1.65 or 1.75 valves

[blaze65]

Have an engine currently out for rebuild and have asked the shop for, a rebuild, mild cam, 2V conversion. I also asked them to look at the option of the 1.75 valves. This is a 75 Head and from all of the great information I have received on this site in the past I have learned that 1975 is a transitional year for the 200 as Ford was undergoing engineering changes heading into the 76-78 heads. So what is actually in a 75 head may be a mixed bag. Point is that the machine shop did not seem too thrilled at the idea of changing to the 1.75 valves. I guess cost was one issue but they also kept saying that it would only increase the valve size 1/1000th as the spec sheet on the 75 head says it has 1.65 valves.

Question is basically , is a change from 1.65 valves to 1.75 valves that significant ? would it make a drastic improvement if I did this change ? would it make a drastic improvement if I did not do this change ?

Many thanks

Bill,

 

[CZLN6]

Howdy Back Bill:

The change is probably not cost effective for a mild street engine. Unless you are in need of new valves anyway.

But, I have some concerns with the math skills of your machinist. The 1.75" are .100" larger in diameter. That's 100/1,000th, not 1/1,000. While .100" may not seem like much in diameter it is significant in area and flow. Having a three angle valve seat with a 30 degree back-cut on the intake valve would be worth the extra money.

Keep it coming.

Adios, David

 

[blaze65]

Hi David,

Great point. I did not catch that. He definitely said 1000th. Maybe I should start to worry. I'll ask about the 3 angle valve work and the back cut. If I stay with the 1.65 valves those mods should help.

If I can ask. When discussing the valve change with him he made reference to how close the sidewall of the casting is to the valves currently. Is this what would constitute shrouding ? where that sidewall interferes with the valve intake area ?

Will keep you posted.

Thanks as always

Bill

 

[xctasy]

The 1.75 " valve was a rare case of Ford doing really well for a low compression 200 or 250 plodder. A valve that size can support well over 250 hp if the head, cam and overall head cfm is brought up to a better level.

Superflow in Australia had some interesting facts on upgraded valve sizes on Falcon and Holden sixes back in 1988. From what I've found from them and others in the head rebuilding industry, you can get away with smaller than 1.75" valves without loosing out any power.

The gasflow with back cut 1.65" valves is better than stock 1.75" valves. Based on curtain area with the right cam , you could get 215 hp with a 1.65" valve, and you only need 0.45 inches of valve per inch of bore to do it.

So 1.65 inches of valve per 3.68" of bore is right on the line for good intake cfm.

In Australia, racing Holden 3.3 sixes with 9 port heads could make 215 hp with just a 1.625" valve head and 3.625" bore. Going to bigger valves would then require chamber work to unshroud the walls, and some blocks would benefit from relief cuts with a 60 thou over bore head gasket needed to get the extra CFM a 1.75" valve could give. Putting V8 spec Holden 308 valves with 1.78" heads in our 250 2v heads yielded poorer gasflow than the stock 1.64" valves unless a lot of work was done opening up the head walls. Big cams with bigger valves then required relief cuts on stock 3.68" bore engines.

It was rare for Ford, but the US post 1975 heads had really good port, valve and intake manifold areas considering the stock engines were right down to sub 100 hp net ratings from 1972. Any big log heads (post 1969 250, and all 1972 on heads) are highly responsive to cam, carb and exhast upgrades even with the 1.65" valve.

 

[rocklord]

If you can wait on doing head work, why don't you find a head with the 1.75 intake valves and rework it.

Any head with a casting code beginning with D7, D8, E0, or E1 would have the larger valves, and larger intake log. They also have hardened valve seats.
Look for late 70's Granadas/Monarchs, or any year Fairmont for the head.

Try http://www.car-part.com for one locally to you.

 

[CZLN6]

Howdy Back Bill and all:

Q- "Is this what would constitute shrouding ? where that sidewall interfers with the valve intake area ?"
A- Yes. And X gave a good description of the need to unshroud a larger diameter valve in that area of the chamber.

But note that shrouding is less of an issue with the 1.65" diameter valves, a three angle valve seat with a back cut on the intake valves works regardless of shrouding. And Milling the head, for whatever reason, helps by dropping the valves deeper into the cylinder and out of the chambers.

Also note that unshrouding in a 200 chamber is limited because of the close proximity of the cylinder bore. Unshrouding also increases chamber volume, reducing CR. Also note that the 1.65 valves are slightly lighter than the larger valves, requiring slightly less spring pressure to control.

So, unless you are capable of doing the unshrouding correctly, I suggest sticking with the 1.65" diameter intake valves and maximizing their performance.

So, What are you thinking?

Adios, David

 

[rbohm]

8) i also agree with keeping the 1.65 valves rather than going to the 1.75. the flow difference is not enough to help unless you are building a high end engine. a better choice would be to, as indicated, back cut the intake valves for better flow, and go to a 1.50 exhaust valve to improve airflow out of the cylinder. this will help more than just going to a 1.75 intake valve.

with these engines you are looking for a net increase in overall airflow through the head.

 

[JackFish]

Unshrouded 1.75 valves with 1.5 exhaust valve.
It's not a very major cut:

 

[blaze65]

Thanks to all for the insight. I can' tell you how much I appreciate the help and this site. I will keep the 1.65 valves. Ultimately my goal is a good solid driver and I wanted to go a little past the basics as the head is apart and I was trying to get as much in the rebuild while it was apart. Right now the plan is

Rebuild
3 angle / back cut the valves
Keep the 1.65 valves ( will check out the 1.50 exhaust - Not sure what is in a 75 head currently)
2V conversion to run an Autolite 2100 1.08
New cam - something in the range of the 264/274-112 From CI
Duraspark
Possibly a Port divider
Headers

There is still a chance this head will end up at CI but we will have to see. I made a somewhat cardinal mistake and told the machine shop "I am not in a hurry". I really wasn't as I have no place to put the engine until spring but it has been over 3 months and so far only the hot tank is done. They also keep mentioning that 'they have to review the 2V conversion'. Will be going to the shop this weekend. If nothing has changed or if they are reluctant to start grinding on the intake for the 2V, I will have to make other plans.

Thanks again to all. Will keep you posted.

 

[Wishbone]

Thanks to all for the insight. I can' tell you how much I appreciate the help and this site. I will keep the 1.65 valves. Ultimately my goal is a good solid driver and I wanted to go a little past the basics as the head is apart and I was trying to get as much in the rebuild while it was apart. Right now the plan is

Rebuild
3 angle / back cut the valves
Keep the 1.65 valves ( will check out the 1.50 exhaust - Not sure what is in a 75 head currently)
2V conversion to run an Autolite 2100 1.08
New cam - something in the range of the 264/274-112 From CI
Duraspark
Possibly a Port divider
Headers

There is still a chance this head will end up at CI but we will have to see. I made a somewhat cardinal mistake and told the machine shop "I am not in a hurry". I really wasn't as I have no place to put the engine until spring but it has been over 3 months and so far only the hot tank is done. They also keep mentioning that 'they have to review the 2V conversion'. Will be going to the shop this weekend. If nothing has changed or if they are reluctant to start grinding on the intake for the 2V, I will have to make other plans.

Thanks again to all. Will keep you posted.

Porting and polishing the Runners will help more than bigger valves and you can do that yourself very cheaply! save money and spend it on other parts!

 

[blaze65]

Looks like I will stay with the 1.65 valves as mentioned. Also talked to the engine shop and they are about to order parts and get the build underway. This may be my last chance to ask before wrenches start turning and I wanted to ask if anyone see's any issues with the build plan below.

3 angle valve job / back cut the valves
Keep the 1.65 valves (75 head)
2V conversion to run an Autolite 2100 1.08 ( I have 2 of them off of 302 V8s that I got with a bunch of spare parts so I figured I would try them)
New cam - something in the range of the 264/274-112 From CI
Duraspark ( will get one from a Advanced or Autozone for a 78 Fairmont)
Port divider
Headers single outlet to dual outlet muffler.

Bill