high comp pistons question

[Aircooled4evr]

Hi there guys!
Here comes my first post, after a long time as a "spectator".
I'm on a 3.0 SC engine project, and my goal is a high compression engine,
(between 11.3 and 12: 1) MS3 box, knock sensor, dual ignition, Sequential Fuel Injector, etc. etc.
I probably have a lot of other questions around the whole set-up. But for now, my question is:
is it possible to get a 95 mm piston to 3.0 l (70.4 stroke) of more than 10.5: 1 in comp ??
I thought JE and Wössner made them up to 12: 1 But now I'm uncertain ...
Hope one or two of you can help?

Hopefully this will not be my last post, so I just want to tell you that I am from Denmark and English is not my native language. So I hope you can understand me, even though my grammar and vocabulary aren't "top notch"

best regards, aircooled4ever

[r lane]

I have a track motor with Vossner at 12.2-1.0. So Vossner, Carrillo will do that for you. I have had problems with misinformation on what the compression was suppose to be and what it was, so check it before installing. Also if you have to machine the valve pockets, you will lose something there. Your English and grammar are quite good.

[trond]

I have 10.5CR CP pistons and measured 10.2CR. I now have to carry octane booster in the car and wish I had gone slightly lower. I have dual spark and stock cams brw

[faapgar]

You can always get a longer rod and move the piston higher.Then machine the top outer edge to fit for your piston to head clearance.These days CP can just make what you need.

[dannobee]

JE kit 353248 shows nominal compression ratio of 11.5:1. Like Fred said, you can juggle that up or down as needed with changes in deck height. Either moving the piston up or down in the bore, or machining the cylinder or head a tiny bit. A little machining goes a long way.

I hope this is strictly a track car, otherwise getting fuel to feed it becomes expensive and a hassle compared to pump gas, and compression is only worth about 2% horsepower per point (give or take).

[911pcars]

If you're building a custom engine, pistons can be sourced for whatever compression ratio you want. Piston manufacturers manufacture their piston blanks to accommodate a range of customer-required compression ratios via domed piston tops.

However, the suggested path to higher compression for more power is not necessarily with domed pistons, but with flat top pistons, ideally shaped combustion chambers and compatible engine pieces.

An interesting article on the subject:
https://www.hotrod.com/articles/0311em-power-squeeze/

Sherwood

[stownsen914]

Originally Posted by dannobee

compression is only worth about 2% horsepower per point (give or take).

To be clear, is a point .1 or 1.0?

[dannobee]

Whole point, as in from going 10:1 to 11:1. Back in the day I did quite a bit of engine dyno work. It's almost universal across various engines. The diminishing returns come when you're going from say, 14:1 to 17:1, where the gains are even smaller, but the risk of burning something up is far greater.

[Aircooled4evr]

I have a track motor with Vossner at 12.2-1.0. So Vossner, Carrillo will do that for you. I have had problems with misinformation on what the compression was suppose to be and what it was, so check it before installing. Also if you have to machine the valve pockets, you will lose something there. Your English and grammar are quite good.

Thanks r lane
I was tired and under a little time pressure because I was on my way to buy "new" used cylinders. so thank you for assuring me!
(also in the communication skills department!)
My idea is to buy pistons with compression ratio above desired, so I can smooth and polish the piston crown, to postpone knocking (to increase compression)

[Aircooled4evr]

I have 10.5CR CP pistons and measured 10.2CR. I now have to carry octane booster in the car and wish I had gone slightly lower. I have dual spark and stock cams brw

Hi Trond (I'm pretty sure I know you from SCC at the Gardermoen race track, and our JPM dynodays!)
thank you for your answer, which makes me a little nervous as we live under the same temperatures .... probably need to make a thread about my engine project to be able to discuss ideas and experiences before I get much further .....

[Aircooled4evr]

You can always get a longer rod and move the piston higher.Then machine the top outer edge to fit for your piston to head clearance.These days CP can just make what you need.

Hi faapgar,
I'm building a "weird" porsche engine!
I've been tuning engines for many years, always in search of (a lot) more horsepower!
But this time i have another target... more mpg.
Of course this also gives more horsepower as a side effect ... But I'm going to use a mild camshaft, max a 964 grind, along with high compression, so I need short connecting rods to ensure a strong piston "suction" at the beginning of stroke, to compensate for the short opening time of the valves, so long connecting rods unfortunate, are out of the question.

[Aircooled4evr]

Hi dannobee

JE kit 353248 shows nominal compression ratio of 11.5:1. Like Fred said, you can juggle that up or down as needed with changes in deck height. Either moving the piston up or down in the bore, or machining the cylinder or head a tiny bit. A little machining goes a long way.

The engine is going to balance on the edge of knocking .. so the "correct" deck height is very essential

I hope this is strictly a track car, otherwise getting fuel to feed it becomes expensive and a hassle compared to pump gas, and compression is only worth about 2% horsepower per point (give or take).

It will be a street engine, and it is not in search of horsepower that it will run at high compression, but to squeeze more mpg out of it.
I think the problem of fuel in Denmark is less than in the US?
We have octane 92 - 95 - 98 and 100 as pump gas.
And I actually think (not sure) that our octane is "richer" than yours to begin with !?

[chrismorse]

Unless they have restrictive speed limits
😎

[Aircooled4evr]

Hi 911pcars

Thanks for your link!!
It is now read from start to finish, and that pdf is saved!
super informative, although some of it refers to small block V8 engines only.
And exactly the theory of the flat pistons must be scrapped in the case of Porsche engines...
As flat pistons, hemi tops and high compression cannot be combined!?.

[Aircooled4evr]

Hi Trond

Just one more question ...

I now have to carry octane booster in the car and wish I had gone slightly lower. I have dual spark and stock cams brw

What kind of injection system are you running?
What kind of ignition system do you have?
Have you done something to get rid of heat in the combustion chamber?

[Cheshire Cat]

As for the custom pistons - Traum pistons can make anything you want for lower price than the rest. Last year they made for me a set of 98mm 11.5:1 for less than a 1000USD

[Aircooled4evr]

wow Cheshire Cat! keep'em coming!
Traum pistons ... I don't know this company, they will be visited!

If it is Australia based, could there be a problem with shipping.. as in time, an tax? hmm..

Do you know the weight of your piston set? I will run with weight-reduced, original connecting rods, so the weight of pistons is important to me.

[Cheshire Cat]

Originally Posted by Aircooled4evr

wow Cheshire Cat! keep'em coming!
Traum pistons ... I don't know this company, they will be visited!

If it is Australia based, could there be a problem with shipping.. as in time, an tax? hmm..

Do you know the weight of your piston set? I will run with weight-reduced, original connecting rods, so the weight of pistons is important to me.

Nope, they`re made in the US of A. The guy who`s in charge - former Arias guy. He was recommended by Bisi (Bisimoto) so I gave him a chance.
As for the weight... 519 gramm each. Tried to insert a link to Instagram but it doesn`t work.
just in case instagram acc is che_cat

probs not the lightest but Beeri is open for a discussion
no affiliation

[Carbster09]

I believe you measure your octance differently than in the US. I have moved to the UK and thought I was getting far better fuel until I did a little research! UK 98 RON is ~ 93 in the US. I hate ethanol but that is creeping into UK fuel with most of it now 5% and likely to become 10%!

[spuggy]

Originally Posted by Carbster09

I believe you measure your octance differently than in the US.

Exactly.

The reason that European octane ratings seem higher than American ratings is because Europe, Japan and Australian only use the RON numbers. American and Canadian fuel uses an octane number derived from the average of the RON and the MON numbers. American fuel pumps have the designation R+M/2 to designation that the octane rating is RON plus MON divided by 2.

Simple math will show you that because of the 8 to 10 point difference of RON over MON, the octane rating shown on American fuel is approximately 5 points lower than the rating shown in Europe for the same fuel. In essence American 90-octane fuel would be the same as European 95 octane fuel.