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GT74 High Compression Six Speed


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I have a set of iridum 8's in at the moment, they seem fine at 1.1 bar but at idle and startup the car is much lumpier, compared to when it was running copper 7's going to try a set of iridum 7's.

 

8s should be fine, what engine speed and afr are you aiming for at idle?

 

Myself, JamieP and several others are running the BKR8EIX plugs ;)

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8s should be fine, what engine speed and afr are you aiming for at idle?

 

Myself, JamieP and several others are running the BKR8EIX plugs ;)

 

I think the 280 cams may have something to do with it;). There is very little vacuum due to the cam duration at start up so it is a delicate balance on the throttle for the first 20 seconds. Once the car is warm it will cycle around 1100 /1000 rpm, below that rpm it is just too rough and sounds an old Peugeot with knackered shells. I was considering running two IAC's to get enough air until the engine is warm then have the extra IAC tuned out of idle and hot start. I am running BKR8IEX 8 at the moment. I don't think will will get above 1.3 bar on road fuel so 7's will probably be OK. It wont take long to swap the plugs over as see if the idle smooths out.

 

What rpm do you idle at Wez?

 

I have nothing against water injection, however I don't want to tune the car so that to achieve a certain power level I must run WI. I have no room in the bay for a decent size tank and don't want a big tank in the boot. We have very good air temperatures in the plenum so charge temps are not an issue. I would rather lose a few bhp, than lose and engine because of a blocked water jet or pump failure. I have a WI kit in the garage and never bothered to fit it.

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I think the 280 cams may have something to do with it;). There is very little vacuum due to the cam duration at start up so it is a delicate balance on the throttle for the first 20 seconds. Once the car is warm it will cycle around 1100 /1000 rpm, below that rpm it is just too rough and sounds an old Peugeot with knackered shells. I was considering running two IAC's to get enough air until the engine is warm then have the extra IAC tuned out of idle and hot start. I am running BKR8IEX 8 at the moment. I don't think will will get above 1.3 bar on road fuel so 7's will probably be OK. It wont take long to swap the plugs over as see if the idle smooths out.

 

What rpm do you idle at Wez?

 

I have nothing against water injection, however I don't want to tune the car so that to achieve a certain power level I must run WI. I have no room in the bay for a decent size tank and don't want a big tank in the boot. We have very good air temperatures in the plenum so charge temps are not an issue. I would rather lose a few bhp, than lose and engine because of a blocked water jet or pump failure. I have a WI kit in the garage and never bothered to fit it.

 

Its never a good idea to map water injection dependent on ECU, you could just add it up when you want so if a jet fails you dont lose nothing apart from cooler-denser air;) I would love to run AEM water injection system.

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I have nothing against water injection, however I don't want to tune the car so that to achieve a certain power level I must run WI. I have no room in the bay for a decent size tank and don't want a big tank in the boot. We have very good air temperatures in the plenum so charge temps are not an issue. I would rather lose a few bhp, than lose and engine because of a blocked water jet or pump failure. I have a WI kit in the garage and never bothered to fit it.

 

this is what i meant by a good system that has all the fail safes http://www.coolingmist.com/pagedisplay.aspx?feature_key=safety i've heard the arguments against mapping with W/I but with the correct safetys in place this can be mitigated against (just like anything else on the car), i fully agree a basic open loop system mapped for higher boost is potentially compromising the safety of the engine but running in closed loop with feedback to the ecu and its just another tuning tool

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This may sound a little crazy:looney:, to some, but so impressed am I with the higher compression engine response (9.5:1) with my GT74, I am thinking of breaking the engine open and rebuilding it with an even higher ratio. There are smaller turbo motors running much higher compression than I am and they seem to be doing just fine, it is all down to the mapping in the end.

 

I also wondered if any one doing a N/A single conversion, has given consideration to maintaining higher compression to get a faster spool time.

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This may sound a little crazy:looney:, to some, but so impressed am I with the higher compression engine response (9.5:1) with my GT74, I am thinking of breaking the engine open and rebuilding it with an even higher ratio. There are smaller turbo motors running much higher compression than I am and they seem to be doing just fine, it is all down to the mapping in the end.

 

I also wondered if any one doing a N/A single conversion, has given consideration to maintaining higher compression to get a faster spool time.

 

From some of the threads I have read on supraforums they have gone to 11 and even 12:1 on some builds. :blink:

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From some of the threads I have read on supraforums they have gone to 11 and even 12:1 on some builds. :blink:

 

I was thinking of going 10.5:1, I must have missed the 12:1's, the highest I had read about was 11.5:1. It is funny that high compression turbo motors are now becoming more common. It was not that long ago when, the idea was treated with a severe intake of breath. I might even fit WI as well.

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I was thinking of going 10.5:1, I must have missed the 12:1's, the highest I had read about was 11.5:1. It is funny that high compression turbo motors are now becoming more common. It was not that long ago when, the idea was treated with a severe intake of breath. I might even fit WI as well.

 

They do seem to run them alot in the US but they also use race fuel most of the time with it. It would worry me using pump fuel at that compression ratio.

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The cosworth guys have been going higher and higher compression for years, seems the way forward for responsive turbocharged engines, at what point would the engine become an interference engine though? would this concern you?

 

Not really, at this level of tune cam belts are changed with the oil. Not sure where interference would come into it. The HKS 280 lift of 9.3, Crower 280's have a lift of 10.79. Stock JDM's lift 8.4(from memory) as far as I know US guys running Crower 280's are still running stock rods and pistons, so there is still some head room there.

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I was thinking of going 10.5:1, I must have missed the 12:1's, the highest I had read about was 11.5:1. It is funny that high compression turbo motors are now becoming more common. It was not that long ago when, the idea was treated with a severe intake of breath. I might even fit WI as well.

 

there is no denying that the higher the compression ratio the sooner the onset of det, i think there is going to come a point where you will think hmmm as the top end power is sacrificed for the bottom end gains, but i have total respect that you have tried this and you have in some ways bucked the trend.

 

How many times do you read an engine spec on this very forum of a 500-600hp single and as you scroll down the spec you read 2mm HKS headgasket :dontget:, i must reason the people fitting them have no more idea about compression ratios and their effect on an engines performance than i have about brain surgery :blink:, at this power level they would have a far nicer car to drive on the stock compression or dare i say a tad higher, instead they go the other way, why do they do it ? who advises them ? or is it just cos its HKS (so it must be good):search:, anyhoo rant over, keep up the good work fella :D

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there is no denying that the higher the compression ratio the sooner the onset of det, ....

 

There lies the challenge, getting the charge to the chambers as cold as possible, and keeping the charge relatively cool inside the cylinder as it is compressed up to the point of ignition. I can't beat the laws of thermodynamics, but I can use them to my advantage.

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To be honest I had not considered it, as up until very recently I had not considered breaking into the engine. But now you mention it, it seems like a very good idea, particularly in my circumstances, ie open motor and high compression. The limited knowledge I have of it certainly makes it worth considering. It appears to be particularly good at helping to prevent piston hot spots, a frequent trigger point for det. I suppose what I am aiming for is likely to make signifiant gains using turbo deisel technology.

 

I am not sure of costs involved, have you any info Dan?

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Current thinking tends toward a very high (for a boosted engine) static compression ratio, that is tempered into a more modest dynamic ratio by long duration cams, with moderate overlap, but very high lift. This was initiated by the turbo inlet restricted WRC cars, that got people experimenting with cam and CR set ups not normally associated with a boosted petrol engine.

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Thanks or your input Chris, much appreciated. When you say high compression, what sort of static ratio are we talking about? The HKS 280 cams I am running do have a long duration and over lap which does cause breathing issues at low rpm, which makes idle interesting, as it just does not want to suck. However lift is still only 9.3mm where as Brian Crower cams lift to 10.79mm, but I am not sure of their duration. Do you know of other cams that meet the high lift a criteria? If I am to open up ther motor I would like to push the compression and fit with the best cams I can afford.

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