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Discussion Starter #1
Hi Guys,
I jacked up the engine on my Mustang. Looking for a silver lining, I'm looking to correct some mistakes while reassembling the engine.
The engine, 351W block bored 0.30 over. Stock crank, Stock rods, TRW L2378 pistons. Comp Cam 270H cam (35-414-3), Stock heads with mild cleanup. Performer manifold, 600 Holly 4160.
The cam specifications are; 270 duration, 110 lobe separation, intake centerline 106, lobe lift .313, valve lift .5 with 1.6 rockers.
Using Summit's compression estimate, 8.6:1.
So, the question, since looking through forums, I measured the deck clearance and estimate the quench at .092".....I know, bad.

I can change the pistons and head gasket to get the compression up to 9.5:1. I estimate the quench to be .035". Sounds better!
But, the pistons are the bath tube style dish. How does that effect the quench? Do I still have .035" or because the piston area is low, is the resulting quench more?

If the current setup would not be prone to pinging, I 'd probably run it until I could plan and build a better engine. I assume .092" would be very prone to detonation. Correct?

I'm not looking for a fire breathing street engine. The Mustang is a convertible. I have no plans to stiffen the body up enough to handle more power.

Thanks,
Scott
 

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Dish does effect comp ratio. But it all depends on the dish. Example is the 351W 2 bbl and 4 bbl used all the same parts but the pistons. The dish or non dish pistons changed the ratios. Some dish is -5ccs some are +6.5ccs. Stock 351W heads are 59-62ccs. I recommend KB151-030 with a standard head gasket .043" thickness, that'll give you around 9.7 ratio. But that's using my numbers since I don't know your's for comp height, head ccs. I run 10-1 on a street driven 331 stroker @ 4200 ft alt, all day. Cam, timing, type of gas, altitude, carb settings, etc all make a difference. Pump gas, you'll be fine as long as the plugs aren't real hot and the timing isn't higher then 36 degs total.
 

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Discussion Starter #3
Thanks Ricky,
The dish volume is 18cc. The dish depth is .18". I can estimate the flat area around the dish, just been too lazy up till now. I think the area around the "bathtub" will be narrow so; would the piston still develop sufficient quench?

I looked at the Keith Black pistons. With my block the way it is and .027" head gasket, I estimate 10.77:1 compression and .042 quench. Since I have iron heads, the compression ratio scares me on pump gas.
 

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Not sure on your math my friend. For example using summit racing calculator, 4.03 bore, 3.5 stroke, 62ccs in head chamber, +6.5cc piston (KB151-030 flattop 2 valve reliefs), .030" deck, .039" gasket thickness (FelPro #10112) = 9.82 ratio. If a .042" deck = 9.56 ratio. Either of those will work fine. What year is your block and the casting # on the heads? Hard to see how a flattop piston with this bore/stroke gets 10.77 comp. I had a 71 429 SCJ with 4.36/3.59 bore/stroke with 72cc chambers and it was 11.2 comp with flattop and 1 valve relief. It's like the appx amount to be removed from a head to decrease chamber ccs is .005" milled for a 1cc decrease. Remember also deck clearance is measured by the top of the block deck, (with no gasket) to the top of the piston flat area, (usually next the the cylinder side) at TDC. Block year makes a difference on that with 351Ws. People would look at 429 & 460 pistons and wonder why with the same rod used and a dished 460 piston, they had the same 10.6 comp ratio? The stroke difference of 3.59 to 3.85 makes the difference. Bigger empty cylinder at BDC = more volume to be compressed.
Not to piss you off or anything, but are you sure they're TRW L2378 Pistons? My info, which isn't always right, shows a dome.
 

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Discussion Starter #5
No worrys about challenging my math. I'm already challenged 😀
I measured the pistons .053 below the deck. Double check with a dial indicator and calipers. The L2378 pistons have an advertised 1.736" compression height and 16.9cc volume.I have not measured either to verify. The heads are stock 60cc combustion chamber, I have measured to check.

With a stock deck height of 9.503" (74 block), I estimate the piston should be .062" below the deck (9.503 + 1.75 + 1.736) so I guess .010 was mill off at some time.

Looking at the H621P30 piston, the compression height is 1.784" or 0.048" higher than the L2378.

If I start with my current .053 and - the difference in piston compression height, I end up with .005 deck clearance. Using a .030" gasket, I have .035 quench at an estimated 9.49: compression ratio. IMG_0796.JPG

To me, the number add up decently.

My question is how the volume of the H621P30 effects the quench. The volume looks like a bathtub. Your 460 piston has the same dish. Sealed Power confirmed the volume at 18cc but not the dimensions. I know from Summit the "bathtub" is .190" deep. So, is the ring around the bathtub provide sufficient area to develop good squish or quench?

Does the 460 piston control detonation well?

Scott
 

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Checking my specs, you have a piston for the 69-72 block which is a lower deck. The 73-74 block use a 1.769 comp height. Makes a big difference in comp ratio. The KB151-030 has a 1.774 which will take up some of that comp height. I think you'll find you'll still have about .035" down in the cylinder. My experience is, there's only one way to really find out. Moke it up, bearings and top ring only. But do one on both sides. When I had my 460 block squared, one side was .020" taller then the other. Machinist even checked his equipment several times just to make sure he was reading them right. A book you might find interesting is "Engine Blueprinting". It has all the formulas to figure any thing out on an engine. Also helps when you work on taking away metal and how that changes down the line. What people also don't figure is when you mill the block or heads or both, you change not only comp ratio, but intake/head mating, pushrod lengths can be an issue, (real touchy on FEs) sometimes acc. mounts.
 

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Discussion Starter #7
For the KB151's, I estimate .038" down so it looks like our math is correct. But, the quench distance is still bad. At this time, I'm trying to avoid block machine work.

Basically, at the point of assembling the engine and running it with the lower compression and huge quench distance. If it pings, I'll back off the timing. After that, I'll buy a used engine to build. One that I have more time and can plan.

I found another reference to a similar build in the Bronco forum. Apparently, low compression and large quench distances were common in the early 90's.
 

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Think the 90s were bad, from 72 on they were really ugly. GM is even worst. Many of their heads use 100+ CCs in the head. That's why you see domed pistons in Chevys all the time. I have a 331 in my 66 Stang with a .437 lift cam and 215 degs @ .050 with Holley 600, ACCEL timed for 8 int 36 total. Cast iron heads with 1.9 int & 1.6 exh running it a 4200 ft elv. Never had a ping and she's about 9.8 comp. Smoke the tires without any problem. Just stay away from the 15%+ Enco gas and you'll be fine.
 

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Discussion Starter #9
I found a reference stating the quench area must be at least 20% of the piston face area to be effective. No offence to forums, but I do not trust information that only shows up once. There are too many people like me who think they know but they don't.

The quench distance has been chewed on enough to know 0.035-.0040" and you are good. For me, getting there seems to be an issue. Something is not to spec. I know the deck is 0.010" low. The rods seem stock, casting numbers and bearing diameters all good.

Of the choices I have, just putting it back together with the parts I have is the easiest. If .044" quench is safe, I can change pistons and stay with the .039" gasket without problems. If the surface finish on my block and heads are good enough for Cometic gaskets, I can use a 0.030" head gasket resulting in a 0.035" quench.

So, will .044" quench end up with a lot of pinging? I doubt my block is smooth enough for a MLS gasket.
 

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Quench as you call it isn't the factor. Quench which I think you mean "deck clearance". Distance the piston sets down from the block's deck. Pinging is brought on by many factors, carbon deposits that are hot in the chanber will do it, bad gas, timing, lean mixture, comp ratio, wrong spark plugs (hot/cold), cam timing, hot running engine, etc. You can have her running like a racecar and get a bad load of gas, and it all turns to garbage until you burn it out or use an additive. Maverick gas is good for that. Deck clearance, dish/flattop pistons and chamber volumn is how the manufactures controlled comp ratios for emissions before they started using computer controlled fuel ejection. Cam technology has come a long way also when it comes to comp ratios, gas type, etc. It was bad enough trying to find the right cam 50 years ago, even harder now due to all the varibles.
 

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Discussion Starter #11
Hi,

Been out a while. My truck scrapped the turbo and now requires TLC.

After looking for another 351W block, I'm thinking of bailing out at going with a Tri Star performance crate engine. The cost for a 380hp engine will be below $4,000.00. I know the engine is not performance by most people here but it works for me in a un-modified mustang convertible.

Anyone had issues with Tri Star?

Scott
 

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Personally, get a 393 stroker rotating kit, good set of complete heads, I have a nice set of WP heads (2.0int 1.6 exh, guide plates, 3/8" studs, new springs work with your cam) that would work nicely for $500, keep the cam, Perf RPM manifold and 700 Holley with a new ignition system. Better fuel pump and 3/8 or #6 fuel line system. Better oil pan with windage tray. ARP bolts or studs everywhere.
Reason, you already have something that fits and all the accessories bolt up. Unless your block is broke, it will work just fine.
 

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Discussion Starter #13
After fixing my truck, I'm a little low on funds. But, I am looking at 393 kits. I figure I have to know what the current deck height is before making a purchase. The machinist I dealing with advises buying a balanced kit so there are no surprises.
If been looking at heads. Mine are 60 CC. I'm thinking of building with my current heads then move to Edlebrock E series when money and time allow. The E series has a 58 cc option so I can pickup a little more compression. Of course, I'm also looking at going with a roller cam.
A buddy claims a roller will not provide anymore performance than a flat hydraulic at the level I'm looking at. I disagree thinking I can obtain the same or better flow with less duration. So, the roller may be more street friendly without giving up anything, except money.

What is the chamber volume on your heads?

Scott
 

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Mine are 61.5 and they'll work with either Hyd or roller and a 393 stroker will still get you in around 10-1. Cast iron so they seem to work better when it comes to bolt holes.
Check the casting numbers, that'll give you the deck height from those being cross referenced. Then you can make a better call when it comes to comp ratio by which pistons you get.
 

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Doing a little research on Summit, 393 stroker kits can give you a 12.2 or down to 9 comp ratio depending on the piston you choose, deck height and using these 61.5 cc heads.
 
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