Lets discuss another engine build

[straightlinespeed]

Hola, guys and gals.

Well I finally have the engine out of my car and taken apart. Im going to be bringing it to a machine shop to have some issues taken care. I want to go in to them with some idea of what Im wanting and would like to discuss that with you all.

What Im looking for is a street-able pump gas (93 Octane here) engine, with around 9.5SCR.

I will be running magnum heads, XE268H Cam, TTI's, Air Gap and a QFT 750 Carb. I did CC the heads and they average out to 64CC. Not sure if that is the correct way to gauge it, if not I do have the individual numbers.

After doing some research on pistons and with out getting some custom made, Im stuck between 2 different ones. The Keith Black KB362's and the Speed Pro H405CP30.

The KB362's have a 19.4CC volume, and sit at zero deck. The H405CP have a 10CC volume and sit at .043 deck. Either one of these pistons gives me a 9.1SCR.

https://www.uempistons.com/index.php?main_page=product_piston_info&cPath=3_4_22&products_id=543

http://fme-cat.com/PerfApplication....4.000 Bore x 3.578 Stroke)&headType=Flat&ga=Y

Now here is one of my questions. If I go with the Speed Pros is it possible to shave the deck down lower than the .043 to bump the compression closer to 9.5 or will that cause to many issue with sealing the intake?

Another question I have is would there be any noticeable difference between 9.5 and 9.1?

 

[Ironmike]

I say don't buy any pistons until you're sure where your deck is. No manufacturer can really be SURE of your deck height. I think they go off of manufacturers stated numbers. Mine needed .012 taken off to get it straight and square. Just a thought....

 

[RustyRatRod]

What heads are you going to use? No way in hell will you run that tiny cam with a TRUE 9.5 compression with no quench with iron heads. If you end up with some quench then different story.

 

[4spdragtop]

Subscribed for learning. ..hopefully

 

[L4staero]

What heads are you going to use? No way in hell will you run that tiny cam with a TRUE 9.5 compression with no quench with iron heads. If you end up with some quench then different story.

I will be running magnum heads, XE268H Cam, TTI's, Air Gap and a QFT 750 Carb. I did CC the heads and they average out to 64CC.

At a guess i would say hes got magnum heads

 

[rumblefish360]

You'll never know a .5 in ratio. Or a 1.5. But you'll notice a cam to small on a ratio to high.

 

[straightlinespeed]

I say don't buy any pistons until you're sure where your deck is. No manufacturer can really be SURE of your deck height. I think they go off of manufacturers stated numbers. Mine needed .012 taken off to get it straight and square. Just a thought....

Good advice, thank you

What heads are you going to use? No way in hell will you run that tiny cam with a TRUE 9.5 compression with no quench with iron heads. If you end up with some quench then different story.

Currently I've got iron magnum heads, these are the heads that I checked the CC's on yesterday. I will be having them checked out to make sure they are ok. Rob, do you have a cam recommendation? Im not looking for a high horsepower engine, just a good reliable cruising engine that will be fun if I get on it.

You'll never know a .5 in ratio. Or a 1.5. But you'll notice a cam to small on a ratio to high.

Noted on not noticing the .5 ratio. Although Im surprised that a 1.5 ratio would not be noticeable. Like I mentioned to RRR Im open to Cam recommendations. The only reason I was planning on using the XE268H cam is because thats what I have in the car now.

 

[moper]

You'll want to make sure of the actual compression ratio as was noted. But I don't see a problem with the XE268 at 9.5:1 actual. I've run more than that with them before. It's not a big deal as in no special timing tricks or anything, but you will probably want to run at least mid-grade fuel if it's 10% ethanol like what we have locally.

 

[straightlinespeed]

You'll want to make sure of the actual compression ratio as was noted. But I don't see a problem with the XE268 at 9.5:1 actual. I've run more than that with them before. It's not a big deal as in no special timing tricks or anything, but you will probably want to run at least mid-grade fuel if it's 10% ethanol like what we have locally.

The plus side is we have 93 Octane non-ethanol here, and I've been running that in the car.

 

[rumblefish360]

1pt. of compression is worth approx. 3% in power increase/decrease which is mostly seen on the mid to big end where the cam shafts power comes into play. (Assuming larger than stock where meaningful torque takes place after 1500rpm.) If the ratio plays better with the camshaft, the difference will be noted ever so slightly via the butt dyno. If the butt is crazy sensitive. It will show at the strip by a very small margin. Very small.

Your camshaft working in a sub 8.0-1 ratio will have a noted gain @ 9.0-1 - 9.5-1.
Going from 9.5-1 to 11-1 will cause octane issues but no real gain noted or worth the expense. Going from 9.5-1 to 8-1 or less will have a noted decrease in performance into a sluggish realm. By compare. And via dyno only. Which will show a better or worse working engine.

345 HP + 3% = 355 HP (10.35 HP gain)
345 HP + 3.5% = 357 HP (12.07 HP gain)
680 HP + 3% = 700 HP (20.4 HP gain)

Your not feeling 10/12 HP on the low powered engine,
your never going to feel 20HP when you started with 680.

Use as much compression as you can get away with BUT do understand undoing that ratio is a head gasket swap. Is that head gasket thickness available to you? I guess it is easier than trying to add more ratio. Octane requirements are limited and must work with the engines compression ratio and cam. You can have a high ratio engine living on pump gas BUT it does (in general) require a rathey larger than ideal cam for the engine set up and car. You can see manual transmission guys get away with this since a manual will need more cam and gear as a norm vs. an automatic car.

As you and many know, the larger cam bleeds off some compression making pump gas a reality. But with a trade off there willing to do.

 

[straightlinespeed]

1pt. of compression is worth approx. 3% in power increase/decrease which is mostly felt on the mid to big end where the cam shafts power comes into play. If the ratio plays better with the camshaft, the difference will be noted ever so slightly via the butt dyno. It will show at the strip by a very small margin. Very small.

Your camshaft working in a sub 8.0-1 ratio will have a noted gain @ 9.0-1 - 9.5-1.
Going from 9.5-1 to 11-1 will cause octane issues but no real gain noted or worth the expense. Going from 9.5-1 to 8-1 or less will have a noted decrease in performance into a sluggish realm. By compare.

And this is why I come here! Proves I know nothing LOL.

Ok, so my engine prior to tearing it down was about 8.2 compression. Now if I understand you correctly, using my current cam (268) I should have a noticeable increase in performance if I bump my compression up to 9.0-9.5? Please correct me if Im wrong.

I figured since tearing it down I would bump the compression up and hoping to use my current cam for a slight performance gain. Again if any of you have other suggestions on what to use feel free to throw out what route you think I should go with it.

 

[rumblefish360]

It's a gain I don't think you'll feel. But it is a gain. Also, what the raw numbers do not tell you is how the engine likes the proper balance so much better. The efficiency and smoothness of the engine will pick up. The engine will feel better on acceleration.

I would yield at 9.5-1 as a MAX! The cam is still small and the octane available to you @ 93 non ethenol is nice but still has its limits. I'm sure someone here is going to chime in and say, "Hey I ran XX.x - 1 ratio and got away with it!" But let's be reasonable and smart about matters. Not greedy and stupid.

 

[Coronet 500]

I think that cam is just right for your "streetable" car.

My deciding factor for piston would be weight, the Speed Pro is quite a bit heavier.

 

[straightlinespeed]

It's a gain I don't think you'll feel. But it is a gain. Also, what the raw numbers do not tell you is how the engine likes the proper balance so much better. The efficiency and smoothness of the engine will pick up. The engine will feel better on acceleration.

I would yield at 9.5-1 as a MAX! The cam is still small and the octane available to you @ 93 non ethenol is nice but still has its limits. I'm sure someone here is going to chime in and say, "Hey I ran XX.x - 1 ratio and got away with it!" But let's be reasonable and smart about matters. Not greedy and stupid.

You nailed what Im looking for, efficiency and smoothness. Im not looking to race and beat everyone on the road. Hell I would be happy to beat a smart car at this point! I want to get in the car and be able to go on a all day drive and enjoy driving it, but I want the engine to be the best possible, for doing just that.

I may take it to the track once or twice a year. I would drive it there (2.5 hours) have some fun and then drive it back home.

The way the engine was prior, was not enjoyable to drive. It never did seem to run correctly. It always seemed to be a chore and I didnt want to go to far from home with it.

I would like to hear your opinion on what cam to run or even what piston.

On another note I just got off the phone with the machine shop. I explained why I was taking it apart (coolant leak between the head and deck). He is almost positive it was never machined straight by the previous builder and thinks that's all the work that needs done to it. He is going to go thru everything anyways just to make sure.

With that being said depending on how much he has to shave the deck, do you think its possible to machine off enough to bump my compression closer to the 9.5 with out intake sealing issues or should I just be happy with a straight deck and go with where ever it comes out at?

 

[straightlinespeed]

I think that cam is just right for your "streetable" car.

My deciding factor for piston would be weight, the Speed Pro is quite a bit heavier.

Weight was not something I looked at, or even dawned on me. Ok for this newbie, how much does weight effect things?

 

[krazykuda]

I think that cam is just right for your "streetable" car.

My deciding factor for piston would be weight, the Speed Pro is quite a bit heavier.

Yes, speed pro is a little heavier, but closer to the stock weight than the KB.

I had a set of KB pistons crack a piece of skirt off while handling it. I didn't like how thin/weak the skirt was on the KB and went speed pro as their skirts are much thicker than the KB and stronger...

food for thought... #-o

 

[rumblefish360]

IIRC, Speed Pro H405CP30 pistons are for a 360. Since we're doing a 360, to raise the compression ratio up right quick, use ether the KB-107's or the Speed Pro/Federal-Mogual Hyper slugs. I JUST picked up the Fed-Mog Hyper slugs for the wife's 360. They cost a little more but also have a coated skirt for scuff resistance and a higher silicone content than the KB's do. There almost identical in compression height. The block will need to be decked in most cases for a zero deck height installation. And that would equal a 9.8-1 @ a zero deck height. (Adjust deck height accordingly.) I have used the KB hypers several times before without issue. These are my first set from this manufacturer.

The cam you have is fine IMO. I always suggest picking a cam in the duration your car uses. What rpm do you cruise in? I also like to use as much valve lift as the head can handle. If your heads flow stalls @ .500, then stay under .500 lift. MY current build is making use of fully ported heads that can use a valve lift over .600. Can you guess what I'm lifting my valves to on my build?

 

[straightlinespeed]

Yes, speed pro is a little heavier, but closer to the stock weight than the KB.

I had a set of KB pistons crack a piece of skirt off while handling it. I didn't like how thin/weak the skirt was on the KB and went speed pro as their skirts are much thicker than the KB and stronger...

food for thought... #-o

Noted!!

IIRC, Speed Pro H405CP30 pistons are for a 360. Since we're doing a 360, to raise the compression ratio up right quick, use ether the KB-107's or the Speed Pro/Federal-Mogual Hyper slugs. I JUST picked up the Fed-Mog Hyper slugs for the wife's 360. They cost a little more but also have a coated skirt for scuff resistance and a higher silicone content than the KB's do. There almost identical in compression height. The block will need to be decked in most cases for a zero deck height installation. And that would equal a 9.8-1 @ a zero deck height. (Adjust deck height accordingly.)

The cam you have is fine IMO. I always suggest picking a cam in the duration your car uses. What rpm do you cruise in? I also like to use as much valve lift as the head can handle. If your heads flow stalls @ .500, then stay under .500 lift.

Thanks for the pics of those pistons. I was looking at those ones also, but thought the SCR was to high with them.

My cruising RPM is about 2500 @ 60mph.

Ok, I have to ask this question, since I dont understand. Although the engine builder will, this is for my curiosity.

You said the deck would have to be zero decked, which I understand. When I was playing with numbers I looked at the KB107's and it looked like my compression with those would be 10.4:1. Now you say 9.8:1 which either way is over the 9.5:1 ratio that I should stay under. So how do you adjust the deck accordingly if your zero decking the block?

 

[nm9stheham]

You'll never know a .5 in ratio. Or a 1.5. But you'll notice a cam to small on a ratio to high.

Sorry but I'll have to strongly disagree on this one; I have noticed a definite difference in .4 or .5 point and a huge difference in .8 point of CR. This is from putting in 3 different pistons in the same engine in 3 successive racing rebuilds, no other changes. A .4 difference is noticeable for sure; this difference was felt at the bottom end of the torque range but not at the top end.

So for a revving drag race engine with a moderate to high stall converter, probably not so much, but it will make a definite difference for a street/cruiser engine. The 3% difference for 1 point in CR is for peak HP only and is totally misleading for the improvements in low end torque numbers and torque band width, so need to be taken with some perspective.

 

[Coronet 500]

Just try and make your quench number from the flat of the piston to the flat of the head.

Down in the hole = thinner gasket. 0 Deck = thicker gasket.

Look into Cometic gaskets as the come in many thicknesses.

 

[rumblefish360]

The amount of deck milling needed or not. The pistons will not sit at zero deck out of the box. Or they shouldn't. If the pistons are .010 in the hole, thats fine. You need to calculate the ratio. In order to do this, the piston to deck clearance must be known as well as cylinder head cc amount and the gasket dimensions.

These pistons at zero deck with a 72cc head and a .039 gasket will yield a 9,8-1 ratio. There is a slight variable with the cylinder heads gasket bore. So you could gain or loose .01 or .02.
If you use a thicker gasket, lets say .055, the ratio drops a bit closer to the 9.5-1. So IF your piston is in the hole .010 or .020, that is OK and actually probably a good thing. 9.5-1 is pushing matters with that small cam. And I do mean pushing it. Your better off @ 9.0-1.

Through usage, the carbon build up will add a little more compression. Though it will take a long time. It does slowly add up. So if 9.5-1 is border line, what will another .03 do? Answer, nothing good.

 

[rumblefish360]

Sorry but I'll have to strongly disagree on this one; I have noticed a definite difference in .4 or .5 point and a huge difference in .8 point of CR. This is from putting in 3 different pistons in the same engine in 3 successive racing rebuilds, no other changes. A .4 difference is noticeable for sure; this difference was felt at the bottom end of the torque range but not at the top end.

So for a revving drag race engine with a moderate to high stall converter, probably not so much, but it will make a definite difference for a street/cruiser engine. The 3% DIFFERENCE FOR 1 POINT DIFFERENCE IN COMPRESSION NEEDS TO BE PUT IN ITS PROPER PERSPECTIVE; THIS IS FOR THE PEAK HP NUMBER ONLY, AND IS TOTALLY MISLEADING FOR THE LOW END TORQUE EFFECTS.

YEs, I agree, to a degree. I do believe I wrote the same sentiment. But I could be wrong. The raw numbers I mentioned earlier and show are not the whole story. Also, if the compression ratio is more complementive to the cam and cars set up, it will be noticed. But it is very small. Very! Did I not say this. Is this not what your stating?

 

[rumblefish360]

Look into Cometic gaskets as the come in many thicknesses.

I'm having my deck machined for there use and will adjust the ratio downwards for the intended cam on the wifes ride. The idea is to have some flexibility and room to grow with bigger cams and smaller head chamber cc's in the future.

 

[nm9stheham]

As for the KB362's, I just added up the numbers and the compression height is 9.558 which is about .041-.042" below stock LA deck height and about .02-.025 below stock Magnum deck height. The H116CP's are more like .055" below stock LA deck and about .035-.040 below stock Magnum deck. DO you have a Magnum block?

So either will need a lot of decking with an LA block if you want to get to zero deck and have a quench gap. The Magnum decking to zero deck would not be so bad with the KB's. Conventional wisdom is that you run a true 9.5:1 CR with iron heads IF you have a quench gap, otherwise keep it down closer to 9:1. With the 262 cam, I would stick with these rules.

I too am getting 9.8:1 SCR with the H116CP pistons with a .051" thick head gasket and assuming a Magnum block, but not zero decked. With the H116CP's at zero deck, I get 10.3 SCR with a .051 head gasket. Either is too high for your street use with pump gas and iron heads and no quench per conventional wisdom.

Going back to the KB's I get 9.25:1 with the KB362's at zero deck and a .039 head gasket (Felpro 1008) and a Magnum block. IIRC, the raised pad on the valve side of the KB pistons is at the top and will form a quench gap with the head's closed area, and so you will have the benefit of a quench gap to help the pump gas be OK with a 9.25 SCR. But check with KB on that raised part to be sure....) Those pistons are pretty much designed to meet your application. That is one thing I have noticed with KB: they seem to have more variety of pistons and look to have done their homework in dome designs to meet both the wilder high CR drag race apps and the pump gas street engines.

And as far as hypers... I have raced hypers a fair while with 14-15 psi boost with no problems; I was a bit worried but they were fine. And we just put some KB hypers into my son's 340 with the tops shaved .030"; the thinnest part of the head is donw to .185" miniumum thickness...so far so good but we yet to have really let 'er rip as we progress through a gradual break-in and wringing out fo small problems.

But with the lighter weight of the KB 362 hypers and pins, you will need to rebalance the engine, as you are dropping about 122 grams per piston and pin. It will make the stresses on the engine less. The H116CP weights are almost identical to stock so no rebalance is needed for those.

 

[nm9stheham]

YEs, I agree, to a degree. I do believe I wrote the same sentiment. But I could be wrong. The raw numbers I mentioned earlier and show are not the whole story. Also, if the compression ratio is more complementive to the cam and cars set up, it will be noticed. But it is very small. Very! Did I not say this. Is this not what your stating?

Now you confused the hell of of me... but that is not hard LOL. CR is important regardless of cam.... Gee, if CR did not matter, we would all run 6:1 and use 55 octane gas.... or coal gas... or cow methane.... or anything that would burn. LOL

For a low RPM, torquey street engine, it will show up by extending the bottom end RPM range, and also in combustion efficiency (power extraction per cycle) and thus help mileage. The older guys here all know firsthand what happened with the mid 70's engines when the CR was lowered to reduce peak compression temps and thus NoX emissions: torque, power and mileage all suffered. And really, the same applies for high RPM drag engines: SCR is boosted way up to make up for the loss of DCR with the wild cams.

So, that is not what I am saying as far as being noticeable.... I'll just go back to my direct experience with changing CR 3 times in increments of about 0.4 or 0.5 in the small engine; the effect was VERY noticeable each step. And again, it was felt at the low end, not at peak HP. For some applications, a big increase in low end torque is very important; street operation is one (perhaps excluding street drag racing). My race engines are for rallying, and there is only one important torque RPM range: ALL OF THEM! You're making 100-2o0 turns per the typical stage, all of them of different radii and speeds, and so a broad torque band is a key engine parameter.

I am going to blame all of this on Rani and his seemingly innocent questions LOL