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305 head flow possibilities?

General engine tech -- Drag Racing to Circle Track

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gmrocket
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305 head flow possibilities?

Post by gmrocket » Sat Oct 12, 2019 9:55 pm

My son picked up a 350 for a dirty dog rebuild that's going into a first gen RX7

The 350 sbc was a runner so for $100 he jumped on it.

Turns out it has 305 small valve 1.72" intake valve heads in it...#450

It's going to be an ultra low buck back yard build ,, once it's all sorted out and running,, later on he will upgrade the power

It's getting a T5 ...

But first off we need to get these heads reusable..I'll be putting in the 1.84" intake and doing some minor bowl work.....are the ports different between the factory 1.84" 305 heads and the 1.72" ones?

Not gonna spend lots of time or money on these heads,, but we do have some 1.84" valves

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Re: 305 head flow possibilities?

Post by F-BIRD'88 » Sat Oct 12, 2019 10:34 pm

Like any other SBC head if you port them generously they
Will flow a lot more than stock.
Recommend 1.94 intake valves.
The twinned exhaust egr passages Rob power.
Not the preferred 305 head casting as a start point.
I've had good results with the #4416 castings for budget stuff.

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Re: 305 head flow possibilities?

Post by gmrocket » Sat Oct 12, 2019 11:11 pm

F-BIRD'88 wrote:
Sat Oct 12, 2019 10:34 pm
Like any other SBC head if you port them generously they
Will flow a lot more than stock.
Recommend 1.94 intake valves.
The twinned exhaust egr passages Rob power.
Not the preferred 305 head casting as a start point.
I've had good results with the #4416 castings for budget stuff.
It's not getting the 1.94" intakes...what I asked was is there a difference in the port behween the two heads?

I know guys don't play with these heads much..I did run a 305 big valve head on a 305 back in the early 90''s in a G body cutlass with 4:33 gear,,it ran low 12's

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Re: 305 head flow possibilities?

Post by Racer71 » Sun Oct 13, 2019 12:39 am

I think I would address the T5 first, they didn’t last in a s10 or v6 Camaro or the much more powerful mustangs of the day.

econo racer
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Re: 305 head flow possibilities?

Post by econo racer » Sun Oct 13, 2019 3:11 am

Man low 12's with a 305 that's rocking. Way better than I ever got out of one. =D>

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Re: 305 head flow possibilities?

Post by Carnut1 » Sun Oct 13, 2019 5:16 am

The ports are the same for 1.72" and 1.84" valve heads. Be sure these castings are not cracked! They are thin walled castings but can flow fairly well if ported.
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Re: 305 head flow possibilities?

Post by Carnut1 » Sun Oct 13, 2019 5:18 am

https://www.google.com/url?sa=t&source= ... N0GmLIsIlk
An older thread I did on 450 castings.
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Re: 305 head flow possibilities?

Post by mag2555 » Sun Oct 13, 2019 6:51 am

With a 1.84" and 1.60" valves it should not be too hard to get 225 cfm Intake flow and 175 out the Exh which could get ya 380 hp into the light weight RX7 body.

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Re: 305 head flow possibilities?

Post by cardo0 » Sun Oct 13, 2019 4:32 pm

Here's what Brzezinski Racing (Cast Iron Heads) says about the 305 heads: https://www.castheads.com/cylinder-head ... 305-heads/

BR mentions using a 1.94" valve in a 305 head will hurt flow under 0.400" lift compared to a 1.84" valve.

Good luck.
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94 Z28: Gen II 350 auto

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Re: 305 head flow possibilities?

Post by econo racer » Mon Oct 14, 2019 7:27 am

With all these new ways of getting lots more power on the 305. What cam and intake should work with the 305 engine to make it run 12.20.?

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Re: 305 head flow possibilities?

Post by RCJ » Mon Oct 14, 2019 12:36 pm

We used those heads 20 years ago it a claimer style dirt track class.They would get a 350 to around 11 c/r,the 1.84 heads ran a lot better than the 1.72.If you are going as cheap as possible they seem to be a good heads.We were only turning about 5200 to 5500rpm

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Re: 305 head flow possibilities?

Post by econo racer » Tue Oct 15, 2019 7:40 am

Would a cam about 230 deg. at 50 and 480 lift on a 106 work good enough to get a 305 motor into the 12's a course a good converter and gear. I always wanted to see how fast I could get a carbed 305 to go.

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Re: 305 head flow possibilities?

Post by RCJ » Tue Oct 15, 2019 8:14 am

That is the cam we used , but by rules we had to use a stock Q jet intake. An RPM performer and some head work should extend the useable rpm range enough to use more cam.

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Re: 305 head flow possibilities?

Post by F-BIRD'88 » Tue Oct 15, 2019 3:16 pm

Try this cam in a hot budget 305 with ported heads.
You want to get the CR up to 10.1 ++.
Melling cam #22402. Elgin cam #E1131-p
282-290 -240-250 @.050" 106 lsa .521"-.521" .024" lash
Budget friendly cost at summit and competitionproducts.
Get a 8" 9" race converter and think 4.56 gears

The realized max stall speed of a off the shelf converter will be about 500 rpm LESS than rated when put behind a 305 cid sbc. Eg: a "3500-3600 stall" 10" converter will only stall about 3000 rpm when behind a 305 cid sbc.
To get the real stall rpm up in the. hot part of the hot rodded 305's power band be generous on the converter selection.
When it comes to converter and gears, more is better.

These melling/elgin lil solids will also run well in a 350 sbc with ported 305 heads.
The poor man's race engine.

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Re: 305 head flow possibilities?

Post by F-BIRD'88 » Tue Oct 15, 2019 4:55 pm

Where many most go wrong in low budget hot rodded 305-350 builds ( eg: with ported 305 heads) is getting the CR wrong.
Worst offender is the wrong non stock compression height rebuilder pistons. 1.54" CH verses correct 1.56" CH.
Felpro .015" thin steel shim head gaskets help on both engine builds. Getting the compression ratio correct is critical to these low buck builds.
KB UEM has a cool .100" dome hyper piston for the hot 305 builds .
KB144

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