porting and polishing cylinder heads. ARe these gains feasible?

[jerry S]

does this sound right?

A port/polish job that increases your head's efficiency by 20 cfm @ 28" calculates to an approximate 40 H.P. gain on a V-8

A port/polish job that increases your head's efficiency by 30cfm @ 28" calculates to an approximate 60 H.P. gain on a V-8

A port/polish job that increases your head's efficiency by 40 cfm @ 28" calculates to an approximate 80 H.P. gain on a V-8

 

[brianj5600]

That is a good theory, but that is only if other changes are made to take advantage of the extra capability. It is much more complicated than that. I don't believe the heads are your problem.

 

[jerry S]

That is a good theory, but that is only if other changes are made to take advantage of the extra capability. It is much more complicated than that. I don't believe the heads are your problem.

I don't really have a problem. I have a 400 hp motor and that is as much as you can realistically expect from a 351W bored .040 over and 10.5:1 CR. I am not unhappy with my engine. I was just wondering about squeezing a few more drops of power out of this turnip if there are in fact a few more drops in there to be squeezed. I have the chance to get the heads ported and polished and I am just wondering if I will see gains such as those I posted.

 

[jerry S]

A lot more to it and I think those gains are high. The statements are comparing apples to oranges. Efficiency is measured in percent and not directly by cfm. Generally, a good full port job and better/larger valves and improve the intake efficiency of C9OE or DOOE heads from the low 40% to the mid 50% range. In terms of cfm it's about 40-50 cfm improvement to around 210 to 220. I haven't even mentioned the exhaust port yet which is just aweful in stock form. The efficiency gains on the exhaust port can go from the mid to high 30% to the mid 50% range with cfm improvement of about 50-60 cfm to about 175-180. HP gains I would estimate to be something like 40-50 HP generally speaking (depending on other components)...definitely something you'll notice.

I have Edelbrock RPM Performers on there right now. If I were to see 40-50 hp increase from a port/polish job on my heads, I would be thrilled and call it a day. The guy will do the following for a $1000:

(Upper/Lower)

-Port match upper/lower polish the runners and port match to the head.

Heads

-Fully port, reshape runners, port match to intake/exhaust gasket, hand blend the short radi (where the hidden power is at), work and reshape into tear drop the valve guide bosses, polish the runners and polish the combustion chambers.

That includes dis and re assembling as the heads and intake are on the car.

 

[Clark]

I feel that you can make that kind of gain on a stock set of heads but not a set like yours because they are already pretty good from the box. Maybe more like 10 to 20.

 

[jerry S]

Everything I said goes out the window since you have aftermarkets. The gains will probably be smaller with that head since it's decent already. $1000 is a whole lot of money if you ask me.

All y'alls are prolly right. If what Clark said is correct, that I might expect only 10-20 hp, let's split the difference and say 15 hp for $1000, that gives me a $:hp ratio of 1 hp for every $67 spent. I figure a new blower and pistons (at 10.5:1 right now) plus labor would run me $5000 for an extra 100 hp or more. That is 1 hp for every $50 spent so I am prolly better off not bothering with the port and polish and just hooking up a bottle until I fry my pistons and then rebuild with lower compression pistons. If I could see 40 hp for $1000, then I would be paying $40 per pony, which I could live with. But $67 is too much to get just one extra horse. Once again, the numbers (as in dollars) have guided me to the right answer. thanks all:SNSign:

 

[ForceFed70]

I agree with Clark. 40hp might be feasible with inefficient stock heads. But almost impossible with performance aftermarket heads.

 

[SuperDave]

Feasible or possible?

You question if the results are "feasible". Feasibilty is a different question than than if the results are "possible". Which is it?

SD

 

[brianj5600]

I'm sorry about my first post. I did not mean to insult. I remembered this from an earlier thread.

You won't be seeing me post here anymore. I am going in the basement to start the car and run a hose from the exhaust to a bag wrapped around my head.

 

[jerry S]

You question if the results are "feasible". Feasibilty is a different question than than if the results are "possible". Which is it?

SD

Feasible as in possible AND likely

 

[10secgoal]

I don't know if I brought this up in another thread, or in one of yours. Have you thought of a power adder ? Unless you want to keep it N/A....10lbs would wake a motor up that size in a big way. It may cost more, or less depending on how you did it. But 30 cfm from and aftermarket head, like already stated, would be pretty hard. But 100hp from a blower, easy. And prolly a little more likely to get the advertised added HP

 

[67staaang]

hey i have a question for you guys. im a newb at this stuff. but if i get say.. gt40 heads. would it be as simple as just taking the bolts out of the stock heads and just bolting this on?

 

[2bav8]

would it be as simple as just taking the bolts out of the stock heads and just bolting this on?

Well, that depends on how you look at it...
Of course, you'll want to remove the bolts from the intake manifold and maybe even remove the distrubutor as well. Oh ya, the exhaust should probably be disconected and draining the coolant out of the motor would make a smaller mess.

 

[65up2d8]

Well, that depends on how you look at it...
Of course, you'll want to remove the bolts from the intake manifold and maybe even remove the distrubutor as well. Oh ya, the exhaust should probably be disconected and draining the coolant out of the motor would make a smaller mess.

Wow, the cynicism in your post rivals that of Historic and LMan.

 

[jerry S]

I don't know if I brought this up in another thread, or in one of yours. Have you thought of a power adder ? Unless you want to keep it N/A....10lbs would wake a motor up that size in a big way. It may cost more, or less depending on how you did it. But 30 cfm from and aftermarket head, like already stated, would be pretty hard. But 100hp from a blower, easy. And prolly a little more likely to get the advertised added HP

I AM going the power adder route i.e. a 125 shot of nitrous. I have new SRP 10.5:1 forged flat tops in there right now with only a few hundred miles on them. I consider it too wasteful to pull these pistons and put in new ones so I can add a blower. Just the wasted materials and labor costs are a grand. I will install the giggle gas and a "go baby go button" and be done with it. Ironically, I had specifed 9.0:1 pistons when I discussed the rebuild but my instructions were not regarded. AFter shipping the car here, I was getting ready to order a blower based on the assumption I had a low enough CR to slap one on when it occurred to me that I really did not know for sure what I had, only a hand scrawled note faxed to me saying 9.0:1 so I got the receipt and the part number sent to me. I did sum cipherin' and sum figgerin' and although I was relieved that I had not yet ordered the blower, I very disappointed to discover I had a 10.5:1 CR. So nitrous it shall be.

 

[10secgoal]

Guess there is no dish in the pistons eh ? 125 shot on top of what you have is going to be a scary ride.

 

[57fairlane]

I have Edelbrock RPM Performers on there right now. If I were to see 40-50 hp increase from a port/polish job on my heads, I would be thrilled and call it a day. The guy will do the following for a $1000:

(Upper/Lower)

-Port match upper/lower polish the runners and port match to the head.

Heads

-Fully port, reshape runners, port match to intake/exhaust gasket, hand blend the short radi (where the hidden power is at), work and reshape into tear drop the valve guide bosses, polish the runners and polish the combustion chambers.

That includes dis and re assembling as the heads and intake are on the car.

I guess the price isn't too bad if he would take the heads off the car, do the work, and then put them back on for you.

You have already decided not to do it (good choice), but I was wondering about this port job.

Polishing, I have found, isn't worth much. Polishing anything whether it be the intake (especially bad idea), combustion chamber, or exhaust is only worth anything for maybe 500 miles. After that it's covered in carbon buildup or if your carb isn't tuned, the intakes have some gas that has fallen out of suspension. This is primarily the reason for not polishing the intake: when gas tears up on the intake wall it falls out of suspension.

The other thing is the short side radius. On your performers, it has a decent radius and I seriously doubt much airflow could be gained on the intake. Doing anything to the short side of the exhaust port on any performance aftermarket head is a joke. The gains here would be minimal considering all you are pretty much doing is making the port bigger.