SBF - Compression ratio and valve to head questions

[GWL]

Compression Ratio and Piston to Valve Clearance
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This past week, I've been studying/researching static and dynamic compression ratios in order to pick the best piston for my engine. I'm new with some of these concepts so maybe you guys can give me some guidance.

I have been looking at several different pistons and think I’m leaning toward the Silvolite 3101hc piston. My only concern will be the valve to head clearance.

Has anyone successfully used this piston with a cam lift of Intake @ .499” and Exhaust @ .510”?

What do you think of my piston choice, Silvolite 3101hc regarding the static and dynamic compression ratios calculated?

Here are my engine specifications and compression ratios with several different pistons. Goal: Street engine run on regular gas in the 300 hp range.

Engine: 1989 Ford 302, Bored +030”
Bore 4.030”
Stroke 3.00”
Cylinder Head Volume: 59cc’s(GT-40p head, 58.3-61.3)
Trick Flow Cam #TFS-51402000 (Intake closing at 38º ABDC at .050”)

For the following I used the Compression Ratio Calculator at United Engine and Machine Co., manufacturer of the Silvolite pistons:

http://kb-silvolite.com/calc.php?action=comp

I also used the Summit Racing Calculator but it does not give the Dynamic Compression Ratio:

http://www.summitracing.com/expertad...sionCalculator


Federal Mogal Speed-Pro pistons +.030” Overbore with GT-40p heads

Bore: (diameter) 4.030”
Stroke: 3.00”
Rod Length 5.09”
Cylinder Head Volume: 59cc (58.3-61.3cc’s)
Piston Head Volume: 8cc
Deck Clearance: 0.0135” (The Official Ford Mustang 5.0 Technical Reference)
Gasket Bore Size 4.1” (Ford Racing Spec.)
Compressed Gasket Thickness .042” (Ford Racing Spec.)

Static Compression Ratio 8.949

Dynamic Compression Ratio 7.746

This piston would give me just about stock compression ratio (advertised 9:1) but note that the original stock head for this engine had 62 cc’s head volume vs. the 59 cc’s of the GT-40p head. This piston has large valve cuts (8cc’s) allowing for larger sized valves.

Silvolite 3101h pistons +.030” Overbore with GT-40p Iron Heads

Bore: (diameter) 4.030”
Stroke: 3.00”
Rod Length 5.09”
Intake Closing Point 53º (Degrees ABDC @ 0.050 lift plus 15º)
Cylinder Head Volume: 59cc (58.3-61.3cc’s)
Piston Head Volume: 3cc
Deck Clearance: 0.0135” (The Official Ford Mustang 5.0 Technical Reference)
Gasket Bore Size 4.1” – Ford Racing Spec.
Compressed Gasket Thickness .042” – Ford Racing Spec.

Static Compression Ratio 9.487

Dynamic Compression Ratio 8.203

Based on the above information I’m leaning toward the Silvolite piston as the numbers really look good for running on regular gas. To be on the safe side, I used the lowest cylinder head volume listed for the GT-40p head.

That range is 58.3-61.3cc’s, so using 58.3cc’s the numbers came out to:

Static Compression Ratio 9.569

Dynamic Compression Ratio 8.272

From what I've read, these calculations look really good for a street engine on regular gas.

Again the questions:

Has anyone successfully used this piston with a cam lift of: Intake @ .499” and Exhaust @ .510”?

What do you think of my piston choice, Silvolite 3101hc, regarding the static and dynamic compression ratios calculated?

Thanks for any feedback, George

[BigLeo69]

i am using the Kieth Black/Silvolite flat tops Hyper's KB-254 and so far very happy and Marco is great to deal with @ Silvolite.

don't know anything about ur piston's, but it seems the CR will work on pump gas with even the CR i am running.
if you plan to set-up piston to deck ht. get a good depth mic, and the block once its surfaced could be out @ different cylinders changing the total CR/DC/SC.
if you run aluminum heads that will help too when its summer if the CR gets higher.
and if this is a roller engine try to push that Intake/exhaust to more, like 520 I and 530 E. i am running a HFT and have a XE cam from compcams and its lift is 512/514 and that HFT, a roller should get you more.
see if that isn't to radical of a cam, the silvolites also have a valve relief in them @ 20* which is what a ford head runs.

good luck and happy wrenching

[KOstrat]

Hi George,

Is this engine intended for a roadster?
I think you have some more work to do (and $$$ to spend) to get to 300hp.
You won't have any piston to head clearance issues with that cam/piston combination.
Assuming that this is not a daily driver, why the regular gas requirement?
What is your budget for the engine, if you don't mind me asking?
Are you building the engine yourself?

No further questions, yoronner.

Tom

[GWL]

BigLeo,

Thanks for taking the time read through that long thread of mine and for your thoughts.

Tom,

1. Mk4 Roadster

2. I have heard about less HP and more with the same set up. The more was a dinoed (sp?) engine tested by Mike Forte that had more than 300. I'm going with a '97 Explorer Intake System with an '89 EEC-IV, EFI and 24lb. injectors, which I will have to have tuned, so I will be able to get the RWHP. I will post those results at a later date. Sometime in the future, I'll possibly add a set of Trick Flow heads to match the cam.

3. My budget is '0' and getting less everyday. Actually, I'm spending $1600 for block cleanup/check, boring, honing, turning crankshaft down .010", balancing, head work, flywheel surfacing, bearings, new cam bearing installed, pistons, rings and valve guides. This work is being done by a reputable race engine shop, here in Vermont. I'll get all the parts clean, boxed, bagged and ready for assembly. I shouldn't have to do anything except checking the valve to piston clearance during my assembly.

4. I will assemble the engine myself. I have built many engines in the past but not to this kind of detail.

Again, thanks for your guys time, George

[KOstrat]

Glad to hear you're building your own motor, George. I just completed my own build for my 68 Mustang, and it was a terrific experience, never having done anything like this before. I asked about your budget, because my build (347) got away from me pretty quickly.....starting out at $3500 (including a used set of Windsor jr's and matching roller cam, 221/230, .545 lift, that I paid $1k, which also included a Mallory dizzy). I'm now at something north of $9K and counting(!).

I know what you mean about the HP predictions being all over the map. Just now checked Richard Holdener's book,
"Dyno Prover SBF Performance" , he rates all manner of SBF engine configurations for HP and torque curves. He shows a 5.0 built very similar to your build, having a Comp XE roller @ 212/218, .512", and 114 LS, with stock E7TE heads at 306hp @ 5300, running an Air Gap intake with Barry Grant Demon 650 carb. He then swaps out a list of different heads and compares them on the dyno. According to his results, going to the GT-40P head yielded an increase to 336hp @ 5700 with a modest increase in torque, from 340 to 360 ft.lbs. @ 4000.

So, according to the above, you're right.....300hp or more is a realistic expectation from your set-up.

I'm still in the "Do I really want to do this?" phase regarding the car build. I am fortunate to live within 40 min. drive of FFR, and 15 min. from Forte's. Went down to FFR a couple of weeks ago just to see tha cars close up, and see if I actually "fit" in a coupe. To my surprise, I found the coupe more comfortable than the roadster......more leg room.
I need to complete the Mustang restoration first, and then decide. I would probably start by building the engine first, because I really enjoy engine building, and now I have gathered all the tools necessary.

Starting a "welding and fabrication" course at the local Tech School on Monday, again, as part of the prep for building a car.....looking forward to the class very much.

George, check out Holdener's book.....it's well worth the $15.

Tom

[GWL]

Tom,

Yes, I have that book on my shelf. I just picked it up and spent some time going through it again. You don't always remember exactly where your thoughts come from but this book must have influence me in some way.

The two cars, Coupe and Roadster, are really very different from each other. Actually, I'd like to have one of each in my garage. If I lived that close to FFR, I'd be spending probably too much time going back and forth from my garage to their show room. I'm making a few modifications and am always trying to think about what spacing will I have once the body is on or when the engine is in. Actually, I do have an empty block with heads that has gone in and out of the engine compartment several times.

That welding course is a good idea. I've actually taught welding many years ago and had considered taking one myself. I didn't and I'm going to struggle, at first, to do some cutting, refitting and welding of some of the 3/4" tubing in my trunk area to make it a bit larger and fix an earlier Mk4 trunk problem. FFR has since fixed that trunk problem.

Based on what I've learned here and elsewhere in the last few days, I'm going to use the Silvolite 3101hc pistons. I don't think I'll have valve/piston interference but will check in upon final assembly. Using the 3101 piston will give me half a point higher in both static and dynamic compression and still be within a safe ratio for regular gas.

Thanks again guys, George