General Head Information
You have found the place with the most current information for 194, 230, 250, and 292 Chevy Inlines.
Bolt in HI-FLOW lumps will add:
Steps for valve enlargement
1. Valve guides- All machining is centered around the valve guides, new guides recommended.
2. Cut valve seat for desired intake valve size. Minimum should be 1.84, and max should be 1.94, a good in-between is 1.90. Use same length valve as SBC.
3. Cut seat for exhaust valve- I like to install hardened seats first (shallowest/ thinnest). Minumum size is 1.60, also same as SBC.
4. Use a 75 degree bowl cutter and remove majority of material from intake valve throat. Cut to within 1/8" of the intake seat.
5. Both the intake and exhaust bowls can be blended using a air powered carbide tipped cutter(as seen in my install video). Do not remove material from the short side radius or either valve, just smooth and blend.
Milling the head
Most heads are open chamber design (except 194 c.u. in heads) and chamber volumes will measure between 72-76CC. The majority being 74CC. It is recommended to mill the heads .030 and this will get you a 70CC chamber. The rule for CC change is for every .007 cut, 1 CC will be lost from chamber.
More info coming!
Which lump kit do I use?
The standard HI-FLOW kit is easier to install and with a 1.94 intake valve with porting will get around 240-250 cfm flow.
Using a 1.84 valve will get about 220-230 CFM flow.
The Premium Kit is somewhat more of a challenge to install. The alignment of the attaching bolt is more crucial for success. Time must be taken when installing this kit. The premium kit will only flow a bit more flow, but the real reward is in the form of less turbulent flow. Turbulence can separate the fuel from air and make it stick to the port walls. Not good!
Which head is best to start with?
All years of heads will work for adding a bolt in lump. Later model heads 1975-newer have some better features you may want. They seem to be better able to take a 1.94 valve enlargement without hitting water. They also will usually have hardened exh seats. A drawback is the EGR tube holes that will need to be plugged.
A common misconception is to use a "194" small chamber head to raise the compression and gain power. I have found that in flow testing and dyno testing, the 194 head produces less power than common open chamber heads (with the same modifications). This is caused by the shrouding of the intake and exhaust valve by the small chamber. Major chamber work is required to make this head flow. Many times this head will not take a 1.94 valve (hit water). 1.84 is a safe size. This head is also a very old casting and often is cracked.
What size valves should be used?
Flow tests and dyno tests have proven that atleast a 1.84-1.94 intake valve should be used. 1.94 valves have shown the most increase in TQ and HP on a 292 and 1.84 has shown to be the best size for a street oriented 250. A stock sized 1.72 intake showed no performance increase with a bolt in lump. For the exhaust a 1.6 is always recommended.
You have found the place with the most current information for 194, 230, 250, and 292 Chevy Inlines.
Bolt in HI-FLOW lumps will add:
- Torq ( Peak and also over RPM range)(almost the same as a cam change)
- Horse Power
- Intake port flow will be at least 10% higher
- Velocity of the intake charge will go up
Steps for valve enlargement
1. Valve guides- All machining is centered around the valve guides, new guides recommended.
2. Cut valve seat for desired intake valve size. Minimum should be 1.84, and max should be 1.94, a good in-between is 1.90. Use same length valve as SBC.
3. Cut seat for exhaust valve- I like to install hardened seats first (shallowest/ thinnest). Minumum size is 1.60, also same as SBC.
4. Use a 75 degree bowl cutter and remove majority of material from intake valve throat. Cut to within 1/8" of the intake seat.
5. Both the intake and exhaust bowls can be blended using a air powered carbide tipped cutter(as seen in my install video). Do not remove material from the short side radius or either valve, just smooth and blend.
Milling the head
Most heads are open chamber design (except 194 c.u. in heads) and chamber volumes will measure between 72-76CC. The majority being 74CC. It is recommended to mill the heads .030 and this will get you a 70CC chamber. The rule for CC change is for every .007 cut, 1 CC will be lost from chamber.
More info coming!
Which lump kit do I use?
The standard HI-FLOW kit is easier to install and with a 1.94 intake valve with porting will get around 240-250 cfm flow.
Using a 1.84 valve will get about 220-230 CFM flow.
The Premium Kit is somewhat more of a challenge to install. The alignment of the attaching bolt is more crucial for success. Time must be taken when installing this kit. The premium kit will only flow a bit more flow, but the real reward is in the form of less turbulent flow. Turbulence can separate the fuel from air and make it stick to the port walls. Not good!
Which head is best to start with?
All years of heads will work for adding a bolt in lump. Later model heads 1975-newer have some better features you may want. They seem to be better able to take a 1.94 valve enlargement without hitting water. They also will usually have hardened exh seats. A drawback is the EGR tube holes that will need to be plugged.
A common misconception is to use a "194" small chamber head to raise the compression and gain power. I have found that in flow testing and dyno testing, the 194 head produces less power than common open chamber heads (with the same modifications). This is caused by the shrouding of the intake and exhaust valve by the small chamber. Major chamber work is required to make this head flow. Many times this head will not take a 1.94 valve (hit water). 1.84 is a safe size. This head is also a very old casting and often is cracked.
What size valves should be used?
Flow tests and dyno tests have proven that atleast a 1.84-1.94 intake valve should be used. 1.94 valves have shown the most increase in TQ and HP on a 292 and 1.84 has shown to be the best size for a street oriented 250. A stock sized 1.72 intake showed no performance increase with a bolt in lump. For the exhaust a 1.6 is always recommended.