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Richard/SIA
Richard Brengman
No. Nevada
(387 posts)

Registered:
01/17/2014 07:47PM

Main British Car:
1969 Triumph GT6+ 225" Buick V6

How much to remove from 215 pistons to lower by one point?
Posted by: Richard/SIA
Date: January 21, 2021 07:44PM

Looking at a 215 engine project but the compression is too high.
Wondering how much I would have to remove to drop at least one point, one and a half might be even better.
Have to keep the crowns thick enough to live.


Jim Stabe
Jim Stabe
San Diego, Ca
(787 posts)

Registered:
02/28/2009 10:01AM

Main British Car:
1966 MGB Roadster 350 LT1 Chevy

authors avatar
Re: How much to remove from 215 pistons to lower by one point?
Posted by: Jim Stabe
Date: January 21, 2021 09:20PM

Cutting the tops of pistons isn't the way to lower compression. Engines rely on the turbulence created by the head of the piston coming in close proximity to the face of the head to provide complete combustion and reduce detonation. The piston to head distance is referred to as the quench area and is critical to reducing detonation from pockets of fuel/air unburned by the flame front. Back in the 70's when unleaded fuel was introduced a lot of the muscle car guys tried adding additional head gaskets to reduce compression/detonation but actually made the problem worse due to the reduced quench. I have a sbc in my MGB that is supercharged to 9 lbs of boost and it has 10.9:1 compression. It doesn't detonate on 91 octane fuel partially because I reduced the stock quench from .070" to .035" by milling the deck of the block.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6003 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: How much to remove from 215 pistons to lower by one point?
Posted by: BlownMGB-V8
Date: January 22, 2021 08:35PM

Yeah, you might be better off with a different cam choice. It's possible to lower the DCR to a manageable level even with a high static compression ratio.

What is the application and what is your existing CR?
Also what is your quench distance?

Buick engines often don't have a lot of quench area anyway and tend towards not being sensitive to knock from what I've seen but that doesn't mean you can ignore it.

Jim



Edited 1 time(s). Last edit at 01/22/2021 08:38PM by BlownMGB-V8.


Richard/SIA
Richard Brengman
No. Nevada
(387 posts)

Registered:
01/17/2014 07:47PM

Main British Car:
1969 Triumph GT6+ 225" Buick V6

Re: How much to remove from 215 pistons to lower by one point?
Posted by: Richard/SIA
Date: January 24, 2021 01:30PM

Cruising the web brought up a very old post on this very forum which mentioned that Buick 300 heads are 57cc chamber.
This was in reference to some 12-1 pistons that were for sale a decade ago.

Pistons for the engine I am looking at are 11.5-1 using 37cc heads, too much for a street engine .
Decking the tops of "Pop-Up" pistons to adjust compression is pretty common.
Even the big name manufacturers do this so that they need fewer forgings to meet demand.
The shape under the crown has to be considered to ensure that sufficient material remains, cannot go too thin.

So the new question becomes.
With all other factors being equal how much will a change from 37cc to 57cc chambers lower the compression of a Buick 215 engine?

And of course, anyone have a set of good 300 aluminum heads for sale?


Jim Stabe
Jim Stabe
San Diego, Ca
(787 posts)

Registered:
02/28/2009 10:01AM

Main British Car:
1966 MGB Roadster 350 LT1 Chevy

authors avatar
Re: How much to remove from 215 pistons to lower by one point?
Posted by: Jim Stabe
Date: January 24, 2021 01:41PM

PM me your email address and I'll give you an Excel calculator that you can plug in data to your heart's content and see what c/r you end up with.


Richard/SIA
Richard Brengman
No. Nevada
(387 posts)

Registered:
01/17/2014 07:47PM

Main British Car:
1969 Triumph GT6+ 225" Buick V6

Re: How much to remove from 215 pistons to lower by one point?
Posted by: Richard/SIA
Date: January 24, 2021 02:19PM

Just tried the Summit Racing calculator.
300 Heads may be too much chamber volume.
3.530 bore by 2.8 stroke and only changing head volume the reduction came out at 3.88.
So 12.48-1 became only 8.6-1. A bit too low.
Of course the fix becomes a 300 crank, but that negates one of the reasons to buy this engine while also driving up expense.
Not sure how much may be safely removed from 300 heads to reduce chamber volume.
Around 50cc chambers would be great.

This brings the "Simple" answer full circle to where I started, decking the pistons.
Unfortunate that Venolia is out of business so cannot ask them what would be a safe amount to remove.

Really do not want to buy the engine without having an answer for how to make it street useable first.
There is also the option of shortening the rods, but custom rods get expensive too.
A shame I have no real use for an 11.5-1 engine at this time.

The other answer is to buy different pistons and try to find a buyer for the Venolia's.
Custom forged is out due to price, and cast are out due to intended use.
The flat-top forged 300 pistons seem to no longer be available.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6003 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: How much to remove from 215 pistons to lower by one point?
Posted by: BlownMGB-V8
Date: January 24, 2021 05:33PM

Well I guess you could weld up the 300 heads and make them closed chamber heads. That would get you the chamber volume you want. Or take metal out of the 215 chambers.

Jim



Richard/SIA
Richard Brengman
No. Nevada
(387 posts)

Registered:
01/17/2014 07:47PM

Main British Car:
1969 Triumph GT6+ 225" Buick V6

Re: How much to remove from 215 pistons to lower by one point?
Posted by: Richard/SIA
Date: January 24, 2021 09:20PM

I have no clue where 215 heads could be safely opened up.
Need to decide, find a way for the 215 to work or just build an MGB engine.
I suspect that the Venolia forged 11.5-1's would not sell quickly, or for a lot of money due to limited demand.
Selling them would off-set the price of new JE's.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6003 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: How much to remove from 215 pistons to lower by one point?
Posted by: BlownMGB-V8
Date: January 24, 2021 10:46PM

8.6 is not necessarily a Bad compression ratio and if you did use the steel shim gaskets it would be pretty close to 9:1 which is certainly acceptable. The stock 2bbl engine had an 8.8:1 CR, made 155hp and 220 ft/lbs of torque. The Olds 2bbl was 8.75:1 with essentially the same specs. So then what you really have there is a 2bbl version of the engine. If the purpose of the forged pistons is to raise the rev limit, that is clearly attainable even with the lower CR.

Again, you can do some impressive things with the camshaft. Study up on Dynamic Compression Ratios to learn what the reasonable targets are and then websearch for a DCR calculator. With the right cam you should be able to easily get the DCR into the 7.5-8.0 range I would think which may not sound like that much until you understand the numbers, because you probably don't want to go much higher than that. I've not attempted such an engine yet myself, but from experience I can tell you that even a 215 with a sub 7:1 SCR is a dynamic and exciting ride compared to the OEM 1800 and only really falls short of the 4bbl 215 in max power output. Which is a small fraction of normal use.

Jim


minorv8
Jukka Harkola

(214 posts)

Registered:
04/08/2009 06:50AM

Main British Car:
Morris Minor Rover V8

Re: How much to remove from 215 pistons to lower by one point?
Posted by: minorv8
Date: January 25, 2021 04:10AM

I assume that you have flat top pistons. Are they now at zero deck height ? You could machine a dish into the pistons, leaving about 3/8" material at the edge of the piston. That would still allow quench. If my math is correct a 1/8" deep dish would increase the volume about 11,5-12 cc. With 5/16" rim you dish would be a hair shallower.

But, it all comes down to what you have to pay for the engine (unless you already own it), rip it apart, have the pistons machined, put it back together, possibly change the cam to a milder one etc.


Richard/SIA
Richard Brengman
No. Nevada
(387 posts)

Registered:
01/17/2014 07:47PM

Main British Car:
1969 Triumph GT6+ 225" Buick V6

Re: How much to remove from 215 pistons to lower by one point?
Posted by: Richard/SIA
Date: January 25, 2021 11:29AM

Engine has never been assembled, pistons are forged Venolia "Pop-Up" high dome type.
Removing some of the dome would lower static compression.
Plan is that this is a build for resale of the finished car. With that in mind I need to keep cost in check.
Since the new owner may have more money than automotive knowledge I need to keep it simple for them.
I will document the build for future reference.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6003 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: How much to remove from 215 pistons to lower by one point?
Posted by: BlownMGB-V8
Date: January 25, 2021 12:51PM

Can you post a photo of the piston crown?


Richard/SIA
Richard Brengman
No. Nevada
(387 posts)

Registered:
01/17/2014 07:47PM

Main British Car:
1969 Triumph GT6+ 225" Buick V6

Re: How much to remove from 215 pistons to lower by one point?
Posted by: Richard/SIA
Date: January 25, 2021 05:08PM

Venolia 11.5-1 piston crown for 215.
I have more pics but cannot get them to attach.

20210120_155027.jpg



Edited 2 time(s). Last edit at 01/25/2021 05:22PM by Richard/SIA.


Jim Stabe
Jim Stabe
San Diego, Ca
(787 posts)

Registered:
02/28/2009 10:01AM

Main British Car:
1966 MGB Roadster 350 LT1 Chevy

authors avatar
Re: How much to remove from 215 pistons to lower by one point?
Posted by: Jim Stabe
Date: January 25, 2021 06:24PM

Judging by the shape of the quench area, it looks more like an Olds piston than a Buick.


Richard/SIA
Richard Brengman
No. Nevada
(387 posts)

Registered:
01/17/2014 07:47PM

Main British Car:
1969 Triumph GT6+ 225" Buick V6

Re: How much to remove from 215 pistons to lower by one point?
Posted by: Richard/SIA
Date: January 25, 2021 08:01PM

Box also says Olds, I think the seller may be a bit confused.
Also think I am going to have to pass on the engine.
Would be a good deal if the parts were Buick and the pistons were not an issue.
As it is, just a bit too complicated for me at this time.



BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6003 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: How much to remove from 215 pistons to lower by one point?
Posted by: BlownMGB-V8
Date: January 25, 2021 08:43PM

I don't know what your intentions are here but it sounds like you want to build a car and then sell it to make money. Good luck with that, if you know enough to make that work I doubt you need our advice.

But maybe you could cut them down to flat-tops?

Jim


Richard/SIA
Richard Brengman
No. Nevada
(387 posts)

Registered:
01/17/2014 07:47PM

Main British Car:
1969 Triumph GT6+ 225" Buick V6

Re: How much to remove from 215 pistons to lower by one point?
Posted by: Richard/SIA
Date: January 26, 2021 11:01AM

I had better know how to build cars for profit, that is to be my new "Retired" livelihood.
Secret is doing nearly all your own work, not have too high of expectations, and turning out a very well detailed product.
Saving money where possible is important too.
The engine I've been looking at may be a good deal, or not.
I really need to see it in person.
If it is Olds rather than Buick it will be too complicated to build unless the pistons may be cut down.
Now leaning toward finding something else to use for this build.


roverman
Art Gertz
Winchester, CA.
(3089 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: How much to remove from 215 pistons to lower by one point?
Posted by: roverman
Date: January 26, 2021 12:52PM

Looks like "old" style alum. alloy. In other words, high expansion. Mfg. likely says .004"-.006" skirt clearance ? Likely ZERO pin offset means " diesel-knock" piston noise, in non racing use. For street use, a noisy bad choice. Art.


John Hamilton
John Hamilton
Navarre, FL
(21 posts)

Registered:
10/28/2009 11:18PM

Main British Car:
1965 MGB 1840 cc MGB

Re: How much to remove from 215 pistons to lower by one point?
Posted by: John Hamilton
Date: February 28, 2021 11:05PM

I'm not sure if you passed on this project, but I would entertain buying the pop up pistons if the price were right. Let me know if that might interest you.

John


MGBV8
Carl Floyd
Kingsport, TN
(4034 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB, Buick 215

authors avatar
Re: How much to remove from 215 pistons to lower by one point?
Posted by: MGBV8
Date: March 01, 2021 12:27PM

"a very old post on this very forum which mentioned that Buick 300 heads are 57cc chamber."

My understanding is that they are about 53cc.


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