1.78 vs 1.88 intake valves

[TheCraigMachine]

Searched for an answer to this for quite a while, haven't been able to find any hard facts on this topic.

A quick rundown of the combo im working with here:
Rebuilt low compression 318 shortblock
.030 over pistons sitting .105 below deck
Fully ported 302 heads running 1.78/1.60 valves, with a .050 cut on the deck
Summit SUM-6901 cam
Weiand Stealth intake
600 Edelbrock carb
Magnum exhaust manifolds, 2 into 1 exhaust, 3" pipe to rear.
Calculated static comp ratio of 8.6:1
Lightweight early valiant.

*Not yet assembled*

I had originally kept the 1.78" intake valves based on the advice of the now discredited BJR, but im not happy with the way the valves are sunk deep into the seats after the 3 angle valvejob i had done. The exhaust valves sit nice and high in the chamber, but the intakes are way down low.

I had these heads running on another factory shortblock with this combo already, and the car ran really strong and would rev to the moon. So much so that I blew the old shortblock in very short order.

My question is: while ive got this thing apart again, does anyone think that it would be worth the ~$200 to have the heads fitted with 1.88 intake valves? Would I ever even notice the difference from before? If it would only be worth another 10 or so HP, the cost would outweigh the gain. Plus, im worried that the closed chambers of the 302's would shroud the valve too much.

If anyone here has any experience with this, please let me know! Thanks.

 

[Mupoo]

If the valve had sunk into the head & you havent got adjustable rocker gear then you need to do something about it - you may have incorrect spring tensions due to this aswell, if you don't need to fix that then forget what I just said. Otherwise if you are happy with how it is going then don't spend up, if you want more then do it - pull the little valves out, port the valve throat area to flow more and fell the ponies come in

 

[JBurch]

I know it's a PIA but go ahead and pull the heads and put in 1.88 and 1.6 valves. If you shop right, you might get them for little or nothing as used take out's.

It's a worth while up grade to a small port head.

Did this to a pair of 273 heads I bolted down to a 318 years ago, went 13.92@98mph; no data of a "before" valve size upgrade run.

 

[66fs]

Searched for an answer to this for quite a while, haven't been able to find any hard facts on this topic.

... I had originally kept the 1.78" intake valves based on the advice of the now discredited BJR, but im not happy with the way the valves are sunk deep into the seats after the 3 angle valvejob i had done. ... QUOTE]

Your feelings are correct. The farther you sink the valves, the less power you make. You only want to grind the valve seat just enough to get a good seal. The other 2 angles are to narrow and center the seat on the valve face. You may want to find another shop to do the install. This alone is worth upgrading to 1.88 intake valves. Open up the bowls under the valves to get more benefit from the 1.88. Not to mention spring heights and rocker geometry which are really messed up when valves are sunk.

 

[TheCraigMachine]

Open up the bowls under the valves to get more benefit from the 1.88

My bowls are already opened wayyy up, hence the statement that the heads are fully ported. At the point they are at now, if i were to "open" them up any further, the valve would fall into the port! Sooo, my thinking is that by going to the 1.88 will allow the valve to sit atop the seat instead of in the seat. How much more power ( or should i say cfm's) would this be worth?

I don't have access to a flow bench as of right now.

Im open to suggestions for different cam choices too. Dont want anything any "lumpier" at idle than what i got now. 3.23 rear gears and tight street converter.

 

[66fs]

then don't open the bowls anymore... Will the 1.88 intake bring the valves back up? How far down are they? What diameter and angle is the top cut on the Intake seats?

 

[moper]

The problem is "full ported" can mean a bunch of things. If the bowls are that big, but the valves aren't, I'd question the work that was done already. There should be some taper in from the valve seat going into the throat. Do you know the inside dimensions of the pushrod pinch (to the thousanth)? Do you have any clear pictures?

 

[Cudafever]

then don't open the bowls anymore... Will the 1.88 intake bring the valves back up? How far down are they? What diameter and angle is the top cut on the Intake seats?

The problem is "full ported" can mean a bunch of things. If the bowls are that big, but the valves aren't, I'd question the work that was done already. There should be some taper in from the valve seat going into the throat. Do you know the inside dimensions of the pushrod pinch (to the thousanth)? Do you have any clear pictures?

With a street eng you shouldn't inlarge the intake bowl more the 88% of the Valve so if you have a 1.78 X.88=1.5664

If the smallest part of the bowl in 1.56" then leave it as is and run it. if it's larger. then the bigger valve may help.

If the bowl diameter is already larger then 1.65 GET A NEW HEAD!

The bowl hogging is what i did with my first set of J/1.88 heads. Had no bottom end and then would scream to 7200.

With your lighter car and smaller port heads(read high air speed, Hard to make the port stall) you probably don't realize the bottom end loss as much as i did. With mine,there was NOTHING below 4000 and then it came alive.

Did you have a tack? any idea how high you were zing you motor........

 

[TheCraigMachine]

How does one get pictures from the computer to here? I took some pics of the heads as they are, but i cant figure out how to post them!

I measured the bowl below the seat, i get 1.53".
Based on that, then the 1.78s would be about right it seems.

As far as how it ran with the 1.78s, the motor had a really flat torque curve and never let up. Better than any 318 ive ever driven. I was doing about 6500 rpm when the number 3 main peeled off its first layer...

 

[TheCraigMachine]

Think I might have figured it out??? YES it worked!

I did all the port work.

 

[moper]

I think you'll be ok with the 1.88s. Have a shop that uses cutters do the valve installation and have them cut the chamber for some unshrouding - which becomes more of an issue with the larger valves. But don't do any more bowl or guide work.

 

[TheCraigMachine]

Anybody else got any input? Im still not convinced that the change will be worth the expense!

 

[Oldmanmopar]

Bigger has to be better . I am married for 35 years.

 

[Cudafever]

I think you'll be ok with the 1.88s. Have a shop that uses cutters do the valve installation and have them cut the chamber for some unshrouding - which becomes more of an issue with the larger valves. But don't do any more bowl or guide work.

Anybody else got any input? Im still not convinced that the change will be worth the expense!

I agree with moper!

 

[69 Cuda 440]

We're working on testing a set of 273 Cylinder Heads with 1.88" Valves cut down
to 1.84".

We believe the added clearance is required to prevent valve shroud. Of course the bowl area will be opened up slightly to match the required flow opening.

During our test, we will keep the 1.50" exhaust valves in place.

 

[clifftt]

We're working on testing a set of 273 Cylinder Heads with 1.88" Valves cut down
to 1.84".

We believe the added clearance is required to prevent valve shroud. Of course the bowl area will be opened up slightly to match the required flow opening.

During our test, we will keep the 1.50" exhaust valves in place.

You got any results yet?

 

[Abodybomber]

The heads are ported,69 Cuda.Actually ,a nice job! 1.88's work well.Somebody ,did a nice job.

 

[Mo-Par]

I would go with the 1.88 valves and mill the heads to get 9-1 comp while its apart. It will be worth it in the end.

 

[Saetun]

I know it's a PIA but go ahead and pull the heads and put in 1.88 and 1.6 valves. If you shop right, you might get them for little or nothing as used take out's.

It's a worth while up grade to a small port head.

Did this to a pair of 273 heads I bolted down to a 318 years ago, went 13.92@98mph; no data of a "before" valve size upgrade run.

This.

I picked up a set for mine here from a member for $20 + the ride.

 

[69 Cuda 440]

You got any results yet?

We will be running a 'Test-and-Tune' this week.

The Cylinder Heads (Casting #2658920) have a 1.84" Intake, with the intake throat opened to
1.61" from 1.52" using a 'cutting-tool'.

The stock 1.50" Exhaust valves will be utilized. The ports are gasket matched, but no porting
other than the high spots removed.

The combustion chambers have been smoothed and polished, and CC'd to '58'.

The engine has been bored +.040.

The same engine with 'stock' #2658920 Cylinder Heads that were CC'd to '58' with a multi-angle
valve job with 1.78" / 1.50" Exhaust Valves - but no port matching or combustion chamber polishing
ran a best of 12.92 @ 108.72 MPH.

We'll see what the Cylinder Head upgrade brings this week.

 

[1wild&crazyguy]

Before making improvements to the int flow with larger valves, assuming you are gonna do the blending work to make sure they acctually flow more, you need to know the flow ratio as is. If you like the way these heads work...then the best bet would be to keep the ratio the same! Especially if you are using the same cam ,intake and exhaust.

So find out the flow numbers and flow ratio at each lift , and when increasing int flow ...increase the exhaust to stay around the same ratio.

Ofcourse...you can always switch to a set of headers if you screw it up ;)

 

[TheCraigMachine]

Hey guys. I decided to just leave the heads as is, mostly due to cost issues. I was quite impressed with the performance of the heads as they were, and i didnt want to lose any chamber volume due to valve unshrouding on the closed chambers. With my ultra high deck clearance, I cant afford to lose one ounce of compression. I was going to have them flowed by a guy here in town, but I got impatient and went ahead and just threw them on the shortblock. I will however be having this engine dyno tuned, so ill keep you posted on the performance of the 1.78s.

 

[69 Cuda 440]

The 1967 Barracuda 273 is ready-to-go -

Previous best was a 12.92 @ 107.72 MPH

With #2658920 Cylinder Heads w/Stock (1.78" / 1.50" Valves) and Blueprinted
Valve Job (Multi-Angle Valve Job, Blended Bowls, Gasket Port Matched and CC'd to 58.0)

They now have a 1.84" Intake (Cut down from a 1.88" Valve), and with the throat opened to 1.61" (from previous 1.52").

And the combustion chamber has been smoothed and polished.

Everything else on the car has stayed the 'same'.

Engine sounds more responsive.

 

[69 Cuda 440]

Test-and-Tune Completed.

Performance Results, lowered E.T. (-.16)

We went from a best of........12.92 @ 107.72 MPH
To best of..........................12.76 @ 108.13 MPH

 

[69 Cuda 440]

Teak,

Car ran a best of 12.92 @ 107.72 MPH with this Cyclinder Head configuration

Cylinder Head....................#2658920
Stainless Valves.................(1.78" Intake) and (1.50' Exhaust)
Combustion Chambers..........57.8 CC
Intake Port Size..................125 CC
Exhaust Port Size................61 CC
Bowl Blended
Seat Angles Radiused
Rounded Valve Guide Area
Gasket/Port Matched
CFM................................195 CFM