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Old 02-07-2008, 08:15 AM
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305 heads on 350

building a 89 formula 305. picked up a 350 4 bolt main motor for cheap. i really like tpi and i heard that i could use the 305 heads on the 350. i was gonna use the 350 short block with the 305 heads and tpi setup. i also got a charger setup for the tpi, thats pretty much the reason for stickin to the tpi. is this setup gonna work or do i have to make a lot of modifications. trying to do this on a budget so cant go too huge with any of the parts. let me know what you think. thanks for the help.

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Old 02-07-2008, 10:15 AM
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Quote:
Originally Posted by BROKENOTCH
building a 89 formula 305. picked up a 350 4 bolt main motor for cheap. i really like tpi and i heard that i could use the 305 heads on the 350. i was gonna use the 350 short block with the 305 heads and tpi setup. i also got a charger setup for the tpi, thats pretty much the reason for stickin to the tpi. is this setup gonna work or do i have to make a lot of modifications. trying to do this on a budget so cant go too huge with any of the parts. let me know what you think. thanks for the help.
This would be better with 350 heads to get the larger passage volume and valves. However, the 305 can be modified with a decent port job and 350 valves. They do provide significantly higher compression on a 350.

You have to careful about compression, it is the result of both combustion chamber volume/design and dish volume of the piston, to a lesser extent the selection of the head gasket thickness and the piston crown to block deck clearance.

A tight chambered head with D shaped dish in the piston is a better solution than something like a 305 head using a large circular dish piston to get the compression to something available fuels can handle. There are many heads from GM/GMPP and the aftermarket that work well. The fastburn technology of the so called heart or kidney shaped combustion chamber offers significant power increases over earlier designs. Open chamber heads are inefficient costing both detonation resistance, power, and fuel economy.

The Vortec is a commonly referred example of this group of heads but there are many GM/GMPP and aftermarket choices of similar characteristics in aluminum and cast iron. The original Vortec isn't a good choice for your TPI as it requires a unique bolt patterned intake, while these can be had for TPI they are pretty expensive.

125508060 is a part number of the original Vortec it can be made from either a 10239906 or a 12558062 casting. The difference between them is that the 906 uses hard seat inserts and the 062 uses induction hardening. The original Vortec "060" heads all use 1.94/1.50 valves with a 165-170 cc intake port.
Both or either makes a production L-31 truck head.

GM recognizing the 060s hot rod limitations resulting from thin wall casting and valve lift limited by the guide and spring design has released part numbers 25534421 and 25534431 which will mate to the TPI intake. These are Vortec style heads with heavier casting thicknesses than production heads with larger 2.02 and 1.55 inch valves; they accept higher lifts without modification to the guides and springs and feature larger intake ports a 180 cc intake for the 421 and 206 cc intake for the 431. These are complete ready to run heads, they are also available bare. An aluminum version called the Fast Burn P/N 12464298 is available from GMPP with a 62cc chamber 2 inch intake, 1.55 exhaust, 210cc intake port and a 78cc exhaust port. Performance from the older 060 Vortec version of these heads is considered good for a 15 HP boost when replacing the L-98 Corvette head and about 40 horses against older open chamber heads. The newer heads are considered for about a 30 hp boost against the L-98 and upwards of 60 horses against earlier heads. These are significant numbers against the cost and the power appears with just the head change and tuning without having to recam or reintake the engine to get this much power.

However, retuning in your case involves changes to the TPI. The change from 305 to 350 alone is more than than the computer can manage. Even the mass flow versions have fuel and ignition map limitations, you can't keep adding air flow without falling off the edge of the known universe at some point. This will require a new chip. Getting to the chip will require a decision to stay with the existing 305 injectors and working them harder to get the needed fuel flow or replacing them with higher flowing injectors which then can back off using such an aggressive duty cycle for flow. Contact some of these people: Keep in mind you can't simply use an over the counter speed chip, these need to be customized.

http://www.fastchip.com/

http://www.tbichips.com/

http://www.hypertech-inc.com/

http://www.superchips.com/

http://www.tpis.com/

Additionally, the intake runners of the 305 TPI are really strapped to supply air to a 350. They can be hogged out. The TPIS people offer some super big manifolds but they are pricey.

Bogie
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Old 02-07-2008, 11:22 AM
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I used a set of 305 heads on a 383, and they worked well for my application, however they had 2.02/1.60 valves and were absolutely ported to the max. They provide excellant power up until about 5500 rpm and then the flow just isn't there. If you are using these heads in a street application then go for it. If it is for racing then go with ported 350 heads.
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Old 02-07-2008, 02:19 PM
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The 081 305 tpi head and the 083 350 tpi head are essentually the same.
The difference is the chamber volume and intake valve size
58cc and 1.84"
other than the difference in the valve bowl size under the slightly smaller 1.84" intake valve, the ports are the same on either head So:

If you want to make a pretty good "TPI head" for a 350 or a 383 using a 081 305 TPI casting, rework it with a 1.94"x 1.60" valve set. Home Port them to your hearts content for improved flow. Just the fact that you swept the chamber wall out a little to physically fit a larger 1.94" valve will change the chamber volume from stock (58cc nominally).
CC your heads after you are all finished and then select the best 350 head gasket for the job (cr and quench clearance). its likely when all done your modded 081 heads will be around 61-62cc +/-. If you want more chamber volume, deshroud the chamber a bit more. If you want less volume, shave 'em down a bit.

The 305 TPI heads have as much power potential (with equal sized valves and work) as the 350TPI heads do. Once you machine for the new larger valves the chamber volume will no longer be stock so that is not a issue to prevent you using these heads either.
If you'll be camming it up as we all tend to do, a moderate increase in the finished cr is a + anyways.
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Old 02-07-2008, 05:26 PM
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ya im plannin on puttin a nice cam in it but i am going to go with bigger injectors and i know i needed the chip just becasue of the supercharger. the paxton i got puts out like 9lbs of boost i guess, how else can i get this motor flowing better, because i dont want the blower to be useless.
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Old 02-12-2008, 07:58 AM
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thanks guys, any suggestion to what size injectors to run with the paxton
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Old 02-12-2008, 09:40 AM
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Quote:
just becasue of the supercharger. the paxton i got puts out like 9lbs of boost i guess, how else can i get this motor flowing better, because i dont want the blower to be useless.
If you're going to use 305 heads,.....

That Blower is Already Useless,......

You're going to be approaching Diesel Compression Ratios.......
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Old 02-12-2008, 10:09 AM
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Quote:
Originally Posted by bondo
If you're going to use 305 heads,.....

That Blower is Already Useless,......

You're going to be approaching Diesel Compression Ratios.......
Gee, why would you let a little detonation stop you from using 305 heads on a blown 400??




tom
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Old 02-12-2008, 02:15 PM
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what should i go with if im still going to use the tpi setup. just try to find 350 tpi heads and just go with bigger injectors and tb. the guy i bought it from had it on a 305 and he said it ran strong. any suggestions????
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Old 02-14-2008, 07:18 AM
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????? anybody??
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Old 02-14-2008, 10:12 AM
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Originally Posted by BROKENOTCH
????? anybody??
Hang on, I wrote an epistle yesterday and just as I was finishing it my hard drive puked. I'll redo it in a while.

Bogie
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Old 02-14-2008, 11:25 AM
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If you're hell bent on using your 305 heads just clean up the chambers until you hit about 62cc's used a inverted dome piston to get you to 8:1 compression and go with the computer/fuel mods you will need along with your procharger. Later when you can afford to upgrade your heads to somethina little better. Oh, and pick a cam with max HP around 5000 RPM, anything more than that and your TPI setup is trash, boosted or not.

TPI's are great for torque, but terrible for top end power.
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Old 02-14-2008, 05:46 PM
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thats what i have been hearing thanks.
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Old 02-14-2008, 06:12 PM
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Quote:
Originally Posted by oldbogie
Hang on, I wrote an epistle yesterday and just as I was finishing it my hard drive puked. I'll redo it in a while.

Bogie
Let me cut to the quick since I'm up to my hip in 'gators. If your bound to staying with a GM head the beast that will bolt to the 350 at one end and the boosted TPI at the other is casting number 12556463; it is the 1985-92, Gen I, "L98", cast iron 350 head.

Bogie
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Old 02-14-2008, 06:48 PM
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EngineQuest makes a Vor-Tec style head that has the older style intake pattern and perimeter-style valve cover bolt holes. In other words, your existing stuff will bolt on.

http://www.enginequest.com/

Part #CC170BA2

This would be better that ANY 305 head.

Period.

tom
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