400 budget compression HELP +++++

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dodge71demon

dodge71demon

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I have a rebuilt 400 that is stock with 30 overbore flat top pistons and trying to find the least expensive way to get a little more compression for now with better quench due to the possibility of doing a stroker sometime in the future not wanting to deck the block etc I have a set of heads that have been ported etc and they are at a shop getting checked for cc etc I'm looking at the KB240 pistons looks like they would raise the CH by .095 (1.813 to 1.908) putting the piston down in the hole around .025 + compared to around .125 now any opinions would be a great help I may be way off base on this
 
How come you wouldn't want to deck the block? Not saying to chop .500" off but maybe if you have it cleaned up say .020" - .030" or so to square things up then get the pistons you're looking at, you'd be close to zero deck, no? Factory blocks tend to be all over the place with deck heights, so you could have some cylinders off enough to make a difference. Just sayin'.

If you're getting pistons, then the whole thing is coming apart anyway. At that point, decking the block wouldn't/shouldn't be a huge deal if you know a reasonable machine shop. Probably two passes on the surface machine.

But if that's a no go, .025" down is not too bad. You could use the .020" steel shim head gasket. Would be good to know the chamber size your real deck height before you buy anything.
 
Stealth heads would be another affordable option compared to pistons etc....
 
Pistons are less than half of what a set of those aluminum heads cost. Even if you took the block to get machined, you'd still be dollars ahead over buying Stealths for $1,100.
 
rmchrgr said:
Pistons are less than half of what a set of those aluminum heads cost. Even if you took the block to get machined, you'd still be dollars ahead over buying Stealths for $1,100.
Click to expand...
He did mention a stoker in the future which would mean putting some $$ heads sooner or later....
 
True. But, for the cost, I don't think the Stealths would offer much over the ported iron heads he said he has and the pistons would still be way down in the hole.

Guess there is the cost of balancing with new pistons as well but I say build the best bottom end you can, heads are just a bolt on deal later when you have the short block to support them.
 
rmchrgr said:
Pistons are less than half of what a set of those aluminum heads cost. Even if you took the block to get machined, you'd still be dollars ahead over buying Stealths for $1,100.
Click to expand...
I'm hoping the heads I have are pretty good I know they have been reworked so they are sort of the determining factor right now
 
The cheapest way to take car of your problem without decking the block or buying pistons at this time is to offset grind the crank.
You mentioned a stroker later and 400 cranks are not valuable, so why not get a set of .060" under rod bearing and have the crank offset ground .060" You'll have $200 in doing it and a little effort, but it will give you what you want without disturbing the block. Or if you really wanted to zero deck the piston you could pickup a 440 crank (yes a little more effort) and play around with the stroke (destroke) and get your piston right at zero deck height

Tom
 
You won't have any quench unless the heads are closed chamber. If you have plans for a bigger motor - save the cash and do that one rather than trying to half-*** it to gain little to nothing for benefit.
 
Search stock 440 by IQ52. He made some very impressive numbers with a 440 with under 8:1 compression.

Learn to use punctuation, too. It really helps others read your posts. No offense meant.
 
New pistons are cheap but then there's block clean up, hone, gasket set, balancing, new rings and bearings, it adds up. While it still maybe cheaper than new heads, it is a lot more work.

What are your cylinder heads cc amount?
What is out there in a small chamber?
I read Edelbrock has a 75cc chamber in there E-Z street heads. I don't know about other heads.
 
If you're going to do a stroker eventually, stop putting money into bottom end parts, that's all going to go away. Put money into the heads and valve train and run a decent camshaft.

Where are you in IN? If the shop you're using doesn't flow your heads, I may be able to flow them if you're willing to bring them up into IL by Wisconsin. So you have some real data to know where you're at and whether it's worth continuing with the heads you have or going with something else. PM me if this interests you. S/F....Ken M
 
Quick question for all, being it is a low compression 400, how much can he increase the ratio with a head swap?

What could we be looking at? A 1 point gain? Better? Less? 90cc head (?) down to a 75cc head (OOTB State) equal 1 point?
This would be a 7.8-1 stock ratio (?) to a 8.8-1 or possible 9.0-1?
Just wondering out loud.
 
Throwing some notional numbers at the problem. Assuming stock bore and stroke, 4.400 gasket .021 thickness, 90cc heads and .080 piston in bore, that's 8.1. Going to 80cc heads bumps that to 8.8.

You can plug in whatever numbers you have .
Engine Compression Ratio (CR) Calculator

S/F....Ken M
 
Thank you! I do not know the specs of a stock low comp 400. Thus the question and food for thought.

I have yet to get my broke butt into my future low buck 400 Duster build.
 
Like moper said, you are not going to get any quench unless you use closed chamber heads. What do you want from this engine? We are always trying to push the compression ratio to the limit on pump gas and risking some detonating piece of crap. Here is a 7.5:1 compression 400 that if we would have tested with a 4-bbl dual plane manifold like the Performer RPM would have really been impressive. Save the compression gig for the stroker.

The slug 400 on the dyno.
 
IQ52. Well, when working with a slug deep in the hole, quench is out of the question. Rebuilding it may not be an option. (It isn't for me) Airflow trumps compression for adding power correct? Adding a cam helps unless the compression ratio is in the bottom of the bowl. I don't think going from a open chambered OE head to a closed chambered aftermarket head would hurt or push anything to far.

How do you help a low compression 400 beyond your thread? Just wondering?
 
Put on a set of service prepped 75cc RPM heads, RPM intake manifold, long tube 1-3/4" headers.

A bigger camshaft is going to make more power still. It was proven over 20 years ago that you could put a bigger and bigger camshaft in a low compression engine and keep going faster in the 1/4 if you were using the proper gears and converter.

The problem we've found.....if you get the top end flowing really good on an old worn engine.....massive blow by.

We've had an old 100,000 mile 8:1 383 making 525 HP on the dyno. We used 5/8" x 3' hoses to tie the valve covers to the pan evac system and we decided to disconnect the hoses off the exhaust once to check the blowby. Those 3' hoses stuck straight out horizontially from the valve covers there was so much blow by.
 
A bigger camshaft is going to make more power still. It was proven over 20 years ago that you could put a bigger and bigger camshaft in a low compression engine and keep going faster in the 1/4 if you were using the proper gears and converter.
Click to expand...

Like the MP book did with the 400.
 
I've put '915' closed chamber heads and steelshim headgaskets on a stock 400 recently.
But because this was just a driver-engine I didn't calculate or measure the results.
 
I don't know anything about bigblocks.
But I can do a litle math
It seems to me,the 400 makes a real nice stroker pkg, and if stroker is in the future, Why not bring the future into today. And then bolt on the top end you already have. It seems to me, that would cover all the bases regarding compression and budget.
The cost of the crank would be offset by some/most of the machining costs.

If your current pistons really are down .125, then a 3.75 crank will raise them up by 1/2 the stroke difference or (3.75 - 3.375) x 1/2 = .193. So now the pistons would be up at (.125 - .193 =) .068 above the deck. subtracting .040 for the gasket, that puts them into the head at (.068 less .040 =) .028. Adding .035say for squish,means the open-chambers need to be (.028 + .035 =) .063 deep. Is that not pretty close? If it is, then your costs are just the crank,making it fit, and a re-balance.How much could that cost;versus some of the other solutions posted here? I guess compression would swing the other way now, and we'll get a new thread "help me reduce the compression of my 450". To answer that, I guess if you cannot machine an appropriately sized dish into your current pistons, then KB(at least) makes pistons for this application.But I get about 10.2Scr with a 90cc head, and those flat-tops.If that math is right, then it wouldn't take much of a cam to drop the Dcr down into street-friendly territory.I worked it out with a 66*ICA to 8.0Dcr/160psi. This puts you into a very mild cam; I'm going to guess something like 276/286/112, in at 108.
Oh and the math comes to 4.372bore x 3.75 = 450.3731 cubes! That is plus 12.5%
Or am I out to lunch?
 
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"451" strokers based on 400-blocks and 440-cranks are the most popular stroker-combo's these days.
Most pistons manufacturers have "stroker"-pistons on stock.
 
IQ52 said:
Put on a set of service prepped 75cc RPM heads, RPM intake manifold, long tube 1-3/4" headers.

A bigger camshaft is going to make more power still. It was proven over 20 years ago that you could put a bigger and bigger camshaft in a low compression engine and keep going faster in the 1/4 if you were using the proper gears and converter.
Click to expand...

As in....my 446ci SP motor, 9.8:1, stock 906's, CC .290@.050-.650/.650 SFT cam, 4.88's, 4800 A1 verter = 11.23@118 added ported 906's 2.14/1.81 nothing else 10.7@125, ok so thats not real low CR but that cam was meant for 12:1+CR......
 
Deck the block to at least make it equal and then angle mill the heads as much as you are comfortable doing.Run a thin head gasket and don't over cam it.
 
I wonder, what's the biggest cam any one has run with stock slugs......
 
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