575 engine on jenvey throttle body injectors

I thought some of you might be interested to see these pics of the throttle bodies on our 575 engine before it goes on the dyno. We just pulled it out of the 250GTO special chassis.
Image Unavailable, Please Login
Image Unavailable, Please Login

 

I'm expecting at least 575bhp and hoping for 600. The valve timing looks very mild, so I think that will be the limiting factor. We have a nice set of exhaust manifolds which aren't in the photos. There are some photos of the car at the early stages a few months ago in the vintage thread 'converted to comp daytonas'. I'll post dyno info when we get it. We'll be trying out shorter injection trumpets to see if we get much power loss, and may use them if it's not too bad. Otherwise the bonnet bulge is fairly outrageous, and we'll probably do it in perspex.

 

42mm bodies tapered out to 45 at the trumpet.
I can't wait to see the numbers myself!

 

This is a 'back of the hangar' job that gets done when there's nothing more pressing. Quite the opposite of the amazing progress you make on the 308 V12 madness!
That coupled with our dyno man being difficult to pin down means I don't think we'll have the figures for at least a month yet, maybe more as I have a house and hangar move coming up.
I will post the figures as soon as we get em!

 

I just received this email from the dyno man (not the same guy that kept dicking us about for 8 months):

''Hi Will

Good news at last, I've finished mapping your 575 engine and power tested it (with the long bell mouths and no bonnet), it has 601.3 bhp at 7000rpm and more than 400blft of torque from 3500rpm to 7500rpm. I called a friend in to help me finish off the mapping, two pairs of eyes are definitely better than one, he is an ex Lotus guy with a huge amount of expertise mapping engines.

Also my concerns regarding the dyno capabilities were put to rest as it coped with the power easily and didn't waver in the slightest.

I will carry out more power tests tomorrow, first with the shorter bell mouths (which I think will be better as it has more than enough torque already) then I will experiment with the bonnet height to see when it starts to restrict the air flow.

Best regards

Darren''


At last! I will be away now until Monday evening and hope I can then post the dyno sheets for the various configurations tested. I notice I can't hide the grin on my face this morning....

 

I just got back and found this email:

''Hi Will

Run all the power tests today, was disappointed to find the shorter trumpets to be worse throughout the entire rev range, did a back to back with the longer trumpets and confirmed the results. Good news regarding the bonnet height though firstly we fitted the bonnet as high as possible to give a base line test with no restriction from air flow, there was a drop in power because the heat from the engine gets trapped under the bonnet, but after this we dropped the bonnet 20mm at a time (mearuring the height from the top of the trumpets to the flat part of the bonnet) the results were again suprising, no further drop in power was recorded until the bonnet was touching the top of the trumpets.

So in conclusion you will want to run the longer trumpets and you could have the bonnet as close as 20mm if required, but the most important area is to get as much clean air ((I assume he means cool air- Will)) to the engine as possible.

Best regards

Darren''


First I'm surprised there was no power increase at the top end with the shorter trumpets traded off against a loss lower down, and then I'm blown away by the fact I can run the bonnet (hood) so close. I should mention that the bonnet has the standard 250GTO power bulge, and also that the trumpets are leaning in to the centreline so it's not quite as nuts as seems.

Maybe it would do even better with longer trumpets but I'm not going there as power is now 'adequate' and then it would start to look like something out of wacky racers.

I will post the full power curve when I get it, and confirm the exhaust primary length and inlet tract length.

 

I can get you the inlet side sent over from Jenveys, choose your ECU (we used DTA), and then you'll need to get someone to make up a set of exhaust manifolds. I think I used 30 inch primaries, but will confirm this.

No work to the heads

 

I'm hoping for 1150kg, but it might be 1200.

 

I went down and picked up the engine today and the dyno sheets.

Discussing it with Darren who did the work he made some interesting comments:

First, the sound! He had visitors arrive from all around the industrial estate enquiring what on earth it was. All thought it was great, including those from Van Diemen (the race car builders) who are not that close by...

The smoothness amazed him. There were a couple of loose nuts on some unused studs on the sump and they didn't even vibrate off. This engine is using a DTA non sequential injection ecu, with wasted sparks, basically a double 6 cyl set up, and seems to confirm DTA's view that sequential is just not neccessary on a 12 cyl engine. He also decided to back off the power at low rpm to ensure that the car is drivable on the road at small throttle openings.

He set the rev limiter in the ecu at 8000.

So here are the dyno sheets with 90mm & 60mm bellmouths. It is interesting that the power is down all through the range with the shorter bellmouths but up at 7500 as one might expect.
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login

 

I remembered this post by Bob Norwood in the thread about Webers on a 550:

''Have you lost your mind?

--------------------------------------------------------------------------------

If individual Throttle bodies were the hot deal the auto manufactures would supply them! This deal will lose a ton of power in the lower and mid range and won't make more on the top end unless you rev it higher than 8500 rpm. Take a close look at the stock manifolds they will be dam hard to beat! Most of the improvments in this series has been on the manifold. ''

It tickled me and I thought I would try to compare my result with a standard engine. I couldn't find a 575 power curve so what I've done is take the RWHP figures posted by Gary Read in the recent thread about RWHP. He got these in his 550:

''We had our annual Northwest Region FCA Dyno Day yesterday and here's my test results sheet.

2000 550 Maranello w/BMC air filters, Tubi rear muffers and a Hughes silenced X-pipe.

418.41 HP, 367.12 torque

I was very pleased with the results.''

I then scaled them up pro rata to give the same max power & max torque of the standard 575 at the flywheel. I know the torque curve is a slightly different shape and this is not completely scientific but think it should be pretty close. Then I've drawn it on top my dyno curve as an approximate comparison.

To be fair to Bob he was talking about the difference that ITBs alone would make, and I have used a better set of exhaust manifolds with 30'' primaries and nearly straight through mufflers, but hey......

I just noticed that I overcalculated the bhp curve for the standard engine and it shouldn't cross the modified power curve at all, but I won't change it for now.
Image Unavailable, Please Login