Half bridge compression

[turbotoaster]

Has anyone on here with a full or half bridge ever have a compression test with a known good engine.

Im trying to work out what sort of numbers you will loose over a stock port etc

Thanks in advance

[yehreally]

I was told that it was pointless compression testing a \'bridged\' engine...  why are you asking ?

[turbotoaster]

well we are trying to work out why my engine has low compression, whether the ports are causing the low comp or if its a clearancing issue, i dont think its been built incorrectly as all the faces on both rotors are low, its not gonna be that a mistake was made on every seal etc
 
The car starts from hot and cold and makes good power, hence wondered if the porting makes a big difference to numbers like i know PP does

[SiH]

I thought you only had a Pineapple templated \'street\' port? :confused:
What clearances were used on the side seals?
What Apex seals were used?
What corner seals?
Were the apex seals clearanced?
Were the housings verified good?

[Jit]

Define low on compression.
When I tested Eds engine (massive street port) it gave readings all in the 8s iirc. Porting does affect compression values but not that drastically IME. I beleive martin at Speedline sold a half bridge once that also showed 8s on reworx tester.

[Jit]

Also following on from sihs post, side seal clearances are critical to compression. Different apex seals also have varying sealing charfteristics. For example mazda seals seal well under all scenarios whereas a one piece hurley race seal doesn\'t seal well from cold but they expand and seal much better when warm (according to Mick hurley).

[Prof]

What rpm\'s are you testing the compression at ?  Week starter motor\'s or tired batteries can give a low cranking speed and consequently low compression results.  The field service manual has a correction graph that shows how much to factor it up by.

[Ed_RX7]

intresting.....!....didnt steve warranty the engine?

[turbotoaster]

I thought you only had a Pineapple templated \'street\' port? :confused:
What clearances were used on the side seals?
What Apex seals were used?
What corner seals?
Were the apex seals clearanced?
Were the housings verified good?

They are racing beat template with a big enlargement on the opening(so the corner seal is supposted 50%)
0.05mm was used on the side seals
all atkins rotary master kit
yep
yep, used different ones

Define low on compression.
When I tested Eds engine (massive street port) it gave readings all in the 8s iirc. Porting does affect compression values but not that drastically IME. I beleive martin at Speedline sold a half bridge once that also showed 8s on reworx tester.

6.1-6.3 on front housing
5.7-6.0 on rear housing

What rpm\'s are you testing the compression at ?  Week starter motor\'s or tired batteries can give a low cranking speed and consequently low compression results.  The field service manual has a correction graph that shows how much to factor it up by.

Done at 240rpm on both

intresting.....!....didnt steve warranty the engine?

Yeh the engine is warranteed, he isnt sure why it should be so low.

You could imagine if he made a mistake on a side seal, one face would be out, but for all faces on front and rear rotor tells us it must be something else.

Hes built loads of engines now, Rotorbunnys car had 8-7.9 on all faces so its not like he cant build an engine and he was extra careful on mine because he knew the power i wanted from it.


The only thing we can think is maybe the ports, hes used the same sized ports on his racecar which is almost finished, so hes gonna run that in and see what comp results that gets.

If they are down then we know its the porting, if not then theres something else wrong.

The car starts from hot and cold everytime and makes good power.

He also said run it for another 3000miles, if the comp drops then we know its an engine problem and will get it sorted no problems, but we both want to see if we can work out what is causing it before a strip down

Just wasnt sure how much porting effects results, that was all

[bnaellis]

Don\'t worry about compression as long as it\'s even and it starts fine hot and cold engine your driving. Different porting does give different compression results, as do different compression testers. Side seal clearance is bigger than what I would do personally but that\'s a personal thing not a generic rotary rule. What\'s ggod for the goose isn\'t necessarily good for the Gander so no point try to compare what someone else has got unless everything is a direct like for like only then can a meaninful comparison be made.


rgds
Brian

[Ed_RX7]

fair enough. what vac readings are you getting on idle?

They are racing beat template with a big enlargement on the opening(so the corner seal is supposted 50%)
0.05mm was used on the side seals
all atkins rotary master kit
yep
yep, used different ones


6.1-6.3 on front housing
5.7-6.0 on rear housing



Done at 240rpm on both



Yeh the engine is warranteed, he isnt sure why it should be so low.

You could imagine if he made a mistake on a side seal, one face would be out, but for all faces on front and rear rotor tells us it must be something else.

Hes built loads of engines now, Rotorbunnys car had 8-7.9 on all faces so its not like he cant build an engine and he was extra careful on mine because he knew the power i wanted from it.


The only thing we can think is maybe the ports, hes used the same sized ports on his racecar which is almost finished, so hes gonna run that in and see what comp results that gets.

If they are down then we know its the porting, if not then theres something else wrong.

The car starts from hot and cold everytime and makes good power.

He also said run it for another 3000miles, if the comp drops then we know its an engine problem and will get it sorted no problems, but we both want to see if we can work out what is causing it before a strip down

Just wasnt sure how much porting effects results, that was all

[turbotoaster]

at around 900rpm im getting 16-17in on the gauge and 320 on the pfc

[Ed_RX7]

hmmm ...thats seems a bit low ....but not sure on what other half bridgers have......your probably gonna have to pull it and see whats up internally

[HaywardRotary]

If the engine is running fine then leave it alone until it really is obvious that it needs something doing.
Compression on bridges should be capable of being higher than that,but as long as it runs it is dynamic (Engine running) compression that matters and not static (Engine not running) compression.
Regards
Carl

[turbotoaster]

Hey carl, i assume theres no way of knowing what the dynamic compression is?

If an engine makes good power(will find out tuesday) for the boost it is running should we assume that the dynamic is good.


ie if its bad would the power be down(like boost is escaping past the rotors)