RyanSS

I have heard that when you install a high lift cam and heads to match that you lose manifold vacuum. Is this true?(pretty sure it is but just figured I'd ask.)
How do you fix this or what problems does it pose?

Was just wondering for future plans.

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89 RS 350 TBI auto Hooker SC/LT headers Open element 3in K&N CVT protorque mini-starter

Daily driver 91 RS auto LO3 63k

ede

as a rule yes you do. power brakes is the biggest problem, you can get an add on aftermarket vacuum canister to hold additional vacuum.

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

Grand Prix

That isn't a very good way to put it honestly. A high lift cam will not affect vacuum. It is the cam duration that primarily affects vacuum. The longer the cam's duration the lower the vacuum will be. As the duration increases the lift usually increases to take advantage of bigger heads. Which is another factor in vacuum. The larger the ports in a set of heads the lower the vacuum will be. If you select a smaller port head, like Edelbrock's Performer RPM series, and a camshaft capable of working with the stock torque converter your idle vacuum will be fairly high. There is no way to "fix" low vacuum levels. The power brakes, fuel economy, PCV system, and driveability are the main things affected. Don't be afraid to use a larger set of heads and cam, just make sure both jive with what you want the car to do. Stock heads and cams tend to be very small so you can increase both without running in to problems.

RyanSS

I am building a street/strip car. It will see mild street usage (weekend cruises) but not a daily driver. Fuel economy is not that big of an issue, say around 10mpg in the city, but no less than 5mpg. I plan on a T56 for ok highway mileage.
Any suggestions? I will probably use the 350 I have in the sig until it dies then build a 406 or big block depending on how long the 350 lasts.
Are 10's possible on an N/A 350? That would be great, but 11's, consistent 12's at least is what I want. Is this realistic?

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89 RS 350 TBI auto Hooker SC/LT headers Open element 3in K&N CVT protorque mini-starter

Daily driver 91 RS auto LO3 63k

Grand Prix

Lets see, 10's and 9's are possibly naturally aspirated. I wouldn't count on them though. A 350 would have to be very radical to make it there. Radical means expensive, very grumpy, and unreliable. The car would be impossible to drive on the street. 11's are possible but still a little bit of a stretch for a 350. 12's are more reasonable but you need to start from the ground up with that idea. Throwing from the top of my head I would say you would want to build up something like this. Rebuild your bottom end using all good parts and machine work. Use forged pistons, better bolts everywhere, make sure all parts are in prime condition. Use a set of AFR 190 heads, good heads that still are good enough for the street. Your block should be a factory roller block. Try a roller cam with about 228 degrees intake duration and about 232 exhaust. 1 3/4" headers if you can afford them. Dump the TBI system, its not going to be much of an advantage and is way too small. Instead jump to a good dual plane with a 4bbl of about 750CFM. Also, keep compression at about 9.5-9.75:1. Set it all up right and you should be around low 12's. The engine will lope and probably idle right around 850RPM but still work well enough for the street. This is a rough combination and will probably need a little more fine tuning to match everything up well. If you start out with the idea you don't want to lose idle vacuum you will never pull 12's or faster.

I should probably add that your current 350 shortblock probably isn't a good platform to run 12's or 11's. If you aren't in to rebuilding it then there are probably dozens of other people here that would have better suggestions to get you to low 13's. 12's and 11's take more power than you should throw on to an old factory short block.

[This message has been edited by Grand Prix (edited June 30, 2001).]

RyanSS

I don't want a carb, and the TBI system is good up to about 450hp. I have the headers already(in sig) I will have a new intake soon. The 350 in my car doesn't have over 40,000 miles on it. If I was gonna go to the trouble to rebuild it I would just go with the 406 now. But I just want to build this at the moment so I can have something to sustain me until I can build the 406(all forged, possibly twin turbo)
It doesn't bother me to lose manifold vacuum, as long as I can use a vacuum canister to remedy it.

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89 RS 350 TBI auto Hooker SC/LT headers Open element 3in K&N CVT protorque mini-starter

Daily driver 91 RS auto LO3 63k

jcb999

I suggest you start with a carburated 350 that makes in the 420 hp range. It will be the easyiest combination to get dialed in. Then when you want to go faster, put NOS on it. The issues involved with 383 (using 5.7 rods) and 400s are significant. As with FI. Get the engine running with a carb. Then switch to FI. You will be much more likely to have a successful project.

Don't try to build the fastest car at first. Get it going and lean on it later. That way, you will have something to drive and enjoy instead of something that you have to work on for 2 to 3 years before you see the fruits of your labor. I know this first hand.

turbos under 3rd gen hoods have many packaging issues to deal with.

[This message has been edited by jcb999 (edited July 01, 2001).]

Bort62

4 bolt 350 block, 30 over.

Forged steel crank, Forged pistons

Unknown cam specs, but Mech Flat tappet.

Brodix Stage II heads, professionally ported and polished


Brodix High Rise Single Plain Intake Manifold, Ported and gasket matched.

Holley 750 DP

12:1 compression


11.1 @ 118 IN a 3500lb 67 Chevelle

Completely streetable, If you don't mind manual valve bodies, Driving on slicks, and 110 Octane )



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver 14.82 @ 91.1 (faster than Ed)
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
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