Twilightoptics

What is the best flowing 305 head's casting number?

Maybe even some flow charts? :O)

F-BIRD'88

The best 305 heads to start with are the 416 and 081 castings



stock head
Flow chart for stock #14101081 305 head 87 91

Intake lift (in) Flow (cfm) Exhaust lift (in) Flow (cfm) Ratio E/I flow (%)
0.050 31 0.050 15 49
0.100 63 0.100 37 58
0.150 92 0.150 61 67
0.200 116 0.200 78 68
0.250 134 0.250 92 69
0.300 157 0.300 101 64
0.350 170 0.350 105 62
0.400 182 0.400 107 59
0.450 189 0.450 109 58
0.500 195 0.500 110 56


This is the stock head with 1.84 and 1.50" valves

Below is what can be achieved with porting and larger 1.94x 1.60 valves

This is actually a 350 head but you can get this out of the 305 heads too. I have.


Ported big valve 350L-98 head
Lift Intake Exhaust
.1 63.8 41.4
.2 120.6 88.2
.3 178.9 124.1
.4 215.2 154.3
.5 240.1 171.8
.6 241 180




@28" H2O intake ex

lift
.100 70.1
.150 105.2
.200 135.27
.250 158.6
.300 187.0
.350 205.41
.400 222.11
.450 225.45
.500 225.45
.550 218.77 140.84cfm

This was my first effort at porting 305 heads.

You can expect this with an honest effort.

F-BIRD'88

Ported 305 head....

Twilightoptics

After porting.. do you need to perform a valve grind?

And also.. stage I ported (blended off seat into valve bowl) if that is already done, am I a step ahead?

Is there REALLY a huge different in 2.02/1.60 Valves VS 1.94/1.50? I can get a set of heads in either. It's going under a TPI with headers/ slp runners/ etc.

F-BIRD'88

Yes you're going to do a valve job after porting them.

Ahead of what? Don't expect to achieve these numbers with just a bowl blend. Don't be a wuss... Fully port the heads.

I do not recommend useing 2.02's in these heads.
No apreciatable gain over 1.94's.
The 1.94's will flow plenty and the head will be stronger.
I recommend the 1.60 exhaust valves.
All these 305 heads have 1.84x 1.50" valves.
So you'll be buying new larger valves.

About $150/175 (can) for a set of budget street valves.

www.competitionproducts.com

EvilCartman

iTrader: (1)

Hummm stock flow numbers for a 305 head woohoo hehe Entered in all my info into desktop dyno and came up with 247 hp 326 tq. Seems a bit high but whatever One of these days I'll get to the dyno, 90 bucks though for 3 runs.

Marshall89ws6

how would the heads flow with all the porting and bowl blending with the 1.84 valves still in there as opposed to the 1.94

F-BIRD'88

Don't know, but a lot less. Why bother.
You're going to need a valve job anyways, and your stock 1.84 valves are going to be pouched too.

You're not going to save anything.
The cost is the same. If a machine shop wants to charge more to cut in new larger 1.94 seats than to remachine the stock 1.84 seat, find a different machine shop. the work is the same.
New budget replacement valves are not expensive.
By the time you regrind your old GM valves the margins
will be too thin too. (run too hot). Get new 1.94" x1.60" or 1.50" valves.

Marshall89ws6

i have 1.94x1.5 but i was just wondering how much difference a tenth of an inch would make.

84 Restore

I just ordered new valves, springs and cam from summit. :lala:
I ordered 1.94 intake and 1.50 exhaust. I thought that was what was stock for my heads
As I read this thread I am gathering that is not correct. If I am right you are saying that the 416 heads have 1.84 and 1.50 is this correct?.
If so can I use 1.94 and 1.50 combination. I have been very slow on ordering parts and this is why. I learn or something changes all the time. so if any one can help.
p.s. I am in the middle of porting the heads now. (which is alot of fun)

Sitting Bull

Oh yeah, the machine shop won't have any trouble fitting the head for new 1.94" intake valves. Routine work for them.

DonP

I have a stock 1990 GTA with a TPI 305/5 speed. Which heads came on this motor?

Thanks,

Don

Sitting Bull

081s.

Apeiron

Hey Todd, you got a use for any more boat-anchors?

Sitting Bull

Not really. What have you got in mind?

Apeiron

Got some 642s and 185s to unload on someone.

Sitting Bull

Better keep lookin' then