high compression forged engine

[ash p]

I am looking to build a high compression forged 4e or 5e what are the pros and cons?

[Phil]

you'll need decent management and run decent fuel.

which is a pro in my opinion.

Phil

[H_D]

pro - More power gains with lower boost.

Con - more likely to det at high power so a good map is very important.

[AdamB]

Depends what you class as high compression. I think you would be hard pushed to get anymore than 9.5:1 due to not being enough meat around the bores and cylinder head.

[richardc9052]

Depends what you class as high compression. I think you would be hard pushed to get anymore than 9.5:1 due to not being enough meat around the bores and cylinder head.

Your thinking of oversized pistons mate

[AdamB]

Your thinking of oversized pistons mate

Overwsized pistons increase the comrpession ratio slightly, and in terms of meat on the cylinder head I ment skimming the head excessively would result in valve to piston contact.

To get up high you would need pistons with a raised dome on the crown and for turbo engine design/modification this isn't the best idea.

[richardc9052]

wouldnt oversized pistons increase the chamber volume and lower compression? (assuming all you changed was the diameter of the pistons)

A smaller headgasket, slight head skim and block deck would do a fine job. ratio depends on your set up but unless your going to be running very good fuel constantly theres no point..

I think 4efe's are the perfect compression ratio tbh and at 0.6 on a ct9 make 160-180 mapped.. A gen 1 would be perfect with the gt sized rods

[AdamB]

Correct your right the volume of the cylinder increases, but the area (volume) above the piston doesn't change, this is the area where the gas gets compressed. The formula for working out the CR is CR = (CV+CCV) / CCV where CV is the cylinder volume, which if you increase the piston size the cylinder volume increases.

The 4E is deffinately way too low on the CR imo, you only have to look at Honda's engines which are running 11:1 and making near enough 400whp at only like 9psi of boost. The only reason they can get away with it is because their peak cylinder pressures are lower.

[richardc9052]

Ahh nice one thanks! I get it now!

Yes hondas make stupid power because of compression and they seem to have better mappers as they run quite well.. It also lets them spool bigger turbos faster which helps again as the cfm that they move is also much larger than that of a td04 at low psi.

Thanks for that bud! Very informative

Edited April 11, 2014 by richardc9052

[5e colin]

^^^^^^^^ sooooo tru richard nothing beats a 600bhp high comp b18cr engine :)

but there wont be any mappers on this side of the pond smart enough to do so ha ha

lets take a quick ferry ride ha ha

[ash p]

What is the compression on a 4efte standard anyone? ?

[maddox710]

What is the compression on a 4efte standard anyone? ?

8:2:1 iirc

[ash p]

Anyone built a higher compression engine on thia forum am thinking about 8:5:1

[maddox710]

Anyone built a higher compression engine on thia forum am thinking about 8:5:1

people will have as that comp ratio can be achieved by just a heads and pistons

[5e colin]

9 can be reached by just a thinner headgasket 0.5

[AdamB]

Depends what turbo and intercooler your going to use really. The more efficient they are ie the cooler the charge the higher the CR you can go without getting knock. 8.5:1 will still be good for well over 2 bar of boost on something like a T3/T4 turbo.

[ash p]

Am thinking 8:5:1 on 5e forged stock head hdi intercooler td04 hybrid either racetech or wepr ect any thoughts ?

[AdamB]

That will be fine, will make for a very responsive fast road/track engine. You may even be slightly better off with a td05 because it will be more efficient than a td04 at 1.4 bar, but again depends on what you want to use it for and what power your aiming for.

Your going to want some Wiseco 10cc dished pistons to get that CR on a 5E.

Edited April 12, 2014 by AdamB

[richardc9052]

A 4e/5e hybrid with standard hg and 4e pistons works out at about 9:1

[ash p]

I will be using it for more drag racing scenario so interested in more 0-60mph figure really

I will be using it for more drag racing scenario so interested in more 0-60mph figure really

[AdamB]

You should focus on getting a good chassis setup as well then along with some good sticky tyres.

[ash p]

Ive got 6 pot ksport brakes miesta racing suspension every possible strut brace you can think of and quaife lsd any other advice ony spec regarding my engine spec in respect for the usage

[AdamB]

You can alawys start off with a td04, then if you get addicted to drag racing go for some more power later on. A lot of the time though power isn't necessarily needed, you might want to check out a guy called -Harry- build thread, he's only running 240whp and managed an 11 second pass. You want to save as much weight as possible.

[ash p]

I can't find his build what engine he running ect you have a link?

[AdamB]

Check here mate

http://www.ukstarletowners.com/topic/9978-5efte-carbon-clad-submarine/?hl=harry#entry236375