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Matching combustion chamber size to blocks bore
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richardparker
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PostPosted: Thu Jun 23, 2011 10:57 pm    Post subject: Matching combustion chamber size to blocks bore Reply with quote

I am well into part collecting and a motor build.
This is a acura v6 build that is/will be bored and stroked when assembled.

First question I have for you guys will be I have my block bored 1mm over sized from 89 to 90mm. I have got custom made 90mm headgaskets.
My heads are fully worked:
intake side
exhaust side
throats
and flaws removed and polished the combustion chambers.

Should I enlarge the combution chambers also to the 90mm bores of the block ?

I have many other questions but,this is my first to test the waters and the knowledge of this forum.
And thanks in advance.
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Paul P
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1971 Chevrolet Chevelle

PostPosted: Thu Jun 23, 2011 11:45 pm    Post subject: Reply with quote

Why do you think you need to do this?

What are you trying to accomplish?

Doing this would lower your compression, possibly affect flame travel,swirl, overall combustion chamber design and efficiency.

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richardparker
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PostPosted: Fri Jun 24, 2011 12:11 am    Post subject: Reply with quote

The only thing I do know it will lower compression.
Right now ,with the build my compression is at 11.1 with my chosen parts and I do want to raise it high as possible to run on pump gas.
I do know what I can do to achive this but I don't want to fight myself opening up the combustion chamber size.
my heads threw the whole intake right threw the throttle body is gasket matched.
I need to know if the 1mm differannce would help/hurt anything matching them up better or just leave it be.
This is my first full custom build so their is alot I'm not sure of.
The site I am on everyone just knows how to bolt on parts.

I guess I'll get to my next question while I'm at it.

I have bought cams for a 3.7 that had +1mm of lift.
I had the re grinded for performance.
Now the cams have a smaller base circle and the lobes look 1/2mm shorter too.
Now with the smaller cams I think the valves will need slightly longer tips to keep the valve train geormtry correct.
Only pieces I have not ordered yet were new valves.
(I did fill out a custom order form for ferrea).
But a friend told me I should build my head with my old valves first then measure and then order valves to the size I need and not jump the trigger and buy new valves first.
Because if I do and the geommtry is off the I may have to use valve tip shims.
Is this correct ?
Are valve shims a bad idea?
And does anyone know if I would need them with the smaller base circle cams.
I really want to order my last pieces but I don't want to make a bad decession.
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Paul P
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PostPosted: Fri Jun 24, 2011 8:57 am    Post subject: Reply with quote

As far as the chamber goes the only thing that might be beneficial is a polished surface. I would not open them up just to match the bore.

This is an overhead cam engine correct? If so there should be buckets or shims on the valves to set the clearances. I would think you are not the first to perform such a mod and they should be available somewhere. If not the longer valves will do the trick at a higher cost.

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6.95@98.6 MPH 1/8mi
10.97@121 MPH 1/4mi
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squeeezer
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PostPosted: Fri Jun 24, 2011 12:53 pm    Post subject: Reply with quote

Only enlarg cc if you are unshrouding a valve
Im pretty sure that's not your problem

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richardparker
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PostPosted: Fri Jun 24, 2011 4:20 pm    Post subject: Reply with quote

Paul P wrote:
As far as the chamber goes the only thing that might be beneficial is a polished surface. I would not open them up just to match the bore.

This is an overhead cam engine correct? If so there should be buckets or shims on the valves to set the clearances. I would think you are not the first to perform such a mod and they should be available somewhere. If not the longer valves will do the trick at a higher cost.

Great, the chambers are polished.
Yes it is a sohc motor . 1 cam in each head.
Far as I know I'm the only one that is wanting the valve train geomertry correct w the j32.
Their have been others that have ran re ground cams but they just slap them in and they complain the re grinds are crap because they get worn quickly. And I am the one that wants to over come this issue.
I plan on buying new valves either way but,would buying new valves and adding shims a bad idea?

So far I'm atleast 3k into parts not including 500 I bought the engine to start with and porting/machine work.
Plus I have all bolt on parts you can buy . So another 6-700 on valves will be needed/wanted.
I also am wondering about increasing the valves head size but I don't know how much more work/money would be needed to do this. I know there is room in the throat to open up for a larger seat but I 'm not sure how much room is in the chamber itself.
I also want to increase compression but I really do not want to deck the block or the head,since adjustable cams gears are not available.We have a guy working on some but he's not done with them,still trying to get the reluctor wheel to work perfectly with the cam sensors.
And the only thing I could think of it to get flat face valves . The factory valves have a dish I want 0 dish but, I don't know anything about them at all and what work would have to be done to run them or if they will work with no added work.

The people that build these engines at most do some porting and very few try custom cams.
I don't know any of them who have went with larger valves or higher compression.
And I only know of one who had their motor bored and stroked to 3.7 like I'm doing.
He used stock 3.7 cams springs and retainers and valves injectors ,ecu and stayed at 11.1
I have custom cams,titainium seats,retainers and light weight stonger seat preasure springs and want valves and higher compression.A larger fuel set up and tunning.
And will possibly lighten and knife edge the crank, balance rods and pistons.
I want more than the next guys has,and he had the most whp than everyone else N/A. I think he was at 315.He crashed his car and now I'm wanting to take off from where he left off and improve.
I'm wanting as much whp as possible. The 3.2 super charged guys are only putting down 330-350 whp and I want to bust their asses 3.7 N/A.
I know it can happen but I need the knowledge to do it.
But No one I deal with on acurazine know's much.
Trying to see if I can get help from guys who might possibly really build.
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clay
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1972 Chevrolet Nova

PostPosted: Fri Jun 24, 2011 7:35 pm    Post subject: Reply with quote

For a 1mm overbore you are only looking at 0.5mm radial increase which is roughly 0.020". I don't think you will gain anything beneficial for the work involved. If valve shrouding is a problem on that particular head there may be some SMALL gains in flow but not worth the trade off of expense and labor. What type of valvetrain is this engine. Does it have some sort of rocker or is it a bucket style of lifter and if so I'm assuming hydraulic but I could be wrong there too. I have messed with some motorcycles with shim over bucket and shim under bucket valvetrains but never the specific engine you are talking about. I'm willing to try to help through. Clay
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richardparker
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PostPosted: Fri Jun 24, 2011 8:48 pm    Post subject: Reply with quote

clay wrote:
For a 1mm overbore you are only looking at 0.5mm radial increase which is roughly 0.020". I don't think you will gain anything beneficial for the work involved. If valve shrouding is a problem on that particular head there may be some SMALL gains in flow but not worth the trade off of expense and labor. What type of valvetrain is this engine. Does it have some sort of rocker or is it a bucket style of lifter and if so I'm assuming hydraulic but I could be wrong there too. I have messed with some motorcycles with shim over bucket and shim under bucket valvetrains but never the specific engine you are talking about. I'm willing to try to help through. Clay

If it's no worth messing with the combustion chambers any further I am happy with that.
I just want to be able to get the most air in and out of them.
I have a pdf file that is my complete engine manual if that may help with some answers. The file would not be able to be posted I'm sure. But if some one want to take a look and try to help me how ever they could I could try to send pages related to the heads.
I probably have pics of the heads already I would just need to go threw my photobucket and find some.
My heads are dissasembled . I have the rocker set up's where I could take pics of those too.
The only thing is this heads that resemble lifters honda calls lost motion assembly's.
I know about lifter and push rod v8's but,I'm not to farmilliar with these and I haven't even looked at them since winter.
But they are here to take any pic's anyone would need but my engine file has everything and every spec to dissasemble and reassemble the whole engine.
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af2
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PostPosted: Fri Jun 24, 2011 10:16 pm    Post subject: Reply with quote

richardparker wrote:

Trying to see if I can get help from guys who might possibly really build.


Think of the squish to get the mix in the chamber and the Quench after the fact to keep from detonation.
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richardparker
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PostPosted: Fri Jun 24, 2011 11:47 pm    Post subject: Reply with quote

This is a pic before even was disassembled
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clay
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PostPosted: Sat Jun 25, 2011 12:05 am    Post subject: Reply with quote

Is this a VTEC engine? Trying to figure out why it appears to have 3 rocker arms for 2 valves on the left side. I don't see why you just can't simply screw the adjuster further down to accomplish the same thing as longer stem valves. Does the company that reground the cam offer any advice in any way? I ran a Ford 2.3 years ago and they had some issues with smaller base circle camshafts - overhead cam but still not like you have. Clay
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10sec.et
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PostPosted: Sat Jun 25, 2011 12:25 am    Post subject: Reply with quote

not a v-Tech but i thought the same thing at first. it has two tiny intake valves and one large exhaust valve. to an extent you could just adjust the lash to compensate for shorter/longer valves but eventually you would run into the same problems as having too long/short pushrods.

beyond repairs, i dont really know much about these engines. i understand wanting to have the valvetrain geometry correct. i would approach it same as a pushrod motor and carefully check how the rocker arms "sweep" across the valve tip. since its an OHC engine, you should be able to set the head up on the work bench once you have the cam youre going to run and take your measurements. just be careful opening and closing those little valves. wont take much to bend them if they hit a bench top or anything else under the head.

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richardparker
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PostPosted: Sat Jun 25, 2011 2:09 am    Post subject: Reply with quote

This a j32a2 type s vtec head these heads have the biger valves and the higher lift cams stock. 4 valves per cylinder.
Intake valves are 36mm
exhaust valves are 30mm
I was thinking I could adjust to compensate some but other wore their cams quick and I'm thinking its because they have not went the little extra to correct what I think where their issue is.

These are the cams going in.



I think the rocker set up has something to do with varible cam timming.
neither the people who did the work to the cams(web) or the middle man company(P2R) would tell me anything about the spec's
[img][/img]
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Paul P
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PostPosted: Sat Jun 25, 2011 11:28 am    Post subject: Reply with quote

Any pics of the chambers?

It is obvious that buckets are not the answer for these heads as they have rockers involved. Maybe lash caps? If you are getting longer valves that should make up the difference.

_________________
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1971 - Chevelle 408 SBC N.A.
6.95@98.6 MPH 1/8mi
10.97@121 MPH 1/4mi
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richardparker
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PostPosted: Sat Jun 25, 2011 12:14 pm    Post subject: Reply with quote

I was thinking I might need valve tip shims/spacers because if I just screw the lash down then it wont sit right/flat on the valve.

How could I figure the exact need for the extra lenth on the valve ?
Use a feeler gauge and just add the number that looks good by eyeball ?

No valves in.
Now that I have put my hands on them maybe I will mess with them this weekend.
And take some higher res close ups so we can see whats going on.
[img]
[/img]
I think I will start a whole new build thread so all can see what I have done so far from begining to the finished product.
and leave this one for my questions
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