The Stovebolt Site Forums The Shop Area The HiPo Shop Ported and Polished 848 Head for my 235

When I first took the 235 out of my grandfather's old '52 two ton grain truck to the machine shop the head was found to be cracked (engine is actually a 55). Kinda sad, because now I can't reuse the whole engine, but gave me an excuse to find the higher compression 848 head. Then figured, what the hell, might as well have it ported and polished. The machine shop I'm using knew a guy and sent it out. Got the results back yesterday, if not the head yet.

If I'm looking at it right, there's an improvement. I'm also going to a cam with a valve lift of .405 vs (what I've researched as stock) .299 stock lift. Looking at the .3 lift before and the .4 lift after, seems like a 23.6% increase in air flow at test conditions overall. Pictures of the before and after air flow bench tests attached.

I realize the head design has it's limitations, but for me getting the most out of it regardless is satisfying.

What kind of racing are you planning to do? Is that increased lift on the intake or the exhaust valves? Porting a stovebolt head is approximately as effective as shoveling sand down a groundhog burrow.
Jerry

Jerry,

Firstly from my previous post in the Engine Shop on using dual carbs, I get that you don't agree with MY vision for My build. That's cool. No issues from me with the difference of opinion. I'm new here, but learn quickly, so I made this next post in the HiPo forum after reading this thread:

https://www.stovebolt.com/ubbthread.../explanation-by-purists.html#Post1457237

It's a good read if you haven't indulged.

Secondly, I specifically stated in the original post, "I realize the head design has it's limitations, but for me getting the most out of it regardless is satisfying." This statement was specifically put there to state that I understand MY choices for MY build are not the cutting edge of performance, but it's what I want for MY build. It was supposed to deter people from poo pooing (your groundhog burrow analogy) MY vision and hopefully spur some positive fun conversation on the topic. I'm sure there are people here that are interested in the results of a ported and polished 235 head.

In my previous post on the dual carbs, I gleaned a lot of useful information from people that wouldn't do MY build, but were helpful regardless. You obviously have a lot of knowledge on these engines. I'd like to benefit from that where applicable, but I'd rather not at the expense of having MY vision called down. If that's the stance you would like to stick with, maybe consider not replying?

As far as the valve lift, it's the intake. My machinist and I are dealing with it and I won't have a piston come into contact with the intake valve with the new cam. I'll post how I dealt with it when the time comes.

For everyone else, I sincerely hope this post doesn't come across as too harsh. Just want positive discussion on 235 engine mod ideas as they used to do in the old days, but keep it street drivable.

Thanks,

Mark

I spent many years working with high school students who had the attitude "My mind is made up- - - -don't confuse me with facts!" I'll be interested to see some dyno run results, particularly where low end and midrange torque is concerned. The mods you're proposing will most likely destroy both, resulting in an engine that will only reach its potential at high RPM and wide open throttle. If that's what you're trying for, I wish you all the luck in the world. Doing race engine stuff on the street usually results in mediocre performance, poor gas mileage, and lots of unintended consequences of making the most common mistakes- - - -too much cam, and too much carburetion, followed closely by too big ports and/or valves. Maybe I've been all wrong in 60-something years of building race winning engines and a few hundred dyno runs, but I sort of doubt it. Good luck, Don Quixote!
Jerry

Drop by my shop in middle Tennessee anytime- - - -you're welcome to use my dyno- - - -free of charge.

Again Jerry, I'm here for constructive conversation.

Too much cam? I've read posts of your own on what level of cam above stock works. Mine is milder than that. In fact, I believe one of your posts said that the biggest benefit would be longer exhaust duration. My cam is barely over spec on inlet duration, but longer on exhaust duration.

Too much carburation? That's why I stared the dual carb post in The Engine Shop. To make sure my vision didn't go too far because I get that too much carburation is a thing. There were many posts on that thread from people who had success with two carbs and were willing to pass on advice. Not success with double digit horsepower gains, but success. I really appreciated CarbKing's advice, even though he wouldn't have done it personally.

Too big of ports or valves? If you look at the porting I had done on the print out I posted, the intake valve opening is .03 over stock. I handed my head over to an expert that understands velocity at the valve can't drop with increased air flow. A 235 head sucks for air flow, but that doesn't mean it can't suck less (or suck more, cause, you know, I want more air)

There are multiple posts on here from experienced engine builders such as yourself that indicated increasing the performance, street or otherwise requires multiple enhancements in coordination. In fact, I read a post of yours today that said an increase in performance requires consideration from air cleaner to exhaust (paraphrasing here), and you can't increase the strength of a chain by beefing up one link. After researching, that's the strategy I've been using.

Bottom line is I would appreciated if you took the time to learn about my build and offer advice on how to optimize it. I'm open to that. Try me.

PS, not hauling my engine from Alberta to Tennessee to use your dyno.

Your plan to use dual carbs is probably where you're going to encounter the biggest disappointment. An inline six with a conventional firing order of 1-5-3-6-2-4 and only three intake ports is simply not compatible with two carburetors- - - -it's much better with either one, or three. Since the firing order only allows the volume of one cylinder at a time to flow through each port, it makes much more sense to go with three small carbs if you intend to get a small, but measurable power gain over the conventional single carb. By choosing a carb that can handle one cylinder's volume on each intake stroke, you'll keep the venturi velocity up through a much wider range of RPM without encountering the dreaded flat spots, backfires, and other gremlins the dual carb system will create. The only hair-pulling frustration a triple setup creates is trying to keep all three throttle plates synchronized. Jaguar, Austin Healey, Nissan, Toyota, and a few exotics such as Aston Martin have all opted for triple side draft carbs on inline sixes, and the 235 Corvette also ran three Carter side drafts. If you've got a few thousand bucks burning a hole in your pocket, scavenge up a Corvette setup, if you can find one that's not worn out or cobbled up to the point it's completely useless.

The only reason to raise the compression ratio above around 9:1 is to compensate for a long duration camshaft profile. The compression pressure (not ratio) stays approximately equal to stock compression, as a lot of the compression stroke id used up by the intake valve duration, resulting in a shorter distance for the piston to actually squeeze the mixture before the spark plug fires. A short duration cam and high compression promotes detonation. That requires the ignition timing to be retarded, which negates the advantage of matching compression, cam profile, and timing advance to the desired RPM where you want the power gain to happen. One of my customers about 40 years ago insisted on running 12:1 compression pistons and a stock cam in a 1968 Morgan +4 (Triumph TR-4 engine). He detonated the tops out of the pistons in a very short time, even with the ignition timing set AFTER TDC!

I'm working on building a 3-carb setup for a destroked 230 engine that's still on the drawing board- - - - -around 200 cubic inches, NASCAR connecting rods, forged pistons, some extensive port work, a roller cam, and three Keihin side draft carbs designed for an 80 cubic inch Harley Davidson EVO engine. If everything comes together as planned, the engine should pull strong from just off idle to over 7K RPM, with no noticeable flat spots. I'll probably use a head for a 194 engine, with smaller combustion chambers, ports, and valves to begin with, to avoid losing low and midrange performance to ports that could ventilate a Kentucky coal mine! It will be one of several engine options in an Excalibur fiberglass kit car, running anything from a Mercruiser 4 cylinder, to various inline and V type 6 cylinders, and a 250 cubic inch small block V8. All those engines share the same bell housing bolt pattern. I'm not against high performance- - - -I just hate to see a newcomer to stovebolts waste time and money on projects that have disappointed people for decades.
Jerry

I have my dad's Superflow air bench in my basement, and have flowed a number of heads using it over the years. I have not had a 235 head on it, but have had 250's and lots of Pontiac's. I am a little surprised to see the operator had 3.5 cfm flow with the valves closed ( .000" lift ) on both intake and exhaust when doing the final check. That shows a leak in the machine or the head somewhere. 3.5 cfm is enough sway the results through out the whole range of lift. I left a sparkplug out once after days of porting, though I had done a really great job, it made a huge difference, and once installed my porting wasn't nearly what I thought it was. The changes made to your head will likely not hurt any of the performance, the change is minimal when looking at flow numbers and the higher lift numbers should help some when you get out to the passing lane. What I really don't like is the second and third pages with all the " calculated " numbers from the computer program from Performance Trends. PT makes really good programs, dad and I have used them for years, but what you have are based on a AMC engine with your numbers plugged in to it. Not that any of the numbers really matter or that you could change any of it, just be aware. The only thing you need to look at is the actual before and after. Flow benches are like dynamometers, each is different and each operator is different. My heads won't flow the same on two different days, let alone two different machines. There are correction factors that need to be set in place everyday, air pressure, altitude, humidity, all can change flow rates, even machine temperature can change numbers. When flowing 250 cfm heads, I have to stop and cool the machine down between lift ranges or the numbers fall, hot air doesn't flow as well as cooler air. Post some pictures when you get the head, and remember this, way back when when racing started, nobody had test equipment, most all of it was done in back garages by guys just like us trying something NEW.

OlBetsysDad Hey your on the HiPo forum,do whatever you want to,it's your truck !! The 235 I had turboed ran like a bullet,the four barrel AFB one (homemade manifold) ran good,283 2x4 cammed one done 70 mile round trip to work daily never let me down,327 .060 over /with overdrive homemade unit 50 mile roundtrip daily never let me down, 54 with reworked hydramatic mom (wife) used it to haul her flowers !! So hang the naysayers,My current 51 6400 ,98 inch wheelbase pickup,8.25 rubber,tandem axle,HEI,Propane burning,coil spring 4 link outfit is as good as any of that other stuff I described,no sludge,oil stays clean,not cold natured,starts without a gasoline wash down of the cylinders each morning just bump it !! So build your engine any way you see fit !! Oh I also put in hard valve seats and do ALL of the above at home.

Your time on the flow bench is interesting to say the least! I have run all kinds of cams in my 235 and 261 motors. My current cam in my 261 is .492 and 282 degrees. I drive it on the street and run it down the track on occasion. It’s an enormous amount of fun. So I am always tinkering with what else I can do to my motors.

So what did your guy do to the head?

Here is one of my motors

I like that you took time to add flow bench numbers. As anyone who works with these engines knows the cylinder heads are the biggest limitation to making power. These engines where designed for low speed torque, basically as is often said here "A Tractor Engine". Jerry is right with his observations but there are those of us who just want to push the issue a little farther.

I have worked with a 292 head, modified with use of lump ports and some combustion chamber work along with port matching. I don't have access to a flow bench so there are no numbers to back anything up. The end result was a very strong running 292 (bored to 301) with a great lope to the idle and responsive throttle. You will need to do your homework. There are several sources for information, the book I keep returning to is "Chevrolet Inline Six-Cylinder Power Manual, 2nd Edition by Leo Santucci". There is a tone of information and refences in this book.

If you just want to watch something on building a Hot Rod Six, Stacy David did a segment on Gears, just worth watching.

In the end it comes down to "It's your Truck, do what you want". I'll be following along.

I am interested in how the "correction" is done so you end up with significant flow at a lift of 0.00.

Flow bench (and dyno) numbers can be massaged to achieve a lot of results that have been pre-determined to be the desired outcome. It's sort of like "researchers" who depend on grant money to keep their jobs "finding" the results their donors want to see. One of the sneaky tricks dyno operators use is to run the RPM up to a specific number at no load, and then throw the brake on full instead of slowly advancing both RPM and load. The inertia of the rotating assembly will give a false torque reading, which can then be used to give an erroneously high HP number. There used to be a saying in the pits at the local round track- - - -"Horsepower is to brag about- - - -torque wins races!"
Jerry

I just think its interestting to see that some work resulted in some improvement. Would still like to know the extent of the porting work. I would love to have access to a flow bench. I might never come back into the house.

I've used the output air from a shop vac and a water manometer to do comparisons between ports at various valve lift settings. All it takes is an adapter between the vac hose and the port which can be positioned accurately and a flow control valve to bypass some of the airflow to prevent overloading the water column. The setup I built cost less that 50 bucks in supplies, and took about four hours to build.
Jerry

Dragsix That is interesting on your setup,best way to find out stuff is put it together and try it !! You do that regularly !! Have been on the hunt for lifters they are expensive. Have you had much experience with reground lifters ?? My current Kwik-way valve machine doesn't do lifters,aa friend with a sioux machine may be able to have to check that. Checked with Ed Iskendarian he still offers 235/261 stuff but big name big price.

It looks like the (successful?) porting work has also affected the intake-to-exhaust flow balance.
Take this into account if changing cams: more exhaust duration than intake.

Lifters are a pain. I am alsways on the hunt for them. At the trifive nationals, I picked up an NOS set of TRW 55-58 hydraulic ifters USA made in 87. First I have come across in a good many years. As for resurfacing, my vote would go to Rocker Arms Unlimited in California., Besides correct rebuilding of the chevy rocker arm assemblies, they also regrind and resurface lifters.

Dragsix Where are you getting your solid lifters ?? All the sets of lifters I see are $$$$ !! Didn't see much stovebolt stuff at frog follies. Iski cams are a fortune,didn't check 6=8 but probably expensive. Bought a ccs-1 170 $ looks fine but need lifters !!

Ebay, Craig’s list, swap meets, classifieds. I have one set of Johnson solid lifters, 45 years old, USA made. Last set in my stash. So like you, I am on the prowl.

That being said, I have not heard of many issues with the new manufactured mechanical lifters. Use the recommended break in grease for the cam, use brad Penn (now Penn grade 1) brake in oil, do a proper brake in and I think you will be in pretty good shape.

Expect somewhere between 12 and 16 per lifter.

Dragsix Thanks for your reply on lifters,will just stay on the hunt or find a way to machine grind my own. Have several cores laying around,may need to build a jig for my refacer think it's a 51 inch circle for the radius or 1 degree.

Mike, do you happen to know what radius is on the bottom of a lifter? It would be very easy to assemble a fixture to dress the bottom of a lifter back to the correct radius, using a long bed lathe and a tool post grinder or a die grinder.
Jerry

I don’t, and truth be told, I don’t know that I have ever actually seen the specification in print.

One of the other challenges I often have when taking apart a 235 that has a lot of miles on it or has been sitting, or a combination of the two, is getting the lifters out without damaging the sides of the lifters. I seem to run half and half. As in half the motors need some sort of persuasion that scratches them up a bit.

I have never reused a lifter and have always been able to source new USA made lifters but that is getting to be more and more of a challenge with each passing year.

I've usually been able to work the lifters up high enough in their bores to slip the cam out, and then use a wooden dowel and a hammer or a dead blow mallet to tap them out from the crankase. With the cam removed, they should also be able to go out the bottom of the bore. I've got a 216 block in the process of a bunch of oddball modifications, including having the lifter bores sleeved down to use AMC/MOPAR lifters. They're a few thousandths smaller diameter than stovebolt lifters, and a LOT less expensive.
Jerry