xbgs351

I'm considering welding up the floor on the exhaust ports of my 2V heads. Has anybody had any experience with this modification?

russxr67

what would be the point of this exercise? Are you considering doing this in an effort to raise airflow based on the myth that 2v,s like their 4v brethren have poor exhaust flow?

buzz

They do.

svo347

why not just use those s/steel port tongues that you can buy nowdays.

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russxr67

they have poor flow do they? On the 2v,s it is the intake which needs work not the exhaust.The stuff all the magazines talk about in relation to poor exhaust flow only pertains to 4v heads.If you actually knew anything about these heads you would know that the exhaust is very strong in relation to the intake.a properly ported exhaust port will yield over 200 cfm (2v) and a properly ported 4v around 220cfm. ported 4v intakes can flow up to 375 cfm and this is where the imbalance lies due to the intake being so strong and the exhaust is restricted somewhat.Thats why most clevo cams are biased towards the exhaust side giving them more duration and lift to alleviate some of the problem,whereas 2v headed motors do not require the use of a split cam.

xbgs351

My exhaust flow as a percentage of inlet.

At 0.500" it is 77%
At 0.400" it is 67%
At 0.300" it is 68%
At 0.200" it is 70%
At 0.100" it is 92%

The modification is rather cheap and there are proven benefits to flow.

russxr67

how much do the heads flow in cfm at 28?

xbgs351

I picked these heads up second hand with a bunch of other gear. Have just got them back from being flow tested.


Intake flowed with Funnelweb, long runner.

0.103 65
0.205 136
0.308 194
0.411 216
0.513 218

Exhaust

0.082 47
0.165 83
0.248 112
0.331 132
0.413 147
0.496 167

Intake Valve dia = 2.055"
Exhaust Valve dia = 1.655"
302 Cleveland heads
Pocket ported bowl & short turn radius
Intake Volume = 170cc
Combustion Volume = 64.5cc

russxr67

Unfortunately the closed chamber heads tend to shroud the valves somewhat so some unshrouding may bring you the desired results at the expense of more cc,s.at least the heads have got the 2v sizes still intact.Are the heads going on a street car or are they to be used on the strip?

xbgs351

Plan on doing some circuit racing whilst still keeping it streetable.

I don't want to open the combustion chamber up any more due to the loss in compression. With a 351 calculated compression will be 10.5 : 1. If I go the 393C route with dished pistons it will drop to 10 : 1.

The heads flowed better with the inlet manifold than with the bellmouthed plasticine on the bare heads.

I'm trying to keep a lid on engine costs so that money can be allocated to the things that will make the car fast being: wheels, rspec tyres, rollcage, seat, harness etc.