I'm gong to be taking off the heads this winter for valve guide work. While I'm there I would like to reduce the size of my intake tract on my Dart SHP heads.
When I bought them they were advertised as 180 cc's. The as cast size was around 195 cc's when they arrived. At the time I knew that it was not ideal for my 350 with the performance goals I had in mind.

I did a little porting on them before install and this increased the volume to about 196 to 197 cc's.
The engine has performed well in spite of the too large intake runners, but my peak torque is later than I would like and it appears that peak HP will be above 6000 RPM, my self imposed RPM limit.
I believe that below peak torque performance could be improved with smaller port runners.
The idea is to increase the velocity of the charge to improve cylinder filling both below and above peak torque. Done right I think it could improve average HP significantly enough to make my efforts worth while.

I know I could buy better heads and be done with it. I would however like to experiment with these heads and try to learn a little about porting along the way. It's a dying skill and one I would like to learn about since I have the opportunity.

The question is how to fill in the runner reliably with minimal risk of epoxy breaking loose and being ingested by the engine.
A rough texture is a must, as I've read, and maybe even anchors in the form of screws in the intake from the outside, or grooves ground into the floor to anchor it.
The floor of the runner is what I want to fill to both reduce volume and increase radius on the short turn side of the port.

Has anyone here done this kind of thing? What epoxy did you use and did it stay in the port?
For me it has to last a few years. After that it will be different heads or a different engine.
Any advice on this kind of mod would be appreciated.

 

Epoxy in heads is done regularly on race stuff...but it gets opened up regularly. I don't like the chances of it coming loose in a long term street deal.

I'd juggle cam...it will have more impact on where TQ/HP hits vs the head port size.

Rectangular port BBC stuff often peaks below 6000 RPM even though the heads can carry 7000+ all day.

I ran some killer serious race ported 207cc heads on a sump piston 350 once. Chambers were cut to 55cc so I gained some compression. Used a mild LT-1 cam w/1.6 rockers and that thing worked great. Plenty of low end, would lug to 1000 RPM in high gear with 3.36's...and scream 7000 rpm when I wanted to.

JIM

 

Get a Cloyes Hex-a-just and play with the Intake centerline....I think that is what Hotrod is saying when he says juggle. A two piece timing cover and Hex-a-just make this a bearable job.
Most street 350's like 106 Int CL.....see what you have and tighten it up to low torque curve.
I would do this before playing with epoxy....
Or try an even smaller head.....out of the box with blending.
Edelbrocks ol' RPM heads are 170cc......they are kick *** on a 350.
Sell the SHP's off....they should go quick.....
Do a killer 5 angle valve job on the RPM's and blend it in nice....

Jebby

 

Ordinary Bondo works very well but the surfaces must be thoroughly cleaned of ALL oil so it adheres well. But the question I have is why do you feel you must reduce the port volumes? The a larger port volume increases the overall runner volume which aids runner packing when the intake valve closes. I have run Darts with 200 cc ports for 20 years and I have always felt the heads work very well for mid range to top end power.

 

What I have now is a 104 ICL. Roller cam with 108 LSA, 270/270 advertised, 219/219 @.050 with .549 valve lift with 1.6 RR's

The duration is relatively short as is. My last dyno indicated that the HP could peak around 6000 RPM, hard to say as it didn't get there. It only got to 5700 RPM due to secondaries not opening all the way and peaked at 406 HP, if I calculate 30% loss through the power train and accessories, but it was still climbing.

I don't think changing the duration or lift will have the desired effect.
I'm not looking to spin it faster. The CR is maxed with the current pistons and head which has been shaved almost to the intake valve seat giving me 61 cc's.
I could take, at most, another .008' off the heads without angle milling $$.
More CR could help a bit but would require significant effort and $$ to get it, making different heads the cheaper option.

I'm at high altitude where air density suffers and this, I believe, makes the low intake velocity problem more pronounced. I'm talking 4000 to 8000 feet depending on DA. 4000 ft would be at 55*. I don't drive much at that temp.
I've read many other forum's posts concerning filling ports and it can be done.
How successfully on a street driven car is a bit of a gamble.
Like Jim says it is usually a race application.

 

Do you have access to a flow bench? That would be awful helpful to do what you plan.

You're right..that is a pretty short cam already and on a 108 LSA...and a roller. It's a single pattern so if anything it's likely not helping the "hanging on" high RPM part and favors the mid/low range RPM's.

What intake?

Follow this thread. Certainly trust Larry Meaux and Darrin Morgan. Two of the best in the world.

http://speedtalk.com/forum/viewtopic.php?t=327

They point out a good question though...our new gasolines aren't going to be as friendly to most epoxies as race gas.

As mentioned, might be easier to sell them and get what you want.

Or just spin that 'lil motor up like it should be!

"Anything under 4000 RPM ought to be pulling into a parking place"!!


JIM

 

While everyone said port size for 350 should be 180 here came GM

GM Fast Burn heads .
210 runner
2.0 intake
1.55 exhaust
........................................ ........................


You have heads that can be utilized and your posting you want to reduce there capacity , I suggest you get the right cam , induction and exhaust and you will be a lot further ahead.

 

Their was only one nut talking about reduced port size on nascar restrictor plate motors, which has nothing to do with Air density altitude.

higher altitude motors need to pack in as much as they can. Your best change would be to cut reversion by using longer duration, retarded valve events, and wide lsa like 112 or even 114

 

I understand where you are coming from diehard. My goal is to work with the existing intake and exhaust (side pipe) to maximize the desired RPM range. In this case 3500 to 5700.
I'm not looking to make a HP monster out of a 350, just a nice responsive, respectably torquey motor with a decent top end. I know I can't have it all. so 400 HP is good with me. More is just bonus.
My logic is this;
If I have suffecient velocity in the intake charge I can pack the cylinder better below peak torque and produce more torque down low.

Since I want and need to keep the duration short due to the thin air this additionally requires more velocity to fill the cylinder as much as possible above peak torque due to the shorter period of time to fill the cylinder because of the shorter duration.

If you can explain to me how with this cam or a similarly short duration cam and high DA you can pack the cylinder better with less velocity and more volume, I'm listening. I just can't wrap my head around how that could work as effectively vs more velocity.
For a greater duration cam, higher RPM engine, and at the sacrifice of low RPM torque with a higher RPM torque peak I can see it. That is not what I have or want.
These runners on these heads could be better utilized with higher RPM's and or greater displacement or for more HP at higher RPM's with this displacement. Maybe I could spin this engine to 6500 with my hydraulic retro roller lifters with better springs, but that is probably about it.

I'm looking to broaden the torque range as apposed to increase the HP at high RPM's.
If I'm figuring this right, increasing the velocity can do that without increasing the size of the overlap triangle or reducing below peak torque cylinder pressures.

 

Don't have access to a flow bench. Not one my area.

I did build a vacuum depression type flow bench last time I ported just as a comparison from as cast to my porting. It only works on a comparison basis.
I plan on doing something similar this time.
I'm not going to reduce the smallest CSA in the port. Just reduce the overall cc of the runner.

Thanks for the link I'll check it out. Have been doing a lot of reading over on speed talk.

 

A simple way is a smaller intake valve . install new seats and reduce it . That will most likely as GM showed provide better velocity. And I hope you have a a flow bench because you could as easily make it less responsive as you can more responsive

But your also using a 350 , not much torque there to gain .. If it runs well you may be better off adjusting final drive ratio.

I also wonder why your worried about any rpm over 6000

 

I agree that is what I believe velocity can do for me.
Longer duration would create more intake reversion not less. Less velocity allows for more intake reversion as I understand it.
The 108 allows for a stronger pull on the incoming charge during overlap allowing for more velocity into the chamber creating better packing giving a higher peak torque.

A question for anyone here.
Has anyone built an NA engine for high altitude use? If so what where your considerations on cam, CR and runner size and what were the results of that build?

 

Do some number crunching on a dynamic compression ratio calc. But bare in mind that it is a tool not gospel. They don't take into account the efficiency or ram effect of a tuned intakes

So like I said before retarded cam timing, wide lobe centers, as much duration as practical to fill the cylinders, and tuned intake runners/head ports

 

I probably shouldn't say this but those heads would be perfect on a 383. OTOH, J-B weld will stay on the manifold if cleaned and prepped properly. It's good for over 400 degs also.

 

Although your ports might be a bit large for your set up I agree with the above that with out a flow bench and some knowledge of what's going on its going to be hard to improve. I realize that you are wanting the fun of learning how. They used to make head porting kits that came with all the templates and sanding cones to do the work. I did a set of 441 heads and had no idea how much work it was. I probably spent 2 weeks working on them. however this was making the ports bigger, not smaller. You might also consider that the big block 396's came with heads that had 300 cc Intakes and the square port heads were that much bigger. And they made torque.

 

I would do some measuring of the port before doing anything. Those CC's can be anywhere. Just shrinking the inlet area before the short turn without considering/measuring what's going to happen in the bowl/throat area could make a mess.

I lived in Denver for about 5 years and had to get used to a different way of thinking. Actually had to do just like you and think through everything. I realized just how easy it is at sea level by comparison. I messed with big blocks mainly, but it was similar. We ran all the compression we could stand, used ported oval ports (which work great at sea level also), and larger carbs...Dominators worked well with the oval ports. Cam selection is critical to pull it all together.

You might reach out to Mark Jones at VortecPro in Colorado Springs. He builds some killer combinations using mild parts that just fly. Recently it was a 10 second 454 based deal with the tiniest "peanut port" heads, around 10.0 compression, off the shelf Summit flat tappet cam. Runs deep 10's in a full weight Chevelle..at altitude!!

If I was thinking through a high altitude combination...Mark is who I'd call.


JIM

 

Devcon is an epoxy made specifically for aluminum. Have you considered
trying an annular booster carburetor to improve the signal?

 

There's no such things as heads that are too big.

Only engines that are too small under them.

Keep the heads as they are, swap the shortblock.

 

I agree with you on this. I have read JB weld has shown that it is not ideal in sonic vibration situations such as the intake environment.

 

Exactly. I guess until you've dealt with it, it is hard to really appreciate the difference it can make.

Yes, I'm gong to cc each port. make measurements along the ports and mock up one with clay shapes to see what works well.
My intention is to only fill the floor. The roof I might raise if there is room, otherwise it will remain unchanged.
I want to fill the floor all the way to the short turn and blend it in to create a larger short turn radius.
May require blending into the intake manifold as well. As it is I know the manifold port is smaller than the head port, so it may not require much if any blending.

I have read many posts that have mentioned using Devcon, so it is high on the list of epoxies. The other one is spash zone A-788. It seems to be favored by many porters.
No problems with signal to the carb.

There is certainly the risk that I could make things worse. I have done extensive research on port shapes and designs to try to arm myself with adequate knowledge on how to improve the situation or least make it no worse.
I will build a vacuum depression type bench to flow the heads with a vacuum cleaner. It's what I did the first time I ported. I can get about 19" of water vacuum that way. I'm also aware that not every improvement shows up on a flow bench. Port shape is critical to a functional port.

Worst case scenario I have to pull the heads and undo what I did or move up my plans to get better heads.
Education can be expensive. Anybody looked at the price of college these days? And that is learning 90% BS that has no practical application in your life or career.

LOL that's one way to look at it.