97TA-WS6-Con

Ok guys. You technical guys.

What am I too look for when it comes to heads and head work for a blown motor?

I have heard that good heads are not AS important for a blown motor as they are for an NA motor. I have also heard that exhaust numbers are more important then intake numbers.

For the purposes of discussion, as I'm sure it could go all over the place, assume my motor. 224/230 ls 114 can about 544 on a 1.6 rocker. 15# D1 on a 383.

If I'm shopping for heads, what is important? What are considered "good" numbers? I know it comes down to having my stage 1 LT1 heads worked, some AFR 190's or possibly 210's. OR I could get some LT4 heads.

Now I currently have LT4 valves in my heads. They are 2.00 / 1.55. Would they be an acceptable valve to leave in some worked LT4 or 210 AFR heads? They are suppose to be cool with hollow stem and sodium filled. Or would I just get some new 2.02 / 1.60 valves.

If intake numbers are low'ish but exhaust numbers fairly high, would I care? (example 241 intake at .500 and 192 exhaust).

I want this as daily drive liveable. Not pushing above 6200 rpms and want low end torque rather then high end power.

Thanks folks.

Lonnie Pavtis

This is hard to define, but here goes...

The exhaust port will have a great effect on power as the supercharger dramatically increases the exhaust volume.
Bigger is generally better.

For the street, keep in mind that a big intake port will be lazy at part throttle, but will help at full throttle (under boost).

Nicely ported LT1 heads are approximately 195cc intake... similar in volume to LT4 stock heads, but ported LT1's are better flowing (using a typical CNC unit as example). This gives good drivability on the street.

Ported LT4's will generate more power, but will result in slightly less part throttle torque. Generally a 205-210 cc port size.

Big flow numbers are meaningless if the cam does not open the valves far enough. Big flow at .600" & .700" (where most race heads perform) is no good with only a .500" street cam.

Flow at .200" lift will result in good midrange power & response.

If considering the big heads (AFR or similar), plan to match it to a fast acting, high lift cam. (preferrably a solid roller) for best power.

For comparison, flow under boost can vary significantly from flow numbers drawn through the port..... most do not have flow tests to support this, but it can be very different.

Sodium filled valves are a way to make them light & still transfer heat to the seat. GM basically did this to allow RPM with light tension springs. (helped fuel economy by lessening frictional losses) I prefer severe duty Stainless valves for safety. Larger diameter valves are generally not detrimental to low end response, but will help marginally in top end power.

Hope this general overview helps a little.

97TA-WS6-Con

Thanks Lonnie.

I noticed from your website we both have VERY similar setups. At least your stage 2 set up.

Thanks for the advise.

Some follow up. Would a 240 / 195 flow number at .500 be a "good" number for a blower car? The exhaust number is fairly good but the intake seems low. For a daily driver car would that "low" number possibly be a GOOD thing? I guess I would want to look at the .200 - .400 range, but again, is a low intake number possibly attractive given that the boost is starting to come in anyway?

My cam specs are 224/230 114 LS 536/544 @1.6. Does that qualify?

SStrokerAce

It all depends upon what you are looking for. If you are looking for a all out Blower motor than there are alot of things you need to do for a blower head. My short answer is maybe, a 80% E/I ratio is getting closer.

First, Valves. Get the biggest exhaust valve in there! That will be the first step to making the exhaust port flow more air. You don't need a intake valve bigger than a 2.02 in a small block blower motor. A BIG Exhaust valve like a 1.80 is pretty dam good!

Second, the exahust flow needs to be as good as possible. If I could have an exahust valve flow 90% of the intake on a race blower motor I would take it!

Third, look at these numbers http://www.totalengineairflow.com/pr.../lt1/index.htm Then see if what you are talking about is good.

One thing that matters big time in a high power blower engine is the intake port volume and the minimum cross sectional area in intake port. Once you start drawing/blowing air at too high of a velocity it will limit the hp level at some point. You'll see it level off and not respond to cam changes and higher boost, all of that will not matter.

You would need more lift to look at a race head. Blower heads do not need high lift. You can do it with duration if you need more lift area, but usually you don't need a large amount.

For example the Top Fuel engines don't open their valves nearly has far as the Pro Stock guys. Pro Stock engines run more lift and more RPMS, but also have to use a transmission and real gas. Still the principal applies here.

I hope that helps more. I'm tired, eating dinner and having a beer after getting back from the shop! (1:30am)

Is this a street car? daily driver? Race car? and how much HP are we looking at here?

Bret

rskrause

Well, Lonnie (glad he's back) and Bret have summed it up pretty well. Just a few thoughts: in a way, it's true that heads are relatively less important on a blower car. This applies to building a fast street car, for sure. With relatively modest heads and boost, you can reach "big" horsepower (in the context of a street car) easily. There are a lot of cars in the 500rwhp range with minimal head work. As an example, at one time, I had stock heads and cam and was making ~450rwhp. A cam and some valve springs would have added another 30rwhp or so quite easily.

OTOH, if you want extremely high power, heads are every bit as important for a blower car. But there are some twists to the story. As Lonnie and Bret explained, the exhaust flow is a big issue, but the intake flow can be a limiting factor as well. And as with an NA car, if you are talking street use, excessive intake runner volumes cause part throttle/low speed issues. One other thing to consider is that no matter how good your heads flow, you can't flow air beyond the capacity of the blower, so you can "waste" money on heads, in a way.

There are lots of permutations and combinations to consider. As Bret said, if you post some more detail about what you have in mind, your budget, etc. you may get more specific answers. In terms of head choices, modified LTx castings are fine for low to moderate boost levels. I like the AFR as a starting point in high boost cars. The thicker deck is nice to help gasket retention, but more to the point is that the larger CC volumes allow you to achieve an appropriate CR without a huge piston dish.

Cam choice is a very long topic. Knowing more about your plans would really help focus any comments in that area.

Rich Krause

97TA-WS6-Con

Thanks a million guys.

Here is a little more info about what I have and what i want.

Forged 383, 9.2:1 CR, ATI D1 with 15 Lbs pulley. Installing a FAST now. This is a daily driver for 8 -9 months of the year and I want to go to the strip 10 times a year. I'm more interested in mid range, streetable 'fun' then 7000 rpm 135 trap speeds. I also have a M6.

I currently have some moderately worked LT1 heads. They have 2.00 / 1.55 LT4 valves with Crane 10308 springs.

Numbers are
200 128/121
300 166/146
400 211/168
500 241/177
550 244/181
600 248/186
Note: the exhaust numbers have been 'corrected' - for barometric pressure I gather.

I saw 527 rwhp before having fuel issues.

The car is apart for a refreash - new rings particularly. At this time, I'm wresteling with upgrading my heads. My target is 600 -625 rwhp and I'm sure I can get there but this is the last time I want to crack open the motor for a long time. In other words, I want to "finish" my modifications at this time and need to know that I have arrived at my final destination. I'm just not sure what route I need to follow to "finish"

Fundamentally there seem to be 4 choices.
1. Work the LT1 some more. Perhaps change valves? or can I live with the LT4 valves?
2. LT4 worked heads. Nice idea but would increase my CR.
3. AFR 190's. These look like an interesting option.
4. AFR 210's / 220's Will the runner be too long and would I give up low end torque?

Of course the next question is, too I CARE about giving up low end torque. It might be argued that I already have more then enough to break the tires anyway.

After I conclude which of the 4 options to proceed with, and given that I know that bigger exhaust numbers are what I'm looking for, what do I want to see on the intake side?

And then finally, value for money. The AFR's ARE attractive to bring down the CR and the thicker deck height but the LT1's probably represent the best value for money option.

And one final question: how much variablility can one expect to see between one flow bench and another? Is it possible for one bench to say 260 and another say 280 and both operators are being honest - for want of a different word?

SStrokerAce

There was a post in here before by Mr Horsepower on cheating a flow bench so it can be done.

You should just have the LT1 heads worked a little more on the exhaust side. The intake side can be touched up more , but don't go beyond about 195cc of runner volume. Make the exhaust side flow much more.

That's my quick take on it.

Bret

Lonnie Pavtis

97TA,
Your heads seem a little short on flow at higher lifts, but not that bad. Flow numbers are for reference & do not always result in power gains.

You are probably seeing 10-12# boost with a D-1 & 15# pulley on a 383. Also 2# boost at 2500 is possible & should help out any midrange laziness if you go large on port volume.

I wasn't aware that your cam was a solid roller.

I have the intake flowing 265@.500-.600 (respective flow of these is over 300 when fed in the positive direction) & the exhaust 210-212@.500-.550 on a set of LT1 castings. For comparison these heads on a 9.3:1comp 383 with a 220/230 114 cam, has more low end than the stock engine. It will pull 6th gear at 900rpm on a grade (36mph) whereas stock in 6th below 42mph it would shudder.

My .200" #'s are 130/109 int/exh for comparison. You are already better than this....still in the good streetability range with your combination. Keep in mind as you port more these #'s will generally decrease. I mentioned these #'s as many "big" heads will not perform well under .300". Less of an issue with aggressive solid roller profiles as these cams spend considerably more time above this lift. On a low rpm street motor this helps your low end efficiency.

You could work on your heads a little, but I would consider using some good aftermarket valves. An undercut stem & head, 2nd back-cut on the valve & stainless material in the stock size may also improve your flow while adding durability. The heat from a high HP blown engine would worry me with stock valves. It's not pretty when the head comes off the valve.

Hope this helps.

INTMD8

One thing that matters big time in a high power blower engine is the intake port volume and the minimum cross sectional area in intake port. Once you start drawing/blowing air at too high of a velocity it will limit the hp level at some point. You'll see it level off and not respond to cam changes and higher boost, all of that will not matter.

SStroker ACE, can you go into some more detail on that statement? What happens exactly when intake air speed is too great?

Ai

Mm.. no time to talk aboot it now, but heads are every bit as important on a blower engine if you're going all out (like Rich said).

Hell, on a blower car you'll pick up more power usually with a more efficient head b/c of the higher pressure ratios involved. 75-80% E/I, but I wouldn't fret b/c I was closer to 75%.

Fast Caddie

Not trying to take away from the thread, but could you guys check out the thread I posted earlier in the FI forum? ("Heads with FI")
Basically all I want to know is if it will make any difference whether: 1)I go all-out and convert to AFR raised runners or 18* SBC race heads or 2) If I should just stay simple and get AFR 227s. This will be done on my 95 someday with a turbo set-up.

This is a great thread!