I wanted an engine with a better flowing head and higher compression for power and economy but I want to spend as little as possible for machine work and parts seeing how I have very little money for engines and cars and such.
I thought about intake valve to exhuast valve size ratio of the slant six and compared it to other engines and came to the conclusion that the slant six could use a much larger intake valve while retaining the stock exhaust valve. By only installing larger intake valve I cut my machining costs and parts needed. (Please share thoughts)
So I installed 1.81" big block mopar exhaust valves on the intakes and extensive bowl porting on both the intake and exhuast ports. I left the runners and floors pretty much stock, just gasket matching.
Had the head milled .100" and the deck milled for a 10.2 comp ratio. Enginebldr 340 springs and retainers and they even come with the single groove keepers needed for the new valves!
Put it together and the pushrods were to long. A good time to try my cut and weld rockers rather than buy new pushrods. Plus the comp 264 cam I have has a little less lift than advertised.
The stock rockers averaged about 1.47 ratio. Now they're about 1.58 after cutting about .070" and I was able to adjust for pushrod length.
We'll see how they hold up, so far so good. My welding skills I would describe as average at best so they're not so pretty but I think they're strong enough.

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Franklin
'61 Valiant

i used a 360, 1.88 cut to 1.80, on my high compression engine with a 1.60 ex valve, i worked really good. nice looking pocket work on your head.

Hi,
Did you do this to a 170 slant 6? If so, would you use the same approach on a 225? Would like to hear how it responds to valve sizes you chose. Cool project! nico

Nice work and nice pics!

Some folks have also moved the Int valve over toward the exh and used a smaller exh valve to change the int/exh flow ratio. 1.80/1.40 or thereabouts without bore notches.

Lou

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Home of Slant6-powered fun machines since 1988

it was a 225,i went from a .030 over bore with 318valves and 10.7/1 compression running 13.40et`s, then i went .060 over bore 360 valves and 11.4 compression running 12.80et`s,the 60ft times really pickup with the extra compression, 1.90`s to 1.70`s.

Be sure to check your spring pressures... the BB Mopar valves tipically use a taller spring and a 1.8 installed height. 340 springs are shorter.
DD

When/where is there benefits for the larger valves. I know that it's common practice no matter what engine you run. I've seen EngrBldrs valves commonly used for cam/compression/carb builds. I haven't seen such large valves, but I'm very interested now.
Why did you go with a larger intake and same exhaust? What would be the benefit of one being larger over the other for N/A, super, turbo builds? Last, can you cut down exhaust valves? Sorry for all the questions at once, but I've been curious ever since I realised that 302 valves would work or a lot of chevy stock ones with some minor modifications.

Depends on what you want to do and how you chose to get there.

For me 1.72 intake and 1.50ex works...in conjunction with a split duration cam (280intake/270 ex)

Mebbe Mr Hemi runs a long exhaust duration cam.......or mebbe big lift on the exhaust.

....I bet he isnt terbowed.....

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Yeah....Im the one who destroyed this rare, vintage automobile.....

I bought the valves directly from Ferrea in FL.
Part #F5053 1.810" X 3/8" X .4910".
I had to use shims to get the right spring height but it wasn't much. I made sure they didn't sink the valves down when they machined.
I'm runnin a comp 264 cam just because that's what I had. My thought was the slant head needed more help on the intake side.
This is just a high compression daily driver motor.

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Franklin
'61 Valiant

With a 10.2 comp ratio I assume premium is what you will put in the tank? What is the rule of thumb for pump gas? How much can you get away with? I know that with more overlap you can bring down static compression. Just curious, thanks!

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66 Lil' Red Piggie Valiant (Mater Crusher) - Thanks Zilla!!!!! 72 Demon (Number 1 Son's)

There are 3 easy ways to measure compression.

You refer to " ten to one"....that is static compression ratio. ,,,,a calculation based on cylinder volume BDC compared to volume at TDC.....mine is 9.5:1

you referred to overlap ....that is a component of dynamic compression ratio ,,,,a calculation based on static CR and valve timing.....mine is 8.48:1

another way is cylinder cranking pressure....mine is about 165/175lbs

All these numbers work for me....today with todays 87 fuel on the right day....sometimes

I spent a ton of time with several on-line calculators before I chose a cam for my already established CR. I chose a Dynamic CR I could live with on the street.

Performance requires homework....or a ton of guess and try

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Yeah....Im the one who destroyed this rare, vintage automobile.....

My junk is at just about 11-1 static. It ran well on regular 87 back when I drove it on the street.

It would pick up about a tenth on 93.

It would slow down 2 tenths on 100.

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Official Cookie and Mater Tormentor.

Sandy and Zilla thank you! If I was building a a Chevy ( been there -couple of smblks) or a 318 ( major sleeper) or a 440 (my personal fav) I think I would have fewer questions. Sure I had help. But........ I have learned more by screwing around with this six cylinder then all of the above. I enjoy the challenge. I am a teacher and I want to thank ALL of you for taking the time to teach me!

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66 Lil' Red Piggie Valiant (Mater Crusher) - Thanks Zilla!!!!! 72 Demon (Number 1 Son's)

+1
I'm planning on helping a friend with his 70 Firebird and building the engine over getting a Pep Boys rebuild. I've learned a ton from this site and continue to read and expirement hoping to try and give back too.

Your in deep poo if Sandy and I are teaching.

At least my shop is closer to you than his is.

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Official Cookie and Mater Tormentor.