Big-ol-bunch-a newb engine questions

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RogerRamRod

RogerRamRod

The Older I Get, The Faster I Was
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You-All here on FABO supplied lots of inspiration and help with the body/sheetmetal part of my project. As that part of the car starts to transition to being ready for paint, its getting closer to the stage of needing the engine done. I have been apprehensive about building my own engine, and had been interested in the posts done by MRL Mike.
Unfortunately as most of you know, Mike had to pull the plug. I have been reading up, and think I might like to tackle the job. I know enough can’t be said for experience, but the way to get it is to do it, right?
My 340 is currently .030 over, cylinders look good, I hope a hone will suffice, but may need to freshen up by taking it to .040, or 4.080. Trip to machine shop soon.
I originally thought I wanted to build a stroker, but have since decided to stay stock stroke. I think I would like to follow the formula Mike used in the linked thread.
MRL 340 for the 21st Century

A stock 340 lists compression height as 1.84, with a 6.123 rod. His formula uses a 6.250 rod, so I assume I would reduce the compression height by .127, am I correct?

I saw the thread on the Trick Flow PowerPort 190 heads. It seems the overall opinion is they are money better spent than on Edelbrocks.

So that I know if my math is correct, will a 4.070 bore, 3.31 stroke, flattop pistons with 5CC valve reliefs, .040 head gasket and 60CC Heads would give me a 10.6 static CR. Kinda high, so I would what…have the heads opened up some? Pistons shaved?

Biggest questions.. How does one go about finding 6.25 rods with the right big & small ends, Pistons with the right compression height and/or shaving them (I lose quench then, correct?) Are these custom made items? Does the cost get crazy, or are these considered minor modifications like I read that its cost effective to get custom made cams these days?

I have an Air Gap RPM intake & was figuring a 750 carb, possibly going to Sniper or FiTech down the road if it makes sense.
 
Thank you, Don’t know why I wasn’t thinking about that, I know you use them on stroker’s.
Is the rest of it (shorter pistons and longer rods) a simple matter of calling a piston and/or rod manufacturer, Or is that high dollar custom work?
 
RogerRamRod said:
You-All here on FABO supplied lots of inspiration and help with the body/sheetmetal part of my project. As that part of the car starts to transition to being ready for paint, its getting closer to the stage of needing the engine done. I have been apprehensive about building my own engine, and had been interested in the posts done by MRL Mike.
Unfortunately as most of you know, Mike had to pull the plug. I have been reading up, and think I might like to tackle the job. I know enough can’t be said for experience, but the way to get it is to do it, right?
My 340 is currently .030 over, cylinders look good, I hope a hone will suffice, but may need to freshen up by taking it to .040, or 4.080. Trip to machine shop soon.
I originally thought I wanted to build a stroker, but have since decided to stay stock stroke. I think I would like to follow the formula Mike used in the linked thread.
MRL 340 for the 21st Century

A stock 340 lists compression height as 1.84, with a 6.123 rod. His formula uses a 6.250 rod, so I assume I would reduce the compression height by .127, am I correct?

I saw the thread on the Trick Flow PowerPort 190 heads. It seems the overall opinion is they are money better spent than on Edelbrocks.

So that I know if my math is correct, will a 4.070 bore, 3.31 stroke, flattop pistons with 5CC valve reliefs, .040 head gasket and 60CC Heads would give me a 10.6 static CR. Kinda high, so I would what…have the heads opened up some? Pistons shaved?

Biggest questions.. How does one go about finding 6.25 rods with the right big & small ends, Pistons with the right compression height and/or shaving them (I lose quench then, correct?) Are these custom made items? Does the cost get crazy, or are these considered minor modifications like I read that its cost effective to get custom made cams these days?

I have an Air Gap RPM intake & was figuring a 750 carb, possibly going to Sniper or FiTech down the road if it makes sense.
Click to expand...

I just read through that MRL thread and he doesn't post piston or rod part no's, maybe that is part of his secret. I would love to know though.
 
D0DEBE2A-34FC-450E-A5F8-E104C398187E.png
New heads not yet released- late next year.
** NEW ** Trick Flow LA cylinder heads introduced at SEMA
Old Man Mopar says Trick Flow specs them at 60. Not exactly sure where he got that info.
Can’t say I blame Mike for not posting that info, he was in business to build engines, not write engine recipes.
 
Oh Yes I missed it in the skimming, sorry. Those look pretty good

As to the compression ratio being too high, that depends on a lotta things, chief of which is the ICA and the Quench.
 
Is there a compelling reason to go with the longer rod? It is not a significant rod length change so the changed performance will be pretty small. You'll get far, far more out of good heads for the same $$ spent. It involves machine work on the crank.

And as far as I know, the pins on the crank were moved at the same time as turned to smaller diameter; that may be how the SCR was made less; I'd have to sit down and work out all the numbers to know. And the bobweight saving is not as large as just going with straight SCAT rods and KB pistons.

That is not your first-performance-engine-building-101 type of set-up and it does not sound like you are anywhere close to that next level if you are even contemplating just honing the bores. IMHO, KISS and stick with stock rod lengths, etc. You'll have plenty on your plate with just that!

Can you share what you objectives are for this car and engine? Drag racing? Pure street cruising? Towing cotton bales on bad Mexican gas? It makes a big difference on some of the decisions you'll make.
 
Hmmm, solid points.
Mostly street, but might like to get involved in local autocross. There is also a road track not too far away. Drag track once or twice a year just to see.
Hoping for honing only in order to keep from thinning the walls any further.
Steel body, full interior, USCar Tool stiffening kit.
3.73 or 3.91 rear with o/d trans-manual v.b. Currently 3.23 w/reverse man 904.
 
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Autocross, road race (which I initially typed as 'toad race' LOL), and rally are best served with engines that have a useful torque curve that extends over an RPM range that is greater than a 2:1 ratio of high to low RPM's. That engine article shows a great flat torque curve but only over a well-under 2:1 RPM range. To see how good it would be for this use, a better view of the low RPM torque on the dyno would be useful.

Keeping the SCR up in the 10:1 neighborhood is a good start; that helps extend the low end of the usable torque RPM range with a cam that is likely gonna be good for this use. For Autocross, you are gonna get all the torque and HP you can use with a simple live rear axle and leaf spring setup from Edelbrock head flow levels. So the Trick Flows might be useful for the drag racing and maybe a road coarse with some long, high speed straights. But I don't have any idea at this time if they have much larger ports that might adversely effect low RPM torque.

IMHO, a solid 350-400 HP engine with good low RPM torque will do you fine for most of what you want. Putting that power down on an autocross course or even on the strip will be a concurrent challenge, so I'd be addressing that as much as the engine, in addition to some really good brakes. Any HP over that is gravy for the drag strip, and maybe on the street if you're going for some sort of High HP street racing or something. (The term 'street' gets used for a lot of different things...)

Understood on the hone; makes sense. Just keep in mind that a good piston-bore clearance and good ring seal is one of the 2 main foundations for a good engine.
 
Thanks for the thoughtful reply, I noticed the "great flat torque curve" but hadn't considered the "2:1 ratio of high to low RPM's". Good to know.
 
Yep, when you down get around 2:1 for a usable torque band, you'll find yourself 'falling off the torque curve' a lot unless you have a 5 or even a 6 speed trans. You just never know what each course may bring as far as what gears and speeds you will have to use as you come out of each corner. So a 2.5:1 or more solid, usable RPM range is a real plus. I rallied for a lot of years on a 4 banger that was gangbusters between 3800 RPM and 7700 RPM, but was deadsville below 3800, and it 'fell off the torque curve' all the time on the 2-3 shift at around 55 mph; it really cost me some time on some stages and was like a 2 stroke motorcycle with just 3 speeds in the trans LOL. I was still learning both the issues and how to make engines behave like it was needed. I then had a smaller 4 banger with a better cam and SCR, and it was solidly in the torque band from 2500 to 6500 RPM; that was as fast or faster a rally car with 16% fewer cubes and a whole let less flailing of the gears. Lesson learned!

Additionally, with RWD, if you learn drive it right, you'll be using the throttle a LOT for torque steering the car. That is where a good wide torque range will give you 'throttle-on-demand' with very good control over the torque going to the rear wheels. If you have a narrow torque curve and put in a high stall converter, then you'll end up 'hunting' for the right throttle position to get the 'right' torque for a corner exit; it's hard to do and suboptimum. Optimally, you ought to consider a manual 4 speed close ratio if you are really serious about to autocross and road race stuff. Once you do that, then you can really use downshifts and engine braking to help in some situations, particularly setting the car's attitude going into a corner.

So, probably a lot more than you wanted to hear, and maybe ZERO useful for your situation, so take it FWIW! Regards....
 
No, in fact I welded a floor hump in for a manual, but I have a partial handicap issue with my left leg, and don’t want to spend all the money going that route to find that two years in, I need to change it all back to an auto. Almost every car i’ve owned has been a manual trans.
 
I'm not trying to be a dick,. but it seems too often it just turns out that way,.....
Stroke it,
you're gonna need to pick up the low rpm, then you can run a smaller cam. And then you can run a smaller head. Stick with aluminum and crank up the cylinder pressure. Bias the build for autocross, and let the strip be what it will be.
With a 3-speed automatic, you can't hit all the targets; but you might hit the 1/8 OK. To ET well in the quarter, will require a gear swap;About 1.3 hours each way.
A big cam on the street is IMO, a royal PITA.Bin there not goin' back.
With an automatic, your idle to stall rpm doesn't much matter. But I'm no fan of a 3500 stall around town. A 2800 is pretty OK. So that allows a cam somewhere in the range of 230/240*@.050; On the lower side with a stroker, or towards the high side with a roller cam.
Even if you only go to a 3.79 stroke, this will get you 381 cubes. Those extra 41 cubes are worth about 2 cam sizes,and will get you a lotta low-end torque, making around-town bombing so much more pleasurable. And you don't have to run as radical a rear-gear. With good heads, a 3.79 crank,and a 230 cam, she will pull to waaay past 6000, try 6800! Mine in a 367 is still pulling reasonably good at 7000.
If you stick with aluminum heads you can run a lotta pressure. 185# on 87. Some guys here are running a tic over 200# on 91. That's where the power is. To run on the edge, your quench needs to be pretty accurately tight.
Cubes pulls up the bottom, rpm the top, and airflow fattens it up everywhere.
Sometimes, the aluminum heads end up cheaper, depending where the compression comes in with your chosen pistons, and the ICA. What I mean is less machining costs, less porting costs.
You can't run those pressures with iron heads, 165# is typically the max on the street

Anyway, I think that's what I would do,lol.
 
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RogerRamRod said:
No, in fact I welded a floor hump in for a manual, but I have a partial handicap issue with my left leg, and don’t want to spend all the money going that route to find that two years in, I need to change it all back to an auto. Almost every car i’ve owned has been a manual trans.
Click to expand...
Ah, so I am preaching to the choir on manuals LOL. Understood totally.

I have no clue about this existing for aftermarket, but I sure wish there was an aftermarket auto trans like in the new Challengers; when you put it in 'stick' mode, the TC stays locked all the time except when you come to a stop; it does a damned good job of simulating a manual with the engine braking, etc. I have a manual R/T and my SIL bought an auto R/T. (She's a 3rd grade school teacher... go figure!) When I drove hers once and used stick mode in the mountains, I said 'THIS is different'; took me a bit to figure out what the tans was doing with the locked TC. It really makes driving the turns a lot better.
 
Thanks for all input so far. This is a project that doesn't need to be done right away (as much as I'da like to been driving by LAST summer) so I have time to contemplate, get to machine shop & see what my starting point actually is, etc. I was originally planning on stroke, but I dare to be different, & it seemed strokers had become ho-hum.


replying to AJ below so that I don't make thread needlessly longer, I personally wasn't thinking ho-hum & have always been stoked about stroked, but reading different threads I see a lot of "everybody does strokers....." thought I might consider modern build on original cubes, but I think I'm rethinkin.
 
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Ho-Hum! are you kidding!?
If you had a choice between; a rebellious,nagging' "I never cook,clean house,or you can forget about sex",wife; and ......the perfect specimen that loves all of those things especially burning rubbers, I mean I know which one I'd choose.

There is no downside to a stroker; consider what Chrysler's game plan was for their small blocks.
Strokers are different; they are TNT ,in a plain turquoise wrapper.
 
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