306 Turbo Or 357

306 turbo or 357 N/A


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Xterminator03

Member
Sep 23, 2004
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I am undecided. I currently have a 306 where I'm having some issues with. ( Oil and gas leaking from throttle body onto valve cover). So I will be pulling out the engine and rebuilding the motor. At that time I would like to go Turbo with an on3 performance kit 66mm. Or there is a new 351 bored .30 that just came out of the machine shop. That is beign offered to me for $1500.00. My question should I spend the money on the 306 turbo or the 357 N/A.

My current set up that I will be re using for the 306 turbo or for the 357

Holley systemax II top end kit. ( Will change he can for both turbo or 351) (will need to change intake for 351)
Bbk shorty headers
24lbs injector (will replace with 60 if turbo)
Aeromotive fuel rail
Jegs distributor (will replace if I go 351)
75mm throttle body

Will the Holley heads work work well with the 351 setup?

I am trying to get this done for around $2,500.00.
The 357 short block will cost me $1500.00
The on3 turbo will cost $1900.00

What do you think I should do.
 
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I can't get past the first part.....

How do oil and gas get into the throttle body??? Neither one goes through around or into it.

It's been a while for me, since my 90mm TB doesn't have stock-location ports, but don't the 75mm and smaller TBs have a vent line from the passenger side valve cover? That could explain the oil.

But gas, yea, no reason there should be gas up there.
 
1500$ for a complete shortblock? That includes pistons,rods,crank,rings,bearings and balancer-flywheel/flexplate? If so it's not a terrible price if quality parts were used. Fresh machined block alone usually brings about a 500$ price tag around here.

As far as your budget...you need a bigger one in either case imo. The Holley heads are very restricted compared to almost all aftermarket options. They are fine for a mild 306 with some boost but for a n/a 357...bleh. Also the on3 kits are known to be hit or miss on quality and you need more parts to complete.
 
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$2,500 won't even get you an HCI combo that's worth the time and investment. Is there a carb involved? If not a megasquirt system with wideband will run a person $700+ alone. There are so many consumables and small pieces that really add to a build that nobody even bothers reporting but I bet @hoopty5.0 @a91what and myself have a stack of receipts that amount to a small fortune in short trips to True Value hardware or a parts store for odds and ends that pester your wallet.
 
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It's been a while for me, since my 90mm TB doesn't have stock-location ports, but don't the 75mm and smaller TBs have a vent line from the passenger side valve cover? That could explain the oil.

But gas, yea, no reason there should be gas up there.

I'm thinking its gas mixed with oil caused by over pressurization of the crankcase, caused by blow by, caused by worn rings or cylinder walls, caused by hard driving, low maintenance, or high mileage.

Or....it could be caused by a clogged pcv screen in the lower intake....or all of the above.
 
I've got well over $2500 in my on3 kit and supporting mods. I'm scared to add it all up or list them...so please don't ask :(
 
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