ziggy89

hey guys pulling the motor out of my car cause it needs a good going through. while its out im going to install the long tubes on it and thinking about swaping heads.

the motor now is a 383 stroker about 10:1 compression xe274h comp cam dart iron eagle heads (72cc chamber 180 intake runners with 2.02/1.60 valves) performer rpm intake and a holley 750 up top.

my thoughts are about swapping to afr heads with 195cc intake runners and 75cc chambers. ill save some weight and hopefully let it breath a little better up top. my only concern is the motor now makes gobs of torque and I love it. drives daily like a dream (for a hopped up sports car that is)

just wondering what you guys thought good idea/bad. if it aint broke don't fix it etc. etc.

1gary

Depending on where you are on the quench,you could go with aluminum heads to 10.5 on pump gas,but 75CC's ant going to cut it.The 195's are going to move your torque curve up,but given the 4.11's,it should be all good with a matching cam to the SCR.It then becomes a question of how high in the RPM are you going to spin it and what the bottom end you own that can handled it safely.

I went the same route(sort of)as you for Iron Eagles 180cc's.But I decked to block,matched the pistons,and cut the heads to 67cc's for a good quench number and SCR.

Orr89RocZ

iTrader: (20)

Imo you will make more power everywhere and not lose a thing. It will be a completely different animal and go 65cc chambers with aluminum and recurve the distributor

1gary

This thread is a prime example of how people can and should tailor a power curve for a intended use.The idea of people who do things because everyone else does is a poor excuse for a bad build plan.The positive side of that statement is all intake runners of the same size are not equal from different companies.The fact the cross sectional size and shape of a port does make a huge difference.


So for ET racers that want to 60'/330' where a bulk of ET is made,torque is important and in the same hand for a game plan to run a car out the back door for mph a tailor build in higher rpm for mph,a build plan should be made for that.

In the same hand,torque is king on the street driven vehicles. It is a power curve that presses the flesh against the seat.

Point being two fold.Iron RHS VS AFR's are not even in the same church or pew.Bigger is not always better either.All of it depends on the intended use.

Lastly,if you go up in intake runner,you will move that power curve up and to capitalize on that much is dependent on what is in use after the flexplate or flywheel.

Orr89RocZ

iTrader: (20)

Bigger isnt always better but in this case that motor will wake up. The eagle 180's are crap out the box. I dont have data on the csa but for a 2.02 valve flowing 208-220 cfm isnt great. Csa i would expect to be around 1.8-1.85 sq.inch and the Afr is only marginally bigger at 1.96 sq inch. Yet afr flows 280 thru a 2.05 valve without much increase in volume. That means more port velocity and velocity is what makes torque and fills cylinder. Cam and intake on that 383 want to go to 6k rpm. Let it eat with a head that will support it.
Even dart shp 180 aluminums would wake up that motor

AutoRoc

iTrader: (1)

Good up grade for sure. ID do 65cc chamber. Close to 11:1 comp would be nice.

This combo should have a 4000 stall. With your trans and gear/sticky tires..it will be nearly untouchable on the street from 0 to 100mph... Hard launching setup! Goodluck!

Bcgalindo68

Hey guys I have a 92 firebied with a 305 TBI and I want to swap it out with carb'ed 350 and wanted to know if it was possible to do and what all do I need to do it

1gary

AFR certainly has found the "sweet spot" that has help a ton to build their rep.and again people don't realize they can and should buy into either AFR's or Brodix's bare castings fairly cheaply.Then fill them with their choice parts.

In terms of RHS 180's,when I went that route,it wasn't by any mistake.It was intended for a specific type of build and based off RHS's long history in R & D.Those heads you can get in different stages and to have RHS port them is a good thing in deed.

The better companies are "wet" bench testing their heads which is one hell of alot closer to the real deal in use of A/F mixtures over just air bench testing.Fuel does have a wt to it and it does effect the air dynamics in flow.This is where the companies experience in yrs of being in business with a strong R & D program to match those yrs shine.

As always.Anytime a company said they are "as good as",it is the company being compared to is what you need to grin and bear the extra costs to buy.

ziggy89

thanks for the input guys. deffinatly makes the decision easier. id go with the 65cc heads but I like being on the safe side when it comes to running pump gas. as far as the bottem end goes its an eagle cast unit. I beam rods hyper pistons etc. etc. pistons are likely to change it is coming out for a rebuild after all.

I know the larger heads will move the torque curve to the right but it makes so much down low I really don't think im goin to miss it espically with a 3k stall.

oh and as far as the hard launches on the street ask my fourth gen friends how much I spin with my drag radials on hahahaha.

ziggy89

bc yes it is possible. mine was originally a 91 tbi car. basically all I did was put in a fuel pressure regulator for the carb and youl have to do something with the ignition. weather it be msd or and hei unit. pretty sure that's all the major changes I had to make.

Orr89RocZ

iTrader: (20)

Plan for this now, consider what pistons will go in and will they make good compression with the heads cc chamber size? IE, flat tops and 70's cc then change to dish piston you just lost compression. If you run on pump gas currently at 10:1 with iron heads you will be fine on aluminum heads at 11:1. Cool thermostat also helps. Just a suggestion to maximize the setup but even low comp will make power on those heads

Bcgalindo68

ok thanks a other question the 350 that I have is a Chevy and I'll it bolt up the same on my firebird and will my gauges work

ziggy89

I don't think Ill lose to much compression. depending on how the block looks it might end up a .040 over block. it has 72cc heads now I wouldn't think 75cc would make that much difference. and im sure the block will need decked again. after all it is a sbc.

Orr89RocZ

iTrader: (20)

Yeah very little in 3 cc change but big deal is aluminum vs iron. Iron holds heat better so chambers are generally hotter. Thats why aluminum generally needs 0.5-1.0 more compression to make same power and heat.

1gary

Get the block/pistons settled in before any choice in heads.

Also if pistons are needed,consider the "D" dish pistons.They give you excellent quench numbers at 0 deck.

Bcgalindo68

will I have to eliminate some of the sensors and what do I do with the ecu

ziggy89

I pretty much rewired a good section of the car. running a carb and a separate ignition set up just through the thing away. I put my 6al in the slot for the stock ecu if that tells you any thing. sensors like the oil pressure and water temp go straight to the gauges in the dash. that really is all there is to it.

ziggy89

Oh another thing it always pulled real good up to the 6100 pill. I want to shift it around 6/6200 with a 6500/6700 pill in it. Do you guys think my eagle sir I beam will be OK for that or should I just drop some h beams in there now?

1gary

ARP bolted

ziggy89

What are you truing to say here Gary?

1gary

Not a fan of ANYTHING Eagle.

DIGGLER

iTrader: (1)

i would probably keep everything the same, especially if its balanced already. im thinking an n/a 383 turning 6200 with those parts will probably be ok. hyper pistons are great for what you are doing.
otherwise, i would swap everything out in favor of forged parts, go with 210-ish heads, and turn it 7k+. and then spray it. lol

1gary

Gonna make a blanket statement.A forged anything internal balanced rotating assembly is more durable.And not a spin term of forged cast steel,but a true forged assembly.

ziggy89

well im pretty sure its going to need at least one rod. been making a noise ever since I hydro locked it. weather or not anything is wrong with the cylinders will determine if I bore it and need pistons.

I checked my dynamic compression compared to now and with 64cc heads. with a 10.7:1 static and my cam it comes out to 8.4ish. how will that hold up to pump gas?

Confuzed1

iTrader: (4)

Just ran across this thread....boy does some of this stuff sound familiar!!

skinny z

Not very well unless you pull out lots of timing. Been there done that and it's not cheap going back. Having 10.4 SCR and 8.4 DCR there was no way to tune this to run without detonation unless I reduced the base timing from the initial 14-16 to around 8 and slowed the curve down so that it didn't start until 2000 and wasn't all in until 4000. Even then, despite the best efforts of a cool running engine (160 stat, cowl induction, 3" rad, etc) it would knock, particularly at the hit when rpms were near peak torque and cylinder pressure at it's highest. That's with an iron RHS Pro Torker Vortec head and .040" quench with flat top pistons. This would have been a sweet combination had the heads been aluminium.
For a real pump gas street engine with iron heads I think the best bet is to keep the DCR less than 8:1. Add a half point to the DCR if the heads are aluminium.
For what it's worth, a change in compression by one full point may yield about a 4% difference in output in a 400+/-hp engine, all else being equal. If the compression is too high, and the optimum timing has to be reduced to compensate, then power drops off dramatically. Much more than 4%.
Here's a great paper on the subject.
Engine Basics.doc

skinny z

Doesn't it though. That said, I'm sure you're happy with your new Scat rods. I agree with Gary on this one.

1gary

Skinny.Your situation still has me scratching my head.Not paper proof,but in real life we have build 8.5 DCR engines without concessions.Off hand the only thing I can think of is in your local area your gas must be real crappy.Same brand gas can vary a bunch in the same town let alone from one region to another.

skinny z

It's got me scratching my head too Gary.
Even on 100 octane fuel, with timing reduced it still knocked. Swapped carbs too. Cranking compression was 205 psi on average. Not unreasonably high I thought.
Interestingly after a tear down, there were no visible signs of spark knock. Nothing on the plugs and nothing unusual in the chambers or piston tops. With a little machine work on the heads, about 2 cc was removed (64 to 66) and I've opened up the piston to head clearance by .013" with a thicker head gasket (goodbye .040" quench). SCR now at 9.85 and DCR at 7.9. Tests will resume once my new rockers are installed and the correct length pushrods determined.

My apologies for the thread jack however there is some relevance to the OPs situation.

Orr89RocZ

iTrader: (20)

Well that doesnt seem to make sense. I would expect plugs to show some signs. Were you sure it was actual knock and not false or something else you were hearing?

skinny z

Now that the engine is back together and running, I'm seeing quite a difference in the cars behaviour. Whiles there's still some evidence of knock when the throttles are mashed open, it's nothing like it was before as the distinct sound of marbles in a coffee can is gone. Plus the butt dyno says that there's more torque than before too. I can see a lean spike at the hit (wide band gauge) and will have to work this carb tune a little more.
The lack of evidence is probably from not beating on it terribly hard while trying to tune. Rarely, after matting it would I keep into the rpms for any duration but then again maybe I overlooked some indication that it was pinging. Perhaps that saved it too.
At any rate, it loks like the move paid off. Time will tell. I've got a dyno session booked in a couple of weeks and then off to the track before I drive cross country (again).

1gary

A bad piston pin sound could mimic the sound your hearing.

ziggy89

allright more questions lol.

ill be doing some measuring when I get everything back from the machine shop as far as deck height and compression ratio. im looking at afr 195 eliminator heads and what I know is this. right now a 65cc head is too small for my liking and that's if the block doesn't need decked. however even if I zero deck the block which it isn't now a 75cc head is too big anybody tried milling afr heads to get a smaller combustion chamber.
and yes 65 and 75 cc are the only options with 195 cc intake runners.

ziggy89

anybody on this?

skinny z

Just catching up on this again.
You're wanting to choose between the 65 and 75 cc chambers is that right? And keep the current flat tappet 274 cam?
Have you gone any further determining if you'll need an overbore or a decking?
Do you have all of the cam specs? Advertised duration, LSA and ICL? I couldn't find them.
The difference between the two chamber volumers with all else being equal would be alittel over a full point. That is, ~ 9.86 vs 10.96:1.
I wouldn't hesitate for a minute to run 11:1 with the aluminum heads but if the cam timing is too short you could have trouble.

ziggy89

I'll grab my can card and give the specs when I get home. Doesn't need bored not sure on the deck yet. 65 cc puts me at 10.6:1 if it doesn't need decked. 75 cc puts me at 9.54:1. I just want to mill the heads to around 72 cc. Keep my compression the same as my iron eagle heads.

ziggy89

.4900.490 lift int open at 29BTDC close at 64 ABDC. Exhaust open 75 BBDC close 30 ATDC 230/236 duration

skinny z

LSA? ICL?
Do you have part number or a grind number?

ziggy89

LSA is 110.0
ICL 106.0

part number 12-246-3
grind number CS XE274H-10

skinny z

Trying to achieve a decent DCR of around 8:1 is workable with the 75cc heads and a quench of .040" See the attached screen shots.
On the downside, you'll be seriously down in compression should you ever want to step up in cam profile and really take advantage of the AFRs.

ziggy89

I wont change cams until ive got a forged bottom end at which point domed pistons are easy.

and my static compression wont be that high. my block isn't zero decked.

skinny z

I was using the best case examples. Without all of the details there's no telling what you might have for a compression ratio.
The point here was that if you can achieve the values in the chart, then that's what you would end up with. If you can't realize that SCR, then you're not as likely to be happy with the results.

ziggy89

that's why I was asking if I could mill the heads. I know ill end up with 10.6 compression with the 65cc heads and about 9.5 with the 75. Id like to be some where between 10 and 10.25. then again what does half a point of compression do.

skinny z

How are you arriving at these compression values? Without the piston/head clearence and the piston valve releif/dish volume you're not going to be able make any meaningful conclusions.
It's the compression ratio combined with the cam that makes up your assembly target.

Remember that one of the most important things you can do at this point is select a static compression ratio that will work with the cam you have. The relatively short 274 cam may build too much compression pressure with a static ratio greater than around 10:1. I know from experience that you're close.
What's half a point of compression worth? About 2% in potential output if it's too low. Something undriveable if it's too high unless you kill it by pulling out the timing. I've just gone through this with a 10.4:1 SCR/ 8.3 DCR albeit with iron heads.
As for milling the heads, absolutely it can be done. AFR has the specs right on their website for amounts milled vs cc reduction.

ziggy89

5cc dished piston with a .016 piston to deck clearance.


however I got the last of the pistons and rods out today (worked all weekend) Ive got one bent rod and a few messed up pistons.

ever see a wrist pin beat the crap out of a retainer and mar the piston? had to tap the wrist pins out with a punch.

skinny z

Sorry about your luck regarding the rods and pistons. It sounded like you were prepared for that eventuality though.
That said, what direction do you intend to go now?
New pistons... possibly the D-dish the Gary mentioned.
Rods...maybe Scats 7/16" cap screw stroker versions.
Now you're at these cross roads, will you still stay with the little flat tappet 274 or step up to a hydraulic roller with a little more duration and a lot more lift?
I suspect making 450 hp with the AFR 195s and a decent cam isn't going to be too difficult. And the low engine speed torque shouldn't be diminished to any great extent provided that you keep the cam specs under control and have a compression ratio to match.

ziggy89

well the motor sees a lot of street time and the 274h has great street maners and ive seen two magazine builds now with that cam and the 195 eliminator heads pushing horsepower and torque above 450 which would make me plenty happy. ill sacrifice a little on compression based again on its a street motor so 75cc chambers and .030 over forged flat tops with 4cc valve reliefs from probe.
as far as rods go. peace of mind goes a long way. so scat h beams it is.
time to have the 383 I wanted when I was a broke college kid.

skinny z

Be careful how you throw that phrase around here. People will cut carve you to bits with the magazine analogy.
However that said, lets look at where you might be heading.
First the 65 cc head.
Let's say you go with the next overbore at .040" and the 4cc flat top piston.
Standard length rods at 5.7".
You mentioned having a .016" piston to head clearance (with your current pistons) and will likely be the same with the new pistons provided you get them with the same compression height.
Combine that .016" clearance with an .026" gasket (Cometic/ Victor Reinz 5746) and you get a nice tight .042" quench.
That'll put your SCR at 11:1.
Add the short duration numbers of your 274H (274/286, 110 LSA, 106 ICL) and the DCR is 9:1.
That's race fuel territory.
Even a .040" thick gasket (which pushes your quench to .056") the DCR is 8.7:1.
Make the move to a 75 head and the numbers are:
SCR 9.95:1
DCR 8.1:1
Although the SCR appears low, especially for an aluminum head, it's the running compression (DCR) that's the more important number. 8.1:1 is getting up there but still reasonable (especially with aluminum).
If or when you step up to a larger cam (and it's inevitable in most cases) then there will be a need to bring the SCR to meet the requirements of the increased duration. You could then have the heads milled and all that goes along with it.
Food for thought.

Orr89RocZ

iTrader: (20)

To answer your other question yes you can mill afr heads. Buy 75 and take it to 68-70 as required. Usually .006-.007 per cc. 5cc roughly .030 mill