 from Smeding.

 

Which engines are you looking at specifically? They have a variety of models of 383s and 400s. One with a hydraulic roller cam could be changed very easily if you need to.

A number of people on here have engines that make, 12,10, or even 8 inches of vacuum while still having functioning power brakes.

 

The GM Small Block Compatible 383 and 400 with 436 and 500 hp. Reading older threads here on vacuum, some were having issues with headlights and other accessories now working, such as the heat and vent controls. BluePrint did not seem to want to give an exact vacuum number and did seem to suggest these engines would cause issues on the C3 corvette. I was hoping someone with a BluePrint engine could chime in on their experience with the engines and if they had issues with low vacuum.

 

So I have a BP 400 SBC and it barely has enough vacuum to run anything. It will work for the car, but you need to be prepared to use leg muscles on the brakes. They are fine once the car builds vacuum after start but I don’t trust it to always be there. Head lights are slow but work, and the air con controls work, again slow.

YMMV, the entire vacuum system on mine is new. If you have any leaks there’s no way anything will work. I will probably add a vacuum pump later, but right now that’s more of a want.

 

I have been running a BB 427 for may years with a moderately aggressive camshaft and I have no issues with my brakes or headlight action due to vacuum issues.

The very best thing I ever did for my Vacuum system was replace all the hoses with DocRebuild Vacuum Hose kit. Having a good, tightly sealed vacuum loop is critical and the new hoses sealed up the system really well. The little check valves in the vacuum system can go bad and leak down the vacuum over time.

I could go for 2 weeks and when I jumped in the Corvette and activated the headlights the vacuum was still there. If you have a slow leak in the system you might try and put some die-electric grease on the nipples that the hoses attach to. Having a well sealed vacuum system to start with is a good place.

Several people have had issues with their vacuum reservoir's developing cracks and leaking vacuum. If you have any leaks in the vacuum system then your vacuum system will not operate the accessories that require vacuum to operate.

You will never get the vacuum system to work right if it has any leaks whatsoever.

 

BIY and have it Your way

 

The Dyno chart attached to their 436HP 383 says 13" of vac at idle at 950rpm.
Vary the idle speed up or down a hundred, and that spec will go up or down to say 12 or 14".
Sounds correct to me.
The cam spec says 230/236 @.050" on a 110 LC, HR.
Honestly that is probably OK if the entire vac system is up to snuff.
All the factory high performance engines, like L46, LT-1 SBC and L71/L72 BBC all had idle vac readings in that range in C3s from the factory. It worked.

Realize as soon as the rpm is past 1200 you have much more vacuum than that, and you have a vacuum storage can.

I ran a slightly bigger camshaft (239/239* on a 114LC) with only 10.5" idle vac, for 30 years, with PB, and never had an issue, at speed, even when racing. Only when idling around the parking lot and using the brake hard, a few times in a row, very quickly, then it took a few seconds to recover. Kind of a rare occurrence. Not a deal breaker. Honestly that engine was lethargic below 3000, when it really woke up. But I put up with it because I was racing and it saw 6800 regularly.

So basically I know you could "get by" with the vacuum issue.

But those are both hot rod street performance cam specs, kind of maxed out, for HP, not driveability.
They drive "OK" at low speeds, they drive better at 3000rpm and up.
There are better cam choices out there for a street driver.

And the heads are "OK". They are budget $ items, but better than stock.

You could easily change the HR cam out to a 224/230* or a 219/225* on a 110-112LC from Howards, and it would drive much better, have much better torque below 3000, crisper throttle, better vacuum, better gas mileage, and lose maybe 7-10 HP up top. If you really want more HP you are far better off with AFR 180 heads, vs the Blueprint heads, or vs fiddling with the cam specs. The AFRs are just "in another league". You would get the 10HP back, and another 20-30+.

See this thread: JB78L-82 explains his 350 build and results in post 20:
https://www.corvetteforum.com/forums...-platform.html
His 355 will kick that Blueprint 383's butt!
With a milder cam and less cubes.

And I am pretty sure you are going to have to swap out that oil pan anyway, for one that fits a C3.

 

I am running the BluePrint 383, 435HP small block in my 69. It droped right in with the supplied oil pan IIRC and wipers, brakes and headlights all work with as installed vacuum. I do not recall what that number is. I run a Lars tuned Quadrajet and HEI dizzy. Runs great and is a blast to drive.

 

My car has about 9-10 inches of vacuum at idle in gear and everything works. Brakes are connected direct to manifold and everything else comes off the vacuum canister.
Pat

 

Thanks. It sounds like it could work fine as long as I am not hitting the brakes a lot at idle. I would like to think my vacuum lines are all fine. I asked BluePrint if they would be able to put in a slightly smaller cam and they do not allow for customization. I may go with Smeding as a result. They appear to have better vacuum since they tend to have the option for a milder cam.

 

Can you choose a local/regional auto machine shop ? Is price too much of a determinant ? Have you given any credence to Chevrolet Performance Parts crates (fka GMPP) ?
Other than CPP aka GMPP, Suggest separate yourself from any builder who will not even consider a relatively small change; especially a milder, less-stressful change.
No matter which builder you seriously consider, suggest you obtain a detailed build list FIRST; exactly which P/N of all middle & major parts. So you can Independently verify attributes such as piston weights and width of piston ring grooves, wrist pin offset (if any) etc etc etc. Crank weight, internal or external or hybrid balance. The devil's in the details and details can make all the difference.

 

I do not think the Chevy Performance Engines have enough HP. If I am going to spend a decent chunk of change, I want over 400HP. I did look into a local builder, but the cost gets to be higher than getting a whole new engine. The 350 block I have now is not original and there is no reason to reuse it. Had it been numbers matching, I may have gone that route. I considered even going big block, but decided to stick with a small block with "big block power". I like that these new blocks have a one piece rear seal and are shipped with roller cam. I would prefer to get away from flat tappet and retrofitting an older block for roller is costly.

Good suggestion on getting a detailed build list. I hope Smeding is willing to do that. If not, that may be a red flag.

 

AFR Heads!

 

Are your brakes & driveline prepped for big HP & TQ ?
CPP's SP383 makes about 430 HP & 440 TQ; with a longer stroke than most other 383

 

Brakes and suspension have all been upgraded. I am hoping the rear end will hold up. There are a lot of different opinions around here regarding how much the stock rear end can handle.

 

In general, capacity is less than one might hope for.