Unfortunately Dave, it's extremely tough (maybe impossible) to start down the path of buliding a blower motor, and then not installing a blower. You're left with pieces that just don't work together for your current application. I don't have much blower motor experience, so hopefully one of the guys on here that does can step in and offer some suggestions. But your engine builder's approach is questionable. The compression ratio is too high (should be ~ 8.5:1), and the cam seems totally out to lunch. (imo)

In the mean time (until the blower gets installed) if you want to drive your car, the simplest and least expensive ($250 US) solution would be to change cams. There are a lot of grinds out there that will work great for your application, however since your lifters are custom (???) rollers you'll want to go to the manufacture of your current cam to get something to match. Based on your other pieces, I'd recommend heading toward something comparable to the Competition Cams Xtreme Energy #XS268R solid roller cam, Lift .552” Intake, .564” Exhaust: Duration 268 Intake, 274 Exhaust (advertised), Your motor can obviously handle much more camshaft, but your current converter and rearend gear ratio really don't support it.

If however you're willing to consider changing the converter and rearend gears, you can afford to get much more aggresive in cam selection. But since the intent would be to just drive the car until you get a blower installed, a cam change seems (to me) like the best move for now. Besides, other parameters will need to change at that point...because frankly, unless you've had the **** built out of that Turbo 350 and rearend which you don't mention, neither will take 800 HP for very long. In fact the transmission might not hold-up long to the ~425 HP the unblown motor will likely produce.

Sorry for the bad news.

Best of luck...and Happy New Year in Scotland!!

...Jerry

 

Very good advice. I might add that a dual plane intake such as a Performer RPM would make for a very good runner with the cam change. It would add considerable bottom end and throttle response on a combo like yours. It would help a lot in matching your converter and gears.

Just the cam and manifold will make this combo easy to tune in. It would probably run on 87 octane and make 400 plus horsepower.

If you look around you can probably find a used Performer RPM, there are lots of them out there.

 

yeah Happy new year to you too

Thanks for the advise guys, I will do some more tinkering with the carb 1st, see what comes of that

I will let you know how it goes

dave

 

Just an opinion Dave...so take it for what it's worth.

I wouldn't waste any more time trying to tune what you have. First, I don't think you'll be successful. Second, a cam change is a (relatively) simple and inexpensive procedure compared to other modifications you've been willing to consider (ie...fuel injection). Later on you can just slide the blower cam back in the block when you install the blower.

At the very least I would avoid making extensive carb mods until you either A. change cams (because they won't be required)...or b. install the blower (because any changes you make now won't apply once the blower is installed, and some may not be reversible.)

Your current intake isn't optimal, but the camshaft is the real offender. Like V2Racing said, a good dual plane manifold would be a better choice based on your current set-up. But if you don't want to spend the money, your current manifold will work ok, just not be as crisp as you'd (ok...I'd) like.

The cam (XR268R) specs listed ( http://www.compcams.com/technical/Ca...67_226-227.pdf [page #156]) (it's a big file so be patient -2 min.+-) will work fine with your converter, but you could still use more gear...although you didn't ever say what the intended use is for the car either. Did you?

Anyway, a different cam (for the time being) would make your life much easier... ...real quick.

 

I didn't really want to sabotage Dave post but I have a similar issue to Daves on my new engine. The engine really runs fine, secondaries 'pull-in' well with no bogging. There is just a 'hole' pulling away from standstill untill engine reaches 1200 rpm or so. This is really irritating as I am sure primary squirter delivers enough gas, pumper cam is maximimized for max shot at earliest opening - it just dosen't cover the 'hole'. Engine is 489, inlet is Edelbrock RPM Air Gap, cam is hydraulic flat tappet 236/242 and starts to develop power at just over 1000 rpm. Brodix Race Rite Oval heads, 10.5 cr, 22 degree lead on timing (38 degree total) I don't think my issue is low vacumn (perhaps like Daves giving a low venturi 'signal'). Carb is Proform 950 DP Primary Idle Bleeds are #71, hi-speed bleeds are #38, primary pumper is #33, secondary is #35 (perhaps pumper jets should be transposed?) . Perhaps I am missing something here as I normally 'tune' primary & secondary jet sized the old fashioned way, i.e. flat out run in lower gear, cut engine, into neutral, coast to standstill & check plugs for correct colour - do the exactly the thing same on constant cruise to check primary jetting, going up/down incrementally untill I get it right. Haven't done this with current engine as it was dyno'd before installing - heres my thought, it was dyno'd for max HP not drivability - perhaps the primary jets are too small - any thoughts guys? I am also intrigued re. the relation ship between idle bleed jets and adjustment sensitivity - the Proform has the 'four corner idle' adjustment - it just seems extremely sensitive i.e. even the smallest discernable rotation (say 1/16") it goes from idling a little weak to idlling too rich. Are we saying here I need to increase the idle bleed jets or decrease the size to make it less sensitive? advise would be helpful

 

Concerning the airbleeds, from what ive read, it suggests the bigger the air bleed = more air, therefore leaner, but a bigger airbleed will slow the transsition between circuits, the main system will be delayed, having bigger airbleed idle jet will make it less sensitive, giving your idle mixture screws more adjustment.

I put in bigger idle air bleeds, which did give me more idle mixture adjustment, but cos of the delay thing, it has made my stumble slightly worse, Im going back down a few size's, my a/f graphs proofs that aswell

In my holley carb book, It says you should not change the airbleeds atall, it can ruin a carb's performance, only change in rare race app's

dave

 

this sounds just like my 1st problem, I put on the bigger 50cc pump, bigger shooter 37, worked good for me.

if its happening when you pull away, its defo not enough gas to start of with, again the a/f graphs proof that with mine

the innovate o2 sensor would be a very usefull tuning tool for you, not cheap, but worth it

dave

 

I thought earlier on this thread that someone suggested just going-up a couple of sizes on the air bleeds - to be honest I can live with the adjustment as it is - they are just very sensitive

 

I think what I'll do here Dave initially is swap front (#33) and rear (#35) squirters to see what happens. BTW I have just checked what the jetting was on my old stock L36 427 with single plane inlet and 750 Holley DP. First figures were carb out of box - in brackets what it ran best with. Primaries #70 (#75) Secondaries #80 (#85), Primary squirter #31 (#34) Power valve 6.5hg (10.5hg) I know yours is a hot small block and mine was a soft big block - but the comparative sizing of jetting is relative. OK, I didn't have benefit of O2 sensor but plug colours were OK

 

Update - I checked my carbs trans slot and throttle blade position, which was incorrect, the slot was not showing atall on primarys, what problems wound this cause??

changed it so you can see 0.20 inch of the slot from the underside of the carb

the secondary blade was showing to much trans slot, so adjusted that too, problem then is the car wont idle, not enough air

I did find that, I ran very rich at idle and the idle mixture screws made no difference to it.

so no choice, had to drill some holes in the throttle blades, I put one in each throtlte blade, using a 2 mm drill bit, it has made a big difference to my idle mixture, alot more adustment can now be had from the idle mixture screws, plus it will idle now

not had a chance to drive the car today, raining again!, so should be interesting to see how it affects my transsition part

I will let you know how it goes

cheers

dave

 

I did this to 780 cfm Holley some 25 years ago Dave when I had a radical cammed BBF powered car - the only way the car would idle was to turn-out idle screws about 4 turns - it accordingly ran very rich on idle - I drilled the primary butterflies, cranked ignition advance up to 12 degrees on crank - job done, perfect(ish) idle.

 

that was a long time ago!, thats good to know

dave

 

Update - I changed the primary jets from 72, now 74 and the secondry jets from 78, now 76

went for a test drive, the stumble at cruise has now gone, no sign of it!

also the cruise a/f is better, sitting lower at around 14 a/f now and at wot, getting a steady 12.5 to 12.7, idle is cleaner aswell, at around 13.5 a/f

so fingers crossed!

only concern is the jet sizes being so close together, but the a/f's all seem good??, any thoughts??

cheers

dave

 

That's great news glad you figured it out just leave it alone for now

Funny how no one could figure out your problem...oh wait post 32 from last month by a guy named MotorHead
"The slight stumble is a lean miss and the reason I don't run mine at 14.7:1 A/F. Tune the carb so you get about 13.5 at idle.

The idle circuit basically controls the cruise up to a certain RPM so you will be in the 13-14 range while at part throttle and the slight stumble will go away "

 

yeah, thanks mate

to me it was the primary jet change and the correct postitioning of throttle blades to the trans slots and the holes in the throttle blades that seems to have solved the issues, with out the o2 sensor, it would been so much harder to work out the problems!

only thing thats different, is when I 1st start the car, for the 1st 10 mins it seems to warm up a alot quicker than before and runs abit leaner at idle, but once its warmed up the leanness goes away and drops back down to 13.5 at idle

is this ok ??

dave

 

I am supprised that someone did not mention checking the blades and trans slot to begin with? What I have learned from this forum over the years from folks like Moterhead and lars () is that when you have issues start over from the begining and put everything back to stock period.

 

These carbs ( Holley and Demon ) are finicky when you start to play with them. I have seen what you are talking about after I adjust my Demon. It goes lean when I first start it up, then goes where it is supposed to be after driving a bit.

This seems to go away after a while for some reason, I don't know why it does it and I doubt I ever will but it should be OK after a few days

 

fingers crossed

cheers

dave

 

Untile the combustion area is up to temp the mixture will continue to get richer. Its one of the reason most carbs have chokes. This saturation time includes the coolant, block, heads and oil. After everyting is up to temp the mixture should stabilize.


Neal

 

V2racing mentioned it in his post #38, he called it the crossover circut, just different terminollogy, he was speaking of the transition circut.

Neal