lets discuss my curves

[GTphil]

So I knew my car would make over 200hp but I thought it would do it with less boost, on this run it only managed 201hp and 189ft/lb's the boost at the manifold was 24psi.

Engine is low comp
285 cam (timed @116 degrees)
T28 t25 core .49 rear o48 comp housing
Standard venturi carb with second stage mods and a smaller A/C
large fmic

Fuels at 11.8 afr up to 7k

To be fair I was expecting more for 24psi.

What would people suggest I do to reach 230hp?

My list is to replace the standard downpipe with a larger item, then give it some more boost and fuel.

[GT Josh]

Maybe retard the cam another 2 degrees?? More higher powerband cause it seems to wanna go late on. Also rev more mate. Plenty left in it, 7.5k do it.

[Haz]

b18ft

[GT Josh]

b18ft

[GTphil]

The power appears to start to tail off at 7k, so no point in more revs, and I can't really retard it any more than it is to be fair.

I'm wondering if it's a mixture of the low comp and standard downpipe.

The idea behind low comp is to replace the comp with boost, not sure on the exact ratio, but it should be only slightly lower than standard with a blue gasket.

[Markey Mark (BD)]

I would of expected abit more than that too mate, not far off the spec of my old tungy and that was around the 230bhp mark

I wouldn't retard cam anymore, 116deg is more than enough. I'm wondering if its being choked at the top end, might need to breath a little better

[James5]

Why low comp? raise the comp and it should make more with same boost monitor det though

[GTphil]

My five came with a c1j from factory and that's what's staying under it's rusty little hood!

[GT Josh]

I think we shall see a difference with a mouuuiuaaaaaaaaahaaaaasivvvvve downpipe...

[GTphil]

The choking idea makes sense, I'm suprised it starts to tail off at the top end to honest, other than a larger downpipe what other options do I have to improve it's lungs.

I went low comp because that's what it was before I built the new lump and it always seemed to perform well enough, I never pushed it as much as this before mind.

[Markey Mark (BD)]

When you done the rebuild did you change anything or was it just a refresh? It does seem like the engine is choking top end if its struggling, i had my cam set to 115deg so little earlier than yours and felt strong past 7.5k so yours should be fine like that, the traps i done equated to about 230bhp.

I would deffinately fit a larger downpipe if you only got a standard one on there, atleast 2 1/2", maybe even try find a BMS/Big Jim downpipe as this will remove the elbow too.

[GTphil]

Nothing was actually changed spec wise of the lump just all new parts, crank re-grind, 285 cam.

One thing I did wish I had done was relive the valve spring seats as the coils on the springs were very close when fully compressed, I did measure them up with feeler blades and according to some random article I found they all added up to enough of an over all clearance to not be a problem.

Would a down pipe really make that much difference?

[Markey Mark (BD)]

If you can get gasses out quicker it'll help mate, i'm also wondering if the rear of the turbo isn't quite right i've had this before. I know its a T25 rear but do you know what the turbo is based on if it is based on anything or what the spec is?

[GTphil]

Not fully, the front wheel measures 55mm across and other than the info above and the fact it was originally destined for a B18FT.

So as far as I'm aware it's a t25 with T3 front housing.

[Markey Mark (BD)]

Not fully, the front wheel measures 55mm across and other than the info above and the fact it was originally destined for a B18FT.

So as far as I'm aware it's a t25 with T3 front housing.

If it was destined for the B18FT then sounds like it should be big enough, i would give the downpipe and elbox a go mate, it'll help but just wondering how much. If you can find a one piece one even better

[GTphil]

Also it's worth pointing out that the print out above was the fourth run it did after being Sat for a while also, it did make 209 Hp and 196ft/lb's on one run but it was just spinning the wheels slightly as it came on boost.

That would be more inline with the 106.7 terminal it did at pod, just under 210hp, it also is quite a lot quicker than my brothers on the road once on boost and his made 196hp.

[Markey Mark (BD)]

Also it's worth pointing out that the print out above was the fourth run it did after being Sat for a while also, it did make 209 Hp and 196ft/lb's on one run but it was just spinning the wheels slightly as it came on boost.

That would be more inline with the 106.7 terminal it did at pod, just under 210hp, it also is quite a lot quicker than my brothers on the road once on boost and his made 196hp.

Ah thats cool, does make sense alittle now 209bhp is better. Deffinately get rid of the standard downpipe and elbow mate (if its not bored already) and fit larger, anything that'll help flow out the engine will help it breath bit more

[GT Josh]

Now thats yours done. lets talk about mine HA

[GTphil]

Start your own thread bellend! And take a proper picture while your at it!

[GT Josh]

Dont cry.

[Mart]

Engine is low comp

Define 'low'. If much lower than o.e (7.9), that's probably why you're down on power.

T28 t25 core .49 rear o48 comp housing

Wheel sizes?

Don't be too hasty in replacing the downpipe for a larger bore. I've made an easy 230hp with the o.e pipe in situ before now.

Has the turbo elbow been touched?

Why so much cam retardation?

[GTphil]

The head is just over 73mm, 73.2 I the old grey matter is correct, the pistons are dished as the old bb low comp ones were



Like a div I never actually worked out the exact comp ratio

As for the blower the front wheel measures 55mm across, and thats all I know about it.

[gtmatt]

It's strange people's c1js all make different power I've got a graph from years ago from my red 5 and it made 197 at 19psi

All it had was 285cam,t28 ,and now James has got it ,t made 237 or something at 22psi ,you can open a can of worms with rr some are generous some are not.
I am not saying scoffs are either.
But everybody knows this.


Same with motor bikes on dynos as well.

All engines are different , is your turbo a full t28 with 60trim wheel ??

[GTphil]

I'm not sure on the trim size, the only thing I have done is measure the comp wheel across at 55mm.

it's also definatly a T25 core.

From what I have seen scoffs rollers are very honest

[rs250nut]

Sack the low comp idea off, it only makes for a motor that drives terrible off boost and when in boost you have to run more to make the same power, also bear in mind that when you keep pissing around the cam timing you are effectively changing the comp ratio (dynamic).

[GTphil]

Timing hasn't been changed since it was built, just set it at 116, I have often wondered what it would be like at 112.

As stated, I don't think it's drastically lower C/R than standard, only reason I didn't work it out is because I don't have any calipers to measure the head properly, all I know is it's over 73mm I had it skimmed years ago and 73.2 rings a bell, it's got a blue headgasket in situe.

[GTphil]

Mart, turbo elbow is o.e and reason for so much retard was to try and get as much power as possable right up at the top for the strip.

[Tony Walker]

Try and advance the timing a bit see how it feels.

[turbo ted]

the only way a c1j makes any good power is fitted the right turbo the exhaust side of the turbo is the most important part the bigger the exhaust wheel the more it will flow.
my old turbo spec
t2 core/t2 63 exhaust housing with a pulsar trim wheel /t3 front housing and wheel,full boost at 4000rpm 26psi made 240hp and at santa pod i run it at 30psi and would pull 12.1sqm at 114mph.
i tried low compression high compression retarding cam and advancing cam it made hardley any differance when i ran at pod, but when i changed the turbo it always made the differance, my opinion is your turbo is letting you down regards turboted.

[rs250nut]

Right on with the turbo, fitting a decent t28 I noticed more of a diffrence than all of the mods put together, measure the wheels on your turbo, if you going to mess about with cam timing do it on the dyno as it leaves nothing to chance then. With you retarding the cam timing you are effectively lowering the cranking compression.

[gtmatt]

There's your answer Phil , turbo ,maybe get standard pistons ?? When scoff did mine many years ago just had a big t28 60trim wheel and 285cam is made 200bhp easy , I've just had the same blower bought for my white 5

[Mart]

and reason for so much retard was to try and get as much power as possable right up at the top for the strip.

It was a rhetorical question mate

116deg' is too retarded with ref' to your setup, imho.

Without not knowing the wheel(s) inducer/exducer, the turbo's capability is an unknown quantity. Saying 'T28 this, T25 core that' means nothing in the grand scheme of things. Measure the wheels, report back

One thing's for definite though - A lower c/r isn't the way to go. I never did understand why the Bridge brothers went down that route/bucked that trend back in the day...

O.E 'red' headgasket is perfectly fine to use as well.

[TNT ANDY]

Like Mart Says - take your turbo apart and measure up. I have exactly the same power output as you, and my turbo seems to be in the same ball park as you see my specs and others on the following link:-

https://www.rtoc.org/boards/showthread.php?t=28903

As mentioned b4 - RR readings can vary a lot depending on who's operating them.

Myset-up made 209bhp with a cam timing of 129 (yes that is correct) that would hold that up intil 6.5K then start to drop off. When we advanced the cam to 115bhp it made 202bhp (both readings @ 24psi). There is a fundamental issue with my car which I think I'm getting to, but the point is you're in the right ball park and if you want more power it is most possible that the .49 rear housing is a part of the overall problem. People with 230+ have bigger rear ends .62 and up. Laggy but powerfull, I won't be getting a bigger rear end as 200bhp is great on track.

I would consider VNT if I could be arsed to find out which would work best.

[Dave Reed]

Like has been said already time the cam in to what the spec sheets says and re dyno to see the difference..

Lower c/r isn't going to affect it too much really, mines meger low c/r but has always made really good power (about 250hp @ 26psi when i was on the carb, and thats not a dyno read out, it was worked out by the Scoff using my terminal speed). But my spec of my cam etc is much different to most.

Lower c/r will also bring the det threshold up and with that ****e carb inplace it isn't a bad thing imo.. Again though, mine was low for a reason, I wanted to use nitrous. Having said that now I'm efi if I had to replace the pistons I'd be taking it back up to near or more than standard.

Also I'd say your exhaust/dp is strangling it, but one thing at a time. And as said get the turbo specs.

[Nialle]

Go and see power flow in burnley phil im sure they could make you a downpipe/elbow all in one. as far as i know ( which isnt all that much) the downpipe and elbow make a massive differance i was told could be talkin 20-30 bhp.

[markey b]

Why low comp? raise the comp and it should make more with same boost monitor det though

whack the TDC fully back too, will be awesome, just keep some spare pistons/liners in stock like i have too

[GTphil]

First port of call then Is a larger downpipe/elbow and I will measure the turbo while I'm on with that, although I don't think thats the issue, as even with the .49 a/r it isn't at full boost till 4.5/4.7k

I think my cam timing might benefit from being slightly advanced, maybe even to the 112 that piper state, with regards to the C/R as I have said, it shouldn't be that much lower than standard as the head has had some meat off.

Maybe the lower c/r coupled with the retarded timing and standrd downpipe/elbow is more than likely the issue, I would have thought that cam timing and more flow may give me an extra 15hp or so as after all thats all I'm really short of give or take.