yes, a big port is not neccessarliy better than small port , if the small port design flows more air .....

 

vic jrs fugger!!!!!

 

Personally, you would be suprised with the AFR heads.

 

I say there is extremely little difference in port volecity when used with boost. How much laggier could it be really? I mean that turbo fills the intercooler & charge piping, it isnt going to "lag" with a 4" long runner for each port in the head, come on lol!

I will stick to my opinion & its worked really good for me. My laggy, overheaded & overcammed motor runs great, and is only gonna get better. I still say, less boost = less heat = more timing = more power. At the end of the day its just a number & not relative to any motor really, many different ways to skin a cat.

-Carm

 

If I were in his shoes I'd stick with the 185s, but ^this^ is something I'll almost always agree on. Always liked your car too btw.

 

fixed

been down this road,
probaly more being a problem with fuel and how it stays in suspension , in the port etc....

cheers

 

The turbo does fill the piping and ports quickly, after it spools. Off boost power and throttle response is something you never worry about?

 

Off throttle response here is GREAT. I dont know about you, but my BYPASS VALVE is open @ idle & at part throttle say 1500rpm, and there's air coming out of it. Do you think a port size 40cc smaller is going to speed up the air through the runner that much when THERE IS AIR BEING PUSHED TO THEM ALL THE TIME??? Oh i forgot to mention, this is based on FACTS - SBC 400 with twin MP 70's both with .68 & .96 housings.

Do you think an N/A MOTOR has air being pushed against the intake valve all the time??? As far as im concerned, port volecity doesnt have any effect on these types of motors, and especially less with a blower. There is no "keep the velocity up to improve your throttle response" bs here, its getting FED AIR at idle! You'll get way more throttle response by bumping the compression or going with a smaller cam, then with 185 vs 225 heads.

-Carm

 

A 185cc head is a small head for 393ci's. I'm fairly certain it wouldn't be top choice for any of us if we were building an all motor n/a 393ci stroker engine.
Sure they will work, he can run them just fine and I say go for it.
But he can make more power with less boost and heat with a larger head as Carm already stated.

 

You have a valid point... But there is a point of going too large of a head on a turbo or even blower motor... So just throwing the largest head on a motor isn't a true statement. I have seen many times were a person places a killer set of heads on a motor but due to the miss match with the cam and turbos they can hardly make the thing run great. In applications such as this the car will launch hard yet when the motor gets in the higher RPM band the turbo and cam fall off because they can't flow the air that the heads require.

 

HMM i dont know if i agree with that entirely either, for the following reason...i've talked to a few different cam company's in the last few days & they ALL seem to say 1 thing thats the same, the turbo/blower will still feed the motor even if the cam is on the small side.

I dont see HOW you could lose power with going to a larger head. At X amount of valvelift, head to head, all things being equal, pound for pound the larger head should & will make more power than the smaller one, its not rocket science. As for spoolup characteristics, i still dont think its even worth mentioning, i'd be surprised if you could even see a difference in time. Like i said, if the turbo can fill 3 1/2" charge piping & intercoolers, a runner thats a few inches long multiplied by 8 and maybe 1/4" wider at the most will NOT have a problem being filled. Just makes sense to me...

-Carm

 

I think the arguement is that a turbo motor is really an NA motor until the turbo spools. So if you have a torquey 185 headed NA motor it will flow more air down low than a high revving motor. Since the 185 headed motor flows more air down low it will in turn spool a turbo quicker

 

not really saying its the extra volume in the heads that are gonna take longer to full

 

^^^^
those heads he wants to run will be fine..
with the rpm range you want ( and more too), put them on , and go have some fun

T/A
it looks like you have ur mind made up about having to run large heads, thats ok, because every one 'skins a cat different".... but ill leave you think thought, and tell me why it worked.....

i had 166cc iron heads, 1.9 intake ,1.5 exhaust on a 355 ttsbc. made 1016hp and 960 ft/lbs on dyno. went 7.2 @ 191 in my current car.
i changed to a different head , to allow bigger , better , badder cams etc. head is a 238cc , ported to flow 630 hp.....
lol, car went the same .... slightly slower spool.

These are my $20 heads, from the junk yard. oem 882 cast iron 166cc intake runners
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Here is the fuel drums from the R & D session on the dyno ....i didnot talk to someone for my info, i actually got it by testing stuff.
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yes, i used methanol, WHICH in fact should have been worse , due to extra fuel in the intake runner , displacing the air /oxygen ...
got bigger turbos now, but thats a different story to tell.
car runs 6.69 @ 204.98

the spool up in drag racing is fairly important, and quick air speed down lowe in engine rpm, i feel is important.
this is a laurnch....
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this is the time slip:
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yes, i would put larger heads on, for the rpm was alot higher..
but for what this guy is doing, the 185cc will be fine.
cool discussion.

 

Sometimes things that seem to make sense don't when it comes to racing, a few years ago I thought the same thing about running the largest head possible. But if the turbo can't fill the area (runners of the head), you will run into issues with spool-up and drastic loss of horsepower. This is especially true if you have a combination where the cam and turbos are small or marginal for the combination. What will happen is when the motor reaches the upper RPM band, it is utilizing all the air that the turbos are capable of producting and because of the larger volumn of the heads the turbos will spend more time trying to replenish this used air in runners. Because of this and the larger runners, the turbos WILL struggle to keep up with an oversized head. Which in turn creates a lower boost pressure in the intake which equals to a loss of horsepower.

As for running a smaller cam, yes you can run a smaller cam and still go fast. That is if the heads, turbo, and RPM band of the motor are matched within reason. Granted with a smaller cam on a turbo/blower motor, you will decrease the overall performance of the motor and depending on how small the cam is will determine how much of a limiting factor. Because you are correct, even with a small cam you have pressure in your advantage forcing air into the cylinder. Even so this isn't what is being discussed, this is a different topic when talking about the larger heads.

I will admit that the AFR 185 heads are not optimal for this combination, I would look at the AFR 205 or AFR 225 if I was buying new heads. But seeing he has the AFR 185 heads I would run them. IF you think you can use math to figure this out good luck, many of the guys that have gone fast have all went through a huge learning curve that has costed a lot of money and time. But what do I know....

 

Didn't Nate make 700+rwhp with a set of TF street heads with a 393 @15lbs? I would think that the AFR 185's would make even more power. How fast do you want to go? Sure a set of larger heads will make more power but how much will it cost you to upgrade. I would run them. If they don't make enough upgrade them down the road.

 

Mr ASH are you saying that you made 1016hp and 996 ft with 882 heads on a 355 sbc ?

 

yeeh,
actually the dyno sheet is posted on here....some where..


960 ft/lbs..my mistake

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well I have to say WOW can you give any specs on the engine combo ?

 

Im hard headed....my mind wont change. I will tell you one thing, those 166cc heads look like theres a lot of work done to them... Regardless, i will stick with the biggest head i can and fill that phucker with lotsa boost

Ash, no wonder that car runs like that!