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Trick Flow 175cc heads on 3.766" bore - valve lifts
Here are some shots of Trick Flow 175cc heads on a 305 bored 0.030" over (3.766" bore).
First with 1.94" and 1.50" valves seated. The combustion chambers measure 3.955" across at the widest and overhand the 3.766" bore a fair bit. The intake and exhaust valves appear equally close to the cylinder walls and the valve spacing is around 1.91"
Next, the 1.94" intake valve opened until it contacts the cylinder wall, which occurred at 0.771" lift.
The 1.50" exhaust valve opened until it contacts the cylinder wall, which occurred at 0.728" lift.
Trick Flow 175's with 2.02" intake and 1.60" exhaust valves installed on the 3.766" bore...
2.02" intake valve opened until cylinder wall contact, which occurred at 0.433" lift (which looks to be as soon as the valve cleared the chamber)...
1.60" exhaust valve opened until cylinder wall contact, which occurred at 0.507" lift...
Take home:
You can use these heads, stock with 1.94" and 1.50" valves, with up to any practical maximum valve lift (0.771" and 0.728"). You can use these heads with 2.02" and 1.60" valves on a 3.766" bore as long as the valve lifts are less than 0.433" and 0.507", respectively. That doesn't consider the effects of shrouding by the close proximity to the chamber and cylinder walls. Also keep in mind that these numbers will change depending on the exact depth of your valve seats.
In comparison with the GM heads it can be seen that Trick Flow widened the valve spacing and moved the exhaust valve closer to the chamber wall - this allows more lift with the 1.94" valve and less shrouding on the intake, but shrouds the exhaust a bit more and allows less exhaust lift with a big valve. Curiously, even though the TF head allowed more lift with a 1.94" valve than the 601, the 601 allowed more lift with a 2.02" valve than the TF, indicating that TF seem to have angled the valve slightly differently than GM, or my 601's had an "off" valve guide job.
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Last edited by Casey Butt; 09-16-2009 at 06:57 PM.
Somebody should make this a sticky. Good, real-world info with pics!
I suspect you are right about Trick Flow's attempts to unshroud the intake at the expense of the exhaust size. Shrouding an exhaust isn't as bad as shrouding an intake.
I also fitted these heads with 0.030" offset locating dowels yesterday. Even though the dowels moved the heads 0.030" further "up" on the deck (towards the intake manifold), the Trick Flows still had plenty of clearance in the bolt holes to bolt on to the block just fine. Because the dowels locate the chamber closer to the center of the cylinder by 0.030" they should also unshroud the valves a little and allow a little more lift before cylinder wall contact. I didn't take valve clearance measurements at that time, though.
I'll try to get to the garage tonight and take some valve clearance measurements with the 0.030" offset dowels in place and see if they allow any significantly higher valve lift before contact.
I suspect you are right about Trick Flow's attempts to unshroud the intake at the expense of the exhaust size. Shrouding an exhaust isn't as bad as shrouding an intake.
For the record, here are the Trick Flow flow numbers for those heads on both a 3.766" and 4.000" bore. It seems that the intake valve is relatively unaffected by the proximity to the cylinder wall - but the exhaust valve a little more so. The E:I flow ratios stay above 71% at the worst even with the more shrouded exhaust valve, so it looks like Trick Flow accepted this trade-off for the sake of unshrouding the intake...
Last edited by Casey Butt; 09-17-2009 at 10:25 AM.
Reason: added E:I info
Are you thinking of doing it the way the 396 blocks had to be done to take the 2.19" intake valves?
More or less, yes, but a smoother transition into the bore than just an abrupt factory cut for clearance...
More like a more flow-friendly 45* or more grind, clearanced out 2.4 mm on each side and down a far as the top ring at TDC will allow (plus a few hundreds safety margin). I've never seen such a thing tried on a bore simulator on a flow bench, although I would suspect it would get back a good chunk of the flow lost on the 3.766" bore as compared to the 4.000" bore in Trick Flow's numbers. I've seen some Dodge 318 guys do it, but again, haven't seen any flow numbers.
Photo is from Valako Race heads in Michigan with accompanying comment...
"This block has been bore notched to increase air flow in the cylinder. By relieving the areas near the valves there is a substantial gain in air flow resulting in added hp. Dyno tests have proven 30hp gains in smaller bore engines. When using our cylinder heads, we strongly recommend this modifaction. All of our performance engines have this, along with deburring of the tops and bottoms of the cylinder walls."
I've never bothered with this on a 305 block, but it looks like it could be in order for those doing a complete (re)build. Add in the small effect of the 0.030" offset dowels and some good flow numbers should be shaping up.
I suspect you are right about Trick Flow's attempts to unshroud the intake at the expense of the exhaust size. Shrouding an exhaust isn't as bad as shrouding an intake.
Here's a shot of a 350 GM head on a 305 bore (which I lifted from a thread on here awhile ago, but can't remember the details). Here the intake valve is opened but you can still see that Trick Flow have clearly moved the exhaust valve over closer to the wall as compared to the GM head (which, incidentally, is common practice on modern aftermarket performance heads).
That seems to make sense to me. When I had my Edelbrock Performer RPM heads they told you in the installation manual that if you use the 2.02/1.60 valve heads on a bore of 3.73 inches or less that valve lift had to be limited to .420 to keep the valves from contacting. Your measurement of .433 seems to fit the bill as it appears that they are taking into account that the valves will expand in size as they get hot.
I would have no hesitation about trying it to a 305 block, but trying it to the polyacrylate bore simulator sleeves is just asking for cracked polyacrylate. Having the numbers would be nice, but the dragstrip results are enough. I suppose someone could do it with wood instead of polyacrylate, maybe?
Just got back from the garage... I installed the Trick Flow heads on the 3.766" bore block again, but this time with 0.030" offset head dowels to position the heads 0.030" further up on the deck (towards the intake manifold). For those who aren't familiar with this, it moves the valves away from the cylinder walls slightly and should give slightly more valve clearance and less shrouding.
With the 0.030" offset dowels in place and the heads bolted down, the 1.94" intake valve opened to 0.807" as compared to 0.771" without the offset. The 1.50" exhaust valve opened to 0.728", the same as without the offset dowel.
The 2.02" valve opened to 0.437" which is essentially the same as without the offset, indicating that contact is still likely happening as soon as the valve clears the chamber. The 1.60" exhaust valve opened to 0.602" with the offset dowel as compared to 0.507" without the offset.
Summary - Trick Flow 175cc heads on 3.766" bore:
Standard head placement max. lifts
1.94" -- 0.771"
1.50" -- 0.728"
It looks like the 0.030" offset allowed 0.036" extra lift on the 1.94" intake valve and a huge 0.095" extra lift on the 1.60" exhaust valve. Oddly, the offset didn't seem to affect the maximum lift with the 1.50" valve - but the lifts involved were well past retainer-seal contact anyway, so it's largely irrelevant. The 2.02" intake valve still looks to be not clearing the bore at all and makes contact as soon as it lifts out of the combustion chamber.
In any case, it appears as though the offset dowels are a worthy "trick" to use on small bore engines to get a little extra valve clearance. The Trick Flow's had sufficiently big head bolt holes to allow the heads to bolt to the deck just fine even though they were shifted 0.030" up on the deck, this might not be the case with GM or other aftermarket heads and they might require all the bolt holes to be bored out slightly in order for the bolts to line up with the block. I had absolutely no problems with the Trick Flow 175's in this regard.
Also, like Atilla said, with the heads offset 0.030" each, the intake manifold might be squeezed to fit properly and either the heads or intake manifold will likely need to be milled at the mating surfaces to re-establish the proper fit. I haven't tried to bolt up an intake manifold with the heads offset as of yet.
Casey- this is solid research in my book. If this doesn't get made into a sticky it'll be a shame.
This certainly helps explain why installing bigger valves in a stock 305 head (particularly a 1.60 exhaust, but also a 1.94 intake) would boost performance on a 305 with very little downside. Something that doesn't necessarily get you the same results from an aftermarket head.
One more, please, if you've got ready access to a set of 350 Vortec heads. I'll bet you dollars to donuts they moved the valves around in a way similar to the aftermarket Trick Flow heads. I've built a few engines with Vortecs and there is definitely some kind of movement of the valves vs. an older stock head. Lotsa guys on this board build Vortec-headed engines. Very few will ever build a motor using those TrickFlow heads. (The pic you swiped above of a stock head definitely isn't a Vortec 350 head- chambers aren't heart-shaped)
As a side note, I did similar observations on a 454 big block I built recently using AFR heads. Totally different engine, obviously, but lots of basic similarities. Chambers overhanging the bores, intake valves close to the bore wall, valves moved around slightly from the stock locations. That kinda stuff. Wish I had taken pictures. My general overall conclusion was "man, these heads would work a lot better on a bigger bore!" In the big block world NOBODY wastes their time with a little 454 any more (4.25" bore). Anyone serious about things starts with a bigger 4.5" bore block (502 or more cubes). And that seems to be what the heads are really designed for. AFR claims their heads will work on anything down to a 396. Yeah, well, good luck using them on anything smaller than a 427 becuase the intake valves just ain't gonna fit very far down the bore of a little pea-shooter 396.
To go along with the flow data of the TFS 175cc heads...
I measured the pushrod pinch area in these heads at 1.86 - 1.89 in^2 (depending on how well I could line up the gauge) - which should be enough to take a 305 to 7300-7400 rpm at peak horsepower, a 350 to 6350-6450 rpm at peak hp, and a 383 to 5800-5900 rpm at peak hp.
something is wrong with your figuring, real dyno testing proves that getting the results you say would require at least something like AFR's 195cc head. You sure won't get your predicted results with these heads.
something is wrong with your figuring, real dyno testing proves that getting the results you say would require at least something like AFR's 195cc head. You sure won't get your predicted results with these heads.
You're right, I should have been clearer and said "enough to potentially take a 305..." instead of just "take". Minimum runner cross-sectional area is directly proportional to maximum rpm at peak horsepower achievable with a given head. The formula is:
minimum port area = rpm*stroke*bore^2/C
where C can be anything from 177000 to 196000 - I used 190000 in the calculations because it's most typical of a high-performance hyd. roller cam.
The formula doesn't mean that the engine will actually peak at that rpm, but that the head is capable of supporting such a peak given the proper cam, exhaust, intake, etc. What the formula does calculate is the cross-sectional area at which airflow in the head reaches terminal velocity (0.55 to 0.60 times the speed of sound) - and airflow speed will not increase past that point, so that denotes the maximum possible peak hp rpm limit. The maximum rpm given is the physical limit of the head on a given engine, not saying an engine will reach that max rpm simply because it has those heads installed.
AFR 195's have a cross-sectional area of 1.98 sq.in, so assuming a correspondingly "larger" cam, exhaust, etc, they would push the potential maximum peak hp rpm point higher.
Last edited by Casey Butt; 09-25-2009 at 06:57 PM.
I played with all of these old ideas back when I was new to performance engines, many years ago. These formulas are leftovers from the sixties, when heads didn't flow, and a huge duration, solid-lifter cam was the only way to make a big peak HP number. Nevermind that you had to keep the engine within 500 rpm of that. Rev any higher, you're past what the head flow can support. rev any lower, you're out of the rpm range where the cam works.
These TFS 175 heads, as they come out of TFS's box, will be okay to 5500 on a 383, but the AFR195 would surpass them as low as 3000 rpm. Throw out those old formulas and embrace modern things. Find a dyno result sheet you like, from a test done within the last 5 years, and copy that. Unless you have a dyno yourself, you can't do any better.
Actually, as a GM Powertrain Engineer whose job it is to mathematically model engines and electric motors, I can assure you that those equations are used in current mathematical modeling and are anything but relics from the 1960s. Yes, the equations themselves are simplifications and are not on the level of sophistication as say wave analysis, but are in the ballpark for guideline purposes if the correct constant is chosen - although head design (and everything else) certainly has improved, the physics governing them hasn't changed.
The theoretical underpinnings provide direction and clues into what's actually happening in an engine, but I certainly agree that dyno results trump everything.
sorry to bring this thread back to life but your obviously highly experienced with these heads... I need to use a 350 head gasket on my 310 with these heads correct?
That wont cause any issues will it?
