Help on 408 build

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So pistons sounds the most appealing to me. If I can run the engine just with new pistons I’ll be happy. I just have to make sure this WILL work and have some kind of useful power.
 
The kit was balanced before it was sent out. I don’t remember getting a sheet but I will look
 
gzig5 said:
Can the current flat top pistons have a dish lathe turned? Trading labor for parts, but should be quick once the first one is set up.
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If this was an old Detroit design piston with a .400"+ thick crown, then very likley 'yes'. But, these UEM pistons from the Icon and KB lines typically have been lightened up a lot with techniques like taking material out everywhere, including the piston crown. So I seriously doubt that the material is there to take out a .100"+ deep dish and keep anything close to an adequate crown thickness. And the weight would go down by over 40 grams if you cut out 17.5 cc's of AL, so the balance would indeed need to be re-worked.
 
Mopar204 said:
So pistons sounds the most appealing to me. If I can run the engine just with new pistons I’ll be happy. I just have to make sure this WILL work and have some kind of useful power.
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That 'lack of useful power' is not directly explained by the excessive CR, unless the engine was perhaps detonating all the time. A 408 sure ought to have good power! Regardless, the CR situation needs to be address.

BTW, it is still important to let us know what you want this engine to do: cruise, pure race, haul logs, or ?? The cam's appropriateness comes from the application.
 
Mostly street driven maybe once a year qaurter mile just to see what It can do
 
Catalogs

On page 27 of the Icon catalog it says the wrist pin for the IC745 piston is 0.984” x 2.75” and weighs 118 grams. On page 1 just below the table of contents the catalog shows light weight tool steel wrist pins. R-73 is listed as 0.984” x 2.75” and weighs 107 grams. That’s 11 grams lighter than the wrist pin that comes with the IC745 piston. Wouldn’t that be close enough to not have to rebalance or am I overlooking something?
 
I just read through this thread
lots of good suggestions from many different directions
On the gasket
They also make a shim to lower compression which might be cheaper than cometics if we are real tight on cash
Cam- duration is based on usage and where you want the rpm band and on converter and gears
do not but in big cam just to lower DCR if it puts you in a different torque curve than you want
Whoever said OEM LA heads are good chambers must be smoking funny stuff
They only work good on high rpm race builds
or builds where the rules say you have to use them
The later heart shaped chambers are much better chamber wise but not the answer here
Whoever said to scribe the gaskets and open the chambers- that always helps but even with thicker gaskets you may not get the compression down enough to make pump gas work- ask the DCR guys after you do the calcs
should be easy to get 5cc out of the heads DIY\
I haven't looked on SBM but there should be some -28cc pistons out there which looks like the answer
and quench closed chamber heads when the budget allows
aluminum and quench both help on the detonation
which may be why you have no power
do fix it before you break or torch something expensive
inspect your ring lands and rings
if not hammered and they are ductile moly tops you can reuse them- keep them in the same holes and fresh fine bottle brush if the bores were torque plate honed in the first place and still look good
 
Just a question
why not the KB Step dome KB356?
I helped design the predecessor to this piston just for OP's head 23.5cc
can mill the step dome off if going to closed chamber heads later
will take a trial assembly to get the gasket right for quench clearance dome to head if the heads have been milled much but down to .030 works and I've run smaller checking every chamber
Other choices are the ICONS for the magnum block
you get no quench but you do not have any anyway
(like B3 pointed our)
27 and 34cc plus .020 less compression height
do your math, play with the pins for the balance
Then ask the guys= there are some sharp builders on this site
cheers
 
Wyrmrider said:
Just a question
why not the KB Step dome KB356?
I helped design the predecessor to this piston just for OP's head 23.5cc
can mill the step dome off if going to closed chamber heads later
will take a trial assembly to get the gasket right for quench clearance dome to head if the heads have been milled much but down to .030 works and I've run smaller checking every chamber
Other choices are the ICONS for the magnum block
you get no quench but you do not have any anyway
(like B3 pointed our)
27 and 34cc plus .020 less compression height
do your math, play with the pins for the balance
Then ask the guys= there are some sharp builders on this site
cheers
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The set of magnum dished pistons could get him down to 9.3 SC and if that works with the current cam he could run it like that with his current push rods without the need for expensive gaskets or shims. I talked to another local Mopar guy and he also said 9.5 was about the limit on local pump gas with iron heads.
He could hang on to the LA compression height flat tops he currently has and in the future get some aluminum heads and a more aggressive cam and put them back into service.
 
If that 34cc -.020 CH magnum piston would not get him down nothing would
down too far? use a thin gasket
someone said it would take an 1/8 shim
that's a bunch
most i've done is stacked two gaskets as a quickie get home band aid
you could retard the cam 4 degrees but that by itself would not solve the problem but it would show if you liked more duration for your driving habits and preferences
I've retarded 8 degrees when running stock class requiring stock camshaft (not a cheater)
low gears and rev the snot out of it
measure twice- cut once
as I said great discussion in this thread
(actually cam was retarded a whole tooth then advanced- not rocket science but not easy for the tech's to catch either)
 
TX9 340 Plymouth said:
Catalogs

On page 27 of the Icon catalog it says the wrist pin for the IC745 piston is 0.984” x 2.75” and weighs 118 grams. On page 1 just below the table of contents the catalog shows light weight tool steel wrist pins. R-73 is listed as 0.984” x 2.75” and weighs 107 grams. That’s 11 grams lighter than the wrist pin that comes with the IC745 piston. Wouldn’t that be close enough to not have to rebalance or am I overlooking something?
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No, your'e not overlooking a thing; that would work fine; good thinking IMHO! I don't think that the OP's engine would overwhelm that thinner pin.
 
Mopar204 said:
Mostly street driven maybe once a year qaurter mile just to see what It can do
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Thank you for that info. That says (to me) to stick with a more modest cam to match the street driven application and reduce the SCR to match that and get the DCR under 8.
 
what NM says
get out your compression ratio calculator and run the numbers on the various option
I already made my suggestions
less compression with non quench dome pistons
and the quench domes make the motor less fussy on timing and gas
 
Only a guestimate but it sounds like compression is in the high 11s assuming zero deck height and with that smallish cam and that total timing im not surprised it is pinging.
Depends on what you want to spend on it now but most stock 360 heads i have cc'd have been around 72cc and if you put another pair of heads on with a slightly bigger cam you might get away with it without pulling the short block apart as compression would be in the mid to high 10s. This option would leave scope for later if you decide you want to step things up with a bigger cam and alloy heads,once you get used to it you may want more,it happens!
That cam is going to peak very early being in a 408, i have a 248 at 50 solid flat tappet in mine and it is still very streetable.
 
Well I think he has a number of choices and he will have to pick one and take his chances....

Install some really thick head gaskets/shims and maybe push rods cost $500-600. Add another $600 for a cam swap. ( the 1/2 *** fix)

Install pistons that get you down to the mid 9’s SC say $700 for pistons $100 for gaskets and $350 if you need to balance. You can probably get back $350-400 for the old pistons or keep them for a future build. Add $600 for a cam swap ( the 3/4 *** fix)

Keep the bottom end and purchase aluminum heads, you may still need a cam swap even with a 65cc head. Say $2000 for heads, $600 for a cam plus odds end ends probably $3000.
You could probably sell those ported J heads you have for $200-300 if you keep the adjustable rockers. ( the complete *** fix)

Leave it alone and burn race gas ( the no *** fix )

You might consider putting it on the dyno if you really want to tune it...around $500
 
I’m just curious if everyone agrees with 67’s statement. Putting money aside which is the best, most proper way of going forward with this? If I decide to not think about money and do this once and only once.
 
If you want to keep the same cam regardless if you leave the j heads or go with some alloys the chamber size is going to be the same so pistons are probably the best option.

If you are willing to change the cam for something bigger and do some alloy heads and slightly thicker gaskets you probably wont need to change pistons.

How available is e85 from the pump over there, could look at retuning it to suit and running it with a bit less timing?
 
Mopar204 said:
I’m just curious if everyone agrees with 67’s statement. Putting money aside which is the best, most proper way of going forward with this? If I decide to not think about money and do this once and only once.
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Honestly, the best way, money aside, is to drop that motor in a shipping crate and send it to a reputable engine builder to have it done. No offense to you at all, but what if you miss something else? You're already going to be into the motor for more than it would have cost for a builder to do it the first time. Let's face it, the money is an issue, or you wouldn't have asked for opinions on how to fix it without having to swap pistons. The thicker head gaskets will allow the compression to be lowered enough that there is no need for a $600 cam swap. You can use your existing cam.

Regardless of Mr 67's opinion, the gasket does the same thing as changing the pistons, and he still hasn't explained how gasket volume is different than piston volume. If you are still leery of the gaskets, call Cometic directly and ask their opinion. They have a reputation as the best Racing gasket manufacturer in North America, if not the world. They will give you a straight answer. I guarantee it's been done many times, for many reasons. It's your money, how far will it go?
 
luv ya b3 but changing to a quench dome piston gives him some quench whereas a gasket change does not an ok budget move if he can come with a balance como
will he have to change pushrods with a super thick gasket?
IMHO yes but TBD
anyway at this point he has all the variables and seems sharp enough to figure it all out
as you say existing cam will be fine -work on 60 foot times
 
Wyrmrider said:
luv ya b3 but changing to a quench dome piston gives him some quench whereas a gasket change does not an ok budget move if he can come with a balance como
will he have to change pushrods with a super thick gasket?
IMHO yes but TBD
anyway at this point he has all the variables and seems sharp enough to figure it all out
as you say existing cam will be fine -work on 60 foot times
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I agree, a quench dome would be a good move. But, I'm still going back to the budgetary concern that was given near the start of this thread. He didn't have quench before, so the gasket is not going to make that any worse. Good grief, if the motor hadn't already been built I wouldn't have suggested a thick head gasket, although, I have used them in builds for specific reasons. But, that knowledge didn't come cheap, so I'll leave it at that.
 
B3RE said:
Honestly, the best way, money aside, is to drop that motor in a shipping crate and send it to a reputable engine builder to have it done. No offense to you at all, but what if you miss something else? You're already going to be into the motor for more than it would have cost for a builder to do it the first time. Let's face it, the money is an issue, or you wouldn't have asked for opinions on how to fix it without having to swap pistons. The thicker head gaskets will allow the compression to be lowered enough that there is no need for a $600 cam swap. You can use your existing cam.

Regardless of Mr 67's opinion, the gasket does the same thing as changing the pistons, and he still hasn't explained how gasket volume is different than piston volume. If you are still leery of the gaskets, call Cometic directly and ask their opinion. They have a reputation as the best Racing gasket manufacturer in North America, if not the world. They will give you a straight answer. I guarantee it's been done many times, for many reasons. It's your money, how far will it go?
Click to expand...
Off course changing the pistons or putting thick gaskets technology does the same thing...the difference is head shims or really thick gaskets are prone to leakage issues, especially on an engine that we have no idea on if the deck surfaces are decent. Does that sum it up For you Mr B3
And if the kid needs help putting together correct I will make sure that he gets good help local....just like I got his head CCed for him even though I didn’t even know him.
 
Yes gaskets only is the least expensive "fix"
and a re-builder shim and thick gasket is cheaper than Cometic
and the cometics like certain finish on the heads and block- so check that
IMHO you can't build a decent street open chamber motor Bib block or small block
racing with race gas, keep the revs up- big cam yes or even premium running super stock
tall gears, stock converter, and pump gas no
Do what you have to do
just do it before you break something
 
So I came across guy that posted a for sale ad in my city selling brand new pistons in box for 500$ cnd

Wiseco Pro Tru dished stroker pistons

4.030 bore -20cc dish PT036H3

9.8:1 cr with 65cc

9.5:1 cr with 68cc
 
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